Unconventional Neel and dimer orders in a spin-1/2 frustrated ferromagnetic chain with easy-plane anisotropy

作者：Furukawa Shunsuke^*; Sato Masahiro; Furusaki Akira

来源：Physical Review B, 2010, 81(9): 094430.

DOI：10.1103/PhysRevB.81.094430

We study the ground-state phase diagram of a one-dimensional spin-1/2 easy-plane XXZ model with a ferromagnetic nearest-neighbor (NN) coupling J(1) and a competing next-nearest-neighbor (NNN) antiferromagnetic coupling J(2) in the parameter range 0<J(2)/vertical bar J(1)vertical bar<0.4. When J(2)/vertical bar J(1)vertical bar less than or similar to 1/4, the model is is in a Tomonaga-Luttinger liquid phase which is adiabatically connected to the critical phase of the XXZ model of J(2)=0. On the basis of the effective (sine-Gordon) theory and numerical analyses of low-lying energy levels of finite-size systems, we show that the NNN coupling induces phase transitions from the Tomonaga-Luttinger liquid to gapped phases with either Neel or dimer order. Interestingly, these two types of ordered phases appear alternately as the easy-plane anisotropy is changed toward the isotropic limit. The appearance of the antiferromagnetic (Neel) order in this model is remarkable, as it is strongly unfavored by both the easy-plane ferromagnetic NN coupling and the antiferromagnetic NNN coupling in the classical-spin picture. We argue that emergent trimer degrees of freedom play a crucial role in the formation of the Neel order.

• 出版日期2010-3-1