BOSE-HUBBARD MODEL AND SUPERFLUID STAIRCASES IN HE-4 FILMS

The recent experimental observation of steplike structure in the super fluid density of He-4 films on graphite is interpreted in terms of pas sage close to Mott insulating lobes in the Bose-Hubbard model. Plateau s develop in the superfluid density near the completion of each layer because of the He-He repulsion. We modify the Bose-Hubbard Hamiltonian , using a density-dependent He-He interaction term to model the He-sub strate potential. Quantum Monte Carlo simulations yield results that a gree well with the experimental data.