Diamagnetic response of cylindrical normal metal - superconductor proximity structures with low concentration of scattering centers

TL;DR

This study examines the diamagnetic response of normal metal-superconductor proximity structures, showing strong induced diamagnetism and analyzing the effects of elastic scattering using quasiclassical theory, with results aligning with experimental data.

Contribution

It provides a detailed analysis of the diamagnetic response in NS proximity structures incorporating elastic scattering, extending the understanding of their behavior across a wide temperature range.

Findings

Strong induced diamagnetism observed in normal layers.

Mean free path values consistent with resistivity measurements.

Nonlinear response breakdown fields follow clean limit theory trends.

Abstract

We have investigated the diamagnetic response of composite NS proximity wires, consisting of a clean silver or copper coating, in good electrical contact to a superconducting niobium or tantalum core. The samples show strong induced diamagnetism in the normal layer, resulting in a nearly complete Meissner screening at low temperatures. The temperature dependence of the linear diamagnetic susceptibility data is successfully described by the quasiclassical Eilenberger theory including elastic scattering characterised by a mean free path l. Using the mean free path as the only fit parameter we found values of l in the range 0.1-1 of the normal metal layer thickness d_N, which are in rough agreement with the ones obtained from residual resistivity measurements. The fits are satisfactory over the whole temperature range between 5 mK and 7 K for values of d_N varying between 1.6 my m and 30 my m. Although a finite mean free path is necessary to correctly describe the temperature dependence of the linear response diamagnetic susceptibility, the measured breakdown fields in the nonlinear regime follow the temperature and thickness dependence given by the clean limit theory. However, there is a discrepancy in the absolute values. We argue that in order to reach quantitative agreement one needs to take into account the mean free path from the fits of the linear response. [PACS numbers: 74.50.+r, 74.80.-g]