Pinning and creep in layered superconductors

Abstract

The thermal- and disorder-induced effects in the mixed state of a layered high- T c superconductor (in a field H ‖ c ) are studied. The flux line lattice is of a quasi-2D type at sufficiently high field H⪆ H 0 where H 0 is proportional to the mass anisotropy m/ M and estimated to be around 3 T for the Bi- and Tl-based superconductors. At H》 H 0 the FLL melts at a temperature T m close to the temperature of 2D dislocation-mediated melting. At T > T m the system is in the normal state. At low temperatures T< T g⋍ T m/ In ( H / H 0) the system is in the vortex glass state with zero linear resistivity: ∂ V/∂ j→0 as j→0. In the intermediate temperature range T g< T< T m the energy barriers for the plastic motion of vortices are finite and thermally activated flux flow (TAFF) occurs. In the vortex glass state, different regimes of flux pinning and creep are identified and the behaviour of the critical current j c as a function of temperature and magnetic field is estimated. Power-law behaviour of the effective pinning energy U( j) at j⪌ j c is obtained for the case of 2D collective creep.