Dichroic Raman probes for chiral edge modes

TL;DR

This paper proposes a novel Raman circular dichroism method to detect chiral edge modes in quantum spin liquids, overcoming previous limitations due to momentum conservation rules.

Contribution

It introduces a new approach using disorder-induced Raman circular dichroism to identify charge-neutral chiral edge modes in Kitaev quantum spin liquids.

Findings

Raman circular dichroism signals can reveal chiral edge modes despite momentum conservation constraints.

The RCD response depends on tunable length and energy scales characteristic of chiral edge modes.

Interaction with boundary charges leaves a unique fingerprint in the RCD signal.

Abstract

The identification and manipulation of charge-neutral fractionalized quasi-particles, in particular chiral edge modes (CEM), is a long-standing quest in physics. Remarkably, the microscopically mediated interaction between light and charge-neutral excitations in Mott-Hubbard insulators can take an identical form to the Raman coupling between light and particles with electric charge. However, since CEMs are Raman-inactive due to conservation of lattice momentum, Raman probes have been deemed unsuitable for their identification. Here, using the Kitaev quantum spin liquid (KSL) as an illustrative example, we demonstrate that the long-range correlated disorder inherent to a closed edge can lead to a Raman circular dichroism (RCD) signal that avoids suppression by linear and angular momentum selection rules, and exhibits a dependence on experimentally tunable length and energy scales that are characteristic of CEM. Having calculated the low-frequency RCD response of generic KSL, we argue that the interaction of the chiral matter fermion with the $\Ztwo$ boundary charge leaves a unique fingerprint of the KSL via the anisotropic Zeeman field dependence.