$\alpha -{\mathrm{RuCl}}_3$ has attracted enormous attention since it has been proposed as a prime candidate to study fractionalized magnetic excitations akin to Kitaev's honeycomb-lattice spin liquid. We have performed a detailed specific-heat investigation at temperatures down to $0.4\mathrm{K}$ in applied magnetic fields up to $9\mathrm{T}$ for fields parallel to the $ab$ plane. We find a suppression of the zero-field antiferromagnetic order, together with an increase of the low-temperature specific heat, with increasing field up to ${\mu }_0{H}_{\text{c}}\approx 6.9$ T. Above $H_{\text{c}}$, the magnetic contribution to the low-temperature specific heat is strongly suppressed, implying the opening of a spin-excitation gap. Our data point toward a field-induced quantum critical point at $H_{\text{c}}$; this is supported by universal scaling behavior near $H_{\text{c}}$. Remarkably, the data also reveal the existence of a small characteristic energy scale well below 1 meV, above which the excitation spectrum changes qualitatively. We relate the data to theoretical calculations based on a $J_1-K_1-{\mathrm{\Gamma }}_1-J_3$ honeycomb model.

Close

PrevNext

View figure in article

• Critical exponents
• Critical field
• Critical phenomena
• Entropy
• Fractionalization
• Frustrated magnetism
• Magnetic anisotropy
• Magnetic interactions
• Magnetic phase transitions
• Magnetism
• Majorana fermions
• Phase diagrams
• Quantum criticality
• Quantum phase transitions
• Quantum spin liquid
• Specific heat
• Spin-orbit coupling
• Antiferromagnets
• Honeycomb lattice
• Magnetic systems
• Mott insulators
• Calorimetry
• Z_2 symmetry