Local probe of vortex pinning energies in the Bose glass

Columnar defects provide strong pinning centers for vortices in high-T_c superconductors, increasing global critical currents. Using a magnetometer array of micron dimensions, we characterize the local held profiles in untwinned single crystals of YBa_2Cu_3O_(7-δ) with equivalent columnar defect densities B_φ. We find that the critical current is large only where the internal magnetic field BB _ φ, 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-T_c superconductors.