Ginzburg-landau Theory of Vortex Phase Diagram in Layered Type Ii Superconductor

Various macroscopic phenomena seen in high temperature superconductors (HTSC) under nonzero magnetic fields have inspired much interest in studying the phase diagram of vortex states of three dimensional (3D) layered type II superconductors. Experimentally, thermodynamic and transport phenomena have been intensively examined mainly in YBCO [1-3] and BSCCO [4]. The resistive broadening [5] in the so-called vortex liquid regime below the crossover line Hc2(T ) is common to these materials with strong fluctuation effect and is well described in terms of the non-Gaussian superconducting fluctuation theory[6]. Since, on approaching a phase transition, macroscopic behaviors tend to become insensitive to microscopic details of each material, one expects that the phase diagram itself should be qualitatively the same between these materials. However, recent data [7-10] in YBCO seem to have shown some details of transition lines in real systems with pinning disorders which have been unseen in BSCCO. It is important to find how such phenomena apparently dependent on the materials are explained within a single GL theory. Theoretically, the phase diagram of vortex states has been tackled from two different points of view. In the literature [11-13] based on the elastic theory for the vortex systems with pinning disorder, one first starts from low fields and low temperatures and hence, works in the London (phase-only) limit of the GL model. Consequently, a glassy solid phase, named Braggglass (BrG) phase, was proposed as the ground state in cleaner real systems. Then, a melting line of BrG phase is estimated in terms of some kind of Lindemann criterion and is usually identified with a simultaneous destruction of positional and glass (superconducting) orders. Since the positional ordering of field-induced vortices in clean bulk systems is believed to occur through