Josephson-junction thermodynamics and the superconducting phase transitionin a SQUID device

Alec Maassen van den Brink; H. Dekker

doi:10.1103/PhysRevB.55.R8697

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Josephson-junction thermodynamics and the superconducting phase transitionin a SQUID device

Alec Maassen van den Brink, H. Dekker

DOI 10.1103/PhysRevB.55.R8697 · Physical Review B

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Abstract

In a model of two ideal BCS superconductors coupled by a tunneling Hamiltonian the nonvanishing of the Josephson internal energy (and entropy) for T→Tc− is shown to be a consequence of superconducting correlations, which persist in the thermodynamic limit even in the mean-field approximation. The ensuing rapid increase of the Josephson free energy as the temperature of a tunneling junction drops below the superconducting bulk transition temperature Tc makes this transition of first order whenever the phase difference across the junction is fixed to a nonzero value. Taking this into account results in an availability potential governing the nonequilibrium thermodynamics of the junction which, in contrast with previously published results, has no unphysical features like latent heat released upon entering (or a superconducting phase dependent value in) the normal state. The analysis inter alia predicts a lowering of the critical temperature (to Tc|IH) for the junction, which has meanwhile been observed in high-quality superconducting quantum interference devices.