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  • Letter
  • Open Access

Electron-boson-interaction induced particle-hole symmetry breaking of conductance into subgap states in superconductors

F. Setiawan1,2,* and Jay D. Sau2

  • 1Pritzker School of Molecular Engineering, University of Chicago, 5640 South Ellis Avenue, Chicago, Illinois 60637, USA
  • 2Condensed Matter Theory Center and Joint Quantum Institute, Department of Physics, University of Maryland, College Park, Maryland 20742, USA

  • *setiawan@uchicago.edu
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Phys. Rev. Research 3, L032038 – Published 11 August, 2021

DOI: https://doi.org/10.1103/PhysRevResearch.3.L032038

Abstract

Particle-hole symmetry (PHS) of conductance into subgap states in superconductors is a fundamental consequence of a noninteracting mean-field theory of superconductivity. The breaking of this PHS has been attributed to a noninteracting mechanism, i.e., quasiparticle poisoning (QP), a process detrimental to the coherence of superconductor-based qubits. Here we show that the ubiquitous electron-boson interactions in superconductors can also break the PHS of subgap conductances. We study the effect of such couplings on the PHS of subgap conductances in superconductors using both the rate equation and Keldysh formalism, which have different regimes of validity. In both regimes, we found that such couplings give rise to a particle-hole asymmetry in subgap conductances which increases with increasing coupling strength, increasing subgap-state particle-hole content imbalance and decreasing temperature. Our proposed mechanism is general and applies even for experiments where the subgap-conductance PHS breaking cannot be attributed to QP.

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Phys. Rev. Research 3, L032038– Published 11 August, 2021
  • Received 6 August 2020
  • Revised 19 July 2021
  • Accepted 23 July 2021
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