QSIT Seminar with Prof. Dr. Frank Koppens

Thursday, October 3, 16:00 HPZ E 35 -  Hoenggerberg


** Speaker: Prof. Dr. Frank Koppens, ICFO

** Title: Nanoscale optics of twisted 2D materials

** Abstract: 

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