Local Spectral Inversion and Bosonic Fine Structure Extraction via Superconducting Scanning Tunneling Spectroscopy

TL;DR

This study uses superconducting scanning tunneling spectroscopy and Eliashberg theory to analyze phonon structures in lead, revealing new fine structures and electron-hole asymmetries in the local electron-boson interactions.

Contribution

It introduces a local spectral inversion method for superconductors, uncovering novel bosonic features and asymmetries not previously observed in Pb.

Findings

Identification of new fine structures in the electron-boson spectral function.

Observation of electron-hole asymmetries in local spectra.

Agreement with previous phonon studies while revealing new details.

Abstract

We perform the scanning tunneling spectroscopy based superconductor-vacuum-superconductor analogue to the seminal McMillan and Rowell superconductor-insulator-superconductor device study of phonons in the archetypal elemental superconductor Pb [W. L. McMillan and J. M. Rowell, Phys. Rev. Lett. 14, 108 (1965)]. We invert this spectroscopic data utilizing strong-coupling Eliashberg theory to obtain a local {\alpha}^2F({\omega}) and find broad underlying agreement with the pioneering results, highlighted by previously unobserved electron-hole asymmetries and new fine structure which we discuss in terms of both conventional and unconventional superconducting bosonics.