Tuning and mapping hybrid polaritons at the nanoscale

• Applicants: Dr. Katja Höflich; Dr. Hannah Nerl, Ph.D.
• Subject Area: Experimental Condensed Matter Physics ; Synthesis and Properties of Functional Materials
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 449639588

This project aims at the investigation of 'optical properties emergingfrom interlayer interactions in 2D vdW materials'. By combiningcutting-edge nanopatterning with nanoscale analysis we will ultimatelyrealize hybrid polaritonic modes with nanoscale confinement and lowlosses for possible applications in light-based future informationtechnology. In two-dimensional (2D) materials light-matter interaction canbe significantly enhanced by polaritons. A polariton is a quasiparticlethat results from coupling between an electro-magnetic wave, such aslight, and a dipole carrying excitation in matter. ‐ Typical matterexcitations are collective oscillations of free electrons (surfaceplasmon polaritons), lattice vibrations (phonon polaritons) or liftingelectrons from the valence to the conduction band (excitonpolaritons). Polaritons lead to changes in charge transport, chemicalreactivity and local potentials but may also provide for extreme lightlocalization and an enhanced density of electromagnetic states.Stacking of different 2D materials enables coupling of polaritons tohybrid modes with a large degree of tunability in the type of excitation,their coupling strength, and their localization and propagationbehaviour. Thereby, 2D heterostructures can serve for on-demanddesign of extraordinary physical properties. Here, we propose to tunehybrid modes of plasmons and phonons in 2D heterostructures fromsingle-crystalline silver or graphene with hexagonal boron nitride(hBN). He ion beam nanopatterning will allow to modify geometrieswith an accuracy <5 nm for the precise adjustment of both, theseparate excitations and the coupling strength between them. Usinglow-loss scanning transmission electron microscopy (STEM) electronenergy-loss spectroscopy (EELS), complete dispersion relations willbe obtained. Hybrid modes will be mapped with a simultaneousspatial resolution of <1 nm, energy resolution of <6 meV, andmomentum resolution of <0.2 nm-1. By using the electron beam as apulse and a probe simultaneously to excite and probe selectedmodes, unprecedented spatial and energy resolution will be combinedwith fs temporal resolution. Given the extremely high spatial resolutionof both, fabrication and analysis techniques, a large parameter spacefor investigation will be realized on a single sample.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr. Christoph Tobias Koch, Ph.D.