Field-Induced Spin Nematic Phase in Low-Dimensional Quantum Spin Systems

The spin nematic phase has attracted a lot of interest in the field of the magnetism. Most theoretical and numerical studies which predicted the spin nematic order so far were based on the spin frustration or the biquadratic interaction. We proposed another mechanism of the field-induced spin nematic phase based on the easy-axis anisotropy[1,2]. When the magnetic field is applied along the easy-axis anisotropy of antiferromagnets, the conventional spin flop transition with a magnetization jump occurs and the canted Neel order is realized. In some one-dimensional systems, however, instead of this transition, two second-order transitions appear and the two-magnon bound state appears as the intermediate phase[1,2]. In this phase the nematic spin correlation perpendicular to the field and the SDW spin correlation along the magnetic field are quasi-long-range orders. Our recent study on several one-dimentional systems using the numerical diagonalization of finite-size clusters and the conformal field theory indicated that the nematic spin correlation dominant region appears. The phase diagrams for the easy-axis anisotropy and the magnetization are obtained for the following systems: the S=1/2 distorted diamond chain[3], the S=1 antiferromagnetic chain with easy-axis anisotropy[4], the S=1/2 bond-alternating chain[5], and the S=1/2 delta chain[6]. In addition the recent numerical diagonalization study indicated that a spin system on the Shasty-Sutherland lattice exhibits the field-induced spin nematic phase with the spin flop transition. The possibility of these spin nematic liquid phase realized in some realistic materials is discussed.