Comment on >quantum phase transition in the four-spin exchange antiferromagnet>

Abstract

In a recent paper Kotov studied the paramagnetic-to-antiferromagnetic transition in the J-Q model. Their findings were claimed to be in >fairly good agreement> with previous quantum Monte Carlo (QMC) results. In this Comment we show that the above claim is misleading and in reality their phase transition point is not only far from the corresponding QMC value but also lies in a region of parameter space not yet explored in the literature. We also show that their reference dimer state is unstable against formation of a plaquette condensate, which could in part explain the large fluctuations they found. © 2010 The American Physical Society.