Experimental evidence for orbital magnetic moments generated by moire-scale current loops in twisted bilayer graphene

Electron-electron (e-e) interactions in the twisted bilayer graphene (TBG) near the magic angle similar to 1.1 degrees can lift the valley degeneracy, allowing for the realization of orbital magnetism and topological phases. However, direct measurement of the orbital-based magnetism in the TBG is still lacking up to now. Here we report evidence for orbital magnetic moment generated by the moire-scale current loops in a TBG with a twist angle theta similar to 1.68 degrees. The valley degeneracy of the 1.68 degrees TBG is removed by e-e interactions when its low-energy Van Hove singularity (VHS) is nearly half filled. A large and linear response of the valley splitting to magnetic fields is observed, which we interpret as arising from the coupling to the large orbital magnetic moment induced by chiral current loops circulating in the moire pattern. According to our experiment, the orbital magnetic moment is about 10.7 mu(B) per moire supercell. Our result paves the way to explore magnetism that is purely orbital in a slightly twisted graphene system.