11. May 2018
A theory for the gapless field-induced quantum spin-liquid phase of α−RuCl3The material α−RuCl3 continues to garner attention as the current poster child for realising the Kitaev model. New work places recent experimental observations on a solid theoretical footing, and concludes that the physics of α−RuCl3 is not dominated by Kitaev interactions.
The Kitaev model on the honeycomb lattice is a fundamental paradigm for quantum spin liquids (QSLs), both of the gapped and ungapped variety. One of the canditate materials for realising Kitaev-type physics is α−RuCl3, a layered honeycomb spin-½ insulator with anisotropic magnetic interactions. Under ambient conditions α−RuCl3 has a magnetically ordered ground state, but in an applied magnetic field it undergoes a transition to a disordered one, which has the behaviour of a QSL. Despite recent experimental progress, the controversy over the gapped or gapless nature of this QSL state continues. Writing in Physical Review Letters , PSI theorist Bruce Normand and Zheng-Xin Liu at Renmin University of China in Beijing now present a model that reproduces behaviour found in α−RuCl3 that deviates from that expected for a pure Kitaev system.
The motivation for the study of Liu and Normand came from a nuclear magnetic resonance (NMR) investigation published last year , to which the two theorists also contributed. NMR is the definitive technique for detecting low-energy, low-density magnetic excitations. The 2017 experiments on α−RuCl3 are the most sensitive NMR measurements, on the best samples and at the lowest temperatures achieved to date. They revealed gapless magnetic excitations with a cone-type dispersion over a broad range of applied in-plane fields; by contrast, these excitations became gapped when the field was applied out of the plane.
ContactDr. Bruce Normand
Paul Scherrer Institute, 5232 Villigen PSI, Switzerland
Phone: +41 56 310 2297, e-mail: email@example.com
Original Publications1. Dirac and chiral quantum spin liquids on the honeycomb lattice in a magnetic field
Liu Z-X, Normand B
Physical Review Letters, 120: 187201, 2018
2. Gapless spin excitations in the field-induced quantum spin liquid phase of α−RuCl3
Zheng J, Ran K, Li T, Wang J, Wang P, Liu B, Liu Z-X, Normand B, Wen J, Yu W
Physical Review Letters, 119: 227208, 2017
Additional readingThe field-induced quantum spin-liquid phase of α−RuCl3 is gapless
(NUM Highlight on the work presented in Ref. 2)