Tunneling into thin superconducting films: interface-induced quasiparticle lifetime reduction

TL;DR

This study uses tunneling spectroscopy to show that interface effects significantly shorten quasiparticle lifetimes in thin superconducting lanthanum films, affecting spectral features and enabling film thickness measurements.

Contribution

It identifies interface-induced quasiparticle relaxation as the main cause of spectral broadening in thin superconducting films, providing a new spectroscopic method for thickness determination.

Findings

Large spectral broadening observed in tunneling spectra.

Quasiparticle lifetimes are extremely short due to interface relaxation.

Spectroscopic method for measuring film thicknesses developed.

Abstract

Scanning tunneling spectroscopy measurements of superconducting thin lanthanum films grown on a normal metal tungsten substrate reveal an extraordinarily large broadening of the coherence peaks. The observed broadening corresponds to very short electron-like quasiparticle lifetimes in the tunneling process. A thorough analysis considering the different relaxation processes reveals that the dominant mechanism is an efficient quasiparticle relaxation at the interface between the superconducting film and the underlying substrate. This process is of general relevance to scanning tunneling spectroscopy studies on thin superconducting films and enables measurements of film thicknesses via a spectroscopic method.