Pinning and creep in layered superconductors

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⪆ H₀ where H₀ is proportional to the mass anisotropy m/ M and estimated to be around 3 T for the Bi- and Tl-based superconductors. At H》 H₀ 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 / H₀) 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.