Senthil Todadri-MIT: Dipole conserving generalized Hubbard models

I will describe simple models of interacting quantum particles on a d-dimensional cubic lattice whose dynamics conserves both total boson number and their center-of-mass (the dipole moment). These models provide a simple framework in which several remarkable consequences of dipole conservation can be explored. As a function of chemical potential and hopping strength, the model can be tuned between gapped Mott insulating phases and various types of gapless condensates. For bosons, the condensed phase realized at moderately large hopping strengths (in d > 1) , which we dub a Bose-Einstein insulator, is particularly interesting: despite having a Bose condensate, it is insulating, and despite being an insulator, it is compressible. For fermions, the corresponding natural ground state is a compressible insulator with a sharp Fermi surface but no Landau quasiparticles.