Quantum Theory of Multisubband Plasmon-Phonon Coupling

TL;DR

This paper provides a theoretical framework for understanding the ultra-strong coupling between multisubband plasmons and optical phonons in two-dimensional electron gases, revealing the formation of mixed polariton states with significant coupling energies.

Contribution

It introduces a Hamiltonian diagonalization approach to describe multisubband plasmon-phonon interactions, demonstrating ultra-strong coupling in various material systems.

Findings

Formation of multisubband polarons with up to 40% phonon energy

Identification of ultra-strong coupling regime in III-V and II-VI materials

Quantitative analysis of coupling energies and mixed states

Abstract

We present a theoretical description of the coupling between longitudinal optical phonons and collective excitations of a two-dimensional electron gas. By diagonalizing the Hamiltonian of the system, including Coulomb electron-electron and Fr\"ohlich interactions, we observe the formation of multisubband polarons, mixed states partially phonon and partially multisubband plasmon, characterized by a coupling energy which is a significant fraction, up to ~40%, of the phonon energy. We demonstrate that multisubband plasmons and longitudinal optical phonons are in the ultra-strong coupling regime in several III-V and II-VI material systems.