Type-II Ising Pairing in Few-Layer Stanene

TL;DR

This paper reports the discovery of a new type of Ising pairing in few-layer stanene, where spin-orbit coupling induces pairing without inversion symmetry breaking, leading to enhanced in-plane critical fields at low temperatures.

Contribution

It demonstrates a novel Ising pairing mechanism in epitaxially strained stanene, distinct from traditional inversion symmetry breaking-based mechanisms.

Findings

Observation of enhanced in-plane critical field at low temperatures.

Identification of spin-orbit locking causing band splitting.

Evidence of a new Ising pairing mechanism in stanene.

Abstract

Spin-orbit coupling has proven indispensable in realizing topological materials and more recently Ising pairing in two-dimensional superconductors. This pairing mechanism relies on inversion symmetry breaking and sustains anomalously large in-plane polarizing magnetic fields whose upper limit is expected to diverge at low temperatures, although experimental demonstration of this has remained elusive due to the required fields. In this work, the recently discovered superconductor few-layer stanene, i.e. epitaxially strained $\alpha$-Sn, is shown to exhibit a new type of Ising pairing between carriers residing in bands with different orbital indices near the $\Gamma$-point. The bands are split as a result of spin-orbit locking without the participation of inversion symmetry breaking. The in-plane upper critical field is strongly enhanced at ultra-low temperature and reveals the sought for upturn.