Proximate Kitaev Quantum Spin Liquid Behaviour in {\\alpha}-RuCl$_3$

Abstract

Topological states of matter such as quantum spin liquids (QSLs) are of great\ninterest because of their remarkable predicted properties including protection\nof quantum information and the emergence of Majorana fermions. Such QSLs,\nhowever, have proven difficult to identify experimentally. The most promising\napproach is to study their exotic nature via the wave-vector and intensity\ndependence of their dynamical response in neutron scattering. A major search\nhas centered on iridate materials which are proposed to realize the celebrated\nKitaev model on a honeycomb lattice - a prototypical topological QSL system in\ntwo dimensions (2D). The difficulties of iridium for neutron measurements have,\nhowever, impeded progress significantly. Here we provide experimental evidence\nthat a material based on ruthenium, {\\alpha}-RuCl$_3$ realizes the same Kitaev\nphysics but is highly amenable to neutron investigation. Our measurements\nconfirm the requisite strong spin-orbit coupling, and a low temperature\nmagnetic order that matches the predicted phase proximate to the QSL. We also\nshow that stacking faults, inherent to the highly 2D nature of the material,\nreadily explain some puzzling results to date. Measurements of the dynamical\nresponse functions, especially at energies and temperatures above that where\ninterlayer effects are manifest, are naturally accounted for in terms of\ndeconfinement physics expected for QSLs. Via a comparison to the recently\ncalculated dynamics from gauge flux excitations and Majorana fermions of the\npure Kitaev model we propose {\\alpha}-RuCl$_3$ as the prime candidate for\nexperimental realization of fractionalized Kitaev physics.\n