Fermi surface segmentation in the helical state of a Rashba superconductor

TL;DR

This paper explores the unique momentum-space segmentation of Fermi surfaces in a Rashba superconductor's helical state, proposing quasiparticle interference as a visualization method and strategies to determine Cooper-pair momentum.

Contribution

It introduces the concept of Fermi surface segmentation in the helical state of Rashba superconductors and suggests experimental methods to observe and analyze this phenomenon.

Findings

Fermi surface sheets are segmented in the helical state due to Rashba coupling.

Quasiparticle interference can visualize the segmentation and its evolution.

Strategies are proposed to determine the finite Cooper-pair momentum from experiments.

Abstract

We investigate the quasiparticle excitations in the FFLO- type helical state of a superconductor with inversion-symmetry breaking and strong Rashba spin-orbit coupling. We restrict to a state with single finite momentum of Cooper pairs in the helical phase that is determined by minimization of the condensation energy. We derive the dependence of quasiparticle dispersions on the Rashba coupling strength and external field. It leads to a peculiar momentum-space segmentation of the corresponding Rashba Fermi surface sheets which has not yet been observed experimentally. We show that it may be directly visualized by the method of quasiparticle interference that identifies the critical points of the segmented sheets and can map their evolution with field strength, bias voltage and Rashba coupling. We also indicate a strategy how to determine the finite Cooper-pair momentum from experimental quantities. This investigation has the potential for a more detailed microscopic understanding of the helical superconducting state under the influence of Rashba spin-orbit coupling.