Collective Modes in a Symmetry-Broken Phase: Antiferromagnetically Correlated Quantum Wells

TL;DR

This paper studies the collective excitations in a low-density quantum well with antiferromagnetic order, identifying specific modes that can be detected experimentally to confirm the symmetry-broken phase.

Contribution

It provides the first theoretical analysis of the intersubband spin-density excitations in an antiferromagnetically correlated quantum well, linking collective modes to experimental signatures.

Findings

Existence of a damped Nambu-Goldstone mode due to broken spin symmetry

Presence of an undamped optical mode in the excitation spectrum

Low-frequency response is key for experimental detection of the antiferromagnetic phase

Abstract

We investigate the intersubband spin-density-excitation spectrum of a double quantum well in a low-density symmetry-broken phase with interwell antiferromagnetic correlations. This spectrum is related to the intensity measured in depolarized inelastic light scattering (ILS) experiments and therefore provides a means of empirically identifying the antiferromagnetic phase. Our computations reveal the existence of two collective modes, a damped Nambu-Goldstone (NG) mode arising from the broken spin symmetry and an undamped optical mode. Since the NG mode contains most of the spectral weight, ILS experiments will need to examine the low-frequency response for signatures of the antiferromagnetic phase.