Charge induced coherence between intersubband plasmons in a quantum structure

TL;DR

This paper demonstrates how Coulomb interactions induce a collective, coherent plasmon mode in quantum wells, enabling ultra-strong light-matter coupling at room temperature by concentrating oscillator strength into a single resonance.

Contribution

It reveals the charge-induced coherence mechanism in intersubband plasmons, leading to a unified resonance and enhanced coupling in semiconductor quantum structures.

Findings

Observation of a single sharp multisubband plasmon resonance

Achievement of ultra-strong coupling regime at room temperature

Enhanced coupling strength with increased electronic density

Abstract

In this work we investigate a low dimensional semiconductor system, in which the light-matter interaction is enhanced by the cooperative behavior of a large number of dipolar oscillators, at different frequencies, mutually phase locked by Coulomb interaction. We experimentally and theoretically demonstrate that, owing to this phenomenon, the optical response of a semiconductor quantum well with several occupied subbands is a single sharp resonance, associated to the excitation of a bright multisubband plasmon. This effect illustrates how the whole oscillator strength of a two-dimensional system can be concentrated into a single resonance independently from the shape of the confining potential. When this cooperative excitation is tuned in resonance with a cavity mode, their coupling strength can be increased monotonically with the electronic density, allowing the achievement of the ultra-strong coupling regime up to room temperature.