Probing Hyperbolic Shear Polaritons in β-Ga₂O₃ Nanostructures Using STEM-EELS

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanophotonics

Background:

• Phonon polaritons couple electromagnetic waves and optical phonons, enabling applications in imaging, sensing, and spectroscopy.
• Hyperbolic shear polaritons (HShPs) are a new class of phonon polaritons observed in low-symmetry monoclinic crystals.
• Previous studies verified HShPs in beta-gallium oxide (β-Ga₂O₃) but lacked detailed nanostructure behavior analysis.

Purpose of the Study:

• To experimentally investigate the behaviors of hyperbolic shear polaritons (HShPs) in β-Ga₂O₃ nanostructures.
• To explore the excitation and propagation characteristics of HShPs in various β-Ga₂O₃ nanostructures across mid-infrared (MIR) and far-infrared (FIR) ranges.

Main Methods:

• Utilized monochromatic electron energy loss spectroscopy (EELS) combined with scanning transmission electron microscopy (STEM).
• Performed simulations of electric field distribution to clarify HShP propagation and reflection dynamics.

Main Results:

• Experimentally observed multiple HShPs in β-Ga₂O₃ nanorods and a nanodisk within the MIR and FIR spectral ranges.
• Demonstrated frequency-dependent rotation and shear effects of HShPs, evidenced by EELS signal distribution.
• Clarified the propagation and reflection phenomena of HShPs within nanostructures through electric field simulations.

Conclusions:

• β-Ga₂O₃ exhibits tunable, broad-spectrum HShPs, making it a promising material for nanophotonic applications.
• The findings provide crucial insights into HShP behavior in nanostructures, paving the way for future device development.