Casimir-Josephson force on a point contact between two superconductors

C. W. J. Beenakker

doi:10.1103/PhysRevB.108.195422

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Casimir-Josephson force on a point contact between two superconductors

C. W. J. Beenakker

DOI 10.1103/PhysRevB.108.195422 · Physical Review B

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Abstract

We calculate the elongation or contraction force F on a point contact (length L) connecting two superconductors with a phase difference ϕ. When L is small compared with the superconducting coherence length ξ0, this force is given by F=−(Δ0/πξ0)ln(ξ0/L)cosϕ per spin-degenerate transverse mode. Quantum fluctuations in states from the continuous spectrum outside the superconducting gap Δ0 give the dominant contribution to this force, which may be understood as the superconducting counterpart of the electromagnetic Casimir force. We compare with earlier work that only included contributions from the discrete spectrum of Andreev levels.