Weak localization coexisting with a magnetic field in a normal-metal–superconductor microbridge

A random-matrix theory is presented which shows that breaking time-reversal symmetry by itself does not suppress the weak-localization correction to the conductance of a disordered metal wire attached to a superconductor. Suppression of weak localization requires applying a magnetic field as well as raising the voltage, to break both time-reversal symmetry and electron-hole degeneracy. A magnetic-field-dependent contact resistance obscured this anomaly in previous numerical simulations.