Enhancement of the electron-phonon scattering induced by intrinsic surface plasmon-phonon polaritons

TL;DR

This paper explores how intrinsic surface plasmon-phonon polaritons in metallic crystals can enhance electron-phonon scattering, enabling control over phonon properties and potentially affecting quantum material behavior.

Contribution

It introduces a theoretical framework for intrinsic surface plasmon-phonon polaritons and demonstrates their role in enhancing electron-phonon interactions in quasi-2D crystals.

Findings

Hybridization of plasmons and phonons occurs when their frequencies are similar.

Surface plasmon-phonon polaritons can be tuned by electron density and crystal thickness.

Enhanced electron-phonon scattering observed in vibrational ultrastrong coupling regime.

Abstract

We investigate light-matter coupling in metallic crystals where plasmons coexist with phonons exhibiting large oscillator strength. We demonstrate theoretically that this coexistence can lead to strong light-matter interactions without external resonators. When the frequencies of plasmons and phonons are comparable, hybridization of these collective matter modes occurs in the crystal. We show that the coupling of these modes to photonic degrees of freedom gives rise to intrinsic surface plasmon-phonon polaritons, which offer the unique possibility to control the phonon properties by tuning the electron density and the crystal thickness. In particular, dressed phonons with reduced frequency and large wave vectors arise in the case of quasi-2D crystals, which leads to large enhancements of the electron-phonon scattering in the vibrational ultrastrong coupling regime. This suggests that photons can play a key role in determining the quantum properties of certain materials. A non-perturbative self-consistent Hamiltonian method is presented that is valid for arbitrarily large coupling strengths.