Pressure-induced melting of magnetic order and emergence of a new quantum state in α−RuCl3

Here we report the observation of pressure-induced melting of antiferromagnetic (AFM) order and the emergence of a new state in the honeycomb-lattice halide α−RuCl3, a candidate compound in the proximity of quantum spin liquid state. Our high-pressure heat capacity measurements demonstrate that the AFM order smoothly melts away at a critical pressure (PC) below 1 GPa. Intriguingly, the AFM transition temperature displays an increase upon applying pressure below the PC, in stark contrast to usual phase diagrams, for example, in pressurized parent compounds of unconventional superconductors. Furthermore, a stable magnetoresistance is observed in the high-pressure phase above PC which is robust against pressure up to ∼140 GPa.