Dynamics of a two-dimensional quantum spin liquid: signatures of emergent Majorana fermions and fluxes

TL;DR

This paper provides an exact theoretical analysis of a 2D quantum spin liquid, revealing clear signatures of emergent Majorana fermions and fluxes through dynamical structure factors, aiding in the identification of topological states.

Contribution

It offers the first complete theoretical study of dynamical structure factors in a 2D quantum spin liquid, highlighting signatures of Majorana fermions and fluxes in both gapless and gapped phases.

Findings

Identification of direct signatures of Majorana fermions and gauge fluxes

Observation of a neutron scattering response with a gap in gapless phases

Discovery of new connections to the X-ray edge problem and quantum quenches

Abstract

Topological states of matter present a wide variety of striking new phenomena. Prominent among these is the fractionalisation of electrons into unusual particles: Majorana fermions [1], Laughlin quasiparticles [2] or magnetic monopoles [3]. Their detection, however, is fundamentally complicated by the lack of any local order, such as, for example, the magnetisation in a ferromagnet. While there are now several instances of candidate topological spin liquids [4], their identification remains challenging [5]. Here, we provide a complete and exact theoretical study of the dynamical structure factor of a two-dimensional quantum spin liquid in gapless and gapped phases. We show that there are direct signatures - qualitative and quantitative - of the Majorana fermions and gauge fluxes emerging in Kitaev's honeycomb model. These include counterintuitive manifestations of quantum number fractionalisation, such as a neutron scattering response with a gap even in the presence of gapless excitations, and a sharp component despite the fractionalisation of electron spin. Our analysis identifies new varieties of the venerable X-ray edge problem and explores connections to the physics of quantum quenches.