Possible Kitaev behaviour in the angle-resolved torque magnetometry of α-RuCl₃

We have measured the magnetic torque of T_N = 7 K, and T_N = 14 K single crystal samples of α-RuCl₃, as a function of the field angle in the ab-plane, focusing on temperatures between 2 and 20 K and fields from 0 to 9 T. There is a 60^◦ periodic (i.e. six-fold periodicity) sawtooth pattern found only within the zigzag ordered phase, which we ascribe to zigzag domain reorientation, and which was only observed in a large single crystal 7 K sample. Further, in both the large and small T_N = 7 K samples there is a sinusoidal six-fold signal at the temperature-field boundary of the zigzag order, and at low temperatures and higher fields. In addition to other contributions, our key findings are features that appear at low temperature along the two non-monoclinic b-axes. We find a sharp step-like feature upon applying a field strong enough to suppress the zigzag order. This feature resembles theoretical predictions for hypothesized field-induced Kitaev Ising Topological Order in the intermediate field phase.