Higher-Order Weyl-Exceptional-Ring Semimetals

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.

Published Version

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• Topological optomechanical amplifier with synthetic $\mathcal{P}\mathcal{T}$-symmetry
• Degeneracy and defectiveness in non-Hermitian systems with open boundary
• Non-Hermitian higher-Order Weyl semimetal with surface diabolic points
• Edge states in a non-Hermitian topological crystalline insulator
• Exceptional Heavy-Fermion Semimetals in Three Dimensions
• A tale of two kinds of exceptional point in a hydrogen molecule
• Anomalous Transport Induced by Non-Hermitian Anomalous Berry Connection in Non-Hermitian Systems