Spin Effects in Bose-Glass Phases

We study the mechanism of formation of Bose glass (BG) phases in the
spin-1 Bose Hubbard model when diagonal disorder is introduced. To this
aim, we analyze first the phase diagram in the zero-hopping limit, there
disorder induces superposition between Mott insulator (MI) phases with
different filling numbers. Then BG appears as a compressible insulating
phase (its compressibility marking the distinction with respect to a
more common Mott insulator). The phase diagram for finite hopping is
also calculated with the Gutzwiller approximation. The bosons’ spin
degrees of freedom introduce another scattering channel in the two-body
interaction modifying the stability of MI regions with respect to the
action of disorder. This leads to some peculiar phenomena such as the
creation of BG of singlets, for very strong spin correlation, or the
disappearance of BG phase in some particular cases where fluctuations
are not able to mix different MI regions.