Thema der Dissertation:
Accessing Anisotropy in Phonon Polaritons
Accessing Anisotropy in Phonon Polaritons
Abstract: Surface phonon polaritons (SPhPs) arise from strong light–phonon coupling in polar dielectrics and have become a cornerstone in subdiffractional light confinement. Operating in the mid- to far-infrared — where many molecular fingerprints and the room-temperature blackbody peak lie — their behavior is tightly governed by lattice dynamics and thus, by crystal structure. As prime examples, naturally hyperbolic materials like hexagonal boron nitride and molybdenum trioxide have advanced the field of phonon polaritonics, enabling extreme confinement, super-resolution imaging, bio-sensing, and negative refraction. This thesis investigates how crystal structure asymmetry shapes the SPhP response, using two alternative material platforms: uniaxial calcite and biaxial β-phase gallium oxide (bGO). For calcite, "leaky polaritons" with lenticular isofrequency contours, high quality factors, and strong directionality are discovered. For bGO, "hyperbolic shear polaritons" with frequency-dependent axis rotation and asymmetric intensity distribution are shown to be frequency-tunable using isotopic substitution. Experimentally, the work complementarily employs Otto-type prism-coupling and scattering-type near-field microscopy, and develops two new methods: SPhP ellipsometry and Fourier-space SPhP imaging, enabling phase- and polarization-sensitive as well as momentum-space analysis. Overall, this thesis thoroughly explores anisotropy in phonon polaritons, and establishes foundations for on-chip light miniaturization in communication technologies.
Zeit & Ort
01.09.2026 | 14:00
Hörsaal A (1.3.14)
(Fachbereich Physik, Arnimallee 14, 14195 Berlin)