Thermally activated dissipation and irreversibility fields of bismuth oxide superconductors

Abstract

Thermally activated dissipation is investigated in epitaxial Bi-2:2:2:3 films in magnetic fields parallel to the c axis. For a wide temperature T and field B range the resistivity \ensuremath{\rho} shows clear Arrhenius behavior with an activation energy ${\mathit{U}}_{0}$=A(1-T/${\mathit{T}}_{\mathit{c}}$)/ \ensuremath{\surd}B : \ensuremath{\rho}(B,T)=${\mathrm{\ensuremath{\rho}}}_{0}$exp(-${\mathit{U}}_{0}$/kT)=${\mathrm{\ensuremath{\rho}}}_{0}$exp[-A(1-T/ ${\mathit{T}}_{\mathit{c}}$)/kT \ensuremath{\surd}B ], which is explained by thermally activated flux motion with the formation of double kinks. Temperature dependence of the irreversibility field ${\mathit{B}}^{\mathrm{*}}$ is predicted by flux-creep theory as \ensuremath{\surd}${\mathit{B}}^{\mathrm{*}}$ =C(1/kT-1/${\mathit{kT}}_{\mathit{c}}$), when ${\mathit{B}}^{\mathrm{*}}$ is defined by an electric-field criterion. This relation holds not only for our films but also for magnetically determined ${\mathit{B}}^{\mathrm{*}}$ of Bi-2:2:2:3 samples, which suggests that the irreversibility line originates from thermally activated plastic motion of pinned flux liquid.