1109.0245 (Markus Mueller)

Magnetoresistance and localization in bosonic insulators    [PDF]

Markus Mueller

We study the strong localization of hard core bosons, motivated by experiments that suggest a bosonic superconductor-insulator transition in strongly disordered films. Using a locator expansion we find that in the insulator, unlike for typical fermion problems, nearly all low-energy scattering paths come with positive amplitudes and hence interfere constructively. As a consequence, the localization length of bosonic excitations shrinks when the constructive interference is suppressed by a magnetic field, entailing an exponentially large positive magnetoresistance, opposite to the analogous effect in fermions. Within the forward scattering approximation, we find that the lowest energy excitations are the most delocalized. Applied to high connectivity lattices, this result suggests that the superfluid transition is due to a delocalization at zero energy rather than due to the closure of a mobility gap in the insulator, in contrast to opposite claims in the recent literature.

View original: http://arxiv.org/abs/1109.0245