Destabilization of magnetic order in a dilute Kitaev spin liquid candidate

Abstract

The insulating honeycomb magnet $\alpha$-RuCl${}_3$ exhibits fractionalized excitiations that signal its proximity to a Kitaev quantum spin liquid (QSL) state, however, at $T=0$, fragile long-range magnetic order arises from non-Kitaev terms in the Hamiltonian. Spin vacancies in the form of Ir${}^{3+}$ substituted for Ru are found to destabilize this long-range order. Neutron diffraction and bulk characterization of Ru${}_{1-x}$Ir${}_x$Cl${}_3$ show that the magnetic ordering temperature is suppressed with increasing $x$ and evidence of zizag magnetic order is absent for $x>0.3$. Inelastic neutron scattering demonstrates that the signature of fractionalized excitations is maintained over the full range of $x$ investigated. The depleted lattice without magnetic order thus hosts a spin-liquid-like ground state that may indicate the relevance of Kitaev physics in the magnetically dilute limit of RuCl${}_3$.