Interstitial and Vacancy Proliferation in Flux Line Lattices

Abstract

We study the formation of interstitials and vacancies in the Abrikosov phase of clean Type II superconductors. The defects are line imperfections, which cannot extend across macroscopic samples at low temperatures. We argue that the entropy associated with line wandering nevertheless causes these defects to proliferate at a sharp transition which can occur below the melting temperature of the vortex crystal. Flux lines are both entangled and crystalline in the resulting “supersolid” phase, which is closely related to a two-dimensional quantum crystal with interstitials or vacancies incorporated in its ground state. We find that the supersolid phase must occur above the thermal decoupling field B _x .Using molecular dynamics simulation we calculate the formation energies of various types of defect lines. We find that interstitials rather than vacancies are the preferred types of defects for B < < φ₀/λ ²_⊥ .