Vortex pinning by twin boundaries in copper oxide superconductors

Abstract

We investigate the pinning properties of twin boundaries in ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ single crystals within a collective-pinning theory. For small angles \ensuremath{\vartheta} between the magnetic field and the twin boundaries, the vortex lattice adjusts to the array of twinning planes. Above the bulk depinning temperature ${\mathit{T}}_{\mathit{p}}$, the pinning properties of the twin boundaries are enhanced as compared with the bulk pinning. The combined effects lead to an increased pinning of the vortex lattice at small angles \ensuremath{\vartheta}, explaining the narrow angular response observed recently in the resistive transition and in torque measurements.