科研之友
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摘要
We study the effect of quantum fluctuations on the half-polarized magnetization plateau of a pyrochlore antiferromagnet. We argue that an expansion around the easy-axis limit is appropriate for discussing the ground-state selection among the classically degenerate manifold of collinear states with a 3:1 ratio of spins parallel and/or antiparallel to the magnetization axis. A general approach to the necessary degenerate perturbation theory is presented, and an effective quantum dimer model within this degenerate manifold is derived for arbitrary spin s. We also generalize the existing semiclassical analysis of Hizi and Henley [Phys. Rev. B 73, 054403 (2006)] to the easy-axis limit and show that both approaches agree at large s. We show that under rather general conditions, the first nonconstant terms in the effective Hamiltonian for s >= 1 occur only at sixth order in the transverse exchange coupling. For s >= 5/2, the dominant terms in the effective Hamiltonian are those of a classical dimer model, which predicts a magnetically ordered state. For s <= 2, more exotic possibilities may be realized. The effective dimer Hamiltonian is then strongly quantum. We describe two likely ground states in that regime.
- 出版日期2007-3
- 单位中国科学院理论物理研究所
