Insensitivity to Time-Reversal Symmetry Breaking of Universal Conductance Fluctuations with Andreev Reflection

TL;DR

This paper investigates why conductance fluctuations in a disordered microbridge with Andreev reflection are unaffected by magnetic fields, combining numerical simulations with analytical and symmetry-based theories.

Contribution

It introduces a theoretical explanation for the insensitivity of conductance fluctuations to magnetic fields in systems with Andreev reflection, supported by random-matrix theory and symmetry analysis.

Findings

Conductance fluctuations are insensitive to magnetic fields in the studied system.

An exact analytical calculation confirms the anomaly.

Symmetry arguments explain the insensitivity phenomenon.

Abstract

Numerical simulations of conduction through a disordered microbridge between a normal metal and a superconductor have revealed an anomalous insensitivity of the conductance fluctuations to a magnetic field. A theory for the anomaly is presented: Both an exact analytical calculation (using random-matrix theory) and a qualitative symmetry argument (involving the exchange of time-reversal for reflection symmetry).