Magneto-oscillations of the mobility edge in Coulomb frustrated bosons and fermions

TL;DR

This paper investigates how magnetic flux influences the mobility edge in Coulomb-interacting bosons and fermions on a honeycomb lattice, revealing oscillations and non-analytic features that differ between particle types and match experimental observations.

Contribution

It introduces a theoretical framework showing how Coulomb interactions cause magneto-oscillations of the mobility edge with distinctive features for bosons and fermions, aligning with experimental data.

Findings

Mobility edge oscillates periodically with magnetic flux.

Bosons show larger oscillation amplitudes than fermions.

Distinct flux-periodic humps differentiate bosonic and fermionic responses.

Abstract

We study the crossover from strong to weak localization of hard-core bosons on a two dimensional honeycomb lattice in a magnetic field, as motivated by recent experiments on structured films. Taking into account long range Coulomb interactions among the bosons, an effective mobility edge in the excitation spectrum of the insulating Bose glass is identified as the (intensive) energy scale at which excitations become nearly delocalized. Within the forward scattering approximation in the bosonic hopping we find the effective mobility edge $\epsilon_c$ to oscillate periodically with the magnetic flux per plaquette, $\phi$. We find non-analytic cusps in $\epsilon_c(\phi)$ at integer or half-integer flux. The bosonic magneto-oscillations start with an increase of the mobility edge (and thus of resistance) with applied flux, in contrast to the equivalent fermionic problem. The amplitude of the oscillations is much more substantial in bosons than in fermions. Bosons exhibit a single hump per flux period, while fermion characteristics undergo two humps. Those are identical for non-interacting fermions, but Coulomb correlations are shown to lead to systematic deviations from this statistical period doubling. Our theory reproduces several key features observed in the activated magneto-transport in structured films.