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Normalized Andreev conductance peak in metal-superconductor point contacts can be enhanced above its ballistic maximum by disorder in the superconductor

Martin Moško1,2,*, Maroš Gregor1, Richard Hlubina1, Antónia Mošková2, Tomáš Roch1, Serhii Volkov1, and Tomáš Plecenik1

  • *Contact author: martin.mosko@savba.sk
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Phys. Rev. B 114, 094505 – Published 10 August, 2026

DOI: https://doi.org/10.1103/kx1t-gwcp

Abstract

The metal-superconductor point contact (PC) is ballistic, if the coherence length ξ0 in the superconductor, the electron mean free path l0 in the metal, and the electron mean free path l in the superconductor are much larger than the PC radius a. The differential conductance G(V) of the ballistic PC at low temperatures and at voltages |V|≤Δ/e, where Δ is the superconducting gap, exhibits the Andreev peak caused by Andreev reflection. In the ballistic PC involving an isotropic superconductor, the Andreev peak at |V|≤Δ/e normalized by the background conductance G(V) at |V|≫Δ/e, is equal to two. It is believed that in a disordered PC, where conditions l0,l≫a fail, the normalized Andreev peak is smaller than two. Here we study the PC between a clean metal (l0≫a) and a weakly disordered (l≳a) isotropic superconductor in the limit l≪ξ0. We show theoretically and experimentally that, surprisingly, disorder on the superconducting side, however weak, raises the normalized Andreev peak above the ballistic value of two. Such disorder does not affect the Andreev reflection and G(V) at |V|<Δ/e. However, it scatters the quasiparticles injected into the superconductor above the gap and reflects a part of them back to the PC before they join the condensate. As a result, G(V) at |V|>Δ/e is lowered and the Andreev peak-to-background ratio becomes larger than two. In the normal state, the backscattering modifies the Sharvin-Maxwell PC resistance by adding a coherent resistance term ∝(a/l)2.

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Phys. Rev. B 114, 094505– Published 10 August, 2026
  • Received 14 October 2025
  • Revised 28 May 2026
  • Accepted 9 July 2026
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