Quantum critical behavior of a three-dimensional superfluid-Mott glass transition*

The superfluid-to-insulator quantum phase transition of a three-dimensional site-diluted quantum rotor model is investigated. In the case of particle-hole symmetry, the Hamiltonian is mapped onto a classical (3+1)-dimensional XY model with columnar disorder which is analyzed by means of large-scale Monte Carlo simulations. The clean, undiluted system is in the 4D XY universality class, showing mean-field behavior with logarithmic corrections. In agreement with the Harris criterion, nonzero dilution destabilizes the clean critical point. Diluted systems exhibit conventional power-law critical behavior for dilutions below the lattice percolation threshold, with dilution independent critical exponents. Our results are discussed in the context of a classification of disordered quantum phase transitions. Relations to experiments in superfluid and magnetic systems are also addressed.