Thermally activated resistive behavior and flux motion in La2-xSrxCuO4 single-crystal thin films.

Abstract

Thermally activated behavior of the resistive transition under magnetic fields has been studied in ${\mathrm{La}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{CuO}}_{4}$ (x=0.1, 0.15, 0.2, and 0.3) single-crystal thin films. It is found that the resistivity \ensuremath{\rho} below ${\mathit{T}}_{\mathit{c}}$ scales as \ensuremath{\rho}(T)=${\mathrm{\ensuremath{\rho}}}_{0}$exp{-${\mathit{U}}_{0}$[1-T/${\mathit{T}}_{\mathit{c}}$(H)${]}^{\mathit{n}}$/${\mathit{k}}_{\mathit{B}}$T}, where n=3 for H\ensuremath{\parallel}c and n=2.5 for H\ensuremath{\perp}c. This behavior is explained phenomenologically as the thermal-depinning of vortices in quasi-two-dimensional superconductors having small-sized dense point pins. Numerical fitting provides values for the effective pinning potential and the mean-field upper critical field, which delineates straight H-T phase boundaries.