Topological excitonic corner states and nodal phase in bilayer quantum spin Hall insulators

TL;DR

This paper investigates how exciton condensates in bilayer quantum spin Hall insulators can induce high-order topological states, including corner states and Weyl nodal phases, tunable by external fields.

Contribution

It reveals the emergence of topological excitonic corner states and Weyl nodal phases in bilayer quantum spin Hall insulators, highlighting new ways to realize exotic topological phases.

Findings

Topological excitonic corner states can be realized by tuning gate and magnetic field.

Application of in-plane Zeeman field induces boundary-obstructed corner states.

Discovery of a 2D excitonic Weyl nodal phase with flat band edge states.

Abstract

Interaction induced topological states remain one of the fascinating phases in condensed matter physics. The exciton condensate has recently sparked renewed interest due to the discovery of new candidate materials and its driving force to realize exotic topological states. In this work, we explore the exciton orders induced high-order topology in the bilayer quantum spin Hall insulators and find that the topological excitonic corner states can be realized by tuning the gate and magnetic field. When an in-plane Zeeman field is applied to the system, two or four excitonic boundary-obstructed corner states emerge in the bilayer system for distinct possible $s$-wave excitonic pairings. Besides, we also find a two-dimensional excitonic Weyl nodal phase, which supports flat band edge states connecting the bulk Weyl nodes.