Locally gauge-invariant spin response of ${}^3$He-$B$ films with Majorana surface states

Abstract

A locally gauge-invariant theory of the spin response of a thin film of ${}^3$He-$B$ film is given that describes fluctuation effects arising from the coupled dynamics of the superconducting order parameter (the collective mode) and in-gap Majorana surface states. In contrast to a mean-field calculation of the spin response, which predicts a nonzero imaginary longitudinal spin susceptibility at frequencies inside the bulk gap due to absorption from the Majorana states, our gauge-invariant theory shows that this response is strongly suppressed above the collective mode frequency and vanishes if dipole-dipole interactions are neglected. In the presence of dipole-dipole interactions, in sufficiently thin films, and at ultra-low temperatures, the Majorana states lead to a distinctive magnetic-field- and temperature-dependent damping of the collective mode, a feature that may be observable in longitudinal NMR experiments.

Published version. 8 pages, 3 figures

References in corpus (8)

• Signatures of Majorana fermions in hybrid superconductor-semiconductor nanowire devices
• Collective modes and electromagnetic response of a chiral superconductor
• Symmetry Protected Topological Order and Spin Susceptibility in Superfluid 3He-B
• Surface Majorana Cone of the Superfluid ${}^3$He B Phase
• Majorana surface states of superfluid 3He A- and B-phases in a slab
• Surface Specific Heat of ${}^3$He and Andreev Bound States
• Anomalous Attenuation of Transverse Sound in 3He
• Surface Majorana fermions and bulk collective modes in superfluid 3He-B