Exceptional topological insulators

M Michael Denner; Anastasiia Skurativska; Frank Schindler; Mark H Fischer; Ronny Thomale; Tomáš Bzdušek; Titus Neupert

doi:10.1038/s41467-021-25947-z

Exceptional topological insulators

Nat Commun. 2021 Sep 28;12(1):5681. doi: 10.1038/s41467-021-25947-z.

Authors

M Michael Denner¹, Anastasiia Skurativska², Frank Schindler^{2

3}, Mark H Fischer², Ronny Thomale⁴, Tomáš Bzdušek^{2

5}, Titus Neupert²

Affiliations

¹ Department of Physics, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland. michael.denner@physik.uzh.ch.
² Department of Physics, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland.
³ Princeton Center for Theoretical Science, Princeton University, Princeton, NJ, 08544, USA.
⁴ Institut für Theoretische Physik und Astrophysik, Universität Würzburg, 97074, Würzburg, Germany.
⁵ Condensed Matter Theory Group, Paul Scherrer Institute, 5232, Villigen PSI, Switzerland.

Abstract

We introduce the exceptional topological insulator (ETI), a non-Hermitian topological state of matter that features exotic non-Hermitian surface states which can only exist within the three-dimensional topological bulk embedding. We show how this phase can evolve from a Weyl semimetal or Hermitian three-dimensional topological insulator close to criticality when quasiparticles acquire a finite lifetime. The ETI does not require any symmetry to be stabilized. It is characterized by a bulk energy point gap, and exhibits robust surface states that cover the bulk gap as a single sheet of complex eigenvalues or with a single exceptional point. The ETI can be induced universally in gapless solid-state systems, thereby setting a paradigm for non-Hermitian topological matter.