Near-field optical characterization techniques of twisted and indirectly nanostructured 2D material heterostructures

Session

Stream 4 (AFM): Functional Scanning Probe Microscopy for Advanced Material Science

Authors

Prof Frank Koppens (1)

Affiliations

1. ICFO

Keywords

Near-field

2D materials

Graphene

Twistronics

Infrared

Terahertz

Photocurrent

Abstract text

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.  

As an example for indirectly patterned polaritons, we introduce and demonstrate a novel multimodal reflection mechanism of the ray-like optical excitations in hyperbolic materials, such as hBN. Using near-field microscopy, we observe mid-IR confinement in BIC-based nanocavities with volumes down to 23x23x3 and quality factors above 100 – a dramatic improvement in several metrics of confinement.  

References

[1] Song, Gabor  et. al., Nature Nanotechnology (2019)

[2] Cao et  al., Nature (2018)

[3] Hesp et al., Arxiv 1910.07893

[4] Hesp et al., Nature Communications (2020)

[5] Epstein et al., Science (2020)

[6] Herzig Sheinfux et al., (2021