Ultrathin Films of Superconducting Metals as a Platform for Topological Superconductivity

TL;DR

This paper explores the potential of ultrathin superconducting metal films, like Pb and Sn, as platforms for topological superconductivity, leveraging their broken inversion symmetry and tunable electronic properties under strain and magnetic fields.

Contribution

It provides a theoretical framework showing how ultrathin superconducting films can host topological superconductivity by tuning Fermi levels and exploiting large g-factors.

Findings

Fermi level tuning via strain in ultrathin Pb and Sn films.

Large g-factors enhance magnetic field effects.

Ultrathin films break inversion symmetry inherently.

Abstract

The ingredients normally required to achieve topological superconductivity (TSC) are Cooper pairing, broken inversion symmetry, and broken time-reversal symmetry. We present a theoretical exploration of the possibility of using ultra-thin films of superconducting metals as a platform for TSC. Because they necessarily break inversion symmetry when prepared on a substrate and have intrinsic Cooper pairing, they can be TSCs when time-reversal symmetry is broken by an external magnetic field. Using microscopic density functional theory calculations we show that for ultrathin Pb and $\beta$-Sn superconductors the position of the Fermi level can be tuned to quasi-2D band extrema energies using strain, and that the $g$-factors of these Bloch states can be extremely large enhancing the influence of external magnetic fields.