Collective-pinning theory and the observed vortex dynamics in RBa2Cu3O7- delta crystals.

Abstract

We establish a framework for the analysis of magnetization data on high-temperature superconductor crystals that allows direct comparison with vortex-pinning theory. When the magnetization loops exhibit scaling behavior, as they do over a large part of the B-T plane for R${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ crystals, the effective pinning energy ${\mathit{U}}_{\mathrm{eff}}$ has to contain power-law field dependences for the characteristic energy and current scales ${\mathit{U}}_{0}$ and ${\mathit{J}}_{0}$; these power-law exponents can be obtained directly from the data. Many regimes of collective-pinning (CP) theory do predict such power laws, but none yield exponents in agreement with those that are measured. The discrepancy appears to arise because ${\mathit{U}}_{0}$ is observed to decrease with B, in contrast to the CP predictions. \textcopyright{} 1996 The American Physical Society.