Paramagnetic resonance in spin-polarized disordered Bose-Einstein condensates

TL;DR

This paper investigates the paramagnetic resonance phenomena in disordered, spin-polarized Bose-Einstein condensates of exciton polaritons, revealing unique double resonance structures and the effects of disorder on resonance widths.

Contribution

It introduces a theoretical analysis of spin susceptibility and resonance behavior in disordered polariton condensates, highlighting the impact of impurity scattering on resonance widths.

Findings

Double resonance structure in magnetic power absorption.

Resonance width for condensed state can be narrower than for non-condensed state.

Disorder causes twofold scattering processes affecting resonance properties.

Abstract

We study the pseudo-spin density response of a disordered two-dimensional spin-polarized Bose gas of exciton polaritons to weak alternating magnetic field, assuming that one of the spin states of the doublet is macroscopically occupied and Bose-condensed while the occupation of the other state remains much smaller. We calculate spatial and temporal dispersions of spin susceptibility of the gas taking into account spin-flip processes due to the transverse-longitudinal splitting. Further, we use the Bogoliubov theory of weakly-interacting gases and show that the time-dependent magnetic field power absorption exhibits double resonance structure corresponding to two particle spin states (contrast to paramagnetic resonance in regular spin-polarized electron gas). We analyze the widths of these resonances caused by scattering on the disorder and show that, in contrast with the ballistic regime, in the presence of impurities, the polariton scattering on them is twofold: scattering on the impurity potential directly and scattering on the spatially fluctuating condensate density caused by the disorder. As a result, the width of the resonance associated with the Bose-condensed spin state can be surprizingly narrow in comparison with the width of the resonance associated with the non-condensed state.