Long-propagating ghost phonon polaritons enabled by selective mode excitation.

Area of Science:

• Nanophotonics
• Condensed Matter Physics
• Materials Science

Background:

• Phonon polaritons (PhPs) are crucial for nanophotonic applications.
• Ghost hyperbolic phonon polaritons (g-HPs) offer long-range, ray-like propagation.
• Selective excitation and directional control of g-HPs are significant challenges.

Purpose of the Study:

• To experimentally demonstrate control over polariton mode excitation by altering nano-antenna shape.
• To achieve highly directional excitation of g-HPs.
• To explore applications in mid-infrared optoelectronics.

Main Methods:

• Fabrication of asymmetric triangular gold nano-antennas on calcite.
• Near-field imaging experiments to observe g-HP propagation.
• Numerical simulations to predict g-HP behavior.

Main Results:

• Demonstrated selective excitation of polaritonic modes by antenna geometry.
• Achieved highly directional g-HP excitation using a triangular antenna.
• Observed g-HP propagation over 80 microns, matching predictions.

Conclusions:

• Structural engineering of nano-antennas enables precise control over g-HP excitation and directionality.
• This work enhances the potential of anisotropic materials for nanophotonics.
• Opens new avenues for mid-IR optoelectronic devices and on-chip communication.