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arXiv · 2505.03915

Microscopic theory of phonon polaritons and long wavelength dielectric response

Olle Hellman·Leeor Kronik
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Abstract

We present a first-principles approach for calculating phonon-polariton dispersion relations. In this approach, phonon-photon interaction is described by quantization of a Hamiltonian that describes harmonic lattice vibrations coupled with the electromagnetic field inside the material. All Hamiltonian parameters are obtained from first-principles calculations, with diagonalization leading to non-interacting polariton quasiparticles. This method naturally includes retardation effects and resolves non-analytical behavior and ambiguities in phonon frequencies at the Brillouin zone center, especially in non-cubic and optically anisotropic materials. Furthermore, by incorporating higher-order terms in the Hamiltonian, we also account for quasiparticle interactions and spectral broadening. Specifically, we show how anharmonic effects in phonon polaritons lead to a dielectric response that challenges traditional models. The accuracy and consequences of the approach are demonstrated on GaP and GaN as harmonic test systems and PbTe and $\beta$-Ga$_2$O$_3$ as anharmonic test systems.

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Olle Hellman, Leeor Kronik. 2025-05-06. Microscopic theory of phonon polaritons and long wavelength dielectric response. https://arxiv.org/abs/2505.03915

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