Abstract
Abstract We performed flux-creep annealing experiments on disordered (overdoped) Bi 2 Sr 2 CaCu 2 O 8+ δ and La 2− x Sr x CuO 4 single crystals in remnant magnetic field at T =10 K, where, as generally accepted, the vortex creep process is thermally activated, and at T =2 and 1.8 K, in the putative quantum creep regime. A simple data analysis shows that the variation of the creep barrier U with the current density J remains qualitatively the same, regardless of T . In the case of La 2− x Sr x CuO 4 single crystals in remnant field U ( J ) diverges in the low- J limit, and flux-creep annealing considerably reduces the normalized relaxation rate S at low T . We emphasize that the relatively large “residual” S values appearing below a certain crossover temperature in “standard” magnetization relaxation experiments are mainly due to the usually fixed relaxation time window in the conditions of a strong U ( J ) nonlinearity.
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