Bypassing Nonlocal Phenomena in Metals Using Phonon-Polaritons.

Area of Science:

• Condensed Matter Physics
• Nanophotonics
• Materials Science

Background:

• Electromagnetic design requires understanding light-matter interactions, but electronic length scales are often neglected.
• Neglecting these scales can cause nonclassical effects like nonlocal response under extreme light confinement.

Purpose of the Study:

• To investigate nanolight confinement using mid-infrared phonon-polaritons in hexagonal boron nitride (hBN) screened by monocrystalline gold.
• To overcome limitations imposed by nonlocal phenomena in van der Waals heterostructures.
• To explore a pathway for bypassing nonlocal effects in high-confinement regimes.

Main Methods:

• Utilized mid-infrared phonon-polaritons in hexagonal boron nitride (hBN).
• Employed monocrystalline gold flakes for screening.
• Applied near-field imaging to probe polaritons in nanometer-thin hBN crystals on gold.
• Extracted the complex propagation constant of the polaritons.

Main Results:

• Achieved nanolight confinement unobstructed by nonlocal phenomena, even at high polariton velocities.
• Observed effective indices exceeding 94 for the polaritons.
• Identified a naturally forming thin low-index interfacial layer on monocrystalline gold, highlighting the importance of sample characterization.

Conclusions:

• Demonstrated a method to bypass nonlocal effects in van der Waals heterostructures for advanced electromagnetic designs.
• Highlighted the critical role of sample characterization in nanophotonic experiments.
• Opened new avenues for pushing the limits of light confinement in nanophotonic systems.