Coherence effects in a normal-metal–insulator–superconductor junction

Coherence effects arising due to Andreev reflections in a superconductor–insulator–normal-metal junction are considered. It is shown that in the absence of electron-electron interaction in the metal at low temperatures, the electrical potential drop on the insulator ${\mathit{I}}_0$ ${\mathit{R}}_{\mathit{I}}$, caused by the current density ${\mathit{I}}_0$ through the junction, vanishes, although the resistance of the device ${\mathit{R}}_{\mathrm{\infty }}$ measured by the two-probe method can be large. The electron-electron interaction determines the zero-temperature value of ${\mathit{R}}_{\mathit{I}}$. The implications of these effects for the theory of the superconductor–normal-metal–superconductor junction are discussed.