When two layers of graphene are twisted by a small angle, a moiré pattern appears. The coupling between the layers depends on the twist angle. With twisted double bilayer graphene, similar effects hold while a band gap can be opened in each bilayer by an out-of-plane electric field for large enough twist angles [1]. Such control allows for a full control of the mini valley wavefunctions [2]. When electron and hole Fermi surfaces overlap, a correlated state forms, which we identify as a density wave state [3]. Using an in-plane magnetic field we are able to control the spin coupling of the correlated state. By tuning the Fermi energy using local gates we are able to choose the spin-polarization locally. We define an inner/outer geometry by electrostatic gating and tune such regions to opposite spin polarizations in order to form a spin valve. We observe an increase in resistance higher than the one stemming from just the carrier depletion induced by applying a Zeeman field. [1] P. Richaus et al. Gap opening in twisted double bilayer graphene by crystal fields [2] F.K. de Vries et al. Combined valley and layer control in twisted double bilayer graphene [3] P. Richaus et al. Density-Wave States in Twisted Double-Bilayer Graphene.

Elias Portolés Marin

ETH Zürich