Journal Article

Proximate Kitaev quantum spin liquid behaviour in a honeycomb magnet

Nagler, S. E., Yan, J.-Q., Mandrus, D. G., Aczel, A. A., Knolle, J., Tennant, D. A., Moessner, R., Yiu, Y., Banerjee, A., Granroth, G. E., Bhattacharjee, S., Bridges, C. A., Stone, M. B., Lumsden, M. D., Kovrizhin, D. L., Li, L.

2016

Overview

Quantum spin liquids (QSLs) are topological states of matter exhibiting remarkable properties such as the capacity to protect quantum information from decoherence. Whereas their featureless ground states have precluded their straightforward experimental identification, excited states are more revealing and particularly interesting owing to the emergence of fundamentally new excitations such as Majorana fermions. Ideal probes of these excitations are inelastic neutron scattering experiments. These we report here for a ruthenium-based material, α-RuCl 3 , continuing a major search (so far concentrated on iridium materials) for realizations of the celebrated Kitaev honeycomb topological QSL. Our measurements confirm the requisite strong spin–orbit coupling and low-temperature magnetic order matching predictions proximate to the QSL. We find stacking faults, inherent to the highly two-dimensional nature of the material, resolve an outstanding puzzle. Crucially, dynamical response measurements above interlayer energy scales are naturally accounted for in terms of deconfinement physics expected for QSLs. Comparing these with recent dynamical calculations involving gauge flux excitations and Majorana fermions of the pure Kitaev model, we propose the excitation spectrum of α-RuCl 3 as a prime candidate for fractionalized Kitaev physics. Inelastic neutron scattering characterization shows that α-RuCl 3 is close to an experimental realization of a Kitaev quantum spin liquid on a honeycomb lattice. The collective excitations provide evidence for deconfined Majorana fermions.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: 639/301/119/997 / 639/766/119/999 / 639/766/483/3926 / Biomaterials / Condensed Matter Physics / Excitation / Excitation spectra / Fermions / frustrated semiconducting layered magnet / Honeycomb / Honeycomb construction / Iridium / Kitaev / Liquids / Low temperature / Magnetism / majorana fermions / MATERIALS SCIENCE / Nanotechnology / Optical and Electronic Materials / Physics / Probes / quantum magnetism / Quantum theory / Ruthenium / Searching / Spin liquid / Topology