Quantum and classical creep in high-<i>T</i>_cand organic superconductors

Abstract

At low temperatures, large, temperature-independent magnetic relaxation effects are found in the high-temperature superconducting ceramics and also in the organic superconductors giving evidence that, at these temperatures, vortex motion involves mainly a form of macroscopic quantum tunneling. At higher temperatures, flux motion is thermally assisted. The measured tunneling rates at T = 6 mK and low magnetic induction are in excellent agreement with the T → 0 values given for single vortex tunneling by the quantum collective creep theory of Blatter, Geshkenbein and Vinokur. The effects of anisotropy and layering in the tunneling rates of single crystals are in very good agreement with the aforementioned theory.