Quantum critical dynamics of the two-dimensional Bose gas

Abstract

The dilute, two-dimensional Bose gas exhibits a novel regime of relaxational dynamics in the regime k_B T > |μ| where T is the absolute temperature and μis the chemical potential. This may also be interpreted as the quantum criticality of the zero density quantum critical point at μ=0. We present a theory for this dynamics, to leading order in 1/\ln (Λ/ (k_B T)), where Λis a high energy cutoff. Although pairwise interactions between the bosons are weak at low energy scales, the collective dynamics are strongly coupled even when \ln (Λ/T) is large. We argue that the strong-coupling effects can be isolated in an effective classical model, which is then solved numerically. Applications to experiments on the gap-closing transition of spin gap antiferromagnets in an applied field are presented.