International Journal of Modern Physics B

We present a study of the role of phonons in the cuprate superconductors. Assuming static spin fluctuations, we find that the self-consistent d-wave state is very sensitive to both the electron-phonon coupling strength and the phonon mode considered.

TFDC (Thomas-Fermi-Dirac-Cheng) electron theory is applied to analyzing the characteristics of the electrons inside the double layer of the nanometer composite thin films. This paper proposes the new mechanism about the high capacity in both theoretical analysis and experimental measurement.

The normal states of simple elemental metal and complex compound superconductors have been studied by using first principle methods and model analysis. The flat/steep band electronic structure and the peak-like structure of electron-phonon coupling have been found as two universal characteristics. A new Hamiltonian is proposed to describe the electronic structure of insulating solids.

Muon spin rotation (μ⁺SR) measurements conducted on crystalline YBa₂Cu₃O₇ are consistent with s-wave pairing, not d-wave, suggesting that the superconducting hole condensate resides in the BaO layers, not in the cuprate-planes. The specific heat and thermal conductivity data are explained by the superconducting BaO layers alone, unlike the failed interpretation based on CuO₂-plane superconductivity. The layer charges of the CuO₂ planes are almost -2 |e|, indicating that those planes are primarily carriers of electrons, not holes. The cuprate-planes are not the dominant hole-carriers of high-T_C superconductivity, as demonstrated by doped YBa₂RuO₆, which has no such CuO₂ lanes, yet superconducts at ~ 93 K. Moreover the trio of related compounds, YSr₂RuO₆ (doped with Cu on Ru sites), undoped GdSr₂Cu₂RuO₈, and undoped Gd_2-zCe_zSr₂Cu₂RuO₁₀ all start superconducting near 49 K in their SrO layers, not in the cuprate planes of the two compounds that have such planes, because those planes are either antiferromagnetic or weakly ferromagnetic and so do not superconduct. In PrBa₂Cu₃O₇, a Pr-on-Ba-site (Pr_Ba) defect kills the superconductivity, but Pr-on-Pr-site (Pr_Pr) does not. Both defects are approximately equidistant from the intervening cuprate plane, suggesting that the cuprate plane does not carry significant superconductivity. In GdBa₂Cu₃O₇, Gd-on-a-Gd-site (Gd_Gd) does not break Cooper pairs, but Gd-on-a-Ba-site (Gd_Ba) does, indicating that the superconductivity is in the BaO layers, and not in the cuprate-planes. In HgBa₂Ca_n-1Cu_nO_2n+2, the BaO layers, not the cuprate-planes, gain positive charge as T_C, pressure, and the number of layers n increase. The reason that theories based on holes in the cuprate-planes have done so poorly is that those planes were incorrectly identified as the source of high-temperature superconductivity on the basis of a single datum by Cava et al., that was first contradicted by Jorgensen et al., and then endorsed by Jorgensen alone on the basis of the Cava datum, not his own. This error is the main reason why cuprate-plane superconductivity, which probably does not exist, has been so widely accepted.

We study Cooper's paring for more than two particles in terms of the BCS model. We consider multiple pairing in terms of the BCS Hamiltonian in a quiescent Fermi sea model and in the BCS ground state. Although there is no interaction between Cooper's pairs in terms of the BCS Hamiltonian, yet we show that four particles are paired and form a bound state in the singlet state with just twice the bound state energy of a single Cooper's pair. Four-particle bound state - quartet only exists as a result of the Pauli principle and the sharp Fermi edge. We have also shown that the smearing of the Fermi edge due to Δ(k) as it is in the BCS ground state weakens the pairing of either two or four particles. We show that in the particle-hole channel there exists the multiple particle-hole resonance for four particles and four holes in a quiescent Fermi sea model similar to the resonance of two particles and two holes. There is no the particle-hole resonance in the BCS ground state as shown, which means that the particle-hole resonance is removed by Δ(k) due to smearing of the Fermi distribution. The wave function for the multiple pairing model is discussed as well.

Within the kinetic energy driven superconducting mechanism, we study the superconducting quasiparticle spectral weight of cuprate superconductors. It is shown that although the spectral weight is continuous along the high symmetry directions, the overall spectral weight is reduced by the strong electron correlation in cuprate superconductors.

As indicated by NMR experimental results, there are two types of electrons in a doped cuprate: the localized Cu3d electrons, which are responsible for magnetism, and the itinerant p-band electrons carrying the charge transports. We show that the uncompensated spins at oxygen sites created by holes can pair into a resonating valence bond (RVB) state via local exchange interactions where the quasi-free local Cu spins play a role of the mediation for spin pairing. The two-component model gives a proper interpretation of the magnetic origin of high T_c superconductivity, especially, in explanation of the cross over from the anti-ferromagnetic to the RVB state.

We solve the t-J model with four holes on a 32-site lattice using exact diagonalization. This is the largest scale calculation ever reported for this model. The size of the matrix involved in this problem is about 3×10⁹ by 3×10⁹. We find that at the realistic parameter J/t = 0.3, holes in the ground state of this system are unbound. They have short range repulsion due to lowering of kinetic energy. The electron momentum distribution function resembles hole pockets. We show that in case antiferromagnetic order is strong, holes form d-wave bound pairs and there is mutual repulsion among the holes. This presumably will occur at low doping level.

Pairing between two fermionic excitations in a non-Fermi liquid is considered in terms of the Bethe-Salpeter equation. We consider the pairing in a Fermi system with vanishing spectral weight. It is well known that the quasiparticle pole in the single-particle Green's function in a Non-Fermi liquid is absent or weak. The examples of such systems can be viewed as the "Marginal" Fermi liquid and Luttinger liquid. Another example that has also been considered is the Fermi system with pseudogap behavior in the spectral weight. Although the pairing between two excitations in a non-Fermi liquid is, in general, absent, nevertheless we show that the Cooper's type of pairing can occur and the conditions for such a kind of pairing are discussed. The results have also been applied to the systems with smeared or non-monotonic Fermi distribution. A system that transits from Fermi-type to Bose-type behavior can serve as an example of such systems as discussed.

In view of increasing emphasis on the use of next-nearest hopping t' term in the t-J Hamiltonian, we examine its effect on the spin susceptibility and its correlation with the structure of phase diagram. We find from this study that the resonance peak of spin susceptibility rapidly decreases with hole concentration in the overdoped region at which the spin singlet pairing order diminishes. It is shown that the doping dependence of resonance energy in both underdoped and overdoped regions is in agreement with observations.

Exploiting the shortness of the coherence length in many of the recently discovered superconductors, we propose a new formulation to evaluate the superconducting transition temperature T_c. Its tentative application to the Hubbard-Holstein model suggests the appearance of very high T_c in a reasonable range of parameters involved in the model.

In the low doping limit, a high T_c cuprate preserves a two band structure. O2p electrons are itinerant, Cu3d electrons are localized. Therefore the two component model is suitable to describe nuclear spin relaxation at copper sites. In addition to the Korringa process, the hyperfine interaction between nuclear spins and local electron spins is considered, which gives rise to the anomalous relaxation rate 1/T₁ = a + bT. The decrease of the susceptibility near T_c, as shown by the Knight shift measurements, can be attributed to the ordering of local spins and the pairing of the uncompensated spins created by holes at the oxygen sites.

The non-monotonic relationship of T_c with the number of Cu-O planes (n) per unit cell for compounds of Tl₂Ba₂Ca_n-1Cu_nO_2n+3 (n=1, 2, 3, 4 and 5) is investigated from the reaction between different structural blocks. The unit cell of the Tl superconductors is treated as two blocks: the perovskite block where the Cu-O planes are located and the rock salt block, which is considered as a charge-reservoir. A model was used to calculate the combinative energy of the two blocks. It is found that the combinative energy between the two blocks is closely related to the value of T_c. The relation demonstrates an interesting way to understand the nonlinear change of T_c with the number of Cu-O planes in the layered superconductors. This means that the interaction between the two blocks plays an important role in superconductivity. The results are somewhat different from that of another Tl-system superconductor, Tl₂Ba₂Ca_n-1Cu_nO_2n+4, with 4 superconductive compounds.

We study the spin oscillations of a quantum dot (QD) embedded in a superconducting ring. The dot is characterized by the Coulomb interaction and the gate voltage. The pairing potential is considered in the superconducting ring. We found that the amplitude and frequency of the oscillations depend sensitively on the pairing potential of superconducting lead, the coupling strength between the dot and superconducting lead. We also show that the magnetic moment on the dot can be controlled by changing the pairing potential of superconducting lead.

An Y₂O₃ film, as seed layer, was directly deposited on the meter long length rolling assisted biaxially textured substrate (RABiTS) NiW tapes by the reactive magnetron sputtering process. Yttria stabilized zirconia (YSZ) and CeO₂ films were further carried out as the barrier and cap layers, and YBCO layer was prepared by magnetron sputtering technique as well. X-ray diffraction was employed to characterize the texture of film. The results showed that on NiW tapes highly textured films were obtained.

The samples of Y_1-xSr_xBa_2-xLa_xCu₃O_y (YSBLCO) were synthesized and characterized by DC magnetization measurements and X-ray diffraction. The structures of the samples were refined by Rietveld method. Although the carrier concentration in the samples is constant at different dopant levels, the superconductivity evidently changes. We attribute decrease in Tc to a charge redistribution in the crystalline lattice. Comparing the change of the T_c value caused by structural influence and carrier concentration, it is suggested that the influence of structural changes on the superconductivity is independent of that induced by carrier concentration.

A helium cryogenic system with cooling capacity of 1 kW at 4.5 K was set up at Institute of High Energy Physics, Chinese Academy of Sciences, Beijing. This helium refrigerating system is dedicated for the cooling of two superconducting radio frequency (SRF) cavities, two interaction region superconducting collision quadrupole (SCQ) magnets, a detector superconducting solenoid magnet (SSM), which are the key items of the upgrade project of Beijing Electron-Positron Collider (BEPC II). Commissioning with the detector and SCQ magnets was carried out, which will be introduced in this paper. The cryogenic system shows very robust as SSM quench. This paper presents the overall status and some test results of superconducting and cryogenic system.

We calculate the singlet and triplet pairing components of F/S/F trilayers by solving the Usadel equation in the dirty limit. Here, S is a conventional singlet s-wave superconductor like Nb and F is a ferromagnet like CoFe. A particular focus is on the odd frequency triplet pairing components which have a long length scale in F region unlike the singlet pairing component. The triplet components in F/S/F are induced by the broken time reversal symmetry and the proximity effects. The cases of parallel and perpendicular orientations of the two F's are calculated and discussed for the fingerprint of the odd frequency triplet pairing components.

In the past years, the typical high Tc superconductor YBa₂Cu₃O₆ has been extensively studied by many authors. And electron paramagnetic resonance (EPR) studies of rare-earth (Re³⁺) ions in high-Tc oxide superconductors have attracted much interest because they can provide valuable information on spin-lattice relaxation, exchange interactions and the ground state properties of Re³⁺ ions, which are further employed as sensitive probes of spin dynamics in high-Tc superconductor. The EPR anisotropic g factors of Dy³⁺ in YBa₂Cu₃O₆ crystal has been measured by M.R. Gafurov et al., and there is no theoretical explanations related to the crystal structural data. In this paper, parameters g factors for Dy³⁺ in YBa₂Cu₃O₆ are theoretically studied from the perturbation formulas of these parameters for a 4f⁹ ion in tetragonal symmetry. In these formulas, the contributions to the EPR parameters from the second-order perturbation terms and the admixtures of various excited states are taken into account. The related crystal-field parameters are determined from the superposition model and crystal structural data. The theoretical results show reasonable agreement with the experimental values.

It is of interest for layered oxides containing copper because they are related to high temperature superconductivity. Among them, LaSrAl_1-xCu_xO₄ solid solution has received much attention due to its elastic and elasto-optic properties and application as promising substrate for high-T_c superconducting thin films. So many theoretical and experimental works have been done to understand the several characteristics of the LaSrAl_1-xCu_xO₄ materials. In this paper, the electron paramagnetic resonance g factors g_//, g_⊥ and hyperfine structure constants A_//, A_⊥ for the tetragonal Cu²⁺ center in LaSrAl_1-xCu_xO₄ solid solution are theoretically explained by the method of diagonalizing the full Hamiltonian matrix. The related crystal field parameters are calculated from the superposition model and the local structural parameters of the impurity Cu²⁺ occupying the host Al³⁺ site. The superposition model parameters used in this work are comparable with those for similar tetragonal (CuO₆)^10- clusters in the previous works. The calculated results are in reasonable agreement with the observed values. The results are discussed.

Superconducting finite-sized Pb square networks with 10×10 square holes fabricated by electron beam lithography have been investigated in view of vortex doping into superconducting networks. Vortex images observed by a SQUID microscope were compared with predictions from the Ginzburg-Landau theory. Exactly reversed pattern was confirmed to appear both in the vortex-doping x into an empty network and in the antivortex doping 1-x into a fully occupied network (x=1/4). We also confirmed a checker-board crystal of vortices at half filling both theoretically and experimentally.

The effects of Sc in high T_c superconductors are seldom discussed due to the difficulty of Sc embedding into the unit cell. Single phase of Y_1-xSc_xBa₂Cu₃O_7-δ (YSBCO) is obtained with x<0.15. The critical current (J_c) varies with the content of Sc in an oscillating way, which has showed two maximum values at x=0.03 and x=0.10, individually. We here discussed the effect of Sc doping on J_c.

Recent STM studies revealed nanoscale electronic disorder on the crystal surface in many cuprates. In BSCCO strong correlations between oxygen defect distributions on its surface and both the gap map and the coherence peak amplitude showed that the off-center distortions in the positions of oxygen atoms are responsible for most of the electronic disorder. Additional information on nanoscale inhomogeneities and its relationship to the lattice strain and oxygen redistribution can be obtained from the electrical transport that uses Percolating Persistent Supercurrents which are known to bypass regions of a reduced order parameter (macroscopic crystal defects). Our investigations identified universal (sample independent) features in the superconducting properties which can be attributed to the presence of a nanoscale inhomogeneity, such as nanogranular Josephson effects, strain-induced filamentary and percolative flow of the transport current, etc. Local oxygen redistribution, induced either by careful low temperature annealing or by room temperature aging, modifies both the superconducting and the normal state properties.

The spatial evolution of the background conductance in the tunneling spectra was investigated with low-temperature scanning tunneling spectroscopy on a slightly overdoped Bi₂Sr_1.74La_0.26CuO_6+δ single crystal at 4.2 K. The asymmetry in the background conductance between positive and negative biases strongly correlates with the local energy gap, which shows the inhomogeneous spatial variation: the tunneling spectra become more asymmetric in the regions where the spectra exhibit larger gap value.

We calculate the Josephson critical current I_c across in-plane (001) tilt grain boundary junctions of high-temperature superconductors. We assume the Fermi surface has either an electron-doped form, or one of three hole-doped forms, and either random or specular tunneling across the junctions. We find that in-plane 'phase-sensitive' experiments are consistent with our results for the electron-doped superconductors. For the hole-doped superconductors, however, the results depend strongly upon the details of both the Fermi surface topology and the nature of the tunneling, and are therefore considerably less robust than has generally been believed. Hence, the tricrystal, tetracrystal, and interferometry experiments on hole-doped high-temperatures superconductors are unreliable, and should be redesigned.

To study the nanoscale electronic order in high-T_c superconductors, we have performed low-temperature scanning tunneling microscopy (STM) experiments on YBa₂Cu₃O_y, single crystals. The electronic state of the underdoped CuO₂ plane is studied through the BaO surface taking advantage of the cleaved surface, which has an insufficient carrier doping into the topmost CuO₂ plane because of the incomplete carrier reservoir. The STM image measured at low bias-voltage below 20 mV shows the one-dimensional (1D) electronic modulation along the Cu-O bonds. The 1D modulation do not have long-range order and the periodicity varies within the range ~ 2a - 4a depending on the position on the surface. These results indicate that electronic order in underdoped YBa₂Cu₃O_y, differs from the 4a×4a checkerboard structure observed in Bi₂Sr₂CaCu₂O_y and Ca_2-xNa_xCuO₂Cl₂.

We explore extremely overdoped regime in the phase diagram of cuprate superconductors. Interlayer tunneling transport measurements under high magnetic fields are employed to detect the field dependence of low-energy density of states (DOS) in hole-doped (BSCCO and TBCO), and electron-doped (SCCO) cuprates. We find a strong doping dependence of the pseudogap closing field whose Zeeman energy universally scales with the pseudogap onset temperature, indicating a preeminent role of spin-singlet correlations in forming the pseudogap regardless of the doping type. Excess dissipation due to the pseudogap is found to follow a 'universal' correlation with the pseudogap closing field. The pseudogap features appear absent in the extremely overdoped TBCO, pointing to a possible quantum critical point very near the edge of the superconducting 'dome'.

We have performed measurements of the out-of-plane resistivity ρ_c in magnetic fields up to 40 T and the scanning tunneling microscopy (STM) in the Pb-Substituted Bi2201. Two kinds of pseudogaps PG1 and PG2 are found at T*₁ and T*₂ below which the nonmetallic ρ_c starts to develop and to be suppressed in magnetic fields with decreasing temperature, respectively. The obtained phase diagram indicates that the pseudogap related to the superconductivity is not PG1 but PG2. STM images of the Bi(Pb)-O plane in the optimally doped sample show bright atom-strings at V ≤ 10 mV. The observed structure may indicate the one-dimensional correlation which is different from the 4a × 4a structure reported in other systems.

To address the structural mechanisms associated with T_c variations induced by Co doping, two samples of the nominal composition (Ga_1-xCo_x)Sr₂(Tm_0.6Ca_0.4)Cu₂O_z with x = 0.5 and 0.7 have been prepared and studied by using neutron powder diffraction and transport measurements. In contrast to the x = 0.5 sample, which shows superconductivity around 35 K, the x = 0.7 sample does not exhibit superconductivity. The neutron powder diffraction studies indicate that both samples exhibit the 1212 structure with space group Ima2 and the Co atoms exclusively substitute for the Cu atoms located on the chain sites of the 123 parent structure. The depression in Tc of the x = 0.7 sample, compared to that of the x = 0.5 sample, is discussed in connection with oxygen content, disorder, and change in hole concentration on the superconducting planes.

Gd is successfully embedded into YBa₂Cu₃O_7-δ by the solid state reaction. Rietveld refinements show that Gd replaces Cu in the unit cell. By magnetization and resistivity measurements, the effects of Gd-doping in YBCO on the critical current density J_c and the critical temperature T_c in YBa₂Cu₃O_7-δ(YBCO) have been investigated. J_c varies with the applied field and the content of Gd and has a maximum at x = 0.03. The characteristic behavior of J_c with varying the Gd content can be explained in terms of the competition between two different effects caused by Gd-doping in YBCO: the inhomogeneity of grains distribution in nano-scale and the variation of superconductivity.

STM/STS is used to examine the charge order in the pseudogap state on underdoped Bi2212 crystals with different hole-doping levels (p). We report that although the data for the period of charge order are slightly scattered, it is nearly 4a × 4a (a: the lattice constant) and exhibits no obvious dependence on p in the p-range examined.

The microwave properties of YBa₂Cu₃O_7-x/LaAlO₃ (YBCO/LAO) and YBa₂Cu₃O_7-x/MgO (YBCO/MgO) thin films have been investigated by microstrip resonator technique. The penetration depth λ₀(0K) and the microwave surface resistance R_s can be obtained by analyzing the experimental data of the temperature dependence of resonant frequency, unload quality factor of the microstrip resonator. The stress in the two thin films can be obtained from their XRD patterns. The result shows that the stronger stress in YBCO/LAO thing film makes it have larger microwave surface resistance at lower temperature.

We observed the distribution of the superconducting gap in Bi₂Sr_2-xLa_xCuO_6+δ (Bi2201-La) by scanning tunneling spectroscopy at x = 0.2 (over doped), 0.4 (optimally doped) and 0.6 (under doped). The superconducting gap was spatially distributed in all samples. As the carrier concentration is reduced, the distribution became much broader and the mean value of superconducting gap, Δ_mean increased. We found that the distribution and Δ_mean in Bi2201-La grew more rapidly than in Bi₂Sr₂CaCu₂O_8+δ with decreasing the carrier concentration.

We have succeeded to prepare Tl-1223 samples with a maximum T_c above 130K at ambient pressure using a conventional sealed quartz tube method. We found that, by adequately controlling the starting composition, it is possible to control the maximum T_c from ~120K to 130K. In order to seek the key factors for a drastic increase in the T_c, we carried out the measurements of the thermoelectric power, powder X-ray diffraction and neutron diffraction for these samples. As a result, it is found that the characteristics in the Tl-1223 samples with high T_c show essentially similar to those in the Hg-1223 with the highest T_c and are different from those in the Tl-1223 samples with low T_c. The details of the synthesis conditions, the transport properties and the refinements of the crystal structure will be presented.

We report the tunneling conductance on a quadruple-layered cuprate, Ba₂Ca₃Cu₄O₈(O_1-xF_x)₂ (2x~1.4, T_c~100K) that includes inequivalent outer (OP) and inner (IP) CuO₂ planes in a unit cell. Typical tunneling conductance displays the spectral dip structures as well as the superconducting gap (SCG) with clear coherence peaks. However we sometimes observe a pseudogap (PG) like structure without coherence peak at 4.2K. The magnitude of PG at 4.2K is larger than that of SCG at 4.2K and its conductance curve displays a faint structure at low energy. Therefore its origin would be different from that of small-PG observed at above T_c. In addition, we find that there are two kinds of SCGs that originate from IP and OP, and this result suggests that the superconducting property at IP is different from that at OP because of the imbalance of doped carrier between IP and OP. The observation of large PG at low temperature suggests the existence of some form of hidden ordered state at T<T_c and it would coexist with superconductivity.

We measured the electrical resistivity under pressure for an antiferromagnet CeCoGe₃ without inversion symmetry in the tetragonal crystal structure. The Néel temperature T_N1 = 21 K at ambient pressure decreases monotonically with increasing pressure, and becomes zero at about 5.5 GPa. Superconductivity appears above 4.3 GPa, with a superconduting transition temperature T_sc = 0.72 K and a large upper critical field H_c2(0) = 7 T at 5.6 GPa. The large upper critical field H_c2(0)= 7 T exceeds the Pauli limitting field H_p (≃ 1.86T_sc)=1.3 T as in CePt₃Si, CeRhSi₃ and CeIrSi₃. The large slope of H_c2 at T_sc, -dH_c2/dT = 18T/K, at 5.6 GPa indicates the heavy-fermion superconductivity in CeCoGe₃.

Series of the samples with nominal compositions Bi_3.2Pb_0.8Sr₄Ca₅Cu₇O_x and Bi_3.2Pb_0.8Sr₄Ca₅Cu₇O_x/Ag (10 wt%) were prepared by the standard solid state reaction at the same calcination and sintering temperature and time. Three starting mixtures were used, carbonates, oxides and silver i) with nanoparticles, ii) with micrometer size of particles and iii) powder obtained by modified sol-gel process. The main phase in all samples was Bi-2223 and silver formed the separate phase. The sol-gel process was found to be effective way in term of porosity, bulk density and connectivity of the grains. The effect of the microstructure on the transport properties were described by the temperature dependence of resistivity and critical current densities.

The EPR g factors g_// and g_⊥ for the six-coordinated Cu²⁺(1) site in YBa₂Cu₃O_6+x are theoretically investigated from the perturbation formulas for a 3d⁹ ion in tetragonally elongated octahedra. The related tetragonal crystal-field parameters Ds and Dt are determined from the superposition model and the structural data for the Cu²⁺(1) site, by considering the effective elongation of the oxygen octahedron due to the Jahn-Teller effect of the Cu²⁺ cluster. Based on the calculations, the effective elongation (≈ 15%) of the ligand octahedron is obtained for the signals at 100K. As for the EPR signals at room temperature, the elongation declines to merely 4%, corresponding to the smaller anisotropy Δg (=g_// - g_⊥). The theoretical results for the g factors are in good agreement with the observed values, and the local tetragonal distortion due to the Jahn-Teller effect is discussed.

The zero-field splitting D of the ⁸S_7/2 ground singlet for the tetragonal Gd³⁺ center in La_2-xSr_xCuO₄ is theoretically studied from the superposition model. Meanwhile, the g factor is also quantitatively investigated from the approximation formula including admixture of the ground ⁸S_7/2 and the excited ⁶L_7/2 (L=P, D, F, G) states via the spin-orbit coupling interactions. The calculated zero-field splitting and g factor are in reasonable agreement with the experimental data. It is found that the significant zero-field splitting can be ascribed to the average impurity-ligand bonding angles [≈ (θ₁ + θ₂)/2 ≈ 62°] related to the four-fold axis larger than that (≈ 54.74°) of the cubic case. Nevertheless, the experimental g factor close to 2 may be largely due to the very slight admixture of the ground ⁸S_7/2 and the excited ⁶L_7/2 states via the spin-orbit coupling interactions.

Underdoped electron-doped La_2-xCe_xCuO₄ (x=0.06-0.09) thin films were successfully grown and investigated for the transport properties in ab-plane. It was found that the in-plane resistivity ρ_ab shows a semiconductor behavior when x=0.06, with increasing the Ce concentration to the optimal doping level, it changes to the two dimensional Fermi-liquid behavior. In the films with x≥0.08, a Kondo effect like scattering is observed in the low temperature range.

A double buffer of EU₂CuO₃/YSZ has been used to grow highly epitaxial thin films of YBa₂Cu₃O_y (YBCO) on Si. These films showed enhanced superconductivity and improved crystallinity in comparing with that of films grown on Si directly. Well defined interfaces with no immediate layers were found. The YBCO film surface was more smooth and stable. The results obtained indicate that highly epitaxial YBCO thin films can be successfully grown on Si wafers, demonstrating advantages of such a double buffer structure.

Recent development in the applications of high temperature superconductor (HTS) filters is introduced. Breakthrough had been made in ultra selective band-pass filter with extremely small fractional bandwidth for 3G mobile base stations. Satisfactory results were achieved in the space qualification mechanical tests of the HTS filters. Field trail of the meteorological radar showed that with HTS subsystem the sensitivity and anti-interference ability of the radar were greatly improved.

We investigate critical current (I_c) modulation of stacked Josephson junctions (SJJs) dc superconducting quantum interference device (dc SQUID) on a Bi₂Sr₂CaCu₂O_8+δ (Bi-2212) whisker. A coupled SJJs with a completely perforated hole of 0.1 μm × 0.2 μm were fabricated by using a 3-D focused-ion-beam (FIB) etching method. Those dc SQUIDs exhibited uniform multi-branch structures and clearly oscillated critical current under external magnetic fields (H_e). With applying H_e, the clear periodic modulation patterns of I_c are obtained and well fitted to the calculated value from the loop area of 0.02 μm².

We present a detecting scheme of high-frequency gravitational waves (HFGWs) which is based upon coupling between superconducting open cavity and electromagnetic fields stored in the cavity. Utilizing zero resistance and perfect diamagnetism of the superconductors, one can obtain very large quality factor and high sensitivity for the cavity to detect the HFGWs in GHz band. In addition, we review other possible superconducting systems for detection of the HFGWs, such as superconducting resonant-mass detector, toroidal waveguide, coupled superconducting spherical cavities and superconducting quantum antennas.

Electrical resistivities of double perovskite oxides Sr₂Fe(W_1-xMo_x)O₆ have been measured at high pressure and high magnetic field to elucidate the transport properties of these materials. It is found that the main mechanism of the transport in the semiconducting phase is variable range hopping conduction and the insulating properties are suppressed by high pressure to show a crossover to metallic state. The magnetoresistances of these oxides are revealed to decrease at high pressure above 1 GPa. Extremely large Grüneisen parameters are found near x = 0.2, where the metal-insulator transition occurs. The origin for these properties will be briefly discussed in connection with the phase diagram.

The magnetic torque of (Cu,C)Ba₂Ca₃Cu₄O_y( (Cu,C)-1234) aligned samples with various carrier concentrations has been measured under a magnetic field of 9 T at 80 K and 90 K. The carrier concentration was determined by Hall effect measurements. From angular dependent torque measurements, the anisotropy ratio γ was estimated using the 3D anisotropic London model. The γvalues decreased from 23 to 10 with an increase in the average Hall number per CuO₂ plane (n_H); however, these samples showed a nearly constant T_c of about 117 K. These results indicate that the anisotropy of (Cu,C)-1234 strongly reflects the doping levels of the outer planes.

The superconducting energy gap of YBa₂Cu₃O₇ (YBCO) varies strongly with and from a sheet of the Fermi surface to another. The strong anisotropic superconducting gap in high Tc materials such as YBCO has led to conflicting d-wave and s-wave interpretations. We have utilized electronic wave functions from the ab-initio density functional calculation and the related electron-phonon interaction matrix elements for the calculation of the superconducting gap values of YBCO. We have found that the superconducting gap on one sheet of the Fermi surface around S-point only shows a minor variation from about 18 meV to 25 meV. Especially, there is no node on this sheet of the Fermi surface around the S-point. We propose a new test measurement of the superconducting gap of YBCO on this sheet of the Fermi surface around the S-point in the Brillouin zone. This measurement is expected to shed light on the gap symmetry properties of high Tc superconductors.

The coherence length ξ, which reflects the non-local interactions and ordering scale of superconductive electrons, is one of the characteristic quantities that describe properties of a superconductor. In this paper, we propose a new experiment scheme of measuring coherence length ξ in a superconductor after analyzing the (Josephson) tunneling effects with the junctions' thickness d <ξ, d > ξ and d ~ ξ, respectively.

Heterostructures consisting of ferromagnetic La_2/3Ca_1/3MnO₃ and superconducting YBa₂Cu₃O_7-x layers were fabricated by conventional pulsed laser deposition in conjunction with shadow mask techniques to define appropriate sample geometries. Using standard dc- four probe measurements we observe a 2% decrease of T_c for injection current densities of 5.10^-2 A/cm² in the case of unpolarized quasiparticles whereas highly spin polarized quasiparticles show a much stronger decrease of 14%. This result clearly demonstrates that the spin plays a crucial role in the T_c reduction. The results are discussed within the frame of a theoretical model based on the Owen-Scalapino approach for nonequilibrium effects in superconductors.

To further understand the argument about the superconductivity in PrBa₂Cu₃O_y, We try to change YBa₂Cu₃O_y to PrBa₂Cu₃O_y gradually, studying the detailed change during the change, and hope to find some clue to the argument. The single-phase samples of Y_1-xPr_xBa₂Cu₃O_y (x = 0, 0.1, 0.2, 0.3, 0.5, 0.6, 0.8, 1.0, respectively) were synthesized and characterized by DC magnetization measurement and X-ray diffraction. The structure of the samples was refined by Rietveld method. After careful analysis, it is found that as the x increasing, Ba moves toward the Cu-O(1) plane, the bond length between Y-Ba, Y-Cu(2), and Ba-O(1), and Cu(1)-0(4) increase simultaneously. It demonstrates that as the Pr content increases, the distance between the active block and the carrier reservoir block becomes farer and farer, and the area of the carrier reservoir block increases. It is suggested that the doping of Pr to Y in YBa₂Cu₃O_y changes some local structure and result in the suppression and vanishing of the superconductivity.

We measured the magneto-optical images (MOIs) and the magnetic hysteresis (M – H) curves of c-axis-oriented MgB₂ thin films to investigate the flux penetration in the form of dendritic avalanches. In order to understand the role of the thermal effects, we prepared Au-coated MgB₂ thin films with different thicknesses of gold. While the MOI provides a spatially resolved flux pattern, the M – H curve presents global and average information about the flux noise associated with avalanches. These two types of measurements complement each other. The upper threshold field, above which the flux noise disappears, was determined from the M-H curves while the lower threshold field was determined from both the M – H curves and the MO images. The field range where the flux penetrates via avalanches is found to be smaller for thicker gold layers. These results are important for many superconducting applications.

We have investigated the two-gap nature of bulk (Mg_1-xAl_x)B₂ for 0 ≤ x ≤ 0.07 by studying the upper critical field H_c2(T). The H_c2(T) is analyzed based on the dirty-limit two-gap model. While the effective diffusivities of the π-band decreased gradually, those of the σ-band were relatively unchanged, which indicated that unlike the 2 dimensional σ-band, the isotropic π-band is seriously affected by the Al doping. The upward curvature of H_c2(T) near T_c is also explained by the dirty-limit two-gap model.

The time evolution of the voltage response (V(t)) of the zero-field-cooled (ZFC) vortex matter for MgB₂ single crystals while applying a constant current application was recorded. Near the peak effect (PE) region, we observed a specific pattern of the V(t), that of a random telegraph signal for which the voltage mainly remained at two different levels. The origin of this random telegraph signal is closely related to the motional ordering of vortices resulting from the competition between the pinning and the Lorentz forces.

On the basis of Fan and Malozovsky theory, which had discussed the non-phonon mechanism of the layered Fermi liquid superconductivity, and of the experimental studies and theoretical analyses obtained by Zhang et al. as well as other scientists, we have analyzed and discussed the extrinsic and intrinsic factors of affecting the transition temperature T_c of cuprate superconductors. We also will present some possible approaches to explore new high T_c superconductive materials, and pay more attention to the non-traditional phonon mechanism, low dimensional or quasi two-dimensional system, and hexagonal structure materials, etc.

A number of studies showed that the AC losses for B//c are much larger than that for B//ab due to the effects of I_c(B) behavior at 77K. We present the relation between AC losses and the orientations of DC magnetic field by a sample of Bi-2223 tapes with 37 filaments of a superconducting core, which were prepared by the powder-in-(Ag) tube (PIT). A universal formula on the relation between AC losses and the orientations of the DC magnetic field will be found out according to the ellipse model of the Norris equation. The formula will provide some useful hints for the theoretical analysis of AC losses.

The amorphous composite metal studied in this paper is a kind of bulk metallic glass (BMG), which has special physical properties at low temperature. Zr-based bulk metallic glass chose as a sample, we report the results of microstructure, superconductivity and its corresponding crystallized sample. According to the results, the superconducting transition temperatures present before and after annealing, Zr-based bulk metallic glass has a negative coefficient of resistivity - temperature before annealing, and the superconducting critical temperature T_c was improved after annealing, for the amorphous T_c = 1.85K and for annealed sample T_c = 3.87K. Amorphous composite structure can help understand the physical properties at low temperature.

In this paper, using the first-principles calculations, we study the crystal structure effect on the superconductivity in CaAlSi. It is proposed that an AF-like superstructure model for Al (or Si) atoms arranged along the c direction may mediate the inconsistency of the electron-phonon coupling estimated from theory and experiment, and explain the anomalous superconductivity in CaAlSi.

Anisotropic superconducting properties in Sc₅Ir₄Si₁₀ and Lu₅Ir₄Si₁₀ single crystals are investigated. Both of these compounds are found to show quasi-one-dimensional superconductivity with better conduction along the c-axis and anisotropy parameter of about 2. Reflecting the partial destruction of the Fermi surface due to charge-density-wave formation, Lu₅Ir₄Si₁₀ shows higher residual resistivity, lower superconducting transition temperature, and longer magnetic penetration depths compared with those of Sc₅Ir₄Si₁₀. Similarity of superconducting properties including the anisotropy in Sc₅Ir₄Si₁₀ and Lu₅Ir₄Si₁₀ indicates that the absence of the charge-density wave in Sc₅Ir₄Si₁₀ is controlled by a subtle difference in the Fermi surface topologies in these two compounds.

Layered nitride superconductor, Li_0.48(THF)_yHfNCl with Tc=25.5 K, was investigated by means of nuclear magnetic resonance (NMR). ⁷Li-, ³⁵Cl-NMR studies clarified that the partial electron density of states at Fermi level at Li and Cl sites are negligibly small. From the ¹⁵N NMR Knight shift studies, the spin susceptibility decreases toward zero below T_c, evidencing that the pairing symmetry is an even-parity spin-singlet. These results indicate that superconductivity is derived from the HfN layer. We also measured ¹⁵N-, ⁷Li-NMR spin-lattice relaxation rate in the temperature range of 4.2K - 100 K and observed the enhancement of the spin-lattice relaxation rate, 1/T₁, by field fluctuations generated by the vortex dynamics.

The discovery of superconductivity in palladium-hydrogen (PdH) and its isotopes (D,T) at low temperature, brought about extensive study of this system. These studies have shown that the critical transition temperature is a function of the H concentration x in the PdH_x system with T_c=9K for x=1. In the last decade we defined a room temperature and room pressure technique to load H and maintain stable the stoichiometry in Pd lattice at levels higher than unit. Several magnetic and electric transport measurements have been performed showing transition temperature in the range of [18K< T_c < 273K]. Moreover in a typical critical current measurement configuration, current density greater than 6*10⁴Acm^-2⊐ has been measured at liquid nitrogen temperature. The 263.5K superconducting transition after a week of sample storage at room pressure and temperature, decreased down to 261.5K and after 2 years it became 160.5K, demonstrating a fairly good stability of the sample. Evidences of the flux exclusion (ZFC measurements) and the flux expulsion (FC measurements) have been found at very high transition temperature (Tc=235K) for the PdH system.

A composite buffer of CeO₂/YSZ/ Y₂O₃ was investigated on the biaxially textured NiW long tape for YBCO coated conductor with magnetron sputtering technique. Every layer's surface morphology was observed by scanning electron microscopy. The seed layer Y₂O₃ film was full coverage of the NiW substrate. The cap layer CeO₂ showed a smooth and crack-free surface and good crystallinity. The roughness of CeO₂ surface was measured by atom force microscopy. The transmission electron microscopy was used to analyze the cross-section of buffer layers and YBCO layer.

To get some information about the interaction of two totally different kinds of superconductors in a mixture, we prepared the samples of mixture of two kinds of superconductors (YBa₂Cu₃O₇₊MgB₂), using normal annealing method at low temperature (400 °C ~ 600 °C). The variations of the transition temperature (T_c) and critical current (J_c) of the mixtures are investigated. We also prepared a series of samples of MgB₂ with small ratios of YBCO or Bi-2223 as addition. Carefully comparison shows that the J_c drops when the ratio of YBCO additions increases, but in the Bi-2223 additions the trend goes just the opposite.

When a magnetic field is applied parallel to the superconducting layers in high-T_c superconductors (HTSCs), vortices become Josphson vortices (JVs). To study the magnetic phase diagram of JVs in strongly anisotropic HTSCs, we propose that the JV flow-resistance measurement is a powerful probe to observe periodic oscillations in the JV flow-resistance against the magnetic field. We could determine the magnetic phase diagram of JVs in Bi-2212, in which there exist a three-dimensionally-ordered state and a two-dimensionally quasi-ordered one.

In order to study the Josephson vortex phase diagram in high-T_c superconductors, we have prepared untwinned single crystals of underdoped YBa₂Cu₃O_y and measured the c-axis resistivity ρ_c(T) in magnetic fields H parallel to the ab plane. In YBa₂Cu₃O_y (T_c ~ 60 K), the vortex liquid phase freezes into the Josephson vortex glass through two-stage processes with decreasing temperature in the high-H region above 5 T. Since the two phase transition lines consist of the first-order transition line T_L(H) and the second-order transition line T_g(H), the intermediated phase in the region of T_g(H) < T < T_L(H) is considered to be the vortex slush phase. We find that the oscillatory field dependence of T_L(H) corresponds to the commensurability between the vortex spacing and the period of the CuO₂ planes. The lower critical point μ₀H_lcp ~ 5 T of T_L(H) and the vortex slush phase result from the moderate disorder due to the oxygen vacancy in the CuO chain.

Ground state of interlayer Josephson vortex systems is investigated on the basis of the Lawrence-Doniach model. For low fields, the ground state is characterized by various rotated-lattice configurations, and inhomogeneity of the internal field and superconducting amplitude plays little role. For intermediate fields, the ground state is characterized by continuously-varying shearing angle of vortex lattices, and the shear instability field is enhanced by inhomogeneity of the internal field. For high fields, the upper critical field H_c2 is determined by inhomogeneity of the superconducting amplitude. For material parameters of cuprate high-T_c superconductors, the shear instability field is significantly increased, and H_c2 becomes infinite. These results are compared with the elastic theory and the London theory with respect to field dependence of the shear modulus c₆₆.

We report on the equilibrium vortex phase diagram and vortex dynamics driven by dc current in the low-temperature liquid phase of thick amorphous (a-)Mo_xGe_1-x and a-Mo_xSi_1-x films containing weak and moderately strong pinning, respectively. The solid state for the a-Mo_xGe_1-x film is an ordered vortex lattice or Bragg glass, which is different from the disordered vortex glass for the a-Mo_xSi_1-x films. We find that the liquid state is similar to each other, involving the quantum-vortex-liquid (QVL) phase at low temperature. The width of the QVL phase is not enhanced by reduced pinning strength. In both systems we detect the unusual vortex flow in (near) the QVL phase.

We report on the measurements of broadband voltage noise generated by the driven vortex matter in and just below the peak-effect regime of a thick amorphous Mo_xGe_1-x film. We focus on a change in broadband noise as the system undergoes the mode-locking (ML) resonance (ML freezing), which occurs when the ac drive superimposed on the dc drive excites the lattice-oscillation modes collectively. Independent of the field studied, the noise spectrum at low frequencies f is of Lorentzian type, while it is f-independent at high f (but well below the ac-drive frequency). We find that the magnitude of noise at high f decreases in the ML resonance.

We report on the dynamic as well as static properties of vortices in the low-temperature (T) solid phase of a thick amorphous Mo_xGe_1-x film with weak pinning. The vortex-solid state is considered to be a weakly disordered vortex lattice, which is inferred from the mode-locking resonance over the broad field region. The peak effect of the critical current I_c with magnetic field is clearly visible down to the lowest T measured (0.2 K), which corresponds to 3.3% of the superconducting transition temperature. We find that largest voltage noise originating from current-driven vortices appears in the field region just prior to the peak field at which I_c takes a peak. This is in accord with the result reported in NbSe₂ single crystals.

Motivated by a recent experiment [R. S. Keizer, et. al., Nature 439, 825 (2006)], we study the Josephson effect in superconductor/diffusive half metal/superconductor junctions. The Josephson π-state is more stable than the 0-junction when the spin-flip scattering at the junction interface opens the Josephson channel of the odd-frequency Cooper pairs.

The polycrystalline samples of La_2/3Ca_1/3Mn_1-xCo_xO₃ (LCMCO) (x ≤ 0.20) with single phase are synthesized by solid-state reaction method. Rietveld refinements proved that Co replaces Mn in LCMCO. The lattice parameters decrease monotonically with increasing Co content, while the bond angles of Mn-O-Mn increases from 160.4° (x = 0.02) to 170.2° (x = 0.20). The metal-to-insulator transition temperature decreases with increasing Co content. The scattering of coupling between e_g electrons and the surface phonons, which is indicated by T_p, decreases with the increase of Co content. Magne-toresistance at T_MI decreases with increasing the Co content from 297.4% to 81.4%, but increases at T_p from 23.8% to 121.2%, respectively.

With varying the content of Ca, single phase of La_0.7Ca_0.3-xMnO₃ (LCMO) with Pnma symmetry have been studied. There is no phase transition detected with varing the content of Ca. The divergence of Mn-O1(ax) and Mn-O2(eq) values indicates the occurrence of lattice distortions. No marked variations of Mn-O1-Mn and Mn-02-Mn bond angles are observed. The insulator-metal transition temperature T_MI of samples shifts to lower values with increasing vacancy content. At low temperature region, a large MR (30∼45%) is observed. We attribute it to the grain boundary tunnel effect.

LiTaO₃ thin films were deposited on Pt/Ti/SiO₂/Si substrates by means of a sol-gel spin-coating technology and rapid thermal annealing (RTA). The influence of various annealing treatments on the characteristics of the thin films were studied by varying the single-annealed-layer thickness (50 ~ 200 nm) and heating temperatures (500 ~ 800°C) of the samples. Experimental results reveal that the single-annealed-layer strongly influences grain size, dielectricity and ferroelectricity of LiTaO₃ thin films. The grain size of LiTaO₃ thin film decreases slightly with increasing thickness of the single-annealed-layer, and highly c-axis orientated LiTaO₃ films can be obtained for a single-annealed-layer of 50 nm. When the thickness of the single-annealed-layer was increased from 50 to 200 nm, the relative dielectric constant of LiTaO₃ thin film decreased from 65 to 35, but the dielectric loss factor (tanδ) was increased. The LiTaO₃ films with the single-annealed-layer of 50 nm showed excellent ferroelectric properties in terms of a remanent polarization (P_r) of 12.3 μC/cm² (E_c ∼ 60 kV/cm), and a low current density of 5.2×l0^-8A/cm² at 20 kV/cm.

Fe₃F₄ with the spinel structure was designed, and its electric and magnetic properties were calculated in system based on density function theories. And then they were compared with those of Fe₃O₄. From our calculation, Fe₃F₄ is a kind of new stable approximate half-metal material because its spin-polarization at fermi level is about 95%, which is near to 100%. The steady constant of crystal lattice is 0.643 nm. The energy distance between the top of the up-spin valence band and the fermi level is about 2.05 eV, which is much larger than 0.6 eV of Fe₃O₄. In the other hand, the resistivity of Fe₃F₄ is lower than that of Fe₃O₄. The molecular magnetic moments 10.68μ_B of Fe₃F₄ are evidently higher than 4.0μ_B of Fe₃O₄. This shows that there is stronger spin-correlation scattering on transmitted carriers in Fe₃F₄ than in Fe₃O₄ so that Fe₃F₄ may have higher magnetoresistance than Fe₃O₄. Extremely localization of 3d-electrons caused by hybrid orbits of F2p and Fe3d orbits is the mechanism of the distribution of electronic charges and magnetic moments of Fe₃F₄.

Microstructures of the Fe₃F₄ granular films doped by transition metal (TM) were analyzed and the phenomenological magnetoresistance theory was proposed in this paper. Influences of technological parameters including the temperature (T), the applied field (H) and the content (x) on the magnetoresistance (MR) are analyzed in detail. Through theoretical analysis, there are the following conclusions. Firstly, variations of MR with x are non-linear and MR may arrive at the maximum at a certain x. Secondly, MR decreases strongly with the increase of T, but the decreases may be reduced by doped TM. Then doped TM can help to improve electric and magnetic properties of half metals. Thirdly, MR increases with the increase of H when the magnetization of grains is unsaturated.

We measured the dielectric dispersion in multi-ferroic TbMnO₃. We observed two kinds of the dielectric dispersions. One dispersion showed the monotonous temperature dependence of the relaxation frequency across the ferroelectric transition temperature, T_c. This dispersion is thought to be originated from the localized charge. The other dispersion existed only near the T_c, attributed to the ferroelectric transition. We found the former dispersion enhanced its strength near T_c. This indicates that the localized charge couples with the electric moment which orders in the ferroelectric phase.

Pulsed laser deposition (PLD) is a unique method for growing highly stoichiometric, materials in the form of epitaxial thin films. Here we discuss the optimization of deposition parameters for laser ablation of multi-component La_0.7Ca_0.3MnO₃-YBa₂Cu₃O_7-δ (LCMO-YBCO) heterostructures grown in situ by sequential deposition of LCMO and YBCO on <100> LaAlO₃ (LAO) substrates using a PLD system. We discuss the growth of these multi-layers, from the device applications point of view.

We have systematically studied the X-ray radiation effects on PZT thin ceramic disk provided by CTS Communications Components, Inc using the X-ray beam line in the Center for Advanced Micro-Structure and Devices (CAMD) in Baton Rouge, Louisiana. The photo energies of the X-ray range from 2000 eV to 8000 eV. The beam size is 10.0cm×1.0cm.We measure the dielectric constant in situ with different dose of the radiation in one sample and in different samples. The dielectric constants as a function of radiation dose are presented in the paper. It demonstrates the effects on the dielectric constant. Unexpectedly, we also found that X-ray radiation on the PZT disk generates charges on the surface of the samples. We measured the surface voltage due to the X-ray radiation with different radiation dose at the same temperature for these samples. This founding may have application potential for photoelectric devices. This is just a preliminary study. More thorough investigations are needed.

Polycrystalline single phase oxides, La_0.7-xNd_xPb_0.3)MnO₃ (0.3≤x≤0.7), have been synthesized by a standard ceramic fabrication method. A phenomenological model is proposed to describe the magnetization process, and to fit the experiment data of hysteresis loops under different composition ratio. The magnetic hysteresis behavior can be modeled by the formula of . The resulted model can satisfy the experiment data ranging from 0.005T to 5T. Explanations on the fitting coefficients of these compounds are addressed.

Four perovskite compounds with nominal compositions of (Gd_0.5Th_0.5)NiO₃, (Gd_0.5Ce_0.5)NiO₃, (Yb_0.5Th_0.5)NiO₃ and (Yb_0.5Ce_0.5)NiO₃ were prepared by a polymeric citrate precursor method. They were either slow-cooled in the furnace or quenched to room temperature. All of them have monoclinic symmetry. Quenched samples have a slightly bigger unit cell volume and longer Ni-O bond length, and a smaller grain size than that of the furnace-cooled compounds. All samples are paramagnetic insulators in the range of 2 K to 300 K. The Th containing compounds have larger tolerance factor and Ni(1)–O(1)–Ni(2) bond angle than that of the Ce containing compounds. No mixed valence of Ce, Th and Ni is observed in these samples.

The preferred (002) orientation Zinc oxide (ZnO) nanocrystalline thin films have been deposited on ITO-coated glass substrates by means of sol-gel spin-coating technology and rapid thermal annealing for use in dye-sensitized solar cells (DSSC). The effects of annealing temperature (400 ~ 700 °C) on the microstructure and morphology of ZnO thin films were studied. With the increase of heating temperature from 400 °C to 700 °C, the grain size of ZnO thin films decreases from 80 to 10 nm. The decreases in grain size of ZnO thin films contributed to the improvement on the absorption of dye onto the films. The ITO/ZnO/RuL₂(NCS)₂ electrodes with high absorption in the wide range containing visible light reveal that the nanoporous structure can adsorb easily the dye and can be expected in the application of DSSC.

The Zr-doped TiN coating, a nanometer (Ti, Zr)N thin film, has been deposited by reactive magnetron sputtering on slides and Al substrates. The crystalline phase and energy band structure have been analyzed by XRD and STS. The results of XRD show that the (Ti, Zr)N film is poly crystalline and consisted of mixed crystal of TiN and ZrN phase. The STS spectra show that Zr-doping didn't change the position and band-gap of energy level, only two new energy levels appeared, E_g = 0.33eV and E_g = 0.42eV. According to the results of measurement, (Ti, Zr)N has higher hardness and better corrosion resistance than TiN by Zr-doping.

Samples of 0.65Pb(Mg_1/3Nb_2/3)O₃-0.35PbTiO₃ single crystal cut in three orientations <001>, <110>, <111> were supplied by H. C. Materials Corporation, Urbana, Illinois, U.S.A. The dielectric constant was first measured for these three samples with different orientations. It shows the samples are of high quality. Then we observed the hysteresis loops at different temperatures for these samples. From hysteresis loops we obtained the remnant polarization as a function of temperature. It is found that the remnant polarization changes with temperature rapidly in the temperature region from 80°C to 130°C. The displacement current without sustained applied electric field on it that is supposed to be proportional to the pyroelectric coefficient in different orientation was measured by a Picoammeter under no applied electric field and the comparison of the displacement current density with the pyroelectric coefficient was presented.

The composition of Mn_0.05Si_0.95 polycrystalline films on (001) Si substrate are prepared by vacuum deposition and post-crystallization processes. X-ray diffraction studies indicate that there are two phases coexist in the film: tetragonal, Mn₄Si₇ and diamond-like Si (Mn). The content of Si(Mn) phase increases with increasing the post-annealing temperature. Temperature dependence of the magnetization shows that there are two ferromagnetic phases with Curie temperature of around 50 K and near room temperature, which is confirmed by x-ray magnetic circular dichroism (XMCD).

Multi-wall carbon nanotubes (MWNTs) thin film was synthesized and its sensing for different flowing solutions was investigated in this paper. The voltage generated from MWNTs thin film was in sublinear fashion and a new discovery in this paper is that the charge-to-mass ratio (q/m) of the ions is an important factor. The results were inconsistent with the conventional idea that a streaming potential is the efficient factor. New mechanism has been discussed about their effects on the charge of MWNTs and the sublinear response based on a pulsating ratchet model. This result would be indicative in nanoscale sensors, detectors and power cells.

We present a universal relation between the densities of states near Van Hove singularities and the effective electron masses in 1-dimensional (1-D) materials. The relation can be utilized as a new method to determine the effective masses of charge carriers of 1-D materials in theoretical calculations and in experimental measurements. The calculated results, utilizing the relation for single-walled carbon nanotubes (SWCNTs), agree well with that of the conventional calculations when both approaches utilize the outputs of ab-initio density functional computations.

Based on the principle of exergy-economy, the equation for the annual total cost of the low-temperature pipeline is derived by analyzing the process of the transport, which can be used to discuss the effects of the pipe diameter and insulation thickness on the annual total cost. An approach of the synchro-design method for the low-temperature pipeline and its insulation is proposed. From the point of reducing the annual total cost, the calculating formulas of the low-temperature pipeline and insulation thickness are obtained.

In order to understand the effect of the magnetic field on surface patterns on semi-conducting silicon melt in industrial Czochralski furnaces, we conducted a series of unsteady three-dimensional numerical simulations of silicon melt flow in a shallow annular pool under the axial magnetic field for the magnetic field strength from 0 to 0.1T. The pool is heated from the outer cylindrical wall and cooled at the inner wall. Bottom and top surfaces are adiabatic. When the magnetic field is weak, the simulation can predict various three-dimensional oscillatory flows depending on the radial temperature difference. With the much larger magnetic field, three-dimensional flow becomes axisymmetric steady flow. Details of flow and temperature disturbances are discussed and the critical magnetic field strengths for the onset of axisymmetric steady flow are determined.

We have prepared Pt-doped WO₃ composite films by sol-gel compounding and DC reactive magnetron sputtering respectively. Spectra change process according to the absorbing hydrogen time has been characterized by UV-VIS, X-ray diffraction spectra of two kinds of samples have been studied in this paper, and the crystallization temperature of film has been observed at the same time. As a result, both two WO₃ composite films are better sensitive to hydrogen by Pt-doping and the Pt sputtered sol-gel film has faster response to hydrogen than the Pt sputtered film by DC reactive magnetron sputtering, but the changes of luminousness are almost equal for two films.

Double-sided magnesium diboride (MgB₂) thin films have been grown on double-sided polished sapphire substrates by the technique of hybrid physical chemical vapor deposition (HPCVD). The zero resistance temperature (Tc) of the films is higher than 37 K. The microwave characteristic of the double-sided MgB₂ thin films at 8.7GHz is studied systematically by the microstrip resonator technique. Surface resistance of the thin films is extracted by analyzing the resonance curves at different temperatures, and it is 1.2 mΩ at 11K.

Based on the analyzing of the thermodynamic performance of the heat transfer process in the low temperature heat exchangers, the exergy efficiency of the heat transfer process is defined and a general expression for the exergy efficiency is derived, which can be used to discuss the effect of heat transfer units number and heat capacity ratio of fluids on the exergy efficiency of the low temperature heat exchanger. The variation of the exergy efficiency for several kinds of flow patterns in the low heat exchangers is compared and the calculating method of the optimal values of heat capacity ratio for the maximum exergy efficiency is given.

The exergoeconomic analysis is carried out on enhanced heat transfer surfaces at low temperature. A new criterion for evaluating the performance of enhanced heat transfer surfaces at low temperature is proposed. It can be applied to various augmentation techniques and generalizes the performance evaluation criteria obtained by means of the first and second law analysis. The validity of the new performance evaluation criterion is illustrated by the analysis of heat transfer characteristics at low temperature and assessment of the heat transfer cost of two types of enhanced heat transfer surfaces.

By analyzing exergy transfer process of the low temperature heat exchangers operating below the surrounding temperature, the concept of exergy transfer coefficient is put forward and the expressions which involving relevant variables for the exergy transfer coefficient, the heat transfer units number and the ratio of cold to hot fluids heat capacity rate, etc. are derived. Taking the parallel flow, counter flow and cross flow low temperature heat exchangers as examples, the numerical results of exergy transfer coefficient are given and the comparison of exergy transfer coefficient with heat transfer coefficient is analyzed.

High-orderly nanotubes of titania were fabricated by anodic oxidation of pure titanium substrate in different electrolytes containing fluoride. Different morphological nanotubes of titania were obtained through controlling the different pH value of inorganic electrolytes, and it was found that nanotubes of titanium oxide would not formed when pH value was above 6. The morphological and structural properties of nanotublar products were characterized by SEM. The synthesized nanotubes of titania in organic electrolytic solutions containing fluoride was of 60 μm in length. The experiments demonstrated the length and orderliness of nanotubes of titanium oxide in organic solutions were much better than those in inorganic solutions.