Mixed-order transition and tricritical point associated with checkerboard supersolidity in the two-dimensional t2 - V1 model

We use quantum Monte Carlo method employing stochastic-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.