  In the magic-angle twisted bilayer graphene (MA-TBG), strong
electron-electron (e-e) correlations caused by the band-flattening lead to many
exotic quantum phases such as superconductivity, correlated insulator,
ferromagnetism, and quantum anomalous Hall effects, when its low-energy van
Hove singularities (VHSs) are partially filled. Here our high-resolution
scanning tunneling microscope and spectroscopy measurements demonstrate that
the e-e correlation in a non-magic-angle TBG with a twist angle {\theta} = 1.49
still plays an important role in determining its electronic properties. Our
most interesting observation on that sample is that when one of its VHS is
partially filled, the one associated peak in the spectrum splits into four
peaks. Our analysis based on the continuum model suggests that such a
one-to-four split of the VHS originates from the formation of an
interaction-driven spin-valley-polarized metallic state near the VHS, lifting
both the spin and valley degeneracies. Our results for this non-magic-angle TBG
reveal a new symmetry-breaking phase, which has not been identified in the
MA-TBG or in other systems.
