Superconducting quantum spin-Hall systems with giant orbital g-factors

TL;DR

This paper predicts a gapless superconducting state in quantum spin-Hall systems with giant orbital g-factors, enabling significant spin polarization and unique transport phenomena without Zeeman interaction.

Contribution

It introduces a novel orbital magnetic-field effect in QSHS/superconductor structures, leading to a giant orbital g-factor and spin-polarized edge superconductivity.

Findings

Prediction of a gapless superconducting state with protected edge modes.

Demonstration of giant orbital g-factors of several hundreds.

Proposal of a three-terminal setup to detect spin-polarized edge superconductivity.

Abstract

Topological aspects of superconductivity in quantum spin-Hall systems (QSHSs) such as thin layers of three-dimensional topological insulators (3D Tis) or two-dimensional Tis are in the focus of current research. We examine hybrid QSHS/superconductor structures in an external magnetic field and predict a gapless superconducting state with protected edge modes. It originates entirely from the orbital magnetic-field effect caused by the locking of the electron spin to the momentum of the superconducting condensate flow. We show that such spin-momentum locking can generate a giant orbital g-factor of order of several hundreds, allowing one to achieve significant spin polarization in the QSHS in the fields well below the critical field of the superconducting material. We propose a three-terminal setup in which the spin-polarized edge superconductivity can be probed by Andreev reflection, leading to unusual transport characteristics: a non-monotonic excess current and a zero-bias conductance splitting in the absence of the Zeeman interaction.