Peculiarities of superconducting properties of thin superconductor-normal metal bilayer with large ratio of resistivities

TL;DR

This paper investigates the unique superconducting properties of thin superconductor-normal metal bilayers with large resistivity ratios, revealing enhanced diamagnetic response, increased critical current, and diode effect, with potential applications in superconducting detectors.

Contribution

It provides the first combined theoretical and experimental analysis of how a normal metal layer influences superconducting properties in bilayers with large resistivity ratios.

Findings

Normal layer dominates diamagnetic response below critical temperature.

Critical current can be increased several times due to the normal layer.

The bilayer exhibits a diode effect under parallel magnetic field.

Abstract

We demonstrate, both theoretically and experimentally, that thin dirty superconductor-normal metal bilayer with resistivity of normal metal $\rho_N$ much smaller than normal-state resistivity of superconductor $\rho_S$ has unique superconducting properties. First of all the normal layer provides the dominant contribution to the diamagnetic response of whole bilayer structure in wide temperature interval below the critical temperature due to proximity induced superconductivity. Secondly, the presence of the normal layer may increase the critical current $I_c$ in several times (the effect is not connected with enhanced vortex pinning), provides strong temperature dependence of both $I_c$ and effective magnetic field penetration depth even at temperatures much below the critical one and leads to the diode effect in parallel magnetic field. Besides of general interest we believe that the found results may be useful in construction of different kinds of superconducting detectors.