Electron-jet collimation by electrostatically defined quantum point contacts in bilayer graphene

An electrostatically-defined quantum point contact (QPC) is a powerful tool to access the valley degree of freedom in bilayer graphene (BLG). As shown by recent scanning gate microscopy experiments [1], QPCs emit angularly-separated current streams in BLG. These ballistic current streams, which occur due to trigonal warping, are predicted to be valley polarized, thus, they can pave the way for applications of valleytronic devices. Here we address these valley-polarized streams by performing collimation experiments between two opposite QPCs that are connected by a 4-um-long ballistic BLG channel. We observe two distinct peaks in nonlocal resistance versus magnetic field which indicates that two current jets have been injected and detected. This is in contrast with previous collimation experiments performed in monolayer graphene [2] and GaAs/AlGaAs 2DEGs [3] where a single peak was observed. Our observations represent a step forward toward a new generation of all-electrical valleytronic devices.

[1] C. Gold et al. Phys. Rev. Lett. 127, 046801 (2021).

[2] A. W. Barnard et al. Nat. Commun. 8, 15418 (2017).

[3] L. W. Molenkamp et al. Phys. Rev. B 41, 1274(R) (1990).