Conductance asymmetries in mesoscopic superconducting devices due to finite bias

TL;DR

This paper investigates how finite bias voltage causes conductance asymmetries in mesoscopic superconducting devices, providing insights that distinguish these effects from other mechanisms like quasiparticle poisoning, and highlighting their non-detrimental impact on topological qubit performance.

Contribution

It introduces a model showing finite-bias effects induce conductance asymmetries without quasiparticle poisoning, aiding experimental identification and understanding of these phenomena.

Findings

Finite bias causes significant conductance asymmetries.

Asymmetries can be distinguished from quasiparticle poisoning effects.

Finite-bias effects do not harm topological qubit performance.

Abstract

Tunneling conductance spectroscopy in normal metal-superconductor junctions is an important tool for probing Andreev bound states in mesoscopic superconducting devices, such as Majorana nanowires. In an ideal superconducting device, the subgap conductance obeys specific symmetry relations, due to particle-hole symmetry and unitarity of the scattering matrix. However, experimental data often exhibits deviations from these symmetries or even their explicit breakdown. In this work, we identify a mechanism that leads to conductance asymmetries without quasiparticle poisoning. In particular, we investigate the effects of finite bias and include the voltage dependence in the tunnel barrier transparency, finding significant conductance asymmetries for realistic device parameters. It is important to identify the physical origin of conductance asymmetries: in contrast to other possible mechanisms such as quasiparticle poisoning, finite-bias effects are not detrimental to the performance of a topological qubit. To that end we identify features that can be used to experimentally determine whether finite-bias effects are the source of conductance asymmetries.