Microcavity phonon polaritons from the weak to the ultrastrong phonon-photon coupling regime.

Strong coupling between molecular vibrations and microcavity modes has been demonstrated to modify physical and chemical properties of the molecular material. Here, we study the less explored coupling between lattice vibrations (phonons) and microcavity modes. Embedding thin layers of hexagonal boron nitride (hBN) into classical microcavities, we demonstrate the evolution from weak to ultrastrong phonon-photon coupling when the hBN thickness is increased from a few nanometers to a fully filled cavity.

Plasmonic antenna coupling to hyperbolic phonon-polaritons for sensitive and fast mid-infrared photodetection with graphene.

Integrating and manipulating the nano-optoelectronic properties of Van der Waals heterostructures can enable unprecedented platforms for photodetection and sensing. The main challenge of infrared photodetectors is to funnel the light into a small nanoscale active area and efficiently convert it into an electrical signal. Here, we overcome all of those challenges in one device, by efficient coupling of a plasmonic antenna to hyperbolic phonon-polaritons in hexagonal-BN to highly concentrate mid-infrared light into a graphene pn-junction.

Broad spectral tuning of ultra-low-loss polaritons in a van der Waals crystal by intercalation.

Phonon polaritons-light coupled to lattice vibrations-in polar van der Waals crystals are promising candidates for controlling the flow of energy on the nanoscale due to their strong field confinement, anisotropic propagation and ultra-long lifetime in the picosecond range. However, the lack of tunability of their narrow and material-specific spectral range-the Reststrahlen band-severely limits their technological implementation. Here, we demonstrate that intercalation of Na atoms in the van der Waals semiconductor α-VO enables a broad spectral shift of Reststrahlen bands, and that the phonon polaritons excited show ultra-low losses (lifetime of 4 ± 1 ps), similar to phonon polaritons in a non-intercalated crystal (lifetime of 6 ± 1 ps).

Substrate Matters: Surface-Polariton Enhanced Infrared Nanospectroscopy of Molecular Vibrations.

Infrared nanospectroscopy based on Fourier transform infrared near-field spectroscopy (nano-FTIR) is an emerging nanoanalytical tool with large application potential for label-free mapping and identification of organic and inorganic materials with nanoscale spatial resolution. However, the detection of thin molecular layers and nanostructures on standard substrates is still challenged by weak signals. Here, we demonstrate a significant enhancement of nano-FTIR signals of a thin organic layer by exploiting polariton-resonant tip-substrate coupling and surface polariton illumination of the probing tip.