Probing signatures of fractionalization in candidate quantum spin liquid Cu2IrO3 via anomalous Raman scattering

TL;DR

This study uses Raman scattering to detect signatures of fractionalized Majorana fermions in the candidate quantum spin liquid Cu2IrO3, revealing strong phonon-Majorana coupling and evidence of spin fractionalization.

Contribution

First experimental observation of phonon anomalies linked to Majorana fermions in Cu2IrO3, supporting its status as a Kitaev quantum spin liquid.

Findings

Anomalous phonon frequency shift and linewidth broadening at low temperatures.

Broad magnetic continuum indicating fractionalized excitations.

Crossover from quantum spin liquid to thermal paramagnet around 120 K.

Abstract

Long-range entanglement in quantum spin liquids (QSLs) lead to novel low energy excitations with fractionalised quantum numbers and (in 2D) statistics. Experimental detection and manipulation of these excitations present a challenge particularly in view of diverse candidate magnets. A promising probe of fractionalisation is their coupling to phonons. Here we present Raman scattering results for the S = 1/2 honeycomb iridate Cu2IrO3, a candidate Kitaev QSL with fractionalised Majorana fermions and Ising flux excitations. We observe anomalous low temperature frequency shift and linewidth broadening of the Raman intensities in addition to a broad magnetic continuum both of which, we derive, are naturally attributed to the phonon decaying into itinerant Majoranas. The dynamic Raman susceptibility marks a crossover from the QSL to a thermal paramagnet at ~120 K. The phonon anomalies below this temperature demonstrate a strong phonon-Majorana coupling. These results provide for evidence of spin fractionalisation in Cu2IrO3.