ENHANCEMENT AND SUPPRESSION OF THE TRANSITION-TEMPERATURE OF A 3-DIMENSIONAL XY FERROMAGNET BY CONTROL OF VORTEX-LOOP FUGACITY

A previous vortex-loop scaling analysis for the three-dimensional XY model is extended to include an external loop-segment chemical potential =kBT. The loop fugacity y0 is suppressed, y0'y0e-2, for >0, enhancing the transition temperature Tc(), in agreement with the Monte Carlo work of Kohring, Shrock, and Wills. One also gets the suppression of transition temperatures Tc(e2) of lattice superconductors by electromagnetic charge e2, by mapping onto this loop-fugacity model. A possible approach to superconductor high-Tc enhancement, by tailored suppression of topological excitations, is briefly conjectured. © 1990 The American Physical Society.