title: Finite-temperature phase diagram of hard-core bosons in two dimensions.
abstract: We determine the finite-temperature phase diagram of the square lattice hard-core boson Hubbard model with nearest neighbor repulsion using quantum Monte Carlo simulations. This model is equivalent to an anisotropic spin-1/2 XXZ model in a magnetic field. We present the rich phase diagram with a first order transition between a solid and superfluid phase, instead of a previously conjectured supersolid and a tricritical end point to phase separation. Unusual reentrant behavior with ordering upon increasing the temperature is found, similar to the Pomeranchuk effect in 3He.
authors.affiliation: Theoretische Physik, Eidgenössische Technische Hochschule Zürich, CH-8093 Zürich, Switzerland.
authors.forename: Guido
authors.initials: G
authors.lastname: Schmid
authors.forename: Synge
authors.initials: S
authors.lastname: Todo
authors.forename: Matthias
authors.initials: M
authors.lastname: Troyer
authors.forename: Ansgar
authors.initials: A
authors.lastname: Dorneich