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Phys. Rev. Lett. 82, 4532–4535 (1999)

Thermodynamics of the Superconducting Phase Transition in Ba0.6K0.4BiO3

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P. Kumar
Department of Physics, University of Florida, Gainesville, Florida 32611

Donavan Hall
National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310

R. G. Goodrich
Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803-4001

Received 12 October 1998; published in the issue dated 31 May 1999

See accompanying Physics Focus

We suggest that the transition to superconductivity in a single crystal of Ba0.6K0.4BiO3 with Tc = 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 Tc/2<T≃Tc) the temperature dependence of the critical fields. We find Hc1(T)∝(1-T/Tc)3, H0(T)∝(1-T/Tc)2, and Hc2(T)∝(1-T/Tc)1 in general agreement with experiments.

© 1999 The American Physical Society

URL:
http://link.aps.org/doi/10.1103/PhysRevLett.82.4532
DOI:
10.1103/PhysRevLett.82.4532
PACS:
74.20.De
 
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