Proximity effects in the superconductor / heavy fermion bilayer system Nb / CeCu_6

TL;DR

This study explores the proximity effect between Nb superconductors and CeCu_6 heavy fermion systems, revealing a strong suppression of superconductivity and unique dimensional behavior compared to normal metals, explained by heavy fermion properties.

Contribution

It provides the first detailed analysis of the proximity effect in superconductor/heavy fermion bilayers, incorporating heavy fermion characteristics into the proximity effect model.

Findings

Critical temperature decreases with Nb thickness on CeCu_6

Absence of dimensional crossover in H_{c2}^{ ext{parallel}}(T)

Data explained by a model considering heavy fermion properties

Abstract

We have investigated the proximity effect between a superconductor (Nb) and a 'Heavy Fermion' system (CeCu_6) by measuring critical temperatures $T_c$ and parallel critical fields H_{c2}^{\parallel}(T) of Nb films with varying thickness deposited on 75 nm thick films of CeCu_6, and comparing the results with the behavior of similar films deposited on the normal metal Cu. For Nb on CeCu_6 we find a strong decrease of T_c with decreasing Nb thickness and a finite critical thickness of the order of 10 nm. Also, dimensional crossovers in H_{c2}^{\parallel}(T) are completely absent, in strong contrast with Nb/Cu. Analysis of the data by a proximity effect model based on the Takahashi-Tachiki theory shows that the data can be explained by taking into account both the high effective mass (or low electronic diffusion constant), {\it and} the large density of states at the Fermi energy which characterize the Heavy Fermion metal.