International Journal of Modern Physics B

With the rapid development of manufacturing technology of high temperature superconductive YB${}_{a2}$Cu₃O${}_{7-x}$ YBCO materials and decreasing in cost of production, YBCO is marching into industrial areas with its good performances as source of high-magnetic field and rather low cost in reaching superconductivity. Based on analysis of the performance of high temperature superconductors YBCO and development of technology in superconductive magnetic separation both home and abroad, we propose a new approach of taking YBCO tape to make a solenoid as the source of a high magnetic field of magnetic separatior of ores. The paper also looks into the future of the YBCO high temperature superconductive magnetic separation from the perspective of technology and cost, as well as its applications in other industries.

ZnO polyhedral structures were fabricated via a rapid thermal evaporation process. The ZnO nanostructures grown had faceted trumpet-like morphologies. The intensity of visible emission in photoluminescence spectra strongly related to growth temperature, indicating different concentrations of oxygen vacancy. These structures exhibited typical sensing property to gaseous ethanol. The sensing property was related to the oxygen vacancies.

We observe that H₃S has a BCC structure and, with nearest neighbor hopping only, a strong singularity occurs at zero energy. This singularity is accompanied with a highly nested Fermi surface, which is not conducive to a stable superconducting instability. Introduction of next-nearest-neighbor hopping removes the singularity, but a “robust” peak remains in the electron density of states. Solution of the BCS equations shows an enhanced superconducting $T_c$ due to this peak. Furthermore, nesting is no longer present, so other instabilities will not compete effectively with superconductivity. We find high critical temperatures are possible, even with very modest coupling strengths. We also examine a limit of the $T=0$ equations (in an Appendix) where an analytical solution is possible over the entire range of coupling strengths, and therefore the BCS-BEC crossover is fully covered.

The generalized Bose–Einstein condensation (GBEC) theory of superconductivity (SC) is briefly surveyed. It hinges on three distinct new ingredients: (i) Treatment of Cooper pairs (CPs) as actual bosons since they obey Bose statistics, in contrast to BCS pairs which do not obey Bose commutation relations; (ii) inclusion of two-hole Cooper pairs (2hCPs) on an equal footing with two-electron Cooper pairs (2eCPs), thus making this a complete boson–fermion (BF) model; and (iii) inclusion in the resulting ternary ideal BF gas with particular BF vertex interactions that drive boson formation/disintegration processes. GBEC subsumes as special cases both BCS (having its 50–50 symmetry of both kinds of CPs) and ordinary BEC theories (having no 2hCPs), as well as the now familiar BCS-Bose crossover theory. We extended the crossover theory with the explicit inclusion of 2hCPs and construct a phase diagram of $T_c/T_F$ versus $n/n_f$, where $T_c$ and $T_F$ are the critical and Fermi temperatures, $n$ is the total number density and $n_f$ that of unbound electrons at $T=0$. Also, with this extended crossover one can construct the energy gap $\mathrm{\Delta }(T)/\mathrm{\Delta }(0)$ versus $T/T_c$ for some elemental SCs by solving at least two equations numerically: a gap-like and a number equation. In 50–50 symmetry, the energy gap curve agrees quite well with experimental data. But ignoring 2hCPs altogether leads to the gap curve falling substantially below that with 50–50 symmetry which already fits the data quite well, showing that 2hCPs are indispensable to describe SCs.

Cuprate superconductors exhibit many features, but the ultimate question is why the critical temperature ($T_c$) is so high. The fundamental dichotomy is between the weak-pairing, Bardeen–Cooper–Schrieffer (BCS) scenario, and Bose–Einstein condensation (BEC) of strongly-bound pairs. While for underdoped cuprates it is hotly debated which of these pictures is appropriate, it is commonly believed that on the overdoped side strongly-correlated fermion physics evolves smoothly into the conventional BCS behavior. Here, we test this dogma by studying the dependence of key superconducting parameters on doping, temperature, and external fields, in thousands of cuprate samples. The findings do not conform to BCS predictions anywhere in the phase diagram.

This paper presents an investigation on ac losses of superconducting bulk caused by various magnetic wave conditions with the help of finite element software of Comsol Multiphysics. Three different magnetic wave conditions are analyzed, which are standing magnetic field, rotated magnetic field and traveling magnetic field. The calculation ac loss result was compared with that from analytical formulas for type-II superconducting slab and cylinder. The influences of the strength of external magnetic field on the ac losses were investigated. Effects of a relatively stable trapped-field of superconducting bulk on ac losses in time-varying magnetic field are clarified. Effect of spatially inhomogeneous distribution of the external magnetic field on the ac loss is studied.

Chemical reactions result from the outside shell electrons of the reacting species being shared in various types of combinations. Typical distances involved are tenths of nm, resulting in binding energies typically in the order of hundreds of kJ/mole (eV/atom). The synthesis of a novel “atomic system” formed from Iron and di-Hydrogen has been achieved. The measured enthalpy of formation is some 40 MJ/moleFe and the distance between the hydrogen proton and the iron nucleus is some 8 pm, hence the proposed name: Iron Pico-Hydride. This compound is a permanent electric dipole of atomic size. Pico-Hydrides could, thus, play a significant role in HT superconductivity and in super-capacitors. The synthesis is compatible with the standard model.

Thin films and heterojunctions of Hf${}^{4+}$-doped LaMnO₃ manganite have been studied. The sole tetravalent state of Hf${}^{4+}$ ensures formation of $n$-type La${}_{1-x}$Hf${}_x$MnO₃ (LHMO) manganite. Photoinduced resistance was also observed as illuminated by visible light. The induced photoresistance (PR) could be greatly enhanced by the compressive strain. The LHMO/Nb-STO heterojunctions showed excellent rectifying characteristics, which are comparable with those $pn$-junctions of conventional semiconductors. Their transport properties are tunable electrically and magnetically. Such LHMO/Nb-STO heterojunctions have the potential to develop novel functional field-effect transistors based on manganite perovskites.

Starting from Cook’s model [D. N. Cook, Models of the Atomic Nucleus (Springer, Berlin, 2006)], we proposed a non-Archimedean approach to show that we can transform his purely mathematical model into a physical one. In the first stage, we kept the f.c.c. lattice model surrounded by a vapor phase from which we can only extract “symmetric” entities (quantons?) which are the electrons. This in our opinion gives a much better global view of what the atom could be. When assembling the nuclei into a lattice, there is reciprocal influence between the vapor phase and the lattice. Consequently, superconductivity occurs when temperature decrease brings to freezing the vapor phase and when the “crystallization” of the vapor phase gives some symmetric tiling of the volume around the lattice, thanks to Curie’s theorem. Looking for high temperature superconductivity therefore is equivalent to finding symmetric crystallization of the vapor phase. In that sense this pleads for the use of heterogeneous materials in the “crystal grid” and the case being play with impurities. We do not see any limit, thanks to our model, for high and even very high temperatures for superconductivity.

To examine the thermodynamic phase stability of Y–Ba–Cu–O superconductors in ultrathin film form, we study the effects of high-pressure oxygen annealing and Cu enrichment on YBa₂Cu₃O${}_{7-\delta }$ films ranging from 8 nm to 15 nm in thickness. The films are grown epitaxially on SrTiO₃ substrates by pulsed laser-ablated deposition, and post-annealed in 475 atm of oxygen at 800${}^{\circ }$C while subjected to varying concentrations of excess CuO. X-ray diffraction (XRD) on the annealed films shows evidence for suppression of YBa₂Cu₃O${}_{7-\delta }$ and formation of Y₂Ba₄Cu₈O${}_{16}$. This structural transformation towards a higher-oxidation phase is expectedly correlated with film thinness and Cu enrichment.

The superconductivity with Rashba and Dressehlaus spin–orbit coupling and Zeeman effect is investigated. The energy gaps of quasi-particles are carefully calculated. It is shown that the coexistence of two spin–orbit coupling might suppress superconductivity. Moreover, the Zeeman effect favors spin-triplet Cooper pairs.

We study the Bardeen–Cooper–Shrieffer (BCS) pairing state of a two-component Bose gas with a symmetric spin–orbit coupling (SOC). In the dilute limit at low temperature, this system is essentially a dilute gas of diatomic molecules. We compute the effective mass of the molecule and find that it is anisotropic in momentum space. The critical temperature of the pairing state is about eight times smaller than the Bose–Einstein condensation (BEC) transition temperature of an ideal Bose gas with the same density.

Applying the generalized Bose–Einstein condensation (GBEC) formalism, we extend the BCS-Bose crossover theory by explicitly including hole Cooper pairs (2hCPs). From this follows a phase diagram with two pure phases, one with 2hCPs and the other with electron Cooper pairs (2eCPs), plus a mixed phase with arbitrary proportions of 2eCPs and 2hCPs. One has a special-case phase when there is perfect symmetry (i.e., with ideal 50–50 proportions between 2eCPs and 2hCPs). Explicitly including 2hCPs leads to an extended BCS-Bose crossover which predicts $T_c/T_F$ values for some well-known conventional superconductors (SCs) (i.e., assuming electron–phonon dynamics). These compare reasonably well with experimental data. We compare with experimental $T_c/T_F$ values for some conventional SCs associated with the new dimensionless number density $n/n_f$ with theoretical curves associated with the extended crossover for the special case of perfect symmetry. They all obey the Bogoliubov et al. upper limit, thus vindicating it.

A hybrid maglev model combining permanent magnet levitation (PML) and superconducting magnetic levitation (SML) was designed and fabricated to explore a heavy-load levitation system advancing in passive stability and simple structure. In this system, the PML was designed to levitate the load, and the SML was introduced to guarantee the stability. In order to realize different working gaps of the two maglev components, linear bearings were applied to connect the PML layer (for load) and the SML layer (for stability) of the hybrid maglev model. Experimental results indicate that the hybrid maglev model possesses excellent advantages of heavy-load ability and passive stability at the same time. This work presents a possible way to realize a heavy-load passive maglev concept.

Energy spectrum of electrons (holes) doped into two-dimensional (2D) antiferromagnetic (AF) semiconductors is quantized in an external magnetic field of arbitrary direction. A peculiar dependence of de Haas–van Alphen (dHvA) magneto-oscillation amplitudes on the azimuthal in-plane angle from the magnetization direction and on the polar angle from the out-of-plane direction is found. The angular dependence of the amplitude is different if the measurements are performed in the field above and below of the spin-flop field.

We have synthesized heterostructures that consist of a layer of a cuprate insulator, La₂CuO₄, and a layer of a nonsuperconducting cuprate metal, La${}_{1.55}$Sr${}_{0.45}$CuO₄. Such bilayers show high-$T_c$ interface superconductivity confined within a single CuO₂ plane. Here, we explore the behavior of interface superconductivity at high frequencies (up to 50 MHz) under high magnetic fields (up to 56 T). We find that interface superconductivity persists up to very high perpendicular fields (exceeding 40 T). The critical magnetic field $H_m(T)$ shows an upward divergence with decreasing temperature suggestive of vortex-lattice melting, similar to what is observed in bulk superconducting cuprates.

Andreev reflection on the interface of ferromagnet/superconductor ($F/S$) junction provides a tool for exhibiting the spin pairing symmetry in superconductors. The triplet tunneling in $F/d$-wave $S$ junction observed in recent experiments revived a fundamental interest: the pairing mechanism of the superconducting cuprate. Here we show that in a doped cuprate, the effective spin coupling between the doped holes on the O sites yields a symmetric bound pair state $|\uparrow \downarrow 〉+|\downarrow \uparrow 〉$ with quantum numbers $S=1$, $S_z=0$ in the CuO₂ layer, which explains the origin of the resonating valence bound state in cuprates, as well as the tunneling experiments. In addition, the $d$-wave is consistent with the triplet pairing since the observable orbital wavefunction is a projection from the total odd-frequency wavefunction onto the quasi-2D superconducting CuO${}_{\mathrm{\text{2}}}$ layer. High-temperature superconductivity as a long-standing puzzle touches upon a hiding symmetry: the triplet state ($S=1$, $S_z=0$) is indistinguishable from the singlet ($S=0$) either in NMR measurements, or in muon detections, but can be identified by tunneling spectroscopy of $F/S$ junction.

Single domain YBCO bulk superconductors with different additions of ZnO have been successfully fabricated by RE$+$011 TSIG process with a new solid phase of [(100-$x$)(Y₂O${}_3+1.2$BaCuO₂)+$x$ZnO] and a new liquid phase of (Y₂O₃+6CuO+10BaCuO₂). The effects of ZnO additions on the growth morphology, microstructure, critical temperature ($T_{\mathrm{\text{c}}}$), the levitation force and trapped field of the YBCO bulks have been investigated. It is found that within the range of ZnO additions $x$=0–1.0 wt.%, all the samples are of the typical characteristic of single-domain YBCO bulk; the $T_{\mathrm{\text{c}}}$ of the samples decreases from 92 K to 80 K when the ZnO addition $x$ increases from $x$=0 wt.% to $x$=1.0 wt.%; the levitation force and trapped field of the samples firstly increase and then decrease with increase of ZnO additions after going through a maximum, which is closely related with the ZnO addition and the resulting flux pinning force caused by lattice distortion due to the substitution of Zn${}^{2+}$ for Cu${}^{2+}$ site in the YBCO crystal; the largest levitation force 36.8 N (77 K, 0.5 T) and trapped field 0.416 T (77 K, 0.5 T) of the samples are obtained when $x$=0.1 wt.%, respectively. This result is significantly important and helpful for us to improve the properties of YBCO bulk superconductors.

The application of the gauge-gravity duality, also known as anti-de Sitter/conformal field theory (AdS/CFT) correspondence to study condensed matter systems has resulted in a number of important findings. Using the analogy, we have studied the phase transitions between a holographic insulator and a metal at zero temperature as well as finite temperature transition between a metal and a holographic superconductor of $s$- and $p$-wave symmetry. The main aim of this note is to look in which way the dark matter might affect the properties of superconductors. The hope is that some of the observed modifications could be used to detect this ubiquitous but still elusive component of matter in the Universe.

In this work, the structure stability of hexagonal Bi(PO${}_4)$(H₂O)${}_{0.67}$ has been investigated by high-pressure synchrotron X-ray diffraction measurements. The results show that the structure is stable within the pressure up to 18.3 GPa. The diffraction data are refined and the lattice constants $a$ and $c$ are determined, which is compressed by 6.3(7)% and 3.5(0)% within the experimental pressure, respectively. By fitting the pressure dependence of $V/V_0$ (unit cell volume divided by that at ambient pressure) with the second-order Birch equation of state, the bulk modulus $B_0$ is given to be about 87.1(0) GPa.

With the development of high temperature superconducting (HTS) maglev, studies on the running stability have become more and more significant to ensure the operation safety. An experimental HTS maglev vehicle was tested on a 45-m long ring test line under the speed from 4 km/h to 20 km/h. The lateral and vertical acceleration signals of each cryostat were collected by tri-axis accelerometers in real time. By analyzing the phase relationship of acceleration signals on the four cryostats, several typical motion modes of the HTS maglev vehicle, including lateral, yaw, pitch and heave motions were observed. This experimental finding is important for the next improvement of the HTS maglev system.

La${}_{0.9}$Hf${}_{0.1}$MnO₃ films were grown on 0.05 wt.% Nb-doped SrTiO₃ substrates by pulsed laser deposition. X-ray diffraction measurements demonstrated that our samples were of good epitaxy and single-crystal. The temperature-dependent resistance has been investigated. It was observed that the as-grown film of La${}_{0.9}$Hf${}_{0.1}$MnO₃ exhibited a typical paramagnetic-ferromagnetic transition. Heterojunctions of La${}_{0.9}$Hf${}_{0.1}$MnO₃/0.05 wt.% Nb-doped SrTiO₃ exhibited-asymmetric current–voltage characteristics and a remarkable temperature-dependent rectifying behavior in a wide temperature range (from 40 K to 300 K). And the most remarkable observation of this work is the existence of a crossover from positive to negative magnetoresistance in the La${}_{0.9}$Hf${}_{0.1}$MnO₃/0.05 wt.% Nb-doped SrTiO₃ heterojunction as the temperature decreases. A temperature-dependent magnetoresistance was studied as well. The rectifying characteristics and tunable magnetoresistance of these heterojunctions may be attributed to band structure of La${}_{0.9}$Hf${}_{0.1}$MnO₃/0.05 wt.% Nb-doped SrTiO₃ heterojunction.

In this paper, we carry out a theoretical calculation of quantum state and quantum energy structure in carbon nanotube embedded semiconductor surface. In this theoretical model, the electrons in the carbon nanotube are considered as in a two-dimensional cylindrical surface. Their motion, therefore, can be described by the Dirac equation. We solve the equation and find that the energy levels are quantized and are linearly dependent on the wave vectors along the $z$-direction that is along the direction of the nanotube. This type of energy structure may have potential application for fabricating high efficiency solar cell or quantum bit in computer chips.

We illustrate the improved empirical methods of estimating atomic masses using Garvey–Kelson like local relations and global equations using generic point functions.