| Cs2CuBr4 is a new two-dimensional spin-1/2 system, where 1/3 and 2/3-plateaux have been observed in external magnetic fields. It is expected that the magnetic behaviors of the material can be well explained by a spin-1/2 2-dimensional antiferromagnetic Heisenberg model on a distorted triangular lattice. In the model, there are two types of interactions, J1 and J2, where J1 chains are coupled with inter chain interactions J2. Using an exact diagonalization method, we investigate magnetic properties in the plateau phases. In the 1/3-plateau phase, three-fold degenerate translational symmetry broken ground state is realized. On the other hand, 2/3-plateau has a translationally symmetry broken sate where M=1 and M=1/3 chains along J1 bonds alternate with each other. |
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