Spectroscopic evidence for a spin and valley polarized metallic state in a non-magic-angle twisted bilayer graphene

TL;DR

This study reveals that non-magic-angle twisted bilayer graphene exhibits a spin and valley polarized metallic state driven by electron-electron interactions, evidenced by spectroscopic splitting of van Hove singularities, indicating a new symmetry-breaking phase.

Contribution

It demonstrates the existence of a spin-valley polarized metallic state in non-magic-angle TBG, expanding understanding beyond magic-angle systems.

Findings

Splitting of van Hove singularity peaks into four in spectroscopy.

Formation of a spin-valley polarized metallic state near the VHS.

Identification of a new symmetry-breaking phase in non-magic-angle TBG.

Abstract

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.