Quantum criticality in a dissipative (2+1)-dimensional XY model of circulating currents in high-Tc cuprates

We present large-scale Monte Carlo results for the dynamical critical exponent z and the spatio-temporal two-point correlation function of a (2+1)-dimensional quantum XY model with bond dissipation, proposed to describe a quantum critical point in high-T-c cuprates near optimal doping. The phase variables of the model, originating with a parametrization of circulating currents within the CuO2 unit cells in cuprates, are compact, {theta(r,tau)} is an element of [-pi,pi >. The dynamical critical exponent is found to be z approximate to 1, and the spatio-temporal correlation functions are explicitly demonstrated to be isotropic in space-imaginary time. The model thus has a fluctuation spectrum where momentum and frequency enter on equal footing, rather than having the essentially momentum-independent marginal Fermi-liquid-like fluctuation spectrum previously reported for the same model.