Superconductive critical temperature of Pb/Ag heterostructures

TL;DR

This paper investigates the superconducting critical temperature of Pb/Ag heterostructures, revealing that a modified density of states assumption explains experimental observations that standard models cannot.

Contribution

It demonstrates that adjusting the local density of states at the interface accounts for the critical temperature behavior without free parameters.

Findings

Critical temperature decreases with layer ratio.

Constant superconducting gap despite lattice differences.

Modified density of states explains experimental data.

Abstract

Recent experimental data (H. Nam et al., Phys. Rev. B 100, 094512 (2019)) of critical temperature and gaps measured on superconductor/normal metal heterostructure Pb/Ag, epitaxially grown, shown a interesting not usual behaviour. The critical temperature decreases strongly but, despite the large differences in the lattice constants and electronic densities of states in the separate components, this heterostructure shows a spatially constant superconducting gap. In the paper it is demonstrated that the proximity Eliashberg equations, whit no free parameters, cannot explain the dependence of critical temperature from the rate $d_{Pb}/d_{Ag}$. However it is sufficient to assume that the density of states at the Fermi level of silver is equal to that of lead in a layer adjacent to the separation interface, presumably of a thickness less than the coherence length of the lead, to perfectly explain the decrease in the critical temperature and the gap value in function of the rate $d_{Pb}/d_{Ag}$ always without free parameters.