Anomalous Hall effect at half filling in twisted bilayer graphene

Abstract

Magic-angle twisted bilayer graphene (tBLG) has been studied extensively owing to its wealth of symmetry-broken phases, correlated Chern insulators, orbital magnetism, and superconductivity. In particular, the anomalous Hall effect (AHE) has been observed at odd integer filling factors ($\nu =1$ and $3$) in a small number of tBLG devices, indicating the emergence of a zero-field orbital magnetic state with spontaneously broken time-reversal symmetry. However, the AHE is typically not anticipated at half filling ($\nu =2$) owing to competing intervalley coherent states, as well as spin-polarized and valley Hall states that are favored by an intervalley Hund's coupling. Here, we present measurements of two tBLG devices with twist angles slightly away from the magic angle (0.96${}^{\circ }$ and 1.20${}^{\circ }$), in which we report the surprising observation of the AHE at $\nu =+2$ and $-2$, respectively. These findings imply that a valley-polarized phase can become the ground state at half filling in tBLG rotated slightly away from the magic angle. Our results reveal the emergence of an unexpected ground state in the intermediately-coupled regime ($U/W\sim 1$, where $U$ is the strength of Coulomb repulsion and $W$ is the bandwidth), in between the strongly-correlated insulator and weakly-correlated metal, highlighting the need to develop a more complete understanding of tBLG away from the strongly-coupled limit.

13 pages, 10 figures

References in corpus (13)

• Graphene Bilayers with a Twist
• Twisted Bilayer Graphene IV. Exact Insulator Ground States and Phase Diagram
• Competing zero-field Chern insulators in Superconducting Twisted Bilayer Graphene
• Spin-orbit driven ferromagnetism at half moiré filling in magic-angle twisted bilayer graphene
• Imaging Chern mosaic and Berry-curvature magnetism in magic-angle graphene
• Global Phase Diagram of the Normal State of Twisted Bilayer Graphene
• Moiré Commensurability and the Quantum Anomalous Hall Effect in Twisted Bilayer Graphene on Hexagonal Boron Nitride
• Evidence of orbital ferromagnetism in twisted bilayer graphene aligned to hexagonal boron nitride
• Quasiperiodicity, band topology, and moiré graphene
• Magnetic Josephson Junctions and Superconducting Diodes in Magic Angle Twisted Bilayer Graphene
• Symmetry constraints on superconductivity in twisted bilayer graphene: Fractional vortices, $4e$ condensates or non-unitary pairing
• Kekulé spiral order at all nonzero integer fillings in twisted bilayer graphene
• Misalignment instability in magic-angle twisted bilayer graphene on hexagonal boron nitride

Cited by in corpus (28)

• Imaging Chern mosaic and Berry-curvature magnetism in magic-angle graphene
• Pair-density-wave and chiral superconductivity in twisted bilayer transition-metal-dichalcogenides
• Tunable moiré materials for probing Berry physics and topology
• Quantum Metric Induced Phases in Moiré Materials
• Local Kekulé distortion turns twisted bilayer graphene into topological Mott insulators and superconductors
• ${\phi }_0$-Josephson junction in twisted bilayer graphene induced by a valley-polarized state
• Helical trilayer graphene: a moiré platform for strongly-interacting topological bands
• Halperin States of Particles and Holes in Ideal Time Reversal Invariant Pairs of Chern Bands and The Fractional Quantum Spin Hall Effect in Moiré MoTe${}_2$
• Electron-phonon coupling and competing Kekulé orders in twisted bilayer graphene
• Spin-orbit coupling-enhanced valley ordering of malleable bands in twisted bilayer graphene on WSe2
• Time-Reversal Invariant Topological Moiré Flatband: A Platform for the Fractional Quantum Spin Hall Effect
• General scatterings and electronic states in the quantum-wire network of moiré systems
• Thermopower probing emergent local moments in magic-angle twisted bilayer graphene
• Low-energy optical sum-rule in moiré graphene
• Continuously tunable uniaxial strain control of van der Waals heterostructure devices
• Quantum Valley and Sub-valley Hall Effect in the Large Angle Twisted Bilayer Graphene
• Double and Quadruple Flat Bands tuned by Alternative magnetic Fluxes in Twisted Bilayer Graphene
• Atomistic theory of moiré Hofstadter's butterfly in magic-angle graphene
• Low-energy optical absorption in correlated insulators: Projected sum rules and the role of quantum geometry
• Stoner ferromagnetism in low-angle twisted bilayer graphene at three-quarters filling
• Twist Angle, Strain, Corrugation and Moire Unit cell in Twisted Bilayer Graphene
• On the angular dependence of anomalous Hall current
• An ab-initio study on engineering quantum anomalous Hall effect in compensated antiferromagnet MnBi${}_2$Te${}_4$
• Effective tight-binding models in optical moiré potentials
• Strongly interacting Hofstadter states in magic-angle twisted bilayer graphene
• Buckling and flat bands in twisted bilayer graphene
• Magnetic aftereffect and Barkhausen effect in thin films of the altermagnetic candidate Mn5Si3
• Moiré Folded Helical States at the Interfaces of Heterostructures