Mixed-order transition and tricritical point associated with checkerboard supersolidity in the two-dimensional t_2 — V_1 model

摘要

We use quantum Monte Carlo method employing stochastie-series-expansion technique to study the ground state properties of the t_2 — V_1 model of hard-core bosons on a square lattice. We find that, away from half fillings, the minimal combination of nearest-neighbor repulsion V_1 and next-nearest-neighbor hopping t_2 may give rise to checkerboard supersolidity. The nature of the quantum phase transition, where the superfluid changes to a checkerboard supersolid, depends on the relative strength of V_1/t_2 and the average site occupancy. Interestingly, at the half filling, the model displays the extreme Thouless effect. As the filling is varied away from half filling, the model exhibits initially a mixed-order transition, next a tricritical point, and finally a second-order transition.