Momentum quantization of hyperbolic phonon polaritons in photonic-crystal cavity.

Momentum quantization of RS1 hyperbolic phonon polaritons in an h-BN photonic-crystal nanocavity yields high-Q cavity states with quality factors exceeding 340 and Purcell enhancements approaching 10^7.

• Why it matters: RS1 HPhP modes in h-BN are weakly accessible to conventional near-field detection and need leakage suppression to achieve high-Q, strongly volume-confined confinement.
• What they did: The team built an h-BN photonic-crystal nanocavity with periodic lateral boundaries for Fabry-Pérot phase matching and used photo-induced force microscopy to visualize quantized modes and reconstruct their discretized momentum-space dispersion.
• The result: The cavity crystal transforms continuous hyperbolic dispersion into a ladder of geometry-defined momentum eigenstates, enabling high-Q, ultrasmall mode volume RS1 polaritonic nanocavities for enhanced light-matter interactions and selective vibrational spectroscopy.