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Effect of inhomogeneous coupling on BCS superconductors

Yue Zou, Israel Klich, and Gil Refael
Phys. Rev. B 77, 144523 – Published 25 April 2008

Abstract

We investigate the influence of inhomogeneity in the pairing coupling constant U(r) on dirty BCS superconductors, focusing on Tc, the order parameter Δ(r), and the energy gap Eg(r). Within mean-field theory, we find that when the length scale of the inhomogeneity is comparable to or larger than the coherence length, the ratio 2EgTc is significantly reduced from that of a homogeneous superconductor, while in the opposite limit, this ratio stays unmodified. In two dimensions, when strong phase fluctuations are included, the Kosterlitz-Thouless temperature TKT is also studied. We find that when the inhomogeneity length scale is much larger than the coherence length, 2EgTKT can be larger than the usual BCS value. We use our results to qualitatively explain recent experimental observation of a surprisingly low value of 2EgTc in thin films.

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  • Received 18 December 2007

DOI:https://doi.org/10.1103/PhysRevB.77.144523

©2008 American Physical Society

Authors & Affiliations

Yue Zou1, Israel Klich2, and Gil Refael1

  • 1Department of Physics, California Institute of Technology, Pasadena, California 91125, USA
  • 2Kavli Institute for Theoretical Physics, University of California Santa Barbara, Santa Barbara, California 93106, USA

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Issue

Vol. 77, Iss. 14 — 1 April 2008

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