Crossover of Ising- to Rashba-Type Superconductivity in Epitaxial Bi2Se3/Monolayer NbSe2 Heterostructures

TL;DR

This study demonstrates a transition from Ising- to Rashba-type superconductivity in Bi2Se3/monolayer NbSe2 heterostructures, revealing a new pathway to engineer topological superconductivity in atomically thin materials.

Contribution

The paper reports the first controlled synthesis and characterization of Bi2Se3/monolayer NbSe2 heterostructures showing a crossover in superconducting pairing types, advancing topological superconductor research.

Findings

Emergence of Rashba-type quantum well bands and spin-nondegenerate surface states.

Suppression of in-plane upper critical magnetic field indicating pairing crossover.

Thickness-dependent transition from Ising- to Rashba-type superconductivity.

Abstract

A topological insulator (TI) interfaced with an s-wave superconductor has been predicted to host an unusual form of superconductivity known as topological superconductivity (TSC). Molecular beam epitaxy (MBE) has been the primary approach in the scalable synthesis of the TI/superconductor heterostructures. Although the growth of epitaxial TI films on s-wave superconductors has been achieved, it remains an outstanding challenge for synthesizing atomically thin TI/superconductor heterostructures, which are critical for engineering the TSC phase. Here, we used MBE to grow Bi2Se3 films with the controlled thickness on monolayer NbSe2 and performed in-situ angle-resolved photoemission spectroscopy and ex-situ magneto-transport measurements on these Bi2Se3/monolayer NbSe2 heterostructures. We found that the emergence of Rashba-type bulk quantum well bands and spin-nondegenerate surface states coincides with a marked suppression of the in-plane upper critical magnetic field of the superconductivity in Bi2Se3/monolayer NbSe2 heterostructures. This is the signature of a crossover from Ising- to Rashba-type superconducting pairings, induced by altering Bi2Se3 film thickness. Our work opens a new route for exploring a robust TSC phase in TI/Ising superconductor heterostructures.