Friday, January 28, 2011

Towards the spin Bose metal

As discussed in earlier posts and this review a strong candidate two-dimensional quantum spin model to have a spin liquid ground state is the Heisenberg model on the anisotropic triangular lattice with some ring exchange K. This model is directly relevant to the Mott insulating state of various charge transfer salts.

Studying such frustrated two-dimensional models numerically is a major challenge, and getting definitive results is currently not possible [see e.g. my post about recent work on the Kagome lattice model]. In contrast in one dimension the  density matrix renormalisation group (DMRG) gives definitive results. Hence, one strategy is then to look at coupled chains in the hope that they capture essential physics.

There is a nice preprint by Block, Sheng, Motrunich, and Fisher which looks at the problem on a four chain system using the density matrix renormalisation group (DMRG). They find that once the ring exchange interaction K is larger than J/5 [quite a physically realistic value] that the ground state is a spin liquid: the spin Bose metal (SBM) proposed by Motrunich. They also studied the effect of spatial anisotropy and produced the   phase diagram below.

It is fascinating that the organic charge transfer salts have parameter values that are approximately in the region where all three different phases can occur.

I thank H.-H Lai for bringing this preprint to my attention.

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