Enhancement and suppression of the transition temperature of a three-dimensional XY ferromagnet by control of vortex-loop fugacity

Abstract

A previous vortex-loop scaling analysis for the three-dimensional XY model is extended to include an external loop-segment chemical potential μ=λk_BT. The loop fugacity y₀ is suppressed, y₀→y₀e^−2πλ, for λ > 0, enhancing the transition temperature T_c(λ), in agreement with the Monte Carlo work of Kohring, Shrock, and Wills. One also gets the suppression of transition temperatures T_c(e²) of lattice superconductors by electromagnetic charge e², by mapping onto this loop-fugacity model. A possible approach to superconductor high-T_c enhancement, by tailored suppression of topological excitations, is briefly conjectured.