Bloch oscillations, wannier-stark localisation and coherent terahertz emission in twisted graphene superlattices
For the next generation of photonic applications, there is a growing need for solid-state devices operating in the terahertz regime. Bloch oscillations – one of the oldest known quantum phenomena–describes the fundamental behaviour of electrons in crystals in which a strong DC electric-field should cause electron oscillations in real-space that emit radiation. The effect thus provides a unique route towards tunable terahertz technologies.   However, experimental studies and the development of technologies based on Bloch oscillations have been hampered due to a lack of suitable materials.  Twisted graphene superlattices have recently emerged as an exciting new class of 2D heterostructures whose electronic spectra can be dramatically modified by twisting the crystal layers relative to one another, creating exotic materials that do not exist in nature. In particular, the superlattice potential that is intrinsic to these systems disperses electronic states within a significantly small Brillouin zone, making them ideal candidates for Bloch oscillations. Using a combination of electrical measurements and world-unique cryogenic near-field/far-field terahertz optics, Project BlochTG combines the disciplines of quantum transport and quantum optics to probe the intrinsic light-matter interactions of Bloch oscillations in twisted graphene superlattices. The action will be carried out by the experienced researcher, who is an expert on quantum transport in twisted graphene superlattices, in the lab of Professor Frank Koppens, who has spent the last ten years pioneering the near-field optics techniques described in this proposal. Project BlochTG hence outlines a timely research effort that seeks to understand the foundations of solid-state physics whilst simultaneously investigating novel device concepts for future terahertz technologies, in-line with key objectives of the Horizon 2020 European Roadmap for Graphene Science and Technology.