Ordering in Cs2CuCl4: Is there a proximate spin liquid?

Abstract

The layered spiral magnet Cs2CuCl4 displays several interesting properties that have been suggested as evidence of proximity to a two dimensional quantum spin liquid. In this paper we study a concrete version of this proposal and suggest experiments that can potentially confirm it. We study universal critical properties of two-dimensional frustrated quantum magnets near the quantum phase transition between a spiral magnetic state and a spin liquid state with gapped bosonic spinons in the framework of the O(4) invariant critical theory proposed earlier(Chubukov et al, cond-mat/9402006). Direct numerical calculation of the anomalous exponent in spin correlations shows that the critical scattering has broad continua qualitatively similar to experiment. More remarkably we show that the enlarged O(4) symmetry leads to the same slow power law decay for the vector spin chirality and the Neel correlations. We show how this may be observed through polarized neutron scattering experiments. A number of other less dramatic consequences of the critical theory are outlined as well.