Density In high-Tc Superconductors Research Articles

Matching field effects at tesla-level magnetic fields in critical current density in high-Tc superconductors containing self-assembled columnar defects

We have investigated the superconductive transport properties of Y Ba2Cu3O7 films containing self-assembled columnar arrays of second phase SrZrO3 or BaSnO3 precipitates. A matching condition between columnar pinning sites (aligned at or near the c axis) and external magnetic flux, tilted with respect to them, is identified in the critical current JC(H) data. The results for the material containing SrZrO3-based pins are analyzed within a simple intuitive model. At matching, the critical current is enhanced above the model prediction. In complementary contact-free investigations of BaSnO3-doped material, matching effects are observed over a wide range of temperatures in the field dependence of JC(H). The deduced matching fields agree reasonably well with the densities of columnar pins directly observed by scanning electron microscopy.

Application of parallel processing technique to shielding current analysis on HTS thin film

Parallelized element-free Galerkin (EFG) method using OpenMP is evaluated and the evaluation of AC loss of axisymmetric high-Tc superconductors (HTSs) by using EFG is presented. Formulation of the electromagnetic behavior of shielding current density in an HTS gives a system of time-dependent integro-differential equations. After discretizing the weak form of the problem based on EFG, the axisymmetric simulation code for analyzing the time evolution of the shielding current density on HTS is developed.In the present study, the simulation code for analyzing the time evolution of the shielding current density in HTS by using EFG is developed. Results of the computation shows that the CPU time of parallelized EFG in the case of 4PU is 3.8 times faster than that of 1PU. Furthermore, the AC loss is calculated numerically by use of the values of the shielding current density.

Solution of a nonlinear system by the adaptively deaccelerated Newton method: application to shielding current analysis in HTS

A numerical method for a nonlinear system is presented. Formulation of the electromagnetic behavior of the shielding current density in high-Tc superconductors (HTS) gives a system of time-dependent integro-differential equations. The behavior can be determined by solving the initial-boundary-value problem of the system using the element-free Galerkin (EFG) method and the complete implicit difference method. After discretizing the problem, we obtain a nonlinear equation. In the present study, the shielding current density in HTS is calculated by applying the deaccelerated Newton method (DNM) and adaptively deaccelerated Newton method (ADNM) for the solution of the nonlinear system. The results of computation show that the DNM does not give a convergent solution in some cases. On the other hand, the ADNM gives a convergent solution in a few iterations.

Condensation, excitation, pairing, and superfluid density inhigh-Tc superconductors: the magnetic resonance mode as a roton analogue and a possiblespin-mediated pairing

To find a primary factor determiningTc and a pairingmechanism in high-Tc cuprates, we combine the muon spin relaxation results onns/m* (superconductingcarrier density/effective mass), accumulated over the last 17 years, with the results from neutron and Ramanscattering, scanning tunnelling microscopy, specific heat, Nernst effect, andangle-resolved photoemission spectroscopy measurements. We identify the neutronmagnetic resonance mode as an analogue of the roton minimum in the superfluid4He, andargue that ns/m* and the resonance mode energy play a primary role in determiningTc in the underdoped region. We propose a picture wherein roton-like excitations in the cupratesappear as a coupled mode, which has resonance modes for spin and charge responses at differentmomentum transfers but the same energy transfer, as detected respectively by means of the neutronS = 1 mode andthe Raman S = 0 A1g mode. We shall call this the ‘hybrid spin/charge roton’. After discussing the role ofdimensionality in condensation, we propose a generic phase diagram for the cuprates withspatial phase separation in the overdoped region as a special case of the Bose–Einstein toBardeen–Cooper–Schrieffer crossover conjecture where the superconducting coupling is lostrapidly in the overdoped region. Using a microscopic model of charge motion resonatingwith antiferromagnetic spin fluctuations, we propose the possibility that the hybridspin/charge roton and higher-energy spin fluctuations mediate the superconducting pairing.In this model, the resonance modes can be viewed as a meson analogue and the‘dome’ shape of the phase diagram can be understood as a natural consequence ofdeparture from the competing Mott insulator ground state via carrier doping.

Scaling of the angular dependence of the critical current density in high-Tc superconductors.

We report a general scaling behavior of the dependence of the critical current density ${\mathit{j}}_{\mathit{c}}$(B,T,\ensuremath{\Theta}) on the direction of the magnetic field at low temperatures in c-axis-oriented high-${\mathit{T}}_{\mathit{c}}$ superconductor thin films with different strengths of interlayer coupling. Measurements of ${\mathit{j}}_{\mathit{c}}$(B,T,\ensuremath{\Theta}) for pure ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$, doped ${\mathrm{YBa}}_{2}$(${\mathrm{Cu}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Zn}}_{\mathit{x}}$${)}_{3}$${\mathrm{O}}_{7}$, ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{8}$, and ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$/${\mathrm{PrBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ superlattice films with different relative orientations of the current j, magnetic field B, and crystallographic direction c allow the identification of the dissipation caused by flux parallel to the superconducting layers moving in the c direction.