Magnetoresistance and localization in bosonic insulators
The Abdus Salam International Center for Theoretical Physics - Strada Costiera 11, 34151 Trieste, Italy, EU
Received: 16 April 2013
Accepted: 14 June 2013
We study the strong localization of hard-core bosons. 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 and significantly stronger than the analogous effect in fermions. Within the forward-scattering approximation, we find that the lowest-energy excitations are the most delocalized. A similar analysis applied to random field Ising models suggests that the ordering transition is due to a delocalization initiated at zero energy rather than due to the closure of a mobility gap in the paramagnet.
PACS: 75.47.De – Giant magnetoresistance / 05.30.Jp – Boson systems / 74.81.Bd – Granular, melt-textured, amorphous, and composite superconductors
© EPLA, 2013