Nanoscale optics of twisted 2D materials

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)