International Journal of Modern Physics B

We theoretically investigate the properties of multiphoton excited states in strongly correlated two-dimensional electron systems at half-filling using the extended Hubbard model in the strong correlation case. We find that the photoinduced d-wave superconducting states are stable against the nearest neighbor Coulomb interaction within the realistic Coulomb parameters.

We examine the effects of positional disorder of the magnetic ion in III-V Diluted Magnetic Semiconductors such as (Ga,Mn)As at low carrier densities on the nature of the low-temperature ordered magnetic state, using numerical mean field and Monte Carlo methods. We find that positional disorder leads to a highly inhomogeneous ferromagnetic order in the low carrier density limit, with unusual thermodynamic and magnetic behavior. Spin-orbit coupling presented in the valence band leads to frustration in the hole-doped system, but does not significantly affect the low temperature magnetization.

The nature of vortex structure in the mixed state of high-temperature superconductors (HTS) is investigated by solving the Bogoliubov-de Gennes equations with consideration of competition between antiferromagnetic (AF) and d-wave superconductivity (DSC) orders. By varying the applied magnetic field and temperature, the geometry of vortex structure can take two different forms: conventional vortex lattice (triangular or square), or vortex stripe phases where all the order parameters including spin density wave, charge density wave and superconducting order exhibit stripe-like behavior. This novel vortex stripe phases may show up at low temperature and adjacent to upper critical field H_c2 Phase diagram of temperature dependence of H_c2 will be presented. Our results may shed light on the understanding of the low-temperature H_c2 anomalies in some HTS. New experiments are proposed to test our predictions.

Starting from an electron-phonon interacting model, by means of the third formalism of quantum statistics, and with the aid of a diagonalization theorem, the Tc of superconductors from weak coupling to strong coupling cases are studied in a unified way. Our results are comparable with those of McMillan's theory, (which is valid up to the electron-phonon (e-ph) coupling parameter λ~1, a good agreement is shown for λ<1.3) and the Allen and Dynes's theory. Especially our results are very close to those of Hg spectrum with λ~2.0 and some strong coupling compounds. The theory is exact in the thermodynamic limit, without introducing variation method, the compensation of the dangerous diagrams in finite order in perturbation theory, abnormal green's function etc.

Though commonly unrecognized, a superconducting BCS condensate consists of equal numbers of two-electron (2e) and two-hole (2h) Cooper pairs (CPs). A new complete (in the sense that 2h-CPs are not ignored) boson-fermion statistical ternary gas model, however, is able to depart from this perfect 2e-/2h-CP symmetry. It yields robustly higher T_c's without abandoning electron-phonon dynamics, and reduces to all the known statistical theories of superconductors, including the BCS-Bose "crossover" picture—but goes considerably beyond it.

Based on a viewpoint of chemical pairwise interactions between electrons, a Hamiltonian was proposed for the "flat/steep band" scenario. This model has been studied analytically, and numerically with the first-principles method. With Hg and MgB₂ as examples, we have explained the characteristics of this model and observed peak-like structures of the electron-phonon coupling constants λ(q) in q space. The strong coupling of the "flat band" electrons with phonons has been corroborated by developing a new functional Psib(Φ), through which we can quantitatively compare different electronic states in coupling to a specific phonon. The relevance of our model to an electronic inhomogeneity is also discussed. Investigations on experimental and theoretical low-energy electronic structures of superconductors support our flat/steep scenario.

Muon spectroscopy of YBa₂Cu₃O₇ and Bi₂Sr₂CaCu₂O₈ produces strong evidence that both materials are s-wave superconductors, while scanning tunneling microscopy (STM) and photoemission data seem to indicate that Bi₂Sr₂CaCu₂O₈ in particular has d-wave character. The resolution of this apparent discrepancy is that the CuO₂ planes (which are responsible for the d-wave character reported by STM and photoemission) do not superconduct and are different from the superconducting BaO or SrO layers sensed by muons.

It is argued that the new theory that combines the precursor BCS-like non-superconducting (SC) pairing and the Cooper-pair condensation into a superfluid Bose-liquid state is more plausible than the standard SC fluctuation approach in describing the distinctive features of the underdoped and overdoped high-T_c cuprates. We show that the scenarios for high-T_c superconductivity in these materials are quite different on the character of the Cooper-pair formation and SC phase transitions.

We show that the well-known BCS Hamiltonian in terms of the BCS ground state represents, in fact, the generator of the particle-hole pairs and that the BCS ground state describes both the particle-hole excitations and the pairing condensate. We calculate the contribution of particle-hole excitation to the ground state energy. We show that the particle-hole pairs in the case of attractive interaction significantly lower the ground state energy, which means that the BCS ground state is not really the superconducting ground state. In contrast, for the repulsive interaction the particle-hole excitations are just to renormalize the ground state energy. Thus, in the case of repulsive interaction the condensate of bound pairs would lead to the real superconducting ground state of the system as shown.

Within the t-t'-J model, the charge transport in electron-doped cuprates is studied. The conductivity spectrum is characterized by a low-energy peak and unusual midinfrared band, while the resistivity exhibits a crossover from the high temperature metallic-like to low temperature insulating-like behavior in the relatively low doped regime, and a metallic-like behavior in the relatively high doped regime, which is qualitative agreement with experiments. Our results show that such unusual charge transport is closely related to a competition between the kinetic energy and the magnetic energy.

The unusual properties of a doped high-T_c oxide can be attributed to its unique electronic structure, here we put emphasis on importance of the O2p band for the origin of magnetism and superconductivity. Antiferromagnetism of a charge transfer type insulator should be described by the Kramers-Anderson theory, the superexchange between localized Cu3d spins is mediated by O2p electrons. A doped hole resided in the O2p orbital in a Cu-O-Cu bond effectively suppresses the superexchange between Cu3d spins creating a local moment or a "Kondo impurity" in the magnetically ordered CuO₂ layer. The interaction between a local moment and O2p electrons yields an effective spin coupling between O2p electrons and pairing. Accordingly, itinerant O2p spins may condense into a paired state or a spin liquid state via local exchange interactions. On the contrary, Cu3d spins merely provide a magnetic background, the existing local field breaks the time-reversal symmetry in a photoemission process. We use a semiclassical approach to estimate the difference between the intensities of photocurrents generated by the left and the right circularly polarized photons observed in Bi₂Sr₂CaCu₂O_8+δ by Kaminski et al.

The c-axis charge transport of the electron doped cobaltate is investigated within the t-J model by considering the incoherent interlayer hopping. It is shown that the c-axis charge transport of the electron doped cobaltate is essentially determined by the scattering from the in-plane fluctuation. The c-axis conductivity spectrum shows a low-energy peak and the unusual broad midinfrared band, which are qualitatively consistent with these of the doped square lattice antiferromagnet.

Within the charge-spin separation fermion-spin theory, the mechanism of superconductivity in Na_xCoO₂·yH₂O is studied. It is shown that dressed fermions interact occurring directly through the kinetic energy by exchanging magnetic excitations. This interaction leads to a net attractive force between dressed fermions(then the electron Cooper pairs), and their condensation reveals the superconducting ground state. The optimal superconducting transition temperature occurs in the electron doping concentration δ≈0.29, and then decreases for both underdoped and overdoped regimes, in qualitative agreement with the experimental results.

We study pairing by the exchange of spin-wave excitations near the ferromagnetic or antiferromagnetic instability in terms of the effective two-particles T-matrix. We show that near the ferromagnetic instability the paring due to the exchange of the paramagnetic excitations can occur in the p-wave state (ℓ=1) and m=±1. We show that near the antiferromagnetic instability the pairing due to the exchange by the paramagnetic excitations occurs also in the p-wave state (ℓ=1) but with m=0 and that there is no pairing in d-wave state.

We evaluate the temperature of superconducting phase transition in terms of the Bethe-Salpeter equation for a many-body system. We consider the case when both electron-phonon interaction and strong Coulomb interaction co-exist. To remove the artificial cutoff at high energy we solve the Bethe-Salpeter equation in terms of the two-particle vacuum scattering amplitude. We show that such an approach leads to the conclusion that the so-called Coulomb pseudopotential appears only due to the artificial cutoff and does not exists at all in terms of the Bethe-Salpeter equation.

Within the t-J model, the c-axis charge dynamics of the underdoped cuprates has been studied based on the charge-spin separation fermion-spin theory. In contrast to the in-plane conductivity, the low energy peak of the c-axis conductivity is located at a finite energy, while the c-axis resistivity exhibits a crossover from the high temperature metallic-like behavior to the low temperature insulating-like behavior, in agreement with experiments.

We propose the solitary wave model of superfluidity. According to harmonic oscillator model of quasi-lattice of liquid, it is proven that superfluid domains (SD) exist in He liquid, in which the resistanceless motion of liquid molecules (LM) can be carry out. At temperature lower than T_c, all SD connect with each other and superflow in whole liquid takes place. Applying Toda's potential, under continuous conditions, we obtain the motion equation of LM, and its exact solution. Substituting these results into Schrödinger equation of LM, we can prove the existence of solitary waves of LM and the non-linear Schrödinger equation of LM. The motion of solitons of LM leads to a superflow. On the basis of coherent condition of wave of LM, we derive the formula of transition temperature T_c of superfluidity. From the formula, the relation of the onset temperature T_c of superflow on inert layers is explained.

The unified model of superconductivity has been discussed ^[1]. In the model the motion of phononic electron (PE) pairs is described by a non-linear schrödinger equation of PE pairs (SEPE). From SEPE the ideal conductivity in superconductors in external magnetic field has been derived. From wave property of motion of PE pairs, Josephson equations have been proven. From the formula of T_c, the relation of T_c to pressure p has been explained.

We present results of numerical calculations emphasizing the central role of the Coulomb interaction in the mechanism of d-wave Cooper pairing in layered cuprate metal-oxides. We demonstrate that many-particle Coulomb correlation described by the Coulomb vertex function Γ substantially enhances the effective electron-electron attraction in the d-wave Cooper-pairing channel in these compounds. Such a "Coulomb" mechanism of anisotropic Cooper pairing may provide high superconducting transition critical temperatures (T_c⩾100 K) for optimum-doped cuprates.

The single-rung t-J ladder is investigated based on the charge-spin separation fermion-spin theory. It is shown that the thermal conductivity increases monotonously with increasing temperature at low temperature, then saturates at moderate temperature, and decreases at high temperature, in qualitative agreement with experiments.

We examine the electronic states in the hole- and electron-doped cuprates by using the t-t′-t″-J model. Numerically exact diagonalization method is employed for a 20-site square lattice under twisted boundary conditions. The density of states in the underdoped region clearly shows a pseudogap behavior near the Fermi level in both hole and electron dopings. In hole doping, the edge of the pseudogap in the occupied side exhibits a large weight that comes from a flat band near k=(π,0). In contrast, the weight near the gap edge in electron doping is larger for the unoccupied side than for the occupied side.

The superconducting system in the two dimensional triangular lattice is investigated by the mean-field treatment of a simple effective model. We calculate the phase diagram of this kind of superconductor for various pairing symmetries and interactions as well as electron occupancies. It is found that the p_x+ip_y-, d+id′-, and f- wave superconducting states are stabilized in different doping regions, and there exist superconducting phase transitions by varying the carrier concentration in the system. The relevance of our results to the recently discovered superconductor, Na_xCoO₂·yH₂O, is briefly discussed.

Metal (M) doped PrBa₂Cu₃O₇, i.e. PrBa₂(Cu_1-xM_x)₃O₇ for M=Al, Co, Fe, Ga, Ni and Zn, and x=0.05, 0.10, 0.15, and 0.20 were fabricated. No significant second phase was found for the Al, Co, Fe and Ga doped samples up to 20% doping level. Impurity phases, however, were detected for Ni and Zn doped samples when doping concentration reached 15% and higher. At 77 K the electrical resistivity for most of these compounds is several orders in magnitude higher than that of the PrBa₂Cu₃O_7-δ. Although the lattice parameters in the doped samples changes toward tetragonal structure, all sample remained in orthorhombic structure and the parameters remain very close to those of the undoped one and YBa₂Cu₃O_7-δ. For this reason these compounds may serve as improved I-layer materials for making YBa₂Cu₃O_7-δ SIS Josephson junction.

A study is made of the dissipative component of the electron transport in a doubly connected Andreev SNS interferometer with elastic mean free paths l_el in the metals of around 100μm and a macroscopic phase–breaking length which is two or more orders of magnitude larger than in disordered nanostructures. At helium temperatures, the samples are found to exhibit new phase–sensitive effects of a quantum–interference nature. Below 2K, the conductance of the macroscopic N region of the system has an oscillatory component of resonance shape which undergoes the phase inversion relative to the phase of the nonresonance oscillations. An explanation for the effects is suggested in terms of the contribution to the Josephson current from coherent quasiparticles with energies of order of the Thouless energy. The temperature behavior of the dissipative transport in a pure normal metal near an isolated NS point contact is studied.

The flux relaxation is one of important topics in the studies of high Tc superconductivity, because it is related to the energy loss in practical applications. There are many mechanisms, theories and relaxation laws suggested in the literatures. It is very interesting to test them according to the characters and compare them with the experiments. Some people think that the characters of the famous theories are their negative curvature. According our inversion solution, the relaxation ArcG law and experimental data analysis, the relaxation law has both positive and negative signs. This prediction is hopeful to be checked by experiments in future. The current densities of many high Tc superconductors decrease very rapidly in the early time in the relaxation. People do not know what their maximums are. In this work, a theory to determine these maximums of the current densities is presented. The theory is concretely realized by inversion for some real data of the YBCO and their maximum current densities are obtained.

Influence of flux creep on ac susceptibility (acs) of a superconductor was examined by simulation. Comparing the acs with and without flux creep, it was found that frequency of ac field shifted the acs with flux creep but did not affect the acs of critical state model. In addition, the amplitude of ac field and dc field affect differently for the two models.

The perturbation formulae of EPR parameters g factors g_x, g_y and g_z for the lowest Kramers doublet of 4f¹ ion in orthorhombic symmetry are established. In these formulae, the contributions of the covalency effects, the admixture between J=7/2 and J=5/2 states as well as the second-order perturbation (which is not considered in the previous works) via crystal-field and orbital angular momentum interactions are all included. According to these formulae, and by using the superposition model, the g-factors g_x, g_y and g_z for Ce³⁺ center in YBa₂Cu₃O_6+x superconductor are calculated. The results are discussed.

Previous interpretations of the thermal conductivity data of YBa₂Cu₃O₇ in terms of d-wave superconductivity have created the impression that this experiment can only be successfully explained in terms of a d-wave model. Here we show that thermal conductivity data can be (better) explained in terms of s-wave hole-pairing, which also handles some outstanding problems with the d-wave interpretation, namely, muon spectra that are s-wave and specific heat data that exhibit a zero-field linear-T term. The basic notion is that a high-temperature superconductor such as YBa₂Cu₂O₇ contains both superconducting and non-superconducting bands. The main superconducting bands are associated with BaO, and the CuO₂ bands are non-superconducting.

Optical conductivity spectra of conducting oxides including high-T_C cuprates - compared to non-superconducting nickelates in particular - deduced from infrared reflectivity spectroscopy in polarized light and their doping and temperature dependence, are discussed with emphasis on the signatures of intrinsic inhomogeneities of charge carrier concentration. The model of disordered metal is shown to be compatible with the general loss of spectral weight in the optical conductivity upon decreasing frequency, instead of a maximum conductivity at zero frequency as found within a Drude description. In high-T_C multilayer cuprates, the discussion focuses upon the c-axis response and the inhomogeneity of the electronic concentration related to the conducting planes alternating with insulating sheets. The onset of stripes that are intrinsic inhomogeneities of the charge carrier distribution is discussed in the example of nickelates.

High quality melt-processed (Sm_0.33Eu_0.33Gd_0.33)Ba₂Cu₃O_7-δ superconductors were grown and microstructural origin of their distinguished superconducting performance was investigated by atomic force microscopy (AFM), transmission electron microscopy (TEM) and the field dependent superconducting transition performed with SQUID. A nanoscopic periodic array of chemical composition was unveiled. This novel structure acted as δT_c-style pinning centers.

The electron-phonon (EP) interaction in ternary silicides MGaSi with M=Ca, Sr and Ba are calculated using the full potential, density-functional-based method. A striking feature of the phonon spectra is the existence of very soft "B_1g" mode, which is strong anharmonic and plays an important role in superconductivity of the MGaSi compounds. The superconducting transition temperatures T_c in these compounds have been evaluated. It is found that the variation trend in T_c can be explained from the strength of the electron-phonon coupling.

The presence of nano-structures, i.e. static or dynamic stripe-like features or nano-domains in HTSC, can cause a quasi-1D flow of a transport current through these materials. We present the experimental results, which reveal the effect of a filamentary flow of the current on the normal and superconducting transport properties of HTSC.

For high–T_c superconductor metal oxides (HTSC) it is shown that the dc resistivity and Hall effect temperature behaviour can be explained by the model of the paraelectric material close to the point of the Mott-Hubbard instability, in the ground state of which the current is carried by a liquid of boson-like pairs of carriers in upper and lower Hubbard bands. The Mott-Hubbard instability corresponds to the order-of-lattice-constant length of the mean free path and results in the temperature insensitivity of Drude conductivity. Nearly linear on T resistivity results from the Curie law via the local (acting) electric field. Fermion-like carriers, temperature excited over the energy of boson-like pair dissociation (pseudo gap), explain the temperature behaviour of Hall effect. Available data are compared with the model.

We present the latest data of the c-axis bicrystal twist Josephson junctions experiments of Liet al. and of the artificial and recent natural cross-whisker junction experiments on Bi₂Sr₂CaCu₂O_8+δ (Bi2212) of Takano et al. and Latyshev et al., respectively. These combined experiments provide strong evidence for a dominant s-wave order parameter and for strongly incoherent c-axis quasiparticle tunneling in Bi2212 for T≤T_c.

Our recent experimental works on the field-induced and impurity-induced magnetic order in La_2-xSr_xCuO₄ are reviewed. The muon-spin-relaxation (μSR) measurements of La_2-xSr_xCu_1-yM_yO₄ (M=Zn, Ni) have revealed that both Zn and Ni impurities develop the magnetic order around x=0.115, though the effect of Zn on the development of the magnetic order is more marked than that of Ni. The field-induced magnetic order around x=0.115 pointed out from the neutron scattering experiments has also been investigated by the thermal conductivity measurements in magnetic fields. Marked suppression of the thermal conductivity by the application of magnetic fields parallel to the c-axis has been observed in x=0.10 and x=0.13, which appears to be in good correspondence to the development of the magnetic order. In conclusion, not only impurities but also vortex cores in the CuO₂ plane seem to operate to pin the dynamical stripes of spins and holes, leading to the development of the magnetic order.

The balance of forces on the superconducting condensate in the presence of currents is discussed. It is shown that the electrostatic potential known as the Bernoulli potential is a useful concept which allows one to establish conditions of a stationary motion.

If the condition for magnetic nesting is fulfilled for the electron dispersion law with spin σ along a certain preferential direction n, ferromagnetism and the inhomogeneous superconducting state can coexist up to very high magnetization I. This fact was used to explain the coexistence of ferromagnetism and superconductivity for layered cuprates of the RuSr₂GdCu₂O₈ type, which possess a finite, though rather high critical magnetization, because the conditions for magnetic nesting are fulfilled only approximately.

Recent Nernst and interlayer transport experiments in Bi₂Sr₂CaCu₂O_8+y (BSCCO) high temperature superconductors report hugely different limiting magnetic fields. We demonstrate that both fields convert to the same pseudogap energy scale T* upon transformation as orbital and Zeeman critical fields, respectively. We suggest a consistent interpretation of this finding based on separation of spin and charge degrees of freedom residing in different regions of a truncated Fermi surface.

Detailed tunneling characteristics of a stack of intrinsic Josephson junctions in a Bi₂Sr₂CaCu₂O_8+x single crystal were obtained both in spin-degenerate and spin-polarized bias configurations. Injection of the spin-polarized quasiparticles effectively weakened the in-plane superconducting strength and the interlayer Jospehson coupling. The superconducting gap and the Josephson critical current of the stack were, in general, further suppressed by an external field applied in parallel with the c-axis direction. Study of the spin-dependent tunneling characteristics may provide valuable information on clarifying the mechanism of high-T_c superconductivity as well as the interlayer phase fluctuation induced by the "pancake vortices" on CuO₂ layers.

We observed subbranch splitting in the low-bias vortex-flow branch of a dense-Josephson-vortex state in current-voltage characteristics of Bi₂Sr₂CaCu₂O_8+x intrinsic Josephson junctions in the long-junction limit. We suggest that each subbranch corresponds to a plasma mode in serially coupled Josephson junctions, manifested in the Josephson vortex-flow current-voltage characteristics resonating with the plasma modes.

Anisotropy of a c-axis aligned Sr_0.9La_0.1CuO₂ infinite-layer superconductor was studied by measuring the magnetization in different temperature (M(T)) and angle (M(θ)). The M(θ) and the critical temperature as a function of the angle (T_c2(θ)) deduced from M(T) was well described by the anisotropic Ginzburg-Landua theory with a moderate anisotropy value γ≈9. This low value, which is comparable to that of YBa₂Cu₃O_7-δ implied strong interlayer coupling between CuO₂ planes. In this compound, the strong interlayer coupling was thought to solely result from the crystal structure without charge reservoir blocks.

In this paper, we generalized the perturbation approach to study the quasi-two-dimension extended Hubbard model. This model is characterizing by intra-chain electron hopping t, on-site Column interaction U, nearest-neighbor interaction V, and inter-chain electron hopping t′ and nearest-neighbor interaction V′. An effective Hamiltonian up to sixth-order in t/U, t/V, t/V′, t′/U, t′/V and t′/V′ expansion was obtained and the spin-spin correlation functions were calculated. We presented results for t=t′, V=V′.

For Bi-based cuprate superconductors, increasing its Cu content by heat-treatment is probably a beneficial way to its superconducting transition. In the paper, the corresponding methods and procedures of the experiment were proposed, and the theoretical analysis and explanation of the experimental results were conducted. The method of increasing Cu content by heat-treatment is innovative.

Systematic studies of x-ray diffraction(XRD), superconductivity and Mössbauer effect on Fe_xCu_1-xBa₂YCu₂O_7+y (x=0.00~0.70) superconductors synthesized by high pressure (HP) were summarized. All the HP-samples have tetragonal structure, smaller lattice parameter c and unit-cell volume than the AM-samples (synthesized by ambient pressure). The HP-samples have higher oxygen content than the AM-samples. Moreover, for the HP-sample with x=0.5, all of the Fe located in the CuO_x chains have fivefold-oxygen coordination.

We present point contact tunneling spectroscopy measured on TlBa₂Ca₂Cu₃O_10-δ (Tl1223) with three CuO₂ planes in a unit cell. Our samples of Tl1223 with T_c~91K are heavily overdoped at the outer CuO₂ planes (OP), but slightly underdoped at the inner CuO₂ planes (IP). The tunneling conductances on Tl1223 exhibit two kinds of gaps that originate from crystallographically inequivalent IP and OP. The overall spectral shape of tunneling conductance for Tl1223 is consistent with that observed on a bilayer Bi₂Sr₂CaCu₂O_8+δ, that is, unusual peak-dip-hump (PDH) structures are observed. The origin of PDH structures is controversial, but these results, especially, the observation of PDH for trilayer Tl1223 in which interlayer effects should be quite different from that in bilayer, put severe constraints on any theoretical model for the origin of these structures.

Spatial variation of low temperature tunneling spectrum on atomic scale was examined on the slightly underdoped Bi2212 sample (T_c~74K, p~0.12) by using a STM/STS technique. We observed a V-shaped gap with sharp coherence peaks, which is expected for d-wave superconductors, over the distance of ~18 nm and no other kind of gap. The spatial variation of gap size Δ₀ is small, ranging from 41 to 53 meV. These results indicate that the superconductivity takes place rather homogeneously in the slightly underdoped sample.

Using photolithography and Ar ion milling, we fabricate small mesas on top of the Bi_2.3Pb_0.1Sr₂CaCu₂O_8+y single crystals to study the inherent tunnelling property of intrinsic Josephson junctions. The I-V characteristics of the mesas show a typical multiple branches with large hysteresis. The return current I_r depends on the N-th branch. The relation of I_r and N follows I_r=I₀*N^m, where -1<m<0 might be related to the Coulomb blockade effect. The McCumber parameter β_c of the samples is also investigated.

The application of transmission electron microscopy in combination with physical-chemical methods has made it possible to discover a large number of discrete oxides of ordered structures in the Ba-Bi-O system, which is the parent system for the K-Ba-Bi-O superconducting system. Cation-ordered superconductors Ba_1-xK_xBiO₃ with the crystalline structure of a non-cubic and layered nature have been synthesized. This result removes the crystallographic contradiction between bismuthate and cuprate superconductors that provides support to the existence of a common non-magnetic pairing mechanism.

Chlorine-containing (Sr,Ca)₃Cu₂O_4+δCl_2-y (0212-Cl) superconductor is the high-T_cCu-oxide superconductor (HTSC) with T_c=80 K and was synthesized under high-pressure and high-temperature. The 0212-Cl has double [CuO₂] planes and the apical oxygen are replaced by Chlorine. We measured the resistance of 0212-Cl under high pressure using a diamond-anvil cell up to 13.3 GPa and two-terminal ac-method to investigate the pressure dependence of T_c. T_c of 0212-Cl increases gently with increasing pressure.

The properties of the normal and superconducting phases of p- and n-type cuprates are investigated in the appropriate low-energy models in the approximation beyond Hubbard I considering spin fluctuations. Calculated chemical potential dependence on doping, Fermi surface and T_c(x) phase diagram for n-type cuprates are in remarkably good agreement with the experimental ones. Comparison of the singlet-triplet t-J model with simple t-J model shows that the spin-exciton mechanism originated from singlet-triplet hybridization leads to small contribution to the T_c(x) - optimal doping value becomes slightly lower and the maximum value of T_c become slightly higher.

The CaCuO₂ with infinite-layer structure (IL CaCuO₂) was synthesized under high-pressure. The p-type doped infinite layer compounds Ca_1-xNa_xCuO₂ with the different carriers concentration (x=0.05, 0.1) were also prepared from high temperature and high-pressure technique. The lattice parameter a decreases with increasing Na content x in the p-type doped Ca_1-xNa_xCuO₂, suggesting that the hole like carriers enter into the CuO₂ plane, and Na is successfully doped into the infinite-layer CaCuO₂. This was confirmed by the systematic evolution of resistance with increasing the doping level. However, no superconductivity was observed in the samples.

The bulge in the doping dependence of the basal plane area of cuprate superconductors is shown to be an effect of the particular inhomogenous electronic structure created by the dense packing of paired self-protected singlets (PSPS) in CuO₂ lattices.

Experimental results in search for pressure-induced superconductivity are reviewed. Typical examples are simple inorganic and organic molecular crystals, magnetic metals, and elements. We have developed complex extreme condition of very low temperature down to 30 mK and ultra high pressure exceeding 200 GPa by assembling compact diamond-anvil cell (DAC) on a powerful ³He/⁴He dilution refrigerator. Using the newly developed apparatus and techniques, we have studied superconductivity in various materials in various pressure range. In this paper, we will shortly review our newly developed experimental apparatus and techniques and discuss about examples of pressure-induced superconductivity in simple metals.

Single crystals of multi-layered Ba₂Ca₄Cu₅O₁₀(O,F)₂ superconductor(F-0245) have been grown under a high pressure of 4.5 GPa. Single crystals with in-plane length of 500μm were typically obtained and flat shiny areas with more than 1mm² were also observed on the surface of fractured samples. T_c values for these samples were determined by electrical resistivity measurements. These values were found to change from 70 K to 85 K by change of oxygen and fluorine contents in the starting mixture. The temperature dependence of resistivity showed characteristic of under-doped cuprate superconductors.

Based on the extended Hubbard model with the next nearest neighbor hopping term, we study the impurity states in a slightly underdoped (with 0.13 hole) system with competition between d-wave superconductivity and antiferromagnetism by solving the mean field Bogoliubov-de Gennes equations self-consistently. Nickel and Zinc impurities are studied respectively using the potential scattering impurity (PSI) model and the Anderson impurity (AI) model. The significant difference in their local density of states may be useful to predict the impurity states in the stripe phase of the superconductors in the slightly underdoped region.

Hysteresis V-I curves were simulated based on flux creep model. The clockwise loop was found for a sample with homogenous flux pinning if a fast current sweeping rate is used. Moreover, it is shown that an applied magnetic field can suppress the loop. The results coincide qualitatively with the relevant measurements.

Single crystals of two-dimensional 2H-NbSe₂, which undergo superconducting transition at T_c=7.1K and charge-density wave (CDW) transition at T_CDW=30K, were synthesized. The resistance residual ratio (RRR=R(300K)/R(8K)) of the samples from different batches varies from 10 to 30, but the superconducting properties hardly change with RRR. The magneto-resistance (MR)is generally small and its temperature and field dependence of MR violate the Kohler's rule that holds for many conventional metals, indicating that the scattering times of charge carriers are no longer isotropic. The steep decrease of Hall coefficient R_H below 50K can be interpreted by the drastic increase of the mean-free-path of electron type charge carrier. The influence of CDW transition on the resistivity and Hall effect is discussed in a two-band model.

Two-dimensional (2D) correlation analysis is applied to the temperature dependence on the Raman spectra of superconducting YNi₂B₂C single crystal. 2D correlation analysis on the temperature dependence of the B_1g superconducting gap peak shows strong correlation with the NiB_1g phonon peak near 200 cm^-1. The analysis on the B_1g phonon peak itself shows that the peak is composed of essentially two peaks at 197 and 203 cm^-1, and only the weight of the two peaks changes as the temperature changes. The result suggests that there are two distinctive environments of the Ni-B bonds in YNi₂B₂C system at the superconducting state.

We present scanning tunneling spectroscopic and high-field thermodynamic studies of hole- and electron-doped (p- and n-type) cuprate superconductors. Our experimental results are consistent with the notion that the ground state of cuprates is in proximity to a quantum critical point (QCP) that separates a pure superconducting (SC) phase from a phase comprised of coexisting SC and a competing order, and the competing order is likely a spin-density wave (SDW). The effect of applied magnetic field, tunneling current, and disorder on the revelation of competing orders and on the low-energy excitations of the cuprates is discussed.

The effect of intermediate deformation (ID) on texturing of Bi-2223 phase was studied by SEM and rocking curve. There exists a peak value for the degree of texturing as a function of ID reduction. The optimum reduction for intermediate rolling and intermediate pressing is 14.3% and 10.7%, respectively. The texturing of the Bi-2223 phase was further improved by the final heat treatment after ID. Moreover, the critical current density (J_c) of the tapes was directly proportional to the texturing of Bi-2223 phase.

In this paper, we study phase separation in the two-dimensional single-band Hubbard model with the unrestricted Hartree-Fock(UHF) method and the restricted Hartree-Fock (RHF) method. We perform the calculation for square lattices and rectangle lattices. It is observed that the stripe phase exists and it depends on three aspects: geometry of the lattice, Coulomb interaction U and band filling n. To gain more physical insights, we consider the Hubbard model with spin dependent hoppings: t_↑ and t_↓, and study the effect of varying on the phase separation.

In this paper the superconducting properties in La_1.85SSr_0.15Cu_1-xMn_xO₄ and La_1.85-2xSr_0.15+2xCu_1-xMn_xO₄ samples are discussed. The superconducting transition temperature keeps constantly at 37 K for all superconducting samples. The suppression of superconductivity in these systems does not fit the Arbrikosov and Gork'ov theory which predicts that T_c should decrease in the presence of magnetic impurities in the lattice. The magnetic pair-breaking effect is not the reason for the suppression of superconductivity in Mn doping systems. The localization of carriers in the CuO₂ plane induced by Mn doping should be responsible for the suppression of superconductivity.

The higher doping level Y_1-xCa_xBa_2-xLa_xCu₃O_y samples were synthesized with x from 0.25 to 0.55. Structure and superconductivity have been investigated. Comparing with the results of lower doping level, the T_c of these samples keeps almost constant when dopant increasing. While some structural characters, such as Cu(1)-O(4), Cu(2)-O(4) bond lengths change randomly in a narrow range. The relationship between Ba/La position and T_c is rather interesting. The results give another evidence that the influence of structural change on superconductivity is independent of carrier concentration.

Three MTG Ag-Y_1.8Ba_2.4Cu_3.4O_7-x samples were fabricated to study the effect of doping Ag on magnetization. Magnetizations measured at various temperatures and fields show two peaks for all samples: the first peak in low field and second peak in middle field. We examined the effect of doping Ag and temperature on these peaks and discussed the origin of the peaks.

It is found in oxygen there are a weight loss and an endothermal anomaly in compound of Y_1-xCa_xBa₂Cu₃O_y starting at about 320 °C, while in nitrogen at about 370 °C and a mixed atmosphere, N₂(50%)+O₂(50%), at about 350 °C. The results are different from those in undoped YBa₂Cu₃O_y and some doped systems. It is suggested that Ca prefers a sixfold coordination, which causes the oxygen loss in Cu(2)-O plane and the weight and heat anomalies at different temperature in different atmospheres. The oxygen loss in Cu(2)-O plane is also responsible for T_c suppression in Y_1-xCa_xBa₂Cu₃O_y.

In YBa₂Cu_3-xNi_xO_y at about 480°C all the samples show a tetragonal phase. Comparing the structural changes at 480°C with those at room temperature, the bond lengths such as Cu(1)-O(4) and Cu(2)-O(4) vary regularly with Ni-content increasing at room temperature, but not at high temperature. It suggests that there is a close correlation between structural changes and superconductivity in this system. The difference of orthorhombic- tetragonal phase -transition is also discussed between undoped YBCO and Ni-doped YBCO at high temperature.

We have performed a detailed study of the conductance characteristics obtained by point contact junctions realized between a normal Pt/Ir tip and syntered RuSr₂GdCu₂O₈ (Ru-1212) samples. Indeed, this compound is subject of great interest due to the coexistence of both magnetic order and bulk superconductivity. In our experiments, the low temperature tunneling spectra reproducibly show a zero bias conductance peak that can be well reproduced by a generalized BTK model in the case of d-wave symmetry of the superconducting order parameter.

The measurements of lower-critical-field H_c1(T), upper-critical-field H_c2(T) and the bulk pinning force F_p(H) were carried out for a superconductor MgCNi₃ sample with T_c=7.5K prepared under high pressure. The sample has a good extensibility. We conclude that the flux pinning at lower fields results from the intra-granular structural defects, such as dislocations, and the enhancement of bulk pinning force near the irreversibility field H_irr is due to the softening of the flux lattice.

Using the apical oxygen doping mechanism, i.e. a partial substitution of divalence O for the monovalence Cl, a p-type copper oxychloride superconductor, Sr₂CuO_2+δCl_2-y, was synthesized at 1050°C under 6.0 GPa for 1h. The X-ray powder diffractions show that the main phase has a tetragonal structure with a=3.93Å, c=15.65 Å. The magnetic susceptibility as well as resistance measurements indicated that the bulk superconducting transition temperature of the sample is 30K.

The evolution of superconducting transition of CuBa₂Ca₃Cu₄O_10+δ (i.e. Cu-1234) superconductor has been studied by using diamond anvil cell technique. The Tc of Cu-1234 can be enhanced continuously from ambient reaching to 123 K at 15 GPa. This seems the one more system besides Hg-12(n-1)n which demonstrate the positive pressure effect on Tc over a wide pressure range above 10 GPa.

Superconducting onset temperatures T_c up to 23-44 K are reported for the new RuCa₂RCu₂O_8+δ (R=Pr, Nd, Sm, Eu, Gd) system with a Ru-1212 RuCa₂PrCu₂O_8+δ-type structure. Preliminary study indicates that the crystal structure is an orthorhombic distortion of the tetragonal RuSr₂GdCu₂O_8+δ-type structure ,which has space group P4/mmm, T_m~136 K, and T_c(max)~65 K. With similar RuO₆ octahedral and CuO₅ pyramidal units, superconductivity from the Cu-O bi-layers apparently coexists with the weak ferromagnetic (WFM) order with magnetic ordering temperature T_m~49 K. Low temperature anomalous in magnetic properties observed in both field-cooled (FC) and zero-field-cooled (ZFC) modes are closely related to the complex interplay and coexistence between weak ferromagnetic order and superconductivity as well as from structural distortion and sensitive sample oxygen concentration variation. No superconductivity or Ru-1212 structure can be detected for larger rare earth compounds R=La and Ce.

Detailed study of the electronic structure of the layered Na_0.7CoO₂, doped Mott insulator with triangular Co lattice is performed by angle-resolved photoemission spectroscopy (ARPES). At low temperature Fermi surface is a centered hole pocket of hexagonal character shape in agreement with LDA. A broad valence band satellite at higher energies showing resonant enhancement at the 2p, 3p→3d excitations indicates large on-site Hubbard-U~5 eV. A momentum dependent quasiparticle band near Fermi level that is flat and vanished at energies already above 70 meV or 80 meV gives a value of the single particle hopping t<10 meV. This band is defined only in the region of non - Fermi liquid transport with linear growth of resistivity up to 120 K.

The crystal structure and magnetic properties of (Ru_1-xSn_x)Sr₂EuCeCu₂O_z and Ru(Sr_2-xLa_x)EuCeCu₂O_z(0≤x≤0.1) samples have been investigated to shed light on the doping-induced changes in the magnetic properties of Ru-1222 system. We show that La substitution for Sr leads to an increase in the temperature where the ferromagnetic component is observed and a moderate suppression of the ferromagnetic component whereas Sn substitution for Ru results in a significant decrease of the volume fraction of the ferromagnetic phase as well as a decrease in the magnetic ordering temperature. The experimental results are discussed in connection with the structural data studied by Rietveld refinement of the x-ray diffraction data.

We have investigated the Ca-doping effects on the structural, electrical and magnetic properties of (Pb_0.5Cu_0.5)Sr₂(Pr_1-xCa_xCu₂O_z(x=0-0.5) bulk ceramic samples. The electrical resistivity, thermoelectric power and magnetic susceptibility measurements reveal that the Ca doping introduces holes into the system and thereby superconductivity with onset T_c, of about 36 K is induced for a phase with x=0.5. These results are discussed in conjunction with the roles of hole doping, structural changes and Pr-O hybridization in CuO₂ layers.

Anisotropic superconducting properties of new layered intermetallic compounds CaAlSi and CaGaSi with AlB₂ structure are studied. These superconductors show moderate anisotropy with anisotropy parameter determined by both magnetic and transport measurements. Despite the small value of γ, angular dependence of H_c2 in CaAlSi shows cusp-like feature for fields parallel to the superconducting plane, suggesting the presence of two-dimensional superconducting units. By contrast, H_c2(θ) in CaGaSi can be reasonably well explained by the anisotropic GL-model. X-ray diffraction measurements reveal the presence of superstructure along the c-axis in CaAlSi but not in CaGaSi. These findings suggest a close relationship between the anomalous angular dependence of H_c2 and the superstructure. Possible origins of the two-dimensional superconducting units in CaAlSi are discussed.

The effect of YBCO nanoparticles added into MgB₂ on T_c, J_c, and flux pinning was studied for MgB₂(YBCO)_x with x=0, 5, 10, 15 wt%. Phase analysis shows that none of elements are doped into the MgB₂ lattice in the samples with YBCO addition. For the samples with YBCO addition, the J_c-H characteristics behave poorly in comparison with the pure sample. Our experimental results show that the nanoscale size of addition dosen't comprise the only condition for its effectiveness as pinning centers.

A solution process was used to grow SrTiO₃ (STO) buffer layers on LaAlO₃ (LAO) and biaxially textured Ni substrates by spin coating technique. The epitaxial STO film obtained has strong cube texture and uniform microstructure. A metal organic decomposition process using trifluoroacetate precursors was applied to deposit YBa₂Cu₃O_7-δ (YBCO) thin films on these buffer layers. The YBCO/STO/LAO was biaxially textured and the T_Conset and ΔT_C is 90.1K and 2.7K, respectively.

Ramp junctions have been successfully synthesized utilizing an Y_1-xPr_xBa₂Cu₃O_y barrier with a continually graded concentration of Pr. The properties of these junctions are dominated by the barrier material rather than the boundary. Also, the damaged ramp surface is excluded from the weak link region so its influence is minimized. The Josephson coupling occurs at the naturally formed S/N interfaces within the Y_1-xPr_xBa₂Cu₃O_y layer. Thus it leads to a highly transparent S/N boundary and greatly enhances the performance of the junctions. The effective thickness of the barrier can be varied even post fabrication, depending on the measuring temperature and the concentration gradient. The temperature dependence of the barrier thickness and Josephson properties were investigated and compared with those junctions with a conventional single barrier. These unique features should motivate further studies on the nature of these junctions.

Integration of a high-temperature superconducting (HTS) narrowband bandpass filter and a HTS bandstop filter onto a single piece double-sided YBCO thin film with 0.5mm-thick LaAlO₃ substrate has been carried out. The 8-pole bandpass filter was designed with a fractional bandwidth about 0.8%. A pair of transmission zeros was implemented, showing typical quasi-elliptical function characteristics. The bandstop filter has a high stopband attenuation (~70dB) to fulfill the special requirement of potential application in communications. Integration of the two filters was successfully achieved.

We fabricated nano-bridges on MgB₂ thin films so as to demonstrate Josephson effect. Those bridges smaller than 200 nm widths show the resistively-shunted-junction (RSJ)-like current (I)-voltage (V) curves with hysteresis. We also observed a few of microwave-induced steps that correspond to the Josephson voltage-frequency relations at 33 K.

The exponential model is proposed for levitation force calculations of high temperature superconductors in place of Bean model according to the Exponential relationship between the critical current density and applied field. The calculated results are larger than the experimental results in both symmetrical and unsymmetrical applied fields. The normalization curves agree well in the symmetrical applied field, however, they much differ in the unsymmetrical applied field.

When the velocity of the normal ground traffic transportation is higher than 350 km/h of the speed limit, not only the running noise of the ground traffic vehicle is higher, but also the 90% driving power is dissipated in the aerodynamic resistance. The high speed may be realized when a high temperature superconducting (HTS) Maglev vehicle runs in low-pressure tube or evacuated tube transport (ETT). Its speed is over 3000 km/h. As a new ground transportation system the HTS Maglev vehicle is presented after the experiment results of HTS Maglev vehicle are discussed in this paper.

A superconducting magnetic levitation system, with permanent magnet guideway and bulk superconductors, can realize a more advantageous system for transportation. The calculations of electromagnetic force characteristics are presented using finite element method analysis. The hysteretic behavior of the forces has been reproduced assuming a critical state model for the superconductor, and the results of the analysis are compared with the experimental data. Prom these results we have confirmed that the three-dimensional structure of magnetic field and the electromagnetic performance of superconductors strongly influence the characteristic of the electromagnetic force. Furthermore, a new hybrid superconducting magnetic levitation system has been designed to optimize the electromagnetic force.

The multiple quasiparticle tunnelling branches with large hysteresis were measured on the mesas of Si⁺ implanted Bi₂Sr₂CaCu₂O_8+x single crystals. For given Si⁺ dosage the tunnelling critical current I_c, decreased for junctions located closer to the mesa surface; meanwhile the voltage interval between the neighboring quasiparticle branches decreased with increasing the Si⁺ dosage.

The grown cross traces on the top surface of single-domain YBCO bulk sample with c-axis normal to the top surface has been clearly revealed. It is found that there are many fish-scale like YBCO layers, which are well connected each other. The c-axis is normal to the top surface of the sample, which indicates that YBCO crystal starts to grow from the center to the edge along a(or b) axis in all the four regions divided by across traces, and forms a 90° angle when the four regions meet each other, The clear traces observed is just because of the slightly difference in height between adjacent regions. A simple model has been afforded to explain the growth mechanism of single-domain YBCO bulks with c-axis normal to the top surface.

The morphology of the top surface and the vertical section of single-domain YBCO bulk samples with c-axis parallel to the top surface have been clearly revealed. The sample with c-axis parallel to the top surface grows epitaxial from the seed (in the center) to the edge in all the four regions divided by grown cross traces on the top surface, but the growth style is different in the adjacent regions. If YBCO crystal grows along a (or b) axis in one region, it must be grow along c-axis in the adjacent regions. The grown traces on the top surface forms a 78° angle when the four regions meet each other. The clear traces are formed by the different growth rates, styles along c-axis and a (or b) axis and also the slightly height difference of YBCO crystal between adjacent regions.

In this paper, we present a high temperature superconducting (HTS) Filter subsystem, which consists of a 14-pole HTS filter, a low noise amplifier (LNA), a Stirling Cooler and an electronic control system. The HTS filter has a 2.1% fractional bandwidth at 814MHz. It was fabricated on MgO substrate which was double sides coated with YBCO thin films. The insertion loss of the HTS filter is less than 0.2dB, the gain of the subsystem is 22dB at 60K. In this subsystem, the out-of-band rejection is better than 70dB and the steepness of the band-edges is larger than 25dB/MHz at 60K.

High-quality YBa₂Cu₃O_7-x (YBCO) thick films with thickness over 4.0μm were deposited by photo-assisted metal-organic chemical vapor deposition (PhA-MOCVD) technique with high growth rates. Microstructures of YBCO thick films have been systematically investigated by scanning electron microscopy, high-resolution transmission electron microscopy, and selected area electron diffraction techniques. The fabricated YBCO thick films are very dense and single-crystal like with no visible grain boundaries or voids. The high quality of the prepared YBCO thick films was confirmed further by the results of X-ray diffraction analyses and J_c measurements. Thus, these thick YBCO films prepared by PhA-MOCVD technique have promising application potential in fields such as coated conductors.

As the information technology grows up and its application penetrates into every area of this world, how to faster and more efficiently transport people and goods is becoming the new social demand, which indicates a new revolution on advanced transportation technology being brewed. High-temperature Superconductivity Maglev (HTSM) is one with the best development potential among most transportation technologies. It could be used in many advanced transportation fields, overcoming the key contradiction and shortcoming of the current transportation patterns such as train, automobile and airplane. On the other hand, HTSM will promote theoretical study and technology exploitation on superconductivity. HTSM's applications in a large scale will bring up profound effect on the forming and development of the superconductivity industry.

A scanning SQUID microscope based on HTS dc SQUID has been developed. One of the applications of this microscope is to detect weak currents inside the sample. Considering that what being detected by the SQUID is the vertical component of the magnetic field on a plan where the SQUID lies, whereas the current which produces the magnetic field is actually located in a plan below the SQUID, a TWO PLAN model has been established. In this model Biot-Savart force laws and Fourier transformation were used to inverse the detected magnetic field into the underneath weak current. It has been shown that the distance between the current and the SQUID and the noise ratio of the experimental data have significant effects on the quality of the inverse process.

Some properties of the ideal and pinned vortex lattice in superconductors are outlined.

We performed simulations on in-plane current driven Josephson vortex systems in high-T_c cuprates at weak parallel magnetic fields and /or low anisotropies. It is found that the in-plane resistivity is Lorentz-force dependent at small current regime below the melting transition. As the current increases, the Josephson vortex lattice melts dynamically, the Lorentz-force independence of resistivity reappears. These results are possibly related to the experiments on YBCO.

One efficient method to investigate the vortex matter in the high-temperature superconductors is to measure the magnetization while shaking vortices by applying a transverse ac magnetic field, H_ac. When a small transverse H_ac is superposed with the dc magnetic field, the vortices will experience time-varying torque by ac field. This vortex shaking gives rise to effective reduction of pinning energy, which in turn gives rise to a rapid relaxation of the irreversible magnetization. This experimental approach has been used to study the nature of the anomalous magnetization peak in a N₂-annealed Tl₂Ba₂CuO single crystal. Shaking vortex unveiled the otherwise unobserved anomalous magnetization peak; when H_ac=0, no noticeable structure in the magnetization loop was observed, but with vortex shaking by H_ac, the magnetization loop deformed to exhibit the anomalous magnetization peak. The evolution of the anomalous peak with H_ac can provide a clue to the understanding of the underlying mechanism for the occurrence of the peak.

c-axis micro-bridges of La_2-xSr_xCuO₄ (LSCO) single crystals were fabricated by the focused-ion-beam (FIB) etching method. Small rectangular LSCO pieces were fabricated by cutting and grinding single crystals of underdoped LSCO of x=0.09. The size of LSCO single crystals between electrodes was cut to 20×40μm² in ab-plane by using the FIB etching method. Superconductor-insulator-superconductor (SIS) like-branch structures on I-V curves of the LSCO stacks were observed for the first time. The branch structures exhibited voltage jumps of several tens mV in the range of from 1.7 K to 5 K with temperature dependence. When the temperature is changed from 5 K to 1.7 K, the critical current and the next branch split into a few of small voltage jumps with the intervals of several mV in the range of from 0.1 mV and 2.0 mV.

Using molecular dynamic simulations for the melting transition of a flux line lattice(FLL) with point disordered pinnings, thermal fluctuations and magnetic interactions between pancake vortices, we study the disorder-driven melting transition from a disentangled and ordered Bragg glass (BG) to an entangled amorphous vortex glass (VG) or a vortex liquid (VL) in the pinning strength-temperature phase diagram. A portion of the BG region is found to be sandwiched in between the VG phase at lower temperatures and VL phase at higher temperatures, exhibiting inverse melting behavior observed recently on BSCCO crystals.

Zero temperature velocity-force curve of a flux-line system driven by Lorentz force in the presence of quenched random point-like disorders is simulated. The velocity shows a sudden increase at the depinning force F_c for both systems with Bragg glass (BG) annealed ground state and vortex glass (VG) one. At driving force slightly above F_c all flux lines move forward incoherently with large fluctuations in velocity as well as in the transverse direction, resulting in winding flow paths and no channel.

Tl₂Ba₂CaCu₂O₁₀ (Tl:2212) thin films were prepared on LaAlO₃ substrates with (0 0 1) direction normal to their surface, and the logR-logH characteristics were measured using the in-plane resistivity measurements in magnetic fields tilted away from c axis to the ab-plane. The H*_c-H_ab phase diagram was obtained by defining a resistance criterion below the vortex phase melting transition resistance. The linear dependence of H*_c on H_ab in most angular range shows that the crossing-lattice structure in the tilted fields exists in Tl:2212. A perpendicular line was observed in the H*_c-H_ab diagram at the range of θ ¡ 0.4 ° at 88K, which was attributed to the lock-in transition.

We show that quantized magnetic vortex lattice in high-temperature cuprate superconductors driven by dc or ac current is a very good model system for investigating physics of friction of solid. Based on the dc I-V characteristic measurement and viscosity measurement using microwave techniques in Bi₂Sr₂CaCu₂O_y and La_1.85Sr_0.15CuO₄, the corresponding kinetic friction was obtained as functions of temperature, magnetic field and driving current density. With increasing magnetic field and temperature, velocity dependence of kinetic friction behaves as that at interfaces with weak interaction of solid. This result means that we can control the kinetic friction, and that systematic experiments are available in a reproducible manner with using this system. Behavior of the kinetic friction at higher velocities (~1 km/s) agrees well with a two-class potential model at finite temperatures. Irradiation of the columnar defects was found to move the system closer to the so-called Amontons-Coulomb friction. This suggests that the random potential created by the strong pinning centers plays an important role of the validity of Amontons-Coulomb law.

Quantum phase slips can induce a phase transition in a single Josephson junction by varying coupling strength R_S to the dissipative environment. We study the finite Josephson junction array with dissipations. For the infinite arrays with no dissipation, a quantum KT phase transition can occur by varying the ratio of the Josephson coupling strength E_J to the charging energy E_c due to the unbinding of instanton pairs. At finite temperature and array size, there will be a rich interplay between instantons and quantum phase slips.

The melting transition in anisotropic type-II superconductors has been studied by the Lindemann criterion in the framework of elastic theory. Using two Lindemann numbers for two transverse directions, we find that the single melting transition can be obtained, when the ratio between the two Lindemann numbers reaches special value.

We have fabricated a small-sized mesa on the surface of the Bi_2.4-xPb_xSr₂CaCu₂O_8+y single crystals and measured the temperature dependence of the out-of-plane resistivity in different magnetic fields. The irreversibility line H_irr(T) follows different law in different temperature regions. But as a whole, the higher doping level x is, the irreversibility line locates in a higher field. The field dependence of activation energy follows U_eff∝H^-m, m increases when doping level x improves.

A single intrinsic Josephson junction has been observed in a Bi_2.3Pb_0.1Sr₂CaCu₂O₈ mesa structure. The isothermal voltage-current curves with hysteresis were measured from 5K to 65.09K. The critical current of the junction is almost a constant while the return current depends on the temperature. The temperature dependence of jumping voltage spacing deviates strongly from the BCS one. The temperature dependence of McCumber parameter β_c is shown.

The spin-polarized quasiparticles injection in YBCO film has been studied by means of current injection into NdSrMnO/SrTiO/YBaCuO heterostructures. Six injection junction windows are all 56μm wide, but 80μm, 40μm, 20μm, 10μm, 5μm, and 2μm long, respectively. Under I_inj=0.5Ma, injection efficiency η increases gradually with the decrease of injection junction length L, but η hardly varies when L is less than 20ηm. η_max is more than 6. These experiment results are related with the spin diffusion length of spin-polarized quasiparticles in a-b plane of YBCO film. "Current-adding principle" would be used carefully to explain the experiment phenomena.

We report on the preparation and the structural characterization of both YBa₂Cu₃O_7-δ/La_0.7Ca_0.3MnO₃ and La_0.7Ca_0.3MnO₃/YBa₂Cu₃O_7-δ bilayers grown onto (100) SrTiO3 substrates. The samples have been realized by sequential dc sputtering processes in high oxygen pressure starting from stoichiometric targets. The X-ray diffractograms and ϕ-scan reveal a high degree of epitaxiality of the heterostructures. In the case of YBa₂Cu₃O_7-δ topmost layer, we have found a superconducting transition temperature T_c of about 84 K while this is highly depressed when La_0.7Ca_0.3MnO₃ is deposited as outer layer. These last structures recover a higher T_c when a long annealing is carried out at T=560°C.

We have prepared Ag/BSCCO and Fe/Ag/BSCCO planar junctions to study the effect of Fe exchange field on the tunneling spectra. The junctions were constructed so that the tunneling direction is within the ab-plane, either along the maximum or minimum gap direction. Andreev bound states were observed as zero energy peak in the minimum gap direction. The exchange field caused major splitting of the zero energy peak, which did not occur in Ag/BSCCO junctions. We had detected a few percent (6 to 7%) of s-wave subcomponent at the interface in many of these junctions. This s-wave subcomponent had a T_c of about 20K.

YBa₂Cu₃O_7-δ/La_0.67Ca_0.33MnO₃ heterostructures were fabricated and patterned to study the interfacial transport between a ferromagnet (FM) and a d_x²-y²-wave superconductor. Zero bias conductance peaks (ZBCPs) in the differential conductance spectra were observed in the interface where a YBCO layer shows a mixed c- and a-axis orientation. In contrast, a zero bias conductance dip (ZBCD) was observed in the interface with a purely c-axis oriented YBCO layer.

The author of this paper has conducted the experimental study and optimal computing for the condenser of automobile air conditioner. Especially studied and computed the properties of heat transfer and flow at the side of air when using louvered fin. Analyzed the influence of several combinations of fin's geometrical dimensions to heat transfer and pressure drop. Furthermore, designed a program to conduct optimal computing, and the computing results are basically consistent with experimental results.

In this experimental research, jet pump is added to the cooling storage circulation of gas hydrates for the first time. The research result shows that: jet pump strengthened the mixture of water and refrigerant and formed the hydrate nucleus in jet pump. Compared with the circling without jet, the sub-cooled nucleation temperature reduced 2~4°C, the mixture time of hydrates shortened 13%~25% in the experimental parameter. There is a best jet proportion, which is about 0.4.

The present HVAC equipments for the residential buildings in the Hot-summer-and-Cold-winter climate region are still at a high energy consuming level. So that the high efficiency HVAC system is an urgently need for achieving the preset government energy saving goal. With its advantage of highly sanitary, highly comfortable and uniform of temperature field, the hot-water resource floor radiation heating system has been widely accepted. This paper has put forward a new way in air-conditioning, which combines the fresh-air supply unit and such floor radiation system for the dehumidification and cooling in summer or heating in winter. By analyze its advantages and limitations, we found that this so called Cooling/ Heating Floor AC System can improve the IAQ of residential building while keep high efficiency quality. We also recommend a methodology for the HVAC system designing, which will ensure the reduction of energy cost of users.

Based on the exergo-economic analysis of low temperature heat exchanger heat transfer and flow process, a new exergo-economic criterion which is defined as the net profit per unit heat flux for cryogenic exergy recovery low temperature heat exchangers is put forward. The application of criterion is illustrated by the evaluation of down-flow, counter-flow and cross-flow low temperature heat exchangers performance.

In the mechanical cutting process, the replacement of traditional cutting solution with cold air can avoid the pollution of environment. In order to high efficient the refrigerating device and flexible adjust the temperature of cold air, it is necessary to use cascade refrigeration system to supply cool quantity for the compressed air. The introduction of a two-component non-azeotropic mixing refrigerant into the cryogenic part of the cascade system, can effectively solve the problems of the system working at too high pressure and the volume expanding of refrigerant in case of the cascade refrigeration sets closed down. However, the filling ratio of mixing refrigerants impact on the relationships among the closing down pressure, refrigerating output and refrigerating efficiency. On the basis of computing and experiment, the optimal mixing ratio of refrigerant R22/R13 and a low temperature of -60° were obtained in this study. A cold air injecting device possessing high efficiency in energy saving has also been designed and manufactured. The cold air, generated from this cascade system and employed in a cutting process, takes good comprehensive effects on machining and cutting.

We calculate the quantum phase diagram of an extended Falicov-Kimball model in the intermediate coupling regime using a constrained path quantum Monte Carlo technique. The mixed-valence regime is dominated by a Bose-Einstein condensation of excitons with a built-in electric polarization.

We extend our previous EXAFS investigations on the relationship between magnetization and local distortions to the bilayer materials La_2-2xSr_1+2xMn₂O₇ and to higher magnetic fields, for quasicubic La_0.7Ca_0.3MnO₃. For each, there is a significant change in the broadening parameter σ of the Mn-O pair distribution function (PDF) associated with polaron formation as T is increased through T_c. Applying a magnetic field reduces the local distortion of the Ca sample for temperatures near T_c. For samples with sharp transitions, there is still a significant change of σ² with T below T_c when the sample is fully magnetized, i.e. distortions are still present and continuing to be removed as T is lowered well below T_c. A simple model is presented for the magnetization process.

We have developed a process to grow SrTiO₃ (STO) thin films showing single (110) orientation directly on Si by means of pulsed laser deposition technique. The growth of STO films directly on Si has been described. The crystallinity of the grown STO films was characterized by X-ray diffraction analysis of θ-2θ scan and rocking curve. Our results may be of interest for better understanding of the growth based on the perovskite oxide thin films on silicon materials.

The double perovskite (Sr₂CrWO₆) has been prepared in polycrystalline state by solid state reaction. At room temperature, the crystal structure is cubic (space group: Fm3m) with lattice parameter of 7.8200(2) (Å). Both ρ(H=0) and ρ(H=5T) show a semiconductor-like behavior over the whole temperature range up to 5 K. The highest MR(magnetoresistance) value of 55% (H=5T) was observed at 25 K. The valence state of Cr was determined by the X-ray absorption spectroscopy at Cr-L edge. The results, compared to the standard sample, show that the valence state of Cr is 3+.

Polycrystalline single phase (La_2-xSr_x)MnO₄ (1.10≤x≤1.40) samples were prepared by a citrate precursor method. They have tetragonal K₂NiF₄ structure with a space group of 14/mmm, increasing x, unit-cell a-axis increases and c-axis decreases, which is a result of decreasing of the Jahn-Teller effect due to the increase of the Mn(IV) ion. Spin glass state exists at low temperature and a hump observed from the susceptibility (χ) measurement is probably caused by the interactions of several magnetic phases. Among them, (La_0.6Sr_1.4)MnO₄ has the largest magnetoresistance ratio ([ρ(H)-ρ(0)]/ρ(0)), which reaches to 78.4% at 48 K. It is not possible to obtain single phase materials with 0.60≤x≤1.00 in the heat treatment temperature range of 1000-1600°C. Impurities were easily observed under SEM and X-ray diffraction patterns. Increasing the heating period and decreasing the temperature, the amount of ABO₃ perovskite phase increases. In order to extend the solubility range, of the SrO in the (La_2-xSr_x)MnO₄, it probably needs a higher temperature (>1600°C) and a shorter heat treatment period (<1 h).

A thick ceramic disk of 0.7Pb(Mg_1/3(Nb_0.9Ta_0.1)_2/3)O₃-0.3PbTiO₃ (PMNT-PT) was prepared by columbite precursor method with PbO powder buffer surrounding the disk during the sintering process. The dielectric and piezoelectric properties and the microstructure of PMNT-PT samples cut from the different depths of the disk are studied. The phase purity is homogenous in the whole disk within our x-ray diffraction resolution. The dielectric constants, and the piezoelectric effect, d₃₃, vary with different samples. The samples cut from the middle parts of the disk have the higher d₃₃. It is believed that the sample processes, especially the Pb volatilization is responsible for these results.

This paper is a brief introduction to the ferroelectric materials and their applications. Ferroelectric materials are very intriguing materials to both fundamental science and technologies. Ferroelectricity is an important critical phenomenon in physics. Ferroelectrics possess unique physical properties which make them very useful in electronics, computer memory unit and micro-electro-mechanic devices. The author proposed some interesting possible applications for the near future.

Barium ferrite films (BaFe₁₂O₁₉) with perpendicular orientation are attractive candidates for microwave device applications and ultrahigh density perpendicular recording. An in situ annealing process is developed for the deposition of Barium ferrite films by rf magnetron sputtering. The substrates are held at temperatures of 550 to 600°C during the sputtering. After the deposition, the substrate temperature is immediately raised to 900°C in the vacuum chamber in Ar and O₂ atmosphere. c-axis orientated films are obtianed. The films exhibit coercivity value of 4270 Oe and squareness of 0.87 in perpendicular direction.

The magnetization behaviors of two manganite oxide systems, La_0.7-xLn_xPb_0.3MnO₃ (Ln=PrandSm), have been synthesized. The replacement of La ions by Pr or Sm results in a considerable decrease in the ferromagnetic ordering temperature T_C and clearly irreversible behavior in the zero-field-cooling-field-cooling curve at a low applied field, showing a short-range spin order phase. These facts are in agreement with the smaller ionic radii of Pr (0.130 nm) and Sm (0.124 nm) ions in contrast to La ion (0.136 nm), and the corresponding larger distortion of perovskite structures. The saturation magnetization M_S decreases as Sm content increases relative to the increase of M_S as Pr content increases. This can be interpreted in terms of the competition between suppression of ferromagnetism due to structure tuning induced by the small ionic radius of the interpolated cations into the La-site and the increase of ferromagnetically interacting spins due to the introduction of magnetic Pr or Sm ions with f-shell electrons.

The electron drag effect of carbon nanotubes in electrolyte was studied. The carbon nanotubes in this study were synthesized by hot filament CVD. The experimental results showed there is a striking induced voltage on the surface of carbon nanotubes in flowing electrolytes. It was also found that the induced voltage was closely depended on the electrolyte concentration. The response time of induced voltage was relative to the kind and concentration of electrolytes. The origin of induced voltage was discussed.

The SEM observation on the cuticle of dorbeetle shows that the cuticle is composed of chitin fibers and protein matrix. The diameter of chitin fibers is from several to several-hundred nanometers. The observation also shows that there is a kind of dendritic fiber in the cuticle. The maximum pullout force of the dendritic fiber is analyzed based on its representative model. The analysis shows that the dendritic fibers can markedly increase the pullout force of the fibers and improve the fracture toughness of the cuticle.

A scanning electron microscope (SEM) observation on a Rufescens shell shows that the shell is a bio-ceramic composite consisting of aragonite sheets with nanometer scale and organic matrix. These nano-aragonite sheets are arranged in the shell in the form of helicoidal layup. The reason of the excellent fracture toughness of the shell is analyzed based on the maximal pullout force of the helicoidal layup of the aragonite sheets in the shell.

The performance of evaporator is of importance in cryogenic and refrigeration systems. In this paper, evaporative heat transfer and pressure drop characteristics of refrigerant R134a boiling inside a new geometry microfinned helically coiled tube is experimentally studied. Compared with corresponding smooth helically coiled tube, the heat transfer enhancement factors of microfinned helically coiled tube are up to 2.2 with the varieties of mass flux and heat flux. The frictional pressure drop values are obtained by subtracting acceleration pressure drop and gravitational pressure drop from the measured total pressure drop. The frictional pressure drop data can be well correlated using Lockhart–Martinelli method.

In this paper, the micro-structure and laser damage threshold of nano-ZrO₂ thin films were investigated. High-purity nano-ZrO₂ particles as the coating materials of samples were prepared by the electron beams evaporation. The micro-structure and crystallitic size of samples were analyzed by X-ray diffraction, a laser by 1064nm, 10ns, 3Hz Nd:YAG laser damage test each for nano-ZrO₂ films. The results showed that oxygen partial pressure has an important influence on the micro-structure of nano-ZrO₂ films, also found that the crystallitic size and different micro-structure influenced the laser damage threshold. The obtained results showed that laser damage threshold of polycrystalline structure is obviously higher than that of amorphous structure.

Nano carbon film was synthesized on a nickel substrate in molten LiCl-KCl-K₂CO₃ salt by an electrolytic deposition method. The influence of pulse frequency on the property of the carbon films was studied. Over the carbonate ion concentration range of 0.10–0.20 mol%, the mass of carbon film on unit area increases with increasing pulse frequency over the range of 0.05–33Hz or 33–166Hz, whereas, it decreases with increasing pulse frequency over the range of 33-166Hz. It means that a critical pulse frequency exists, which can be thought to correspond to the natural vibration frequency of the film. When the electrolytic pulse frequency is equal to the natural vibration frequency of film, a resonance maybe happen, and the film exfoliates.

Magnetorheological (MR) fluids are materials that respond to an applied magnetic field with a change in their rheological properties. Upon application of a magnetic field, MR fluids have a variable yield strength. Altering the strength of the applied magnetic field will control the yield stress of these fluids. In this paper, the method for measuring the yield stress of MR fluids is proposed. The curves between the yield stress of the MR fluid and the applied magnetic field are obtained from the experiment. The result indicates that with the increase of the applied magnetic field the yield stress of the MR fluids goes up rapidly.

The yield stress is one of the most important parameters that characterize viscoplastic properties of magnetorheological (MR) fluids. Based on the microstructure of magnetic-chain a theoretical model is developed to analyze the effect of the applied magnetic field on the yield stress. It has been shown that the values of the yield stress calculated by the model agree well with the experimental data.

The fabrication of the carboxyl-modified CNT electrode was described. The electroanalytical investigation of sulfadiazine has been conducted in alkaline aqueous solution at the CNT electrode by voltammetry. Highly reproducible and well-defined cyclic voltammograms were obtained for sulfadiazine with a very good signal to background (S/B) ratio. However, no fouling of the electrode was observed at the CNT electrode within the experimental period of several hours, which illustrated that the CNT electrode was much better than traditional electrodes. Meanwhile, the detection of trace sulfadiazine in milk was also conducted by cyclic voltammetry with satisfactory ratio of recovery, indicating that the nanotube electrode can be used in routine monitoring of sulfadiazine residues in food.

Electrochemical behaviors of dopamine and ascorbic acid have been studied at the carbon nanotube electrode using cyclic voltammetry. Electrocatalysis has been found for dopamine redox reactions at the carbon nanotube electrode in comparison with the glassy carbon electrode. A well-defined oxidative peak for ascorbic acid was observed at the carbon nanotube electrode with the peak potential negative shift versus the glassy carbon electrode. The important discover was that the carbon nanotube electrode can be used to detect low level of dopamine selectively with high sensitivity in the presence of a large excess of ascorbic acid in the acidic media and in the physiological pH buffer solution as well.

The magneto resistive effect in nanocystalline diamond films was investigated at room temperature. The nanocystalline diamond films on silicon were deposited by hot filament chemical vapor deposition. The experimental results showed that a striking magneto resistive effect in p-type doped nanocystalline diamond films was observed. The relative changes in the resistivity of the films were about 0.3 at room temperature under the magnetic field of 5T, and increased with decreasing the geometrical size of the devices. It was found that the magneto resistive effect in the nanocystalline diamond films was less than that of epitaxial diamond films. This was ascribed to a large number of grain boundaries. The results are discussed in detail.

Using the Ternary alloy NiFeNb as a new seed layer, (Ni₈₂Fe₁₈)_72.9Nb_27.1(35Å)/Ni₂₈Fe₁₈(tÅ)/Ta(30Å) films with various NiFe thickness (t) are prepared with a DC magnetron sputtering system. The zero field resistivity ρ and other electric properties are measured. Variations of ρ with t are studied systematically. Dong's model based on Fishman Model has been adapted to analyze our measurements. Results show that: 1) the new seed layer NiFeNb is better than both NiFeCr and Ta in significant enhancing ρ of permalloy films, which decreases the current shunting effect in sensors; 2) Decreasing of grain sizes caused by NiFeNb seed layer and rough interface between the NiFeNb and NiFe layers contribute to improvement of ρ and other electric properties.

Using the Ternary alloy NiFeNb as a new seed layer, (Ni₈₂Fe₁₈)_72.9Nb_27.1(35Å)/Ni₂₈Fe₁₈(tÅ)/Ta(30Å) films with various NiFe thickness t are prepared with a DC magnetron sputtering system. Magnetoresistance (MR) and other magnetic properties of as-grown and annealed films are measured. Variations of MR with t are studied systematically. The approach of Li and co-workers is adapted to analyze our measurements. Result shows that: 1) the new seed layer NiFeNb is better than both NiFeCr and Ta in significant enhancing MR of permalloy films through medium temperature annealing; 2) Small grain sizes caused by NiFeNb seed layer and rough interface between the NiFeNb and NiFe layers contribute to improvement of MR and other magnetic properties.

The strain-induced resistance changes of both SWNT and MWNT films have been studied. Carbon nanotubes in this study were synthesized by hot filament chemical vapor deposition. Experimental results showed that there is a striking piezoresistive effect in carbon nanotube films. The relative change in resistance of carbon nanotube films was increased with the increasing strain. In the same strain, the resistance changes of SWNT films exceed that of MWNT films. The origin of the resistance change in the films may be caused by strain-induced change in the bandgap and intertube contact resistance.

Nanocrystalline ZnO films were prepared by thermally oxidizing the Zn films deposited on mirror-polished quartz substrates by thermal evaporation of Zn granule. The structure of the films was studied by X-ray diffraction (XRD). The results showed that highly preferred (002) orientation of the ZnO films has been achieved. The oxidation temperature has an important effect on preferred orientation of ZnO films.

This paper firstly presented a physical model, which is designed to study on the phase change of liquefied carbon dioxide in an adiabatic capillary tube. The study mainly gained corresponding temperature at a certain point of adiabatic capillary tubes, which external diameters were kinds of 3.0mm & 1.7mm, lengths were kinds of 4.0m & 3.3m, Based on the results, the author deduced the process of phase change and gas-liquid mixture of CO₂ in an adiabatic capillary tube. And also the author researched into the mass flow characteristic of liquefied CO₂ in adiabatic capillary tubes.

Heat transfer coefficients was experimentally determined for a horizontal micro-fin tube (2m in length, 11.44mm ID) with HC290-oil mixtures. The oil is Suniso 3GS, which is a widely used oil in refrigerant systems. The micro-fin tube is a internally enhanced tube, which has 60 fins with a height of 0.25mm and 20° spiral angle. The condensation temperatures varied from 40° to 45° and the refrigerant mass flux was varied from 40kg/(m²s) to 220kg/(m²s). The results showed that the mean condensation heat transfer coefficients on the test section (inlet vapor quality 1, outlet vapor quality 0.1~0.25) decreased as the oil concentrations were increased and the condensation temperature had negligible effect on the heat transfer coefficients.

In this paper, the Seebeck effect of mutilwalled carbon nanotube films has been studied. The carbon nanotubes were synthesized by hot filament chemical vapor deposition using Ni-Fe as a catalyst. It was found that the thermoelectromotive force (thermo emf) changed approximately linearly with the temperature at the hot end at room temperature, and the Seebeck coefficient of carbon nanotube films was about 10~50 μv/k. The experimental results were discussed in detail.

Carbon nanotips were grown on a silicon substrate by negative bias-enhanced hot filament chemical vapor deposition without catalyst, using a mixture of methane, ammonia and hydrogen as the reaction gases. It was evidenced that the plasma caused by the bias played a key role in the formation of the carbon nanotips. Due to occurrence of plasma during growing carbon nanotips, the gases were ionized into various ions. Based on different effects of the ions, a growth mechanism of the carbon nanotips was put forward.

The Magnetothermoelectric and thermoelectric power of nano-ZnO films was investigated. The ZnO films in this study were prepared by DC reactive sputtering using a Zn target (99.99%) containing AL of 1.5%. The films obtained were characterized by SEM, x-ray diffraction, optical and electrical measurements. It was found that the sputtering ZnO films were highly orientation growth with the c-axis perpendicular to the substrate surface. The measurements showed that there was a striking seebeck effect in the ZnO films, and their thermoelectric power was linearly increased with increasing temperature. The experimental results were also demonstrated that the thermoelectric power was degraded under the magnetic field. This finding may ascribe to the magneto resistive effect.

High-T_C Superconducting Cable for transmitting electricity will scale up application extension before long. Superconducting Cable consists of cable core made up of superconducting material and cladding argentine and structure-functional material complying with cable requirement for transmitting electricity. As a kind of composite with high tensile strength, high elastic module, moderate elongation and high heat-exchange, low thermal expansion, SiCp/6066Al composite will have extensive application as sheath of high-T_C superconducting cable for transmitting electricity. Thus the advance in high-T_C superconducting cable has been referred .The detailed experiment on preparation of SiCp/6066Al composite as sheath of high-T_C superconducting cable for transmitting electricity by new-style powder metallurgy technology—sheathed hot extrusion. Mechanical, damping and thermal characteristics have been tested. Even microstructure and clean interface between SiCp and Al alloy matrix have been found via OM, SEM, TEM, etc. The authors explained internal relations between characteristics and microstructure. The characteristics of the composite reach to established characteristic requirement for high-T_C superconducting cable for transmitting electricity.

A new preparation process of the vanadium catalyst with nano-V₂O₅ particles was introduced in this paper. The inorganic sol-gel method is used to prepare the sols and gels with p nano-V₂O₅ particles. The morphology, size and distribution of the nano-V₂O₅ particles in the sols-gels and vanadium catalyst had been studied by TEM, SEM, XRD and DSC. The results show that with the w/v (the ratio of water and vanadium) declining, the morphology of the nano-V₂O₅ particles varies from needle to near-ball then to sphere; the better process parameter to prepare the sols and gels with nano-V₂O₅ particles is 800~860°C×10~15min; the sols and gels and catalyst with 30~60nm V₂O₅ particles had been obtained by this process.

We have experimentally found out that an obvious tunnel current begins to appear between nano-CaCO₃ film and tip of STM when the bias voltage reaches 0.6V, above which there is a non-linear rise quickly. We further measure the scanning tunneling spectrum (STS) of nano-CaCO₃ and analyze it compared to that of Au and Silicon. The results show that CaCO₃, an insulating material, after nanometer processing presents a characteristic similarly to a metal, and the constraint to electrons is even smaller than a semiconductor. STS has not only well explained the spectroscopic mechanism of conducting performances of nano-CaCO₃, but also expanded applications of STM to one of the most important research areas. Moreover, the method can be applied to the study of the structure of superconductive materials and energy spectrum characterization.

A new kind of electrolytic deposition method to obtain activated carbon atoms to prepare nano carbon film in molten salt was developed. The experimental results on various substrates indicated that nano carbon film could be synthesized on substrates of nickel, copper, iron and titanium by an electrolytic deposition method in molten salt under suitable conditions. Decreasing reasonably carbonate ion concentration is an efficient methods to accelerate the growth of deposition film and improve its quality.

The Fe³⁺-TiO₂ thin films obtained through sol-gel method were characterized by x-ray diffraction, AFM and Raman spectroscopy. It was found that TiO₂ films consisted of nanometer particles. The experimental results shows that the nanometer TiO₂ thin films doped with Fe³⁺ were greatly improved in the activity aspect. This may be ascribed to change their structure and electrical properties after doping with Fe³⁺. The results were discussed theoretically in detail.

We have developed a novel technique to fabricate extremely uniform arrays of nano-sized dots. Regular arrays of nanometer-sized metallic dots are obtianed by magnetron sputtering deposition through a nanochannel glass replica mask. The platinum replica masks are fabricated using thin film deposition on an etched nanochannel glass and contain hexagonally patterned uniform voids with diameters as small as 50 nanometers. The metallic dot density can be as high as 5×10¹¹ per square centimeter. The magnetic properties of Ni and Co dot arrays have been studied by a Alternating Gradient Magnetometer. The magnetic dot array can be used as pinning centers for superconductors and also can be used as the discrete magnetic media for magnetic recording.

A molecular dynamics simulation (MDS) was performed to investigate the characteristics of the interfacial feature between coexisting phases in equilibrium. It is considered that the interface is a fractal surface. The fractal configuration and the dimension of it were presented in the paper.

Using a simplified model, the surface energy of the Si/SiO2 interface in silicon nanowires (SiNWs) is derived. Our theoretical results show that the nanowires along <112> and <110> have very low surface energy, so their yields should be high. Experimental observation testifies that the SiNWs fabricated by the oxide-assisted growth (OAG) are mostly of these two orientations. This supports the consideration that during growth process, surface energy is the chief factor to determine the axis orientation of nanowires under OAG.

An area-coordinate quadrilateral shell element in dynamic explicit finite element analysis is proposed with a modified interpolation function based on area coordinates, Mindlin shell theory and co-rotational formulations. The element is applied to and verified to have a good performance through comparison with experimental data and results from Belytschko-Tsay element. Computation precision is improved while the efficiency is kept.