Magnetoresistance and localization in bosonic insulators

TL;DR

This paper investigates how strong localization of bosonic particles leads to a large positive magnetoresistance due to constructive interference effects, contrasting with fermionic systems, and explores implications for phase transitions.

Contribution

It reveals that bosonic localization involves predominantly positive scattering amplitudes, causing a unique magnetoresistance effect and providing new insights into bosonic insulators and related phase transitions.

Findings

Bosonic localization involves constructive interference with positive amplitudes.

Magnetic fields suppress constructive interference, shrinking localization length.

Lowest energy excitations are the most delocalized.

Abstract

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.