THz excitations in {\alpha}-RuCl3: Majorana fermions, rigid-plane shear and compression modes

TL;DR

This study uses THz spectroscopy to detect signatures of Majorana fermions in { extalpha}-RuCl3, revealing a temperature-dependent continuum indicative of spin fractionalization, and identifies phonon modes related to layer sliding and compression.

Contribution

It provides experimental evidence of Majorana fermions in { extalpha}-RuCl3 through THz spectroscopy, linking spin excitations with phonon modes in a Kitaev spin liquid.

Findings

Detection of a temperature-dependent excitation continuum consistent with Majorana fermions.

Identification of phonon modes related to layer sliding and compression.

Observation of the continuum vanishing at higher temperatures.

Abstract

Spin liquids may host emergent quasiparticles, collective excitations of the spin degrees of freedom with characteristic features of Majorana fermions, which experimentally are detectable by broad excitation continua due to spin fractionalization. The latter is predicted for the Kitaev spin liquid, an exactly solvable model with bond-dependent interactions on a two-dimensional honeycomb lattice. Here we report on detailed THz experiments in {\alpha}-RuCl3, identifying these characteristic fingerprints of Majorana fermions. The continuum intensity decreases and finally vanishes on increasing temperature. It partly overlaps with phonon modes representing characteristic sliding and compression modes of the van der Waals bonded molecular layers.