Spin effects in Bose-Glass phases

TL;DR

This paper investigates how disorder induces Bose glass phases in a spin-1 Bose-Hubbard model, revealing unique phenomena like singlet Bose glasses and the suppression of BG phases due to spin interactions.

Contribution

It introduces the role of spin degrees of freedom in the formation and stability of Bose glass phases under disorder in the Bose-Hubbard model.

Findings

Disorder causes superpositions of Mott insulator states with different fillings.

Spin interactions modify the stability of Mott insulator regions against disorder.

Unique Bose glass phases of singlets can form under strong spin correlations.

Abstract

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 but still insulating phase. The phase diagram for finite hopping is also calculated with the Gutzwiller approximation. The bosons' spin degree of freedom introduces 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.