Thermodynamics of the Superconducting Phase Transition in Ba_{0.6}K_{0.4}BiO_3

Abstract

We suggest that the transition to superconductivity in a single crystal of Ba_{0.6}K_{0.4}BiO_3 with a T_c = 32K, and having critical fields with anomalous temperature dependencies and vanishing discontinuities in specific heat and magnetic susceptibility, may well be an example of a fourth order (in Ehrenfest's sense) phase transition. We have derived a free energy functional for a fourth order transition and calculated (for the temperature range $T_c/2<T\simeq T_c$) the temperature dependence of the critical fields. We find $H_{c1}(T)\propto (1-T/T_c{)}^3,H_0(T)\propto (1-T/T_c{)}^2$ and $H_{c2}(T)\propto (1-T/T_c{)}^1$ in general agreement with experiments.

arXiv comment12 pages, 3 figures, accepted for publication in PRL; This version corrects reference numbering and other minor typographical changes made while prepairing page proofs. (No content change.)

References in corpus (1)

• Properties of Phase transitions of a Higher Order

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