Two-step melting of three-sublattice order in S=1 easy-axis triangular lattice antiferromagnets

摘要

We consider S = 1 triangular lattice Heisenberg antiferromagnets with a strong single-ion anisotropy D that dominates over the nearest-neighbour antiferromagnetic exchange J. In this limit of small J/D, we study low temperature (T similar to J D) properties of such magnets by employing a low-energy description in terms of hard-core bosons with nearest neighbour repulsion V approximate to 4J + J(2)/D and nearest neighbour unfrustrated hopping t approximate to J(2)/2D. Using a cluster Stochastic Series Expansion (SSE) algorithm to perform sign-problem-free quantum Monte Carlo (QMC) simulations of this effective model, we establish that the ground-state three-sublattice order of the easy-axis spin-density S-z((r)over-right-arrow) melts in zero field (B = 0) in a two-step manner via an intermediate temperature phase characterized by power-law three-sublattice order with a temperature dependent exponent eta(T) is an element of [1/9, 1/4]. For eta(T) 2/9 in this phase, we find that the uniform easy-axis susceptibility of an L x L sample diverges as chi(L )similar to L2-9 eta 1 at B = 0, consistent with recent predictions that the thermodynamic susceptibility to a uniform field B along the easy axis diverges at small B as chi (easy-axis) (B) similar to B-4-18 eta/4-9 eta in this regime.