Eight-color chiral spin liquid in the $S=1$ bilinear-biquadratic model with Kitaev interactions

Abstract: Multipolar spin systems provide a rich ground for the emergence of unexpected states of matter due to their enlarged spin degree of freedom. In this study, with a specific emphasis on $S=1$ magnets, we explore the interplay between spin nematic states and spin liquids. Based on the foundations laid in the prior work [R. Pohle et al., Phys. Rev. B 107, L140403 (2023)], we investigate the $S=1$ Kitaev model with bilinear-biquadratic interactions, which stabilizes, next to Kitaev spin liquid, spin nematic and triple-$q$ phases, also an exotic chiral spin liquid. Through a systematic reduction of the spin degree of freedom -- from $\mathbb{CP}^{2}$ to $\mathbb{CP}^{1}$ and ultimately to a discrete eight-color model -- we provide an intuitive understanding of the nature and origin of this chiral spin liquid. We find that the chiral spin liquid is characterized by an extensive ground-state degeneracy, bound by a residual entropy, extremely short-ranged correlations, a nonzero scalar spin chirality marked by $\mathbb{Z}_{2}$ flux order, and a gapped continuum of excitations. Our work contributes not only to the specific exploration of $S=1$ Kitaev magnets but also to the broader understanding of the importance of multipolar spin degree of freedom on the ground state and excitation properties in quantum magnets.