Fig. 6: Polariton dispersions.
From: Microcavity phonon polaritons from the weak to the ultrastrong phonon–photon coupling regime
a Measured (black symbols) and calculated (black curves) phonon polariton dispersion obtained from hBN layers that fully fill the cavity. Green curves show the bulk phonon polariton dispersion of hBN. Red dashed lines indicate the light cones \(\omega \left(k\right)=\frac{{kc}}{\sqrt{\varepsilon (\omega =0)}}\,\) and \(\left(k\right)=\frac{{kc}}{\sqrt{{\varepsilon }_{{{{{{\rm{hBN,\infty}}}}}}}}}\), where \(\varepsilon (\omega =0)\) = 6.29 and \({\varepsilon }_{{{{{{\rm{hBN,\infty}}}}}}}\) = 4.52 are the low- and high-frequency permittivities. The Reststrahlen band of bulk hBN is marked by the purple area. b Calculated (black curves) phonon polariton dispersion obtained from cavities that are filled with a 10 nm thick hBN layer. c Calculated (black curves) polariton dispersion obtained for cavities that are fully filled with molecules exhibiting a C=O vibration. Green curves show the bulk polariton dispersion of the filling material. d Dispersion for a 10 nm thick molecular layer embedded in the cavity. e Calculated (black curves) polariton dispersion obtained for cavities fully filled with hypothetical molecules exhibiting a vibration of arbitrarily reduced oscillator strength. Green curves show the bulk polariton dispersion of the filling material. f Dispersion for a 10 nm thick hypothetical molecular layer of arbitrarily reduced coupling strength embedded in the cavity. Schematics illustrate the cavities’ cross sections.
