Paramagnetic resonance in spin-polarized disordered Bose-Einstein condensates

V M Kovalev,I G Savenko

doi:10.1038/s41598-017-01125-4

Abstract

We study the pseudo-spin density response of a disordered two-dimensional spin-polarized Bose gas 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, considering microcavity exciton polaritons as a testbed. 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 surprisingly narrow in comparison with the width of the resonance associated with the non-condensed state.

Highlights

Conventional paramagnetic resonance referred to as the electron spin resonance, is a phenomenon known from the physics of electrons in metals[1]
We propose a new type of the paramagnetic resonance applied to bosonic systems
Substituting (5) into (4) and keeping only zero and first-order terms with respect to, we find that zero-order terms describe the ground state of exciton polaritons (EPs) condensate in the impurity potential:

Summary

Introduction

Conventional paramagnetic resonance referred to as the electron spin resonance, is a phenomenon known from the physics of electrons in metals[1]. Another alternative is exciton polaritons (EPs) in a semiconductor microcavity We will consider the latter system and show that the paramagnetic resonance in bosonic gases possesses new features over against two-dimensional (2D) electronic systems. Due to their hybrid half-light–half-matter nature, EPs demonstrate a number of peculiar properties, standing aside from other quasiparticles in solid-state. Their small effective mass (10−4–10−5 of free electron mass) inherited from the photons together with strong particle-particle interaction taken from the excitons make EP systems suitable for observation of quantum collective phenomena at astonishingly high temperatures[7, 8]. Semiconductor microcavities under incoherent background pumping (for instance, electric current injection) can be used in optical routers[21, 22], detectors of terahertz radiation[23, 24], high-speed optical switches[25, 26] and more

Objectives

Results

Conclusion