Insensitivity to time-reversal symmetry breaking of universal conductance fluctuations with Andreev reflection

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).