Probing topological valley currents by angular layer alignment in van der Waals heterostructures

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The relative angular alignment between the stacked 2D layers of a van der Waals (vdW) heterostructure can dramatically alter its fundamental properties. A striking example is the recent observation of strongly correlated states and intrinsic superconductivity in twisted bilayer graphene. Another remarkable effect of angular layer alignment predicted for certain vdW heterostructures is the emergence of phases of matter with non-trivial topological properties, where charge carriers flow without dissipation, being protected against perturbations. In graphene aligned with boron nitride (BN), such a phase has been predicted, with topological protection linked not to the spin, as commonly observed, but rather to the valley degree of freedom. However, due to the scarcity of experimental tools to demonstrate this topological protection, or tune the transition between topologically trivial and non-trivial phases, the few experimental observations available remain inconclusive. The objective of TWISTRONICS is to contribute, with fundamental concepts, to future advancements of valleytronics, where the control over the valley degree of freedom is used for technological developments including quantum technologies. To reach this goal I propose a novel approach using dynamically rotatable heterostructures, combined with Berry curvature and real-space supercurrents distribution measurements, to tune and investigate the topological phases driven by crystal alignment on graphene/BN structures. This powerful triad will allow a rigorous investigation of the valley electronic states and phase transitions of this system, answering two important questions: i) What are the characteristics, origin and topology of the valley currents previously measured in graphene/BN aligned structures; and ii) how the valley currents and electron topology can be controlled by crystal axes alignment. This will trace a practical route to investigate and design topological phases in other vdW structures.