Spin-orbit coupling-enhanced valley ordering of malleable bands in twisted bilayer graphene on WSe2

Abstract

New phases of matter can be stabilized by a combination of diverging electronic density of states, strong interactions, and spin-orbit coupling. Recent experiments in magic-angle twisted bilayer graphene (TBG) have uncovered a wealth of novel phases as a result of interaction-driven spin-valley flavour polarization. In this work, we explore correlated phases appearing due to the combined effect of spin-orbit coupling-enhanced valley polarization and large density of states below half filling ($\nu \lesssim 2$) of the moiré band in a TBG coupled to tungsten diselenide. We observe anomalous Hall effect, accompanied by a series of Lifshitz transitions, that are highly tunable with carrier density and magnetic field. Strikingly, the magnetization shows an abrupt sign change in the vicinity of half-filling, confirming its orbital nature. The coercive fields reported are about an order of magnitude higher than previous studies in graphene-based moiré systems, presumably aided by a Stoner instability favoured by the van Hove singularities in the malleable bands. While the Hall resistance is not quantized at zero magnetic fields, indicative of a ground state with partial valley polarization, perfect quantization and complete valley polarization are observed at finite fields. Our findings illustrate that singularities in the flat bands in the presence of spin-orbit coupling can stabilize ordered phases even at non-integer moiré band fillings.

17 pages, 15 figures

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Cited by in corpus (9)

• Topological flat bands, valley polarization, and interband superconductivity in magic-angle twisted bilayer graphene with proximitized spin-orbit couplings
• Nonlinear electrical transport unveils Fermi surface malleability in a moiré heterostructure
• Emergent inhomogeneity and non-locality in a graphene field-effect transistor on a near-parallel moire superlattice of transition metal dichalcogenides
• Twisted bilayer graphene reveals its flat bands under spin pumping
• Topological phases, van Hove singularities, and spin texture in magic-angle twisted bilayer graphene in the presence of proximity-induced spin-orbit couplings
• Dirac-Rashba fermions and quantum valley Hall insulators in graphene-based 2D heterostructures
• Review of the tight-binding method applicable to the properties of moiré superlattices
• Increasing the proximity induced spin-orbit coupling in bilayer graphene/WSe${}_2$ heterostructures with pressure
• Enhanced Phonon-Assisted Tunneling in Metal -- Twisted Bilayer Graphene Junctions