Bad topological semimetals in layered honeycomb compounds

TL;DR

This paper investigates a novel semimetallic phase in honeycomb compounds with strong spin-orbit coupling, characterized by incoherent charge transport but ballistic edge spin transport with topological properties.

Contribution

It introduces a new type of topological semimetal with no charge gap, no quasiparticles, and gapped spin excitations, expanding understanding of phases near the Mott transition.

Findings

Identifies a semimetal phase with incoherent charge conduction.

Shows ballistic spin transport along edges with quantized conductance.

Suggests experimental realization in twisted bilayer transition metal dichalcogenides.

Abstract

The Mott transition in honeycomb compounds with significant spin-orbit coupling is explored. At finite temperatures we identify a novel semimetallic phase located between a topological insulator and a topological Mott insulator. This semimetal is characterized by having no charge gap, no quasiparticles and gapped spin excitations with non-trivial topological properties. While charge conduction is incoherent involving mean-free paths violating the Mott-Ioffe-Regel limit, spin excitations can be transported ballistically along the edges giving rise to a quantized spin conductance. Such bad topological semimetal could be searched for close to the Mott transition in certain twisted bilayers of transition metal dicalchogenides.