Ground-state phase diagram of an extended Kitaev-Gamma model on a honeycomb lattice*

Abstract: Alpha-RuCl3 has been studied extensively due to the possible realization of Kitaev spin liquid physics. The Kitaev-Gamma (KGamma) model on the honeycomb lattice has been proposed as a minimal model of alpha-RuCl3. So far, the KGamma model has mostly been studied considering equal coupling strength along the three bond directions of the honeycomb lattice. However, the details of the ground states have been under debate. In this study, we extended the model to include an additional parameter that controls the coupling strength on one of the bonds; we connect the limit of isolated KGamma chains to the isotropically interacting two-dimensional (2d) model. We investigate the ground-state phase diagram by using numerical exact diagonalizations and density-matrix renormalization group methods. We find that TLL appearing in the chain limit [2] persist for finite interchain couplings. In this proximate TLL phase, the low-energy excitation is characterized by spinon-like gapless excitation that is similar to that is observed in S=1/2 antiferromagnetic Heisenberg chain. In contrast, D4 magnetically ordered state [2] in the spin chain limit becomes 90-degree non-coplanar ordered state in the 2d model. Furthermore, we find that two magnetically ordered states seem to exist near the limit of the antiferromagnetic Kitaev spin chain. These two states also become corresponding ordered states in the 2d model.

 

[1] J. G. Rau, E. Lee, and H.-Y. Kee, Phys. Rev. Lett. 112, 077204 (2014).

[2] W. Yang, et al., Phys. Rev. Lett. 124, 147205 (2020).