Spectroscopic Evidence\nfor a Spin- and Valley-Polarized\nMetallic State in a Nonmagic-Angle Twisted Bilayer Graphene

In\nthe magic-angle twisted bilayer graphene (MA-TBG), strong electron–electron\n(e–e) correlations caused by the band-flattening lead to many\nexotic quantum phases such as superconductivity, correlated insulator,\nferromagnetism, and quantum anomalous Hall effects, when its low-energy\nvan Hove singularities (VHSs) are partially filled. Here our high-resolution\nscanning tunneling microscope and spectroscopy measurements demonstrate\nthat the e–e correlation in a nonmagic-angle TBG with a twist\nangle θ = 1.49° still plays an important role in determining\nits electronic properties. Our most interesting observation on that\nsample is when one of its VHSs is partially filled, the one associated\npeak in the spectrum splits into four peaks. Simultaneously, the spatial\nsymmetry of electronic states around the split VHSs is broken by the\ne–e correlation. Our analysis based on the continuum model\nsuggests that such a one-to-four split of the VHS originates from\nthe formation of an interaction-driven spin-valley-polarized metallic\nstate near the VHS, which is a symmetry-breaking phase that has not\nbeen identified in the MA-TBG or in other systems.