Higher-Order Weyl-Exceptional-Ring Semimetals

TL;DR

This paper introduces a new class of higher-order topological semimetals featuring Weyl exceptional rings characterized by spectral winding and Chern numbers, supporting both surface and hinge Fermi arcs, and explores their topological phase transitions.

Contribution

It identifies and characterizes higher-order topological semimetals with Weyl exceptional rings in non-Hermitian systems, revealing their unique topological features and phase transition mechanisms.

Findings

Weyl exceptional rings possess both spectral winding and Chern numbers.

These semimetals support coexisting surface and hinge Fermi-arc states.

Dissipative effects can induce topological phase transitions by coupling exceptional rings.

Abstract

For first-order topological semimetals, non-Hermitian perturbations can drive the Weyl nodes into Weyl exceptional rings having multiple topological structures and no Hermitian counterparts. Recently, it was discovered that higher-order Weyl semimetals, as a novel class of higher-order topological phases, can uniquely exhibit coexisting surface and hinge Fermi arcs. However, non-Hermitian higher-order topological semimetals have not yet been explored. Here, we identify a new type of topological semimetals, i.e, a higher-order topological semimetal with Weyl exceptional rings. In such a semimetal, these rings are characterized by both a spectral winding number and a Chern number. Moreover, the higher-order Weyl-exceptional-ring semimetal supports both surface and hinge Fermi-arc states, which are bounded by the projection of the Weyl exceptional rings onto the surface and hinge, respectively. Noticeably, the dissipative terms can cause the coupling of two exceptional rings with opposite topological charges, so as to induce topological phase transitions. Our studies open new avenues for exploring novel higher-order topological semimetals in non-Hermitian systems.