Twisted bilayer graphene reveals its flat bands under spin pumping

Sonia Haddad, Takeo Kato, Lassaad Mandhour

Published 2023-03-22Version 1

The salient property of the electronic band structure of twisted bilayer graphene (TBG), at the so-called magic angle (MA), is the emergence of flat bands around the charge neutrality point. These bands are associated with the observed superconducting phases and the correlated insulating states occurring at the MA. Scanning tunneling microscopy combined with angle resolved photoemission spectroscopy are usually used to visualize the flatness of the band structure of the TGB at the MA. Here, we theoretically argue that spin pumping (SP) provides a direct probe of the flat bands of TBG and an accurate determination of the MA. We consider a junction separating a ferromagnetic insulator and an heterostructure of TBG adjacent to a monolayer of a transition metal dichalcogenide. We show that the Gilbert damping of the ferromagnetic resonance experiment through this junction depends on the twist angle of TBG, and shows a sharp drop at the MA. Our results open the way to a twist switchable spintronics in twisted van der Waals heterostructures.