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Quantum spin liquids are a central theme in current condensed matter physics as they host emergent topological order and fractionalized excitations. An important example are interacting Kitaev spins on a honeycomb lattice which are theoretically predicted to exhibit topological and quantum spin liquids. Identifying signatures of Kitaev physics, however, is extremely challenging as real materials, such as the iridates (Na,Li)2IrO3, inevitably entail an isotropic Heisenberg and additional spin-exchange interactions, thereby stabilizing a magnetically ordered state. Hexagonal Ru trichloride α-RuCl3 has been recently reported to be near the Kitaev spin-liquid phase boundary. The layered honeycomb structure of α-RuCl3 contains layers weakly coupled by van der Waals interaction, i.e. it is a correlated 2d-material offering many possibilities for “materials engineering”. We have characterized the electronic and magnetic properties of α-RuCl3 by a broad spectrum of experimental techniques. From electron spectroscopy basic parameters determining the insulating state of α-RuCl3 are extracted. Moreover, strongly anisotropic magnetic properties as measured from magnetization, specific heat, thermal conductivity, and NMR measurements will be presented and discussed. Both, the behavior of α-RuCl3 in the paramagnetic phase as well as the properties of the ordered state strongly differ from that found in conventional two-dimensional magnets. In particular, we find a very unusual field-temperature phase diagram with evidence for a novel quantum critical point.

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Bernd Buechner, IFW Dresden
Seminar Room of the Institute of Physics II
Contact: Markus Braden