Dynamical and thermal properties of the Kitaev honeycomb-lattice magnet RuCl₃

Honeycomb-lattice magnet RuCl3 is considered to be a potential candidate of realizing Kitaev spin liquid [1], although this material undergoes a phase transition to the zigzag ordered state at a low temperature. Recent inelastic neutron-scattering (INS) measurements on RuCl3 have unveiled characteristic dynamical properties [2]. In this study, we calculate dynamical spin structure factors of three ab-initio models [3-5] and an empirical model [6] for RuCl3 with an exact numerical diagonalization method. We also calculate the temperature dependences of the heat capacity, C(T) by using thermal pure quantum states. We find that the four models are difficult to explain experimental key features observed in C(T) and the INS simultaneously. This suggests that the Kitaev interactions estimated in the ab-initio calculations are small. We thus propose the model with larger Kitaev coupling that can reproduce the key features not only qualitatively but also quantitatively. [1]J．Chaloupka, et al., PRL 110, 097204 (2013). [2] A. Banerjee, et al., Science 356, 1055-1059 (2017). [3] H. S. Kim and H. Y. Kee, PRB 93, 155143 (2016). [4] S. M. Winter, et al., PRB 93, 214431 (2016). [5] R. Yadav, et al., Sci. Rep. 6, 37925 (2016). [6] S. M. Winter, et al., arXiv:1702.08466.