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

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanophotonics

Background:

• Anisotropic van der Waals materials exhibit hyperbolic dispersion relations for phonon-polaritons (PhPols).
• These properties enable high-momentum states, directional propagation, subdiffractional confinement, and enhanced light-matter interactions.
• Gallium Selenide (GaSe) is a 2D material with two hyperbolic regions, making it a candidate for studying PhPols.

Purpose of the Study:

• To investigate phonon-polaritons in 2D GaSe using Raman spectroscopy.
• To reveal the dispersion relations and understand the confinement effects of PhPols in GaSe.
• To assess GaSe as a material for PhPols, considering its propagation losses and confinement factors.

Main Methods:

• Utilized Raman spectroscopy in a backscattering configuration to probe PhPols in GaSe samples.
• Varied the incidence angle to reveal dispersion relations for samples with thicknesses ranging from 200 to 750 nm.
• Performed Raman spectra simulations to confirm experimental observations and analyze PhPol frequency evolution with vertical confinement.

Main Results:

• Observed one surface and two extraordinary guided polaritons in GaSe.
• Simulations successfully matched the experimental evolution of PhPol frequency with vertical confinement.
• GaSe demonstrated low propagation losses and confinement factors comparable to or exceeding other 2D materials.
• Resonant excitation near the 1s exciton significantly enhanced PhPol scattering efficiency.

Conclusions:

• 2D GaSe supports phonon-polaritons with properties suitable for advanced photonic applications.
• The material exhibits favorable characteristics, including low losses and strong confinement.
• PhPols in GaSe can be coupled to other solid-state excitations, opening avenues for novel optoelectronic devices.
• Resonant excitation offers a powerful method to enhance and study PhPol interactions.