Recent progress on magnetic-field studies on quantum-spin-liquid candidates

Quantum spin liquids(QSLs) represent a novel state of matter in which quantum fluctuations prevent the conventional magnetic order from being established, and the spins remain disordered even at zero temperature. There have been many theoretical developments proposing various QSL states. On the other hand, experimental movement was relatively slow largely due to limitations on the candidate materials and difficulties in the measurements. In recent years, the experimental progress has been accelerated. In this topical review, we give a brief summary of experiments on the QSL candidates under magnetic fields. We arrange our discussions by two categories: i) Geometrically-frustrated systems, including triangularlattice compounds YbMgGaO_4 and YbZnGaO_4, κ-(BEDT-TTF)_2 Cu_2(CN)_3, and EtMe_3 Sb[Pd(dmit)_2]_2, and the kagom′e system ZnCu_3(OH)_6 Cl_2; ii) the Kitaev material α-RuCl_3. Among these, we will pay special attention to α-RuCl_3, which has been intensively studied by ours and other groups recently. We will present evidence that both supports and rejects the QSL ground state for these materials, based on which we give several perspectives to stimulate further research activities.     

Evidence for Magnetic Fractional Excitations in a Kitaev Quantum-Spin-Liquid Candidate α-RuCl3

It is known that α-Ru Cl₃ has been studied extensively because of its proximity to the Kitaev quantum-spin-liquid（QSL） phase and the possibility of approaching it by tuning the competing interactions. Here we present the first polarized inelastic neutron scattering study on α-Ru Cl₃ single crystals to explore the scattering continuum around the Γ point at the Brillouin zone center, which was hypothesized to be resulting from the Kitaev QSL state but without concrete evidenc...