PINNING OF VORTICES AND LINEAR AND NONLINEAR AC SUSCEPTIBILITIES IN HIGH-T_c SUPERCONDUCTORS

摘要

The flux-line lattice in type-II superconductors can be calculated from various phenomenological theories. Static properties like the energy of arbitrary vortex arrangements and the nonlocal elasticity of the flux-line lattice are discussed and some consequences of the strong anisotropy and layered structure of high-temperature superconductors given. Vortex dynamics deals with moving flux lines, pinning, thermal depinning, flux creep, and nonlinear and linear complex resistivities. The concept of a demagnetization factor is discussed. Solutions of the Bean model in various geometries and some analytic expressions for nonlinear and linear ac susceptibilities are given. A numerical method is presented by which the magnetic response of superconductors can be computed in any geometry. This method is then applied to thin and thick superconductors in a perpendicular magnetic field and to the geometric barrier for flux penetration.