Spin Nematics and Magnetization Plateau Transition in Anisotropic Kagome Magnets

摘要

We study S=1 kagome antiferromagnets with an isotropic Heisenberg exchange J and strong easy-axis single-ion anisotropy D. For D J, the low-energy physics can be described by an effective S = 1/2 XXZ model with antiferromagnetic J_z～ J and ferromagnetic J_⊥ ～ J~2/D. Exploiting this connection, we argue that nontrivial ordering into a "spin-nematic" occurs whenever D dominates over J, and discuss its experimental signatures. We also study a magnetic field induced transition to a magnetization plateau state at magnetization 1/3 which breaks lattice translation symmetry due to ordering of the S~z and occupies a lobe in the B/J_z-J_z/J_⊥ phase diagram.