Magnetic tilting and emergent Majorana spin connection in topological superconductors

TL;DR

This paper theoretically investigates how magnetic fields influence surface Majorana modes in topological superconductors, revealing a transition in their cone structure and a universal magnetic response that could aid detection.

Contribution

It introduces a novel theoretical framework describing the magnetic response and tilting of Majorana cones, including the emergence of a Majorana spin connection in curved geometries.

Findings

Surface Majorana cones tilt under magnetic fields due to orbital effects.

A transition from type I to type II Dirac-Majorana cones occurs at a critical field.

Finite geometries exhibit a universal magnetic response enabling detection.

Abstract

Due to the charge neutral and localized nature of surface Majorana modes, detection schemes usually rely on local spectroscopy or interference through the Josephson effect. Here, we theoretically study the magnetic response of a two-dimensional cone of Majorana fermions localized at the surface of class DIII Topological Superconductors. For a field parallel to the surface the Zeeman term vanishes and the orbital term induces a Doppler shift of the Andreev levels resulting in a tilting of the surface Majorana cone. For fields larger than a critical threshold field $H^*$ the system undergoes a transition from type I to type II Dirac-Majorana cone. In a spherical geometry the surface curvature leads to the emergence of the Majorana spin connection in the tilting term via an interplay between orbital and Zeeman, that generates a finite non-trivial coupling between negative and positive energy states. Majorana modes are thus expected to show a finite response to the applied field, that acquires a universal character in finite geometries and opens the way to detection of Majorana modes via time-dependent magnetic fields.