Work package 1
European twistronics platform
Task 1
Led by UCL
Numerical simulations of twisted vdW heterostructures
UCL will perform numerical simulations to reduce the spectrum of angles to explore in twisted devices. Home-made codes have been developed based on the Green’s function formalism in order to investigate the electronic and quantum transport properties of twisted bilayer graphene systems with a number of atoms up to the order of 105, thus being able to reach the size of experimental devices. We propose to rely on these numerical simulations to find efficiently the best range of angular alignment that will give rise to QAHE and superconductivity phenomena.
Task 2
Led by UPSaclay
Sample fabrication and characterization
UPSaclay will develop samples where the crystallographic angle between layers can be tuned in situ. The first step will be to control the angle between two monolayers of graphene to find the alignment with optimized properties. This will validate the results obtained in numerical simulations by UCL. The following step will be to set the angle between the MATBG and to add a BN layer on the top that will allow us to tune the QAHE properties. The characterization of the electronic transport properties at low temperatures, performed by UPSaclay and UCL, will allow us to establish the phase diagram of SC and QAHE in these heterostructures. UPSaclay and LMU will fabricate devices with the optimum twist angle (best quantum properties). AMO and UCL will provide proof of principle regarding the scalability of these samples by preparing vdW heterostructures made of CVD graphene (commercially available), characterizing the morphology of the stack, and optimize the interface.
Task 3
Led by UCL
Electronic properties of MATBG devices
UCL will perform electron transport measurements at low temperature to characterize the electronic properties of MATBG devices, made at UPSaclay, using a scanning gate microscopy (SGM) to spatially map the electronic properties of the devices. SGM will be particularly useful to probe the homogene- ity of quantum states (e.g., presence of a percolating superconducting network), and the robustness of quantum states with respect to local perturbations. UCL will rely on low temperature scanning probe microscopy, either with a magnetic tip or with an ”on-tip” Hall sensor to evidence spontaneous magnetism in the bulk of the QAH phase and to investigate its origin. These characterizations will allow us to establish the relation between the electronic properties of MATBG, disorder and doping.
Task 4
Led by UPSaclay
European Twistronics platform and scalability
All the sample fabrication processes and techniques developed as well as the results of our numerical simulations will be gathered in a virtual platform open to other European users. This platform coor- dinated at UCL will be updated constantly to guarantee that the users have access to state-of-the-art fabrication techniques.
