Coexistence of diagonal and off-diagonal long-range order: A Monte Carlo study

The zero temperature properties of interacting two dimensional lattice bosons are investigated. We present Monte Carlo data for soft-core bosons that demonstrate the existence of a phase in which crystalline long-range order and off-diagonal long-range order (superfluidity) coexist. We comment on the difference between hard- and soft-core bosons and compare our date to mean-field results that predict a larger coexistence region. Furthermore, we determine the critical exponents for the various phase transitions.