Frustrated Magnetism Probed by X-ray Scattering in the Honeycomb Magnet RuCl3

Jennifer Sears¹, Li Ern Chern², Subin Kim², Pablo J. Bereciartua³, Sonia Francoual³, Yong Baek Kim² and Young-June Kim²

¹Brookhaven National Laboratory, 98 Rochester Street, Upton NY 11973, USA
²Department of Physics, University of Toronto, Toronto, Ontario, Canada M5S 1A7
³Deutsches Elektronen-Synchrotron (DESY), 22607 Hamburg, Germany

α-RuCl₃ is a layered honeycomb material that has emerged as a leading candidate in the search for Kitaev spin liquid physics. The exactly solved Kitaev model is a highly frustrated magnetic Hamiltonian, which supports a remarkable spin liquid ground state¹. However, the picture in RuCl₃ is complicated by the presence of competing magnetic interactions allowed by symmetry in the real crystal. We present resonant x-ray scattering measurements that identify the magnetic moment direction², a quantity which is highly sensitive to the form of the magnetic Hamiltonian³. We determine that in α-RuCl₃ the Kitaev magnetic interaction is negative, while a competing interaction known as the Gamma term is positive. Further, the observed out-of-plane tilting angle of the magnetic moments constrains the ratio between these two interactions. These unambiguous experimental constraints on two of the leading magnetic interactions in α-RuCl₃ provide an important foundation for our understanding of this remarkable magnetic material.

References:

[1] A. Kitaev, Ann. Phys., 321, 2-11 (2006).

[2] J. A Sears et al., Nat. Phys. 16, 837-840 (2020).

[3] J. Chaloupka and G. Khaliullin, Phys. Rev. B 94, 064435 (2016).