Three signatures of phase-coherent Andreev reflection

An efficient numerical scheme is developed to compute the differential conductance ${\mathit{G}}_{\mathrm{NS}}$ of a disordered normal-metal–superconductor (NS) junction at voltages V and magnetic fields B. A sharp peak is found in ${\mathit{G}}_{\mathrm{NS}}$ around V,B=0 in the case of a resistive NS interface, as observed experimentally and confirming the theory of ‘‘reflectionless tunneling.’’ An ideal interface shows a conductance dip, due to an enhanced weak-localization effect. Finally, it is demonstrared that time-reversal-symmetry breaking does not reduce the ‘‘universal conductance fluctuations’’ in ${\mathit{G}}_{\mathrm{NS}}$ by a factor of 2.