Speaker
Description
Combining multiple atomic-scale layers of polar crystals allows for active modification of phonon frequencies, lifetimes, and hence engineering of the dielectric response. Specifically, new hybrid optical phonon modes emerge in these so-called crystalline hybrids (XHs) due to the modification of chemical bonds at the interfaces and confinement effects.
In our experiments, we study the nonlinear optical response of an AlN/GaN superlattice with varying layer thicknesses from 2 nm to 4 nm independently for both constituent materials by means of second-harmonic phonon spectroscopy using the FHI free-electron laser. The improved spectral resolution of the second-harmonic spectra compared to linear measurements allows for unique assignment of peaks to specific XH modes as well as a demonstration of their tunability based on the constituents' layer thicknesses.
