Raman fingerprints of fractionalized Majorana excitations in honeycomb iridate Ag$_3$LiIr$_2$O$_6$

TL;DR

This study uses low-temperature Raman spectroscopy to identify signatures of Majorana fermions in the honeycomb iridate Ag$_3$LiIr$_2$O$_6$, supporting its candidacy as a Kitaev quantum spin liquid with fractionalized excitations.

Contribution

It provides experimental evidence of Majorana fermions and spin fractionalization in a honeycomb iridate, advancing understanding of quantum spin liquids.

Findings

Observation of a magnetic continuum consistent with Majorana fermions

Detection of a crossover to a Kitaev paramagnetic state below 80 K

Coupling between vibrational modes and Majorana excitations

Abstract

We report low-temperature (down to $\sim$5 K) Raman signatures of the recently discovered intercalated honeycomb magnet Ag$_3$LiIr$_2$O$_6$, a putative Kitaev quantum spin liquid (QSL) candidate. The Kitaev QSL is predicted to host Majorana fermions as its emergent elementary excitations through a thermal fractionalization of entangled spins $S = 1/2$. We observe evidence of this fractionalization in the low-energy magnetic continuum whose temperature evolution harbours signatures of the predicted Fermi statistics obeyed by the itinerant Majorana quasiparticles. The magnetic Raman susceptibility evinces a crossover from the conventional to a Kitaev paramagnetic state below the temperature of $\sim$80 K. Additionally, the development of the Fano asymmetry in the low frequency phonon mode and the enhancement of integrated Raman susceptibilities below the crossover temperature signifies prominent coupling between the vibrational and Majorana fermionic excitations.