Exceptional degeneracies in non-Hermitian Rashba semiconductors

TL;DR

This paper explores how non-Hermitian effects in Rashba semiconductors lead to exceptional points forming rings in momentum space, with tunable properties and potential for experimental detection.

Contribution

It demonstrates the emergence and control of exceptional degeneracies in a non-Hermitian Rashba system, revealing new topological phenomena and signatures for detection.

Findings

Exceptional points form rings in momentum space.

In-plane Zeeman field tunes the degeneracies.

Exceptional degeneracies induce large spectral weights.

Abstract

Exceptional points are spectral degeneracies of non-Hermitian systems where eigenvalues and eigenvectors coalesce, inducing unique topological phases that have no counterpart in the Hermitian realm. Here we consider a non-Hermitian system by coupling a two-dimensional semiconductor with Rashba spin-orbit coupling to a ferromagnet lead and show the emergence of highly tunable exceptional points along rings in momentum space. Interestingly, these exceptional degeneracies are the endpoints of lines formed by the eigenvalue coalescence at finite real energy, resembling the bulk Fermi arcs commonly defined at zero real energy. We then show that an in-plane Zeeman field provides a way to control these exceptional degeneracies although higher values of non-Hermiticity are required in contrast to the zero Zeeman field regime. Furthermore, we find that the spin projections also coalescence at the exceptional degeneracies and can acquire larger values than in the Hermitian regime. Finally, we demonstrate that the exceptional degeneracies induce large spectral weights, which can be used as a signature for their detection. Our results thus reveal the potential of systems with Rashba spin-orbit coupling for realizing non-Hermitian bulk phenomena.