Theory of two-dimensional nonlinear spectroscopy for the Kitaev spin liquid

TL;DR

This paper develops a theoretical framework for two-dimensional nonlinear spectroscopy to detect fractionalized excitations in Kitaev spin liquids, revealing distinctive signatures of Majorana fermions and fluxes that are not visible in conventional methods.

Contribution

It introduces a novel spectroscopic approach to identify fractionalized excitations in quantum spin liquids, specifically applying it to the exactly solvable Kitaev model.

Findings

Distinctive signatures of Majorana fermions identified

Flux excitations show unique features in nonlinear spectra

Provides a new method for probing quantum spin liquids

Abstract

Unambiguous identification of fractionalized excitations in quantum spin liquids has been a long-standing issue in correlated topological phases. Conventional spectroscopic probes, such as the dynamical spin structure factor, can only detect composites of fractionalized excitations, leading to a broad continuum in energy. Lacking a clear signature in conventional probes has been the biggest obstacle in the field. In this work, we theoretically investigate what kinds of distinctive signatures of fractionalized excitations can be probed in two-dimensional nonlinear spectroscopy by considering the exactly solvable Kitaev spin liquids. We demonstrate the existence of a number of salient features of the Majorana fermions and fluxes in two-dimensional nonlinear spectroscopy, which provide crucial information about such excitations.