Ultrastrong plasmon–phonon coupling via epsilon-near-zero nanocavities

• Published in: Nature photonics Vol. 15; no. 2; pp. 125 - 130
• Main Authors: Yoo, Daehan, de León-Pérez, Fernando, Pelton, Matthew, Lee, In-Ho, Mohr, Daniel A., Raschke, Markus B., Caldwell, Joshua D., Martín-Moreno, Luis, Oh, Sang-Hyun
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01-02-2021; Nature Publishing Group
• Subjects: 142/126; 639/301/1019/1021; 639/624/399/1098; 639/766/400/1103; 639/766/400/2797; Applied and Technical Physics; Arrays; Chemical reactions; Coupling (molecular); Infrared spectra; Light; Phonons; Photonics; Physics; Physics and Astronomy; Plasmons; Quantum Physics; Resonant frequencies; Silicon dioxide; Silicon wafers; Spectrum analysis
• ISSN: 1749-4885; 1749-4893
• DOI: 10.1038/s41566-020-00731-5

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 (SiO
2
) 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.
An epsilon-near-zero medium is used to demonstrate ultrastrong coupling between phonons and gap plasmons. The approach may pave the path to exploitation of vibrational transitions.