EXACT SOLUTIONS OF THE FLUX-CREEP MODEL AND SOLITON-FLUX DYNAMICS AND THEIR APPLICATION IN TYPE-II SUPERCONDUCTORS

Abstract

Recently, much attention has been focused on the exactly solvable model of flux-creep in high-Tc superconductors. In this paper, the exact solution of the flux-creep model based on both thermal-activation and quantum-tunneling flux-creep theories is explicitly given. For a typical weakly periodical or quartic pinning potential and/or flux-flux interaction in a viscous medium, both classical motion in the thermal-activation region and quantum motion in the quantum-tunneling region are semi-classically analyzed, and the dependencies of activation energy and crossover temperature on several important parameters of the system are studied in more detail. The exact and explicit expression of the flux relaxation rate is derived for the full parameter range. We calculate the flux relaxation rate as a function of temperature and the current density as a function of time and find that this simple phenomenological theory is very effective in accounting for the experimental observations obtained in both high-Tc and low-Tc superconductors.