Boson Physics and Vortex Pinning Via Splayed Columnar Defects in Superconductors

Abstract

Concepts from many particle nonrelativistic quantum mechanics can be used to understand vortex line fluctuations in high-temperature superconductors. Flux lines are essentially classical objects, described by a string tension, their mutual repulsion, and interactions with pinning centers. The classical partition function, however, is isomorphic to the imaginary time path integral description of boson quantum mechanics. Recent double-sided decoration experiments in BSCCO compounds in a frozen flux liquid state have now revealed the “phonon-roton” spectrum which describes the decay of density fluctuations along the field direction. Parallel columnar pins lead to a low temperature “Bose glass” phase. Controlled splay of artificial columnar defects in cuprate superconductors can enhance transport properties in a field compared to parallel columns. The theory predicts a new “splayed glass” characterized by a greatly reduced flux creep and an entangled ground state similar to dislocation tangles in a work hardened metal. Recent experiments suggest that controlled splay leads to significant improvements in critical currents.