Probing hyperbolic and surface phonon-polaritons in 2D materials using Raman spectroscopy

Abstract

The hyperbolic dispersion relation of phonon-polaritons (PhPols) in anisotropic van der Waals materials provides high-momentum states, directional propagation, subdiffractional confinement, large optical density of states, and enhanced light-matter interactions. In this work, we use Raman spectroscopy in the convenient backscattering configuration to probe PhPol in GaSe, a 2D material presenting two hyperbolic regions separated by a double reststrahlen band. By varying the incidence angle, dispersion relations are revealed for samples with thicknesses between 200 and 750 nm. Raman spectra simulations confirm the observation of one surface and two extraordinary guided polaritons and match the evolution of PhPol frequency as a function of vertical confinement. GaSe appears to provide relatively low propagation losses and supports confinement factors matching or exceeding those reported for other 2D materials. Resonant excitation close to the 1s exciton singularly exalts the scattering efficiency of PhPols, providing enhanced scattering signals and means to probe the coupling of PhPols to other solid-state excitations.

Optical Imaging of Ultrafast Phonon-Polariton Propagation through an Excitonic Sensor

“…Varying the pump–probe time delay allows building movies of species propagation over femtoseconds–nanoseconds and nanometers–micrometers. Although there are many processes through which optical excitation can excite low-frequency PhPs, ,− the Raman spectra displayed in Figures e and S3 suggest that interlayer exciton–phonon interactions in our heterostructures promote excitation of upper reststrahlen PhPs primarily through a resonant Raman process. We further posit that the presence of pump-generated PhPs in hBN locally modifies the dielectric function of the heterostructure.…”

Mapping Phonon Polaritons with Visible Light

“…Initial works demonstrated resonant Raman spectroscopy as a valuable tool to probe PhP modes at Van der Waals (VdW) material interfaces, revealing effects such as Raman activity of silent phonons 26 , enhancement of PhP Raman features 27 , and PhPs outside the Reststrahlen band 28 . Further, recent investigations have shown that conventional backscattering Raman can probe PhP modes in 2D gallium selenide, utilizing the polarizability selection rules 29 . Such techniques are not restricted to 2D materials, micro-Raman investigations of 4H-SiC nanopillars found that spatial dispersion of the permittivity in dielectric nanostructures can play a major role in the spectral behavior of PhPs 20 .…”

“…The basis for our approach comes from the polarizability selection rules, which have been used to calculate the Raman scattering intensities of propagating PhP modes in VdW materials 29 . We modify this approach to make it more suitable for describing localized SPhPs in nanostructures by expressing the Raman response of the nanostructure in terms of its resonant eigenmodes.…”

Portable Detection of Lysine Acetyltransferase Activity in Lung Cancer Cells Based on a Miniature Electrochemical Sensor

“…1,2 Despite the advent of novel targeted therapies and immunotherapies aimed at enhancing cancer survival rates, lung cancer mortality continues to rise. 3 Characteristically, lung cancer remains largely undetected in its nascent stages, often manifesting symptoms only at its most aggressive phase. 4 The imperative for early diagnosis cannot be overstated as it facilitates the timely detection and treatment of lung cancer, thereby curtailing disease progression and reducing mortality rates.…”

“…Lung cancer is a serious threat to human life and health and has become one of the leading cause of cancer-related fatalities globally. , Despite the advent of novel targeted therapies and immunotherapies aimed at enhancing cancer survival rates, lung cancer mortality continues to rise . Characteristically, lung cancer remains largely undetected in its nascent stages, often manifesting symptoms only at its most aggressive phase .…”