Seminar coming up tomorrow

[Cond.Matt. & Stat.Mech.Section]

SEMINAR on  Disorder and strong electron correlations



Thursday, 22 April      -  11:30 a.m.



Luigi Stasi Seminar Room,  Leonardo Building - first floor



Matthias TROYER    ( Eidgenossische Technische Hochschule, Zürich )



"Localization of interacting bosons in a lattice: Competition  
between   disorder and commensurability"



Abstract



We establish the phase diagram of the disordered three-dimensional  
Bose-Hubbard model at unit filling, which has been controversial for  
many years.  We prove the absence of a direct quantum phase transition  
between a superfluid and a Mott insulator in a bosonic system with  
generic, bounded disorder: the Bose-glass phase always intervenes  
between the Mott insulating and superfluid phases.

This conclusion follows from a general theorem of inclusions, which  
states that for any transition in a disordered system, one can always  
find rare regions of the competing phase on either side of the  
transition line.  A highly nontrivial overall shape of the phase  
diagram is revealed with the worm algorithm.  The phase diagram  
features a long superfluid finger at strong disorder and on-site  
interaction.  Moreover, bosonic superfluidity is extremely robust  
against disorder in a broad range of interaction parameters; it  
persists in random potentials nearly 50 (!) times larger than the  
particle half-bandwidth.