Moiré enhanced infrared photodetection and THz emission in twisted graphene superlattices

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Light-matter interactions underlies the operation of modern optoelectronics. In the past decade, graphene and related 2D materials (GRMs) have shown great promise in the field of optoelectronics including gate-tuneable modulation, ultra-fast detection and THz capabilities. Graphene itself exhibits weak optical absorption (2.3 %) and exploiting its broadband optical response relies on the integration of extrinsic device architectures. By contrast, twisted bilayer graphene (TBG) superlattices exhibit strikingly different properties as the moiré superlattice potential strongly modifies the band structure, creating exceptionally narrow energy bands and spectral gaps in the range 10-100 meV. Consequently, their intrinsic optical conductivity exhibits a strong mid-infrared and terahertz (THz) response thanks to the moiré induced electronic reconstruction. Combined with other unique properties such as exceptionally high density of states and in-situ tuneable topological bands make TBG an promising candidate for a new generation of infrared and THz optoelectronic devices. The project PhotoTBG aims to study the fundamental light-matter interactions of TBG in the linear and non-linear response regime. The first goal is to study the intrinsic infrared and THz photoconductivity of TBG in the linear response regime, uncovering novel mechanisms for electrical tuneability and photoexcitation enhanced by topology. The second effort focuses on the highly biased regime in search for Bloch oscillations – one of the oldest and yet most elusive phenomena in condensed matter physics – paving the way for a new generation of THz sources.