Phonon-plasmon coupled modes in hetero-superlattices

The spectrum of coupled phonon-plasmon modes is considered in a mesoscopic system of thin conducting planes separated by insulating layers. The reflectance of such a sample in the infrared region is calculated. Reflectance minima are determined by the longitudinal and transverse phonon frequencies in the insulating interlayers and by the van Hove singularities of the coupled modes. Measuring the differential Raman cross section allows the spectrum of these modes to be found directly.