{"ID":23629748,"CreatedAt":"2026-09-18T07:04:54.147703138Z","UpdatedAt":"2026-09-18T07:04:54.147703138Z","DeletedAt":null,"paper_url":"https://arxiv.org/abs/2609.20639","arxiv_id":"2609.20639","title":"First-principles theory of phonon renormalization from nonlinear electron-phonon interactions","abstract":"Electron-phonon interactions renormalize phonon frequencies and lifetimes and are central to the dynamical properties of solids. While these effects are usually described within linear electron-phonon coupling, the role of nonlinear electron-phonon interactions for phonon properties remains largely unexplored. In this work, we study phonon renormalization arising from the long-range linear one-electron-one-phonon and the nonlinear one-electron-two-phonon interactions within a diagrammatic framework. We derive the corresponding self-energy diagrams, which depend on the chemical potential and temperature, and evaluate them from first principles for the two polar semiconductors LiF and KTaO$_3$. In both materials, the two interaction channels renormalize the phonon spectrum in qualitatively distinct ways. The linear contribution is sharply localized near the Brillouin-zone center, whereas the nonlinear process couples an incoming phonon to other branches throughout the spectrum. As a result, it renormalizes phonons across the entire Brillouin-zone, with a pronounced temperature dependence governed by the thermal occupation of those branches. This behavior provides a clean experimental signature of the one-electron-two-phonon coupling. While the nonlinear phonon renormalization is small in LiF, it is somewhat larger in KTaO$_3$, which we attribute to its greater number of thermally populated phonon branches at room temperature. Our results establish a general framework to assess nonlinear electron-phonon effects on the phonon properties in materials with stronger lattice fluctuations, including soft semiconductors such as lead-halide perovskites.","short_abstract":"Electron-phonon interactions renormalize phonon frequencies and lifetimes and are central to the dynamical properties of solids. While these effects are usually described within linear electron-phonon coupling, the role of nonlinear electron-phonon interactions for phonon properties remains largely unexplored. In this...","url_abs":"https://arxiv.org/abs/2609.20639","url_pdf":"https://arxiv.org/pdf/2609.20639v1","authors":"[\"Florian Kluibenschedl\",\"Matthew Houtput\",\"Jacques Tempere\",\"Cesare Franchini\",\"Mikhail Lemeshko\",\"Ragheed Alhyder\"]","published":"2026-09-17T16:22:29Z","proceeding":"cond-mat.mtrl-sci","tasks":"[\"cond-mat.mtrl-sci\"]","methods":"[]","has_code":false}