Topological spinon semimetals and gapless boundary states in three dimensions

TL;DR

This paper demonstrates the existence of topological semimetals with gapless boundary states in three-dimensional Kitaev spin models, revealing novel interacting gapless topological phases with stable Majorana fermion excitations.

Contribution

It introduces exactly solvable 3D Kitaev models exhibiting topological spinon semimetals with protected boundary states, a novel class of gapless topological phases in interacting systems.

Findings

Topological Majorana spinon semimetals in 3D lattices.

Explicit topological indices and boundary states computed.

Stable gapless phases protected by discrete symmetries.

Abstract

Recently there has been much effort in understanding topological phases of matter with gapless bulk excitations, which are characterized by topological invariants and protected intrinsic boundary states. Here we show that topological semimetals of Majorana fermions arise in exactly solvable Kitaev spin models on a series of three dimensional lattices. The ground states of these models are quantum spin liquids with gapless nodal spectra of bulk Majorana fermion excitations. It is shown that these phases are topologically stable as long as certain discrete symmetries are protected. The corresponding topological indices and the gapless boundary states are explicitly computed to support these results. In contrast to previous studies of non-interacting systems, the phases discussed in this work are novel examples of gapless topological phases in interacting spin systems.