A strongly fluctuating quasi-two-dimensional insulator (invited)

Abstract

We describe neutron-scattering data for SrCr8−xGa4+xO19, a layered compound containing planes of S=3/2 Cr3+ ions which form Kagomé lattices. Despite strong antiferromagnetic interactions (θCW ≊ −500 K), fluctuations account for more than 75% of the free ion moment at 1.5 K. The spectrum (averaged over reciprocal space) is gapless and resembles that of a 2D long-range-ordered antiferromagnet, as does the low-temperature specific heat of the compound. Even so, the static correlation length does not exceed 7±2 Å. Monte-Carlo simulations of the antiferromagnetic three-state Potts model on the Kagomé lattice show that this model does not have a finite temperature phase-transition. Even at T=0, there does not seem to be true long-range antiferromagnetic-order. However, the magnetic correlations decay algebraically rather than exponentially. The implications of this result for the ground-state of SrCr8−xGa4+xO19 is discussed.