Speaker: 
Frank Koppens  - ICFO

Title: 
Nanocavities and polaritons in twisted and indirectly nanostructured 2D materials

Abstract:
Two-dimensional (2D) materials offer extraordinary potential for control of light and light-matter interactions at the atomic scale. In particular, twisted 2D materials has recently attracted a lot of interest due to the capability to induce moiré superlattices and discovery of electronic correlated phases [1,2]. In this talk, we present nanoscale optical techniques such as near-field optical microscopy and photocurrent nanoscopy, and reveal with nanometer spatial resolution unique observations of the optical properties of twisted 2D materials. We report on the topological domain wall boundaries [4] of small-angle twisted graphene and interband collective modes in charge neutral twisted-bilayer graphene near the magic angle [3]. The freedom to engineer these so-called optical and electronic quantum metamaterials [1] is expected to expose a myriad of unexpected phenomena.

We will also show record-small nanoscale polaritonic cavities [4,5], where the resonances are not associated to the eigenmodes of the cavity. Rather, they are multi-modal excitations whose reflection is greatly enhanced due to the interference of constituent modes. We demonstrate mid-IR cavities with volumes more than a billion below the free-space mode volume, while maintaining quality factors above 100.

[1] Song, Gabor et. al., Nature Nanotechnology (2019)
[2] Cao et al., Nature (2018)
[3] Hesp et al., Nature Communications (2020)
[4] Hesp et al., Nature Physics (2021)
[5] Epstein et al., Science (2020)
[6] Herzig Sheinfux et al., under review

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QuCoLiMaTalks are the weekly seminar of the collaborative research center TRR 306 QuCoLiMa (Quantum Cooperativity of Light and Matter). The talks are given by (external) experts, whose research falls within the scope of QuCoLiMa.
More information at www.qucolima.de/talks