Paramagnetic reentrant effect in high purity mesoscopic AgNb proximity structures

TL;DR

This paper investigates the paramagnetic reentrant effect in high-purity mesoscopic AgNb proximity structures, revealing temperature-dependent behavior and specific coherence length conditions that influence magnetic susceptibility.

Contribution

It provides experimental evidence of the paramagnetic reentrant effect in AgNb structures and details the conditions under which it occurs, expanding understanding of mesoscopic superconductor-normal metal systems.

Findings

Observation of paramagnetic reentrant effect superimposed on Meissner screening.

Logarithmic temperature dependence of susceptibility limited by coherence length conditions.

Identification of integer multiple coherence length conditions in different wire geometries.

Abstract

We discuss the magnetic response of clean Ag coated Nb proximity cylinders in the temperature range 150 \mu K < T < 9 K. In the mesoscopic temperature regime, the normal metal-superconductor system shows the yet unexplained paramagnetic reentrant effect, discovered some years ago [P. Visani, A. C. Mota, and A. Pollini, Phys. Rev. Lett. 65, 1514 (1990)], superimposing on full Meissner screening. The logarithmic slope of the reentrant paramagnetic susceptibility chi_para(T) \propto \exp(-L/\xi_N) is limited by the condition \xi_N=n L, with \xi_N=\hbar v_F/2 \pi k_B T, the thermal coherence length and n=1,2,4. In wires with perimeters L=72 \mu m and L=130 \mu m, we observe integer multiples n=1,2,4. At the lowest temperatures, \chi_para compensates the diamagnetic susceptibility of the \textit{whole} AgNb structure.