Orbital Response of Evanescent Cooper Pairs in Paramagnetically Limited Al Films

TL;DR

This study investigates how perpendicular magnetic fields influence the pairing resonance in ultra-thin aluminum superconducting films, revealing a linear energy shift and spectral modifications due to orbital effects.

Contribution

The paper extends existing theory to account for strong perpendicular magnetic fields, explaining the observed resonance energy shifts and spectral changes in thin Al films.

Findings

Resonance energy shifts upward linearly with perpendicular magnetic field.

Broadening and attenuation of the resonance with increasing field.

Spectral distribution altered by the exclusion principle at high fields.

Abstract

We report a detailed study of the pairing resonance via tunneling density of states in ultra-thin superconducting Al films in supercritical magnetic fields. Particular emphasis is placed on effects of the perpendicular component of the magnetic field on the resonance energy and magnitude. Though the resonance is broadened and attenuated by $H_\bot$ as expected, its energy is shifted upward linearly with $H_\bot$. Extension of the original theory of the resonance to include strong perpendicular fields shows that at sufficiently large $H_\bot$ the overlap of the broadened resonance tail with the underlying degenerate Fermi sea alters the spectral distribution of the resonance via the exclusion principle. This leads to the shift of the the resonance feature to higher energy.