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

Abstract

Here we report the observation of pressure-induced melting of antiferromagnetic (AFM) order and emergence of a new quantum state in the honeycomb-lattice halide -RuCl 3 , 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 (P C ) of 0.7 GPa. Intriguingly, the AFM transition temperature displays an increase upon applying pressure below the P C , in stark contrast to usual phase diagrams, for example in pressurized parent compounds of unconventional superconductors. Furthermore, in the high-pressure phase an unusual steady of magnetoresistence is observed. These observations suggest that the high-pressure phase is in an exotic gapped quantum state which is robust against pressure up to ~140 GPa.

Pressure-induced dimerization and valence bond crystal formation in the Kitaev-Heisenberg magnet α−RuCl3

“…The transition temperature T S2 increases rapidly with pressure and reaches room temperature around p = 1.3 GPa. This phase diagram is in good agreement with previous studies under hydrostatic pressure [24,25] and further shows that the pressure-induced transition is of a first-order nature. In order to elucidate the microscopic mechanisms underlying the pressure-induced transition at T S2 , we performed high-resolution XRD under hydrostatic pressure.…”

“…Thermal expansion measurements at ambient pressure predicted also the suppression of the magnetic order under pressure [26]. However, the initial slope value dT N /dp p=0 −23 K/GPa from thermal expansion is in contradiction with the phase diagram drawn by the other techniques under the application of hydrostatic pressure [24,25]. Magnetization measurements indicate a reduction of the inplane magnetization and a high-temperature transition of unknown origin, while NMR indicates no long-range magnetic order and gapped magnetic fluctuations in the high-pressure state [25].…”

“…Magnetization measurements indicate a reduction of the inplane magnetization and a high-temperature transition of unknown origin, while NMR indicates no long-range magnetic order and gapped magnetic fluctuations in the high-pressure state [25]. Furthermore, electrical resistivity studies under hydrostatic pressure exclude the possibility of a pressureinduced insulator-to-metal transition [24].…”

“…While electronic-structure calculations indicate that K is ferromagnetic in α-RuCl 3 and indeed defines the largest exchange energy scale [7,8,14,15], the debate on the minimal effective spin model and precise magnitude of the different couplings is not fully settled yet. By applying a magnetic field in the basal plane, the magnetic zigzag ground state can be suppressed [6,16,17] and the phase above this transition was identified as a quantum spin liquid, by NMR [18], thermal conductivity [19][20][21], terahertz spectroscopy [22], and neutron scattering experiments [23].Further, it was very recently shown by specific heat, magnetization, and NMR measurements [24,25] that the Néel …”

High-pressure magnetization and NMR studies of α−RuCl3

“…For instance, the magnetic ordering in α-RuCl 3 is suppressed by magnetic fields larger than 7.6 T aligned in the ab-plane, where unconventional properties were reported in the magnetically disordered phase [28][29][30][31][32][33] . More surprisingly, a recent high-pressure specific heat measurement on α-RuCl 3 reveals that the Néel temperature T N is enhanced by pressure; above 0.7 GPa, however, no signature of magnetic transition is seen at low temperatures, where a spin-liquid ground state was proposed 34 . High-temperature magnetic studies are highly desired to uncover the true nature of this high-pressure phase.…”