Relation between Kitaev magnetism and structure in alpha-RuCl3

Abstract

Raman scattering has been employed to investigate lattice and magnetic excitations of the honeycomb Kitaev material alpha-RuCl3 and its Heisenberg counterpart CrCl3. Our phonon Raman spectra give evidence for a first-order structural transition from a monoclinic to a rhombohedral structure for both compounds. Significantly, only alpha-RuCl3 features a large thermal hysteresis, consistent with the formation of a wide phase of coexistence. In the related temperature interval of 70-170 K, we observe a hysteretic behavior of magnetic excitations as well. The stronger magnetic response in the rhombohedral compared to the monoclinic phase evidences a coupling between the crystallographic structure and low-energymagnetic response. Our results demonstrate that the Kitaev magnetism concomitant with fractionalized excitations is susceptible to small variations of bonding geometry.