Angle-Resolved Specific Heat Measurements under High Magnetic Fields in the Kitaev Material α-RuCl₃

The Kitaev model proposed by A. Kitaev features bond-directional interactions that generate strong frustration and host a quantum spin liquid (QSL) ground state exactly [1]. In the Kitaev QSL, spin degrees of freedom fractionalize into itinerant and localized Majorana fermions. Due to their non-Abelian statistics, these Majorana excitations are promising for topological quantum computation. A nontrivial topological invariant leads to a chiral Majorana edge current consistent with bulk–edge correspondence. Experimentally, α-RuCl₃ exhibits a half-quantized thermal Hall effect [2] and a six-fold symmetry in specific heat consistent with the predicted Majorana-gap anisotropy [3], establishing a phase diagram up to 12 T [3].

In our research, we apply in-plane magnetic fields up to 24 T to the Kitaev candidate α-RuCl₃ and measure field-angle-resolved specific heat. The angular dependence reveals that the six-fold symmetry characteristic of the Kitaev model disappear around 16 T and in the similar magnetic field range, the behaviors of other several physical quantities such as the Majorana gap exhibit noticeable changes, indicating that a phase start to change from Kitaev QSL phase around 16 T. In addition, magnetization measured up to 25 T suggests that the system undergoes a crossover at finite temperatures. Although the phase is not completely changed up to 24 T, we observed signatures of a crossover from the Kitaev QSL phase and we successfully extend the phase diagram of α-RuCl₃ to higher magnetic fields.