Nematic correlations and nematic Berezinskii-Kosterlitz-Thouless transition in spin-1 kagome lattice antiferromagnets

Nematicity plays an important role in strongly correlated electron systems. We explore the spin nematicity of a spin-1 kagome lattice antiferromagnet with the bilinear-biquadratic model and single-ion anisotropy using a generalized semiclassical approximation and Monte Carlo simulations. We reveal a rich ground state phase diagram, characterized by two main regions: a pure spin nematic phase and a region featuring the coexistence of a classical spin liquid and ferroicities for both dipolar and quadrupolar moments. The thermal fluctuation melts the spin nematic order into a critical phase with a quasi-long-range nematic order. Due to the fluctuating vortices of the spin nematic order, this critical phase further undergoes a nematic Berezinskii-Kosterlitz-Thouless transition to a paramagnetic phase, marked by an anomalous stiffness jump. Additionally, the single-ion anisotropy leads to weak ferromagnetism, resulting in spontaneous time-reversal symmetry breaking at very low temperatures. Remarkably, both two types of ferroic ordering are accompanied by classical spin liquid behaviors. Our results provide an intriguing glimpse into the interplay between geometric frustration and intertwining spin orders with different ranks and are expected to stimulate further studies on spin-1 systems and relevant materials.