Resumen: Vibrational ultrastrong coupling, where the light–matter coupling strength is comparable to the vibrational frequency of molecules, presents new opportunities to probe the interactions between molecules and zero-point fluctuations, harness cavity-modified chemical reactions and develop novel devices in the mid-infrared spectral range. Here we use epsilon-near-zero nanocavities filled with a model polar medium (SiO2) to demonstrate ultrastrong coupling between phonons and gap plasmons. We present classical and quantum-mechanical models to quantitatively describe the observed plasmon–phonon ultrastrong coupling phenomena and demonstrate a modal splitting of up to 50% of the resonant frequency (normalized coupling strength η > 0.25). Our wafer-scale nanocavity platform will enable a broad range of vibrational transitions to be harnessed for ultrastrong coupling applications Idioma: Inglés DOI: 10.1038/s41566-020-00731-5 Año: 2021 Publicado en: Nature Photonics 15 (2021), 125–130 ISSN: 1749-4885 Factor impacto JCR: 39.728 (2021) Categ. JCR: PHYSICS, APPLIED rank: 2 / 161 = 0.012 (2021) - Q1 - T1 Categ. JCR: OPTICS rank: 1 / 101 = 0.01 (2021) - Q1 - T1 Factor impacto CITESCORE: 56.3 - Physics and Astronomy (Q1) - Materials Science (Q1)