quantum phase transition; critical phenomena; correlation function
KOREAN PHYSICAL SOC
JOURNAL OF THE KOREAN PHYSICAL SOCIETY, v. 52, Page. S158-S161
We investigate correlation functions in critical phenomena at zero temperature. We find that the equal-time correlation function of a quantum system at criticality does not have a diverging correlation length in the absence of time-reversal symmetry. We illustrate our main results analytically in the quantum spherical model as well as more explicitly by Monte Carlo calculations in the two-dimensional quantum rotor model.