Strain-induced Superfluid-Insulator Transition for Atoms Adsorbed on Graphene

Strongly correlated bosons deposited on an atomic mono-layer substrate are an exciting playground to engineer two-dimensional (2D) quantum phases for both theoretical and experimental physics. It is known that the first layer of 4He adsorbed on graphene is a strongly correlated insulator, with subsequent layers displaying superfluid, and even possibly supersolid-like order. In this talk, we explore the possibility of a quantum phase transition between insulating and superfluid phases by applying uniform isotropic strain to graphene. As the strain increases, changes in the adsorption potential drastically alter the phase boundary of the 2D atom layer. It leads to a variety of Mott phases with different filling fractions unrealized in the triangular lattice hard-core Bose-Hubbard model. Using large-scale quantum Monte Carlo simulations, we determine the low temperature phase diagram which displays robust superfluidity in the first layer, which is analyzed within the context of Kosterlitz-Thouless theory. In the zero temperature limit, we discuss a possible quantum phase transition between insulating and superfluid states driven solely by the uniform strain.