Phase transitions in the two-dimensional quantum rotor model at finite temperature

Abstract

We study phase transitions in the two-dimensional quantum rotor model with zero-point quantum fluctuations at finite temperature through Monte Carlo simulations. The high-quality finite-size scaling behavior of the superfluid stiffness clearly confirms the nature of the Kosterlitz-Thouless transition and the universal jump at the critical point. The compressibility shows a thermally activated behavior, from which the energy gap is obtained in the insulating region. Some anomalous properties of the specific heat in the normal state are discussed as possible remanent effects of quantum fluctuations at low temperature.