Finite field regime for a quantum spin liquid in α−RuCl3

Abstract

An external magnetic field can induce a transition in $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{RuCl}}_{3}$ from an ordered zigzag state to a disordered state that is possibly related to the Kitaev quantum spin liquid. Here, we present field-dependent inelastic neutron scattering and magnetocaloric effect measurements implying the existence of an additional transition out of the quantum spin-liquid phase at an upper field limit ${B}_{u}$. The neutron scattering shows three distinct regimes of magnetic response. In the low-field ordered state the response shows magnon peaks; the intermediate-field regime shows only continuum scattering, and above ${B}_{u}$ the response shows sharp magnon peaks at the lower bound of a strong continuum. Measurable dispersion of magnon modes along the $(0,0,L)$ direction implies non-negligible interplane interactions. Combining the magnetocaloric effect measurements with other data, a $T\text{\ensuremath{-}}B$ phase diagram is constructed. The results constrain the range where one might expect to observe quantum spin-liquid behavior in $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{RuCl}}_{3}$.