Search

Abstract: The theory of structural transformation of the vortex lattice in a fourfold symmetric in a–b plane type-II superconductors is constructed using both the London and the lowest Landau level Ginzburg–Landau model. Thermal fluctuations and quenched disorder influence the location of the square to rhomb structural transition line. The self consistent harmonic approximation for lattice anharmonicity within the fourfold symmetric generalization of the London model is used. Without disorder in the T–B plane the slope of the line is generally negative: thermal fluctuations favour a more symmetric square lattice. The theoretical line’s location and slope are in good agreement with the experimental “second magnetization peak” line measured in both LaSCCO and YBCO in a wide range of doping. We find that, while the thermal fluctuations are negligible for the transitions in low T c materials, disorder plays an important role and creates a positive slope in the T–B plane since disorder favours a symmetric square lattice. [Copyright &y& Elsevier]

Abstract: Dynamics of the flux lattice in the mixed state of strongly type-II superconductor near the upper critical field subjected to AC field and interacting with a periodic array of short range pinning centers is considered. The superconductor in a magnetic field in the absence of thermal fluctuations on is described by the time-dependent Ginzburg–Landau equations. For a special case of the δ-function shaped pinning centers and for pinning array commensurate with the Abrikosov lattice (so that vortices outnumber pinning centers) an analytic expression or the AC conductivity is obtained. It is found that below a certain critical pinning strength and for sufficiently low frequencies there exists a sliding Abrikosov lattice, which vibrates nearly uniformly despite interactions with the pinning centers. At very small frequencies the conductivity diverges at the critical pinning strength. [ABSTRACT FROM AUTHOR]