Higher-Order Weyl-Exceptional-Ring Semimetals

Tao Liu, James Jun He, Zhongmin Yang, Franco Nori

Published 2021-04-15Version 1

For first-order topological semimetals, non-Hermitian perturbation 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. Our studies open new avenues for exploring novel higher-order topological semimetals in non-Hermitian systems.