Superconducting spin properties of Majorana nanowires and the associated superconducting anomalous Hall effect

TL;DR

This paper explores the spin properties of Majorana nanowires and introduces the superconducting anomalous Hall effect, proposing new ways to detect Majorana zero modes through spin-related phenomena and Josephson junction behaviors.

Contribution

It demonstrates the role of spin-triplet pairing and the superconducting anomalous Hall effect in Majorana nanowires, offering novel detection methods for Majorana zero modes.

Findings

Superconducting anomalous Hall effect (ScAHE) observed in Majorana nanowires.

SOC induces anomalous supercurrent at zero phase difference in U-shape junctions.

Spin degree of freedom enhances detection of Majorana zero modes.

Abstract

It is difficult to unambiguously confirm the existence of Majorana zero modes (MZMs) due to the absence of smoking-gun signatures in charge transport measurements. Recent studies suggest that the spin degree of freedom of MZMs may provide an alternative detection method. We study the spin properties of the superconducting state in Majorana nanowires and the associated unconventional Josephson effect with realistic experimental parameters taken from [Zhang {\it et al.}, Nature 556, 74 (2018)]. For a superconducting thin film with in-plane polarized spin-triplet pairing, an out-of-plane electric field can generate a supercurrent perpendicular to both the superconducting spin polarization and the electric field, so we name this phenomena as superconducting anomalous Hall effect (ScAHE). In a Majorana nanowire, the regime with finite polarized spin-triplet pairing almost coincides with the chiral regime, which includes the topological regime. We further study the effects of polarized spin-triplet pairing in two types of Josephson junctions. One dramatic finding is that SOC can induce an anomalous supercurrent at zero phase difference only in the U-shape junction, a basic ingredient of scalable topological quantum computation. This can be viewed as a consequence of the ScAHE. Our work reveals that the spin degree of freedom is indeed helpful for detecting MZMs.