Nanocavities and Polaritons in Twisted and Indirectly Nanostructured 2D Materials

at the atomic scale. In particular, twisted 2D materials has recently attracted a lot of interest due to the capability<br/>to induce moiré superlattices and discovery of electronic correlated phases [1,2]. In this talk, we present<br/>nanoscale optical techniques such as near-field optical microscopy and photocurrent nanoscopy, and reveal with<br/>nanometer spatial resolution unique observations of the optical properties of twisted 2D materials. We report on<br/>the topological domain wall boundaries [4] of small-angle twisted graphene and interband collective modes in<br/>charge neutral twisted-bilayer graphene near the magic angle [3]. The freedom to engineer these so-called optical<br/>and electronic quantum metamaterials [1] is expected to expose a myriad of unexpected phenomena.<br/>We will also show record-small nanoscale polaritonic cavities [4,5], where the resonances are not associated to<br/>the eigenmodes of the cavity. Rather, they are multi-modal excitations whose reflection is greatly enhanced due<br/>to the interference of constituent modes. We demonstrate mid-IR cavities with volumes more than a billion<br/>below the free-space mode volume, while maintaining quality factors above 100.<br/>References<br/>[1] Song, Gabor et. al., Nature Nanotechnology (2019)<br/>[2] Cao et al., Nature (2018)<br/>[3] Hesp et al., Nature Communications (2020)<br/>[4] Hesp et al., Nature Physics (2021)<br/>[5] Epstein et al., Science (2020)<br/>[6] Herzig Sheinfux et al., under review