Local probe of vortex pinning energies in the Bose glass.

Abstract

Columnar defects provide strong pinning centers for vortices in high-${\mathit{T}}_{\mathit{c}}$ superconductors, increasing global critical currents. Using a magnetometer array of micron dimensions, we characterize the local field profiles in untwinned single crystals of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ with equivalent columnar defect densities ${\mathit{B}}_{\mathrm{\ensuremath{\varphi}}}$. We find that the critical current is large only where the internal magnetic field B${\mathit{B}}_{\mathrm{\ensuremath{\varphi}}}$. In regions of the crystal where B\ensuremath{\gtrsim}${\mathit{B}}_{\mathrm{\ensuremath{\varphi}}}$, the critical current is sharply reduced. We model both local and global critical current measurements by generalizing the Bean picture to the case of irradiated high-${\mathit{T}}_{\mathit{c}}$ superconductors.