Quantum magnetism of the spin-1 kagome-lattice antiferromagnet

Abstract

We investigate the spin-1 kagome-lattice Heisenberg antiferromagnet using large-scale Lanczos diagonalization and the finite-temperature Lanczos method. The zero-temperature magnetization process exhibits plateaus at $m=0$, $1/3$, $7/9$, and $8/9$, where $m$ is the normalized magnetization. The $m=0$ plateau is identified as a trimer valence-bond-crystal state, while the high-field plateaus at $m=7/9$ and $8/9$ are identified as magnon crystals. In particular, the $m=8/9$ plateau corresponds to the exact localized-magnon crystal state. A smoothed zero-temperature magnetization curve constructed using the Gaussian-kernel smoothing method indicates magnetization jumps at the lower-field edge of the $m=1/3$ plateau and at the upper-field edges of the $m=7/9$ and $8/9$ plateaus. At finite temperatures, the specific heat exhibits a double-peak structure with peaks around $T/J\simeq0.1$ and $T/J\simeq1.1$, and the low-temperature peak may be related to trimer valence-bond-crystal ordering. The finite-temperature magnetization curves show that the $m=1/3$ plateau remains visible at low temperatures, whereas the high-field plateaus are rapidly smeared out by thermal effects. These results provide benchmark data for thermodynamic and high-field magnetization measurements in candidate spin-1 kagome-lattice materials.