Magnetic excitations in the helical Rashba superconductor

TL;DR

This paper analyzes the magnetic excitation spectrum in a helical Rashba superconductor, revealing characteristic anisotropies in susceptibility that can be detected via inelastic neutron scattering, advancing understanding of noncentrosymmetric superconductors.

Contribution

It derives general expressions for the dynamical spin response in a helical Rashba superconductor, accounting for strong spin-orbit coupling and finite momentum pairing, which was not previously detailed.

Findings

Identification of anisotropic features in magnetic susceptibility

Prediction of observable signatures in neutron scattering

Analysis of quasiparticle dispersions in helical states

Abstract

We investigate the magnetic excitation spectrum in the helical state of a noncentrosymmetric superconductor with inversion symmetry breaking and strong Rashba spin-orbit coupling. For this purpose, we derive the general expressions of the dynamical spin response functions under the presence of strong Rashba splitting of conduction bands, superconducting gap, and external field which lead to stabilization of Cooper pairs with finite overall momentum in a helical state. The latter is characterized by momentum space regions of paired and unpaired states with different quasiparticle dispersions. The magnetic response is determined by i) excitations within and between both paired and unpaired regions ii) anomalous coherence factors and iii) additional spin matrix elements due to helical Rashba spin texture of bands. We show that as a consequence typical correlated real space and spin space anisotropies appear in the dynamical susceptibility which would be observable as a characteristic fingerprint for a helical superconducting state in inelastic neutron scattering investigations.