Koppens, Frank

Date:   Thursday, October 3, 2019
Time:   16:00
Place:   ETH Zurich, Hönggerberg, HPZ E 35
Host:    Lukas Novotny

Nanoscale optics of twisted 2D materials

Frank Koppens
ICFO – The Institute of Photonics Sciences, Spain

Moiré patterns are well-known phenomena in art, textiles and mathematics, which originate from the overlay of two periodic patterns. Intriguingly, atomically thin materials can be stacked on top of each other such that a new periodic pattern can emerge: the moiré superlattice. This can result in a dramatic modification of the electronic and optical properties of twisted 2D materials, compared to those of a single layer. The moiré superlattice can give rise to a plethora of interesting phenomena such as topological bands [1] and many-body phases like superconductivity and magnetism.

A tantalizing example is twisted bilayer graphene near the magic angle (MABG), which exhibits flat superlattice minibands, effectively localizing electrons in a periodic lattice with a period of about 15 nm. Several strongly correlated phases have been observed, including superconductivity and the Mott-like insulating state [2].

In this talk, we give an overview of the nano-optical properties of stacked and twisted 2D materials. Nanoscale optical techniques such as near-field optical microscopy reveal unique observations of strongly confined propagating optical fields, topological domain wall boundaries, and a different type of collective modes in charge neutral TBG near the magic angle [3].

The freedom to engineer these so-called optical and electronic quantum metamaterials [4] is expected to expose a myriad of unexpected phenomena.

References
[1] Ju et al., Nature (2015)
[2] Y. Cao et al. Nature 556, 80 (2018), Cao et al. Nature 556, 43 (2018)
[3] Hesp et al., in preparation
[4] Song, Gabor et. al., Nature Nanotechnology (2019)