Weakly Pinned Bose Glass vs. Mott Insulator Phase in Superconductors

Abstract

We study the properties of the Bose glass phase of localized flux lines in irradiated superconductors near the matching field $B_{\Phi}$. Repulsive vortex interactions destroy the Mott insulator phase predicted to occur at $B=B_\Phi$. For ratios of the penetration depth to average defect distance $\lambda / d \leq 1$ remnants of the Mott insulator singularities remain visible in the magnetization, the bulk modulus, and the magnetization relaxation, as B is varied near $B_{\Phi}$. For $\lambda \geq d$, the ensuing weakly pinned Bose glass is characterized by a soft Coulomb gap in the distribution of pinning energies.