Topological flat bands, valley polarization, and interband superconductivity in magic-angle twisted bilayer graphene with proximitized spin-orbit couplings

Abstract

We study theoretically the magic-angle twisted bilayer graphene with proximity-induced Ising and Rashba spin-orbit couplings on the top layer. Topological flat bands (with three distinct phases) are generically realized by the spin-orbit couplings. Using a mean field analysis, we find that (partial) valley polarization prevails for a wide range of doping, suppressing the usual superconductivity with a pairing between time-reversal partners. Remarkably, we uncover that observable unconventional intervalley interband phonon-mediated superconductivity (with the highest $T_c\approx 1.2$K) can coexist with strong valley imbalance due to the approximate Fermi surface nesting between two flat bands not related by time-reversal symmetry, and the dominant pairing is an intersublattice Ising pairing, corresponding to a mixture of $p$- and $d$-waves. In contrast, the intrasublattice Ising phonon-mediated superconductivity with $s$- and $f$-wave mixing emerges in the absence of valley imbalance. Our work reveals an unprecedented route of realizing unconventional superconductivity.

9+16 pages, 4+5 figures; published version

References in corpus (49)

• Tunable Phase Boundaries and Ultra-Strong Coupling Superconductivity in Mirror Symmetric Magic-Angle Trilayer Graphene
• Signatures of Fractional Quantum Anomalous Hall States in Twisted MoTe2 Bilayer
• Integer and fractional Chern insulators in twisted bilayer MoTe2
• Bulk Topological Invariants in Noninteracting Point Group Symmetric Insulators
• Electric field tunable unconventional superconductivity in alternating twist magic-angle trilayer graphene
• Superconductivity in rhombohedral trilayer graphene
• Isospin magnetism and spin-triplet superconductivity in Bernal bilayer graphene
• Observation of integer and fractional quantum anomalous Hall effects in twisted bilayer MoTe2
• MATBG as Topological Heavy Fermion: I. Exact Mapping and Correlated Insulators
• Twisted Bilayer Graphene IV. Exact Insulator Ground States and Phase Diagram
• Spin-orbit driven band inversion in bilayer graphene by van der Waals proximity effect
• Spin-Orbit Enhanced Superconductivity in Bernal Bilayer Graphene
• Twisted bilayer graphene III. Interacting Hamiltonian and exact symmetries
• Twisted Bilayer Graphene V: Exact Analytic Many-Body Excitations in Twisted Bilayer Graphene Coulomb Hamiltonians: Charge Gap, Goldstone Modes and Absence of Cooper Pairing
• Spin-orbit driven ferromagnetism at half moiré filling in magic-angle twisted bilayer graphene
• Band structure and insulating states driven by the Coulomb interaction in twisted bilayer graphene
• Twist-angle dependence of the proximity spin-orbit coupling in graphene on transition-metal dichalcogenides
• Strain-induced quantum phase transitions in magic angle graphene
• Global Phase Diagram of the Normal State of Twisted Bilayer Graphene
• Superconductivity and correlated phases in non-twisted bilayer and trilayer graphene
• Acoustic-phonon-mediated superconductivity in rhombohedral trilayer graphene
• Kondo lattice model in magic-angle twisted bilayer graphene
• Acoustic-phonon-mediated superconductivity in Bernal bilayer graphene
• Heavy fermion representation for twisted bilayer graphene systems
• Kondo Lattice Model of Magic-Angle Twisted-Bilayer Graphene: Hund's Rule, Local-Moment Fluctuations, and Low-Energy Effective Theory
• Superconductivity in Twisted Double Bilayer Graphene Stabilized by WSe${}_2$
• Superconductivity from electronic interactions and spin-orbit enhancement in bilayer and trilayer graphene
• Heavy quasiparticles and cascades without symmetry breaking in twisted bilayer graphene
• Pairing symmetry of twisted bilayer graphene: a phenomenological synthesis
• Determining spin-orbit coupling in graphene by quasiparticle interference imaging
• Twist- and gate-tunable proximity spin-orbit coupling, spin relaxation anisotropy, and charge-to-spin conversion in heterostructures of graphene and transition-metal dichalcogenides
• Symmetric Kondo Lattice States in Doped Strained Twisted Bilayer Graphene
• Spontaneous time-reversal symmetry breaking in twisted double bilayer graphene
• Flavor symmetry breaking in spin-orbit coupled bilayer graphene
• Acoustic-phonon-mediated superconductivity in moiréless graphene multilayers
• Enhanced superconductivity through virtual tunneling in Bernal bilayer graphene coupled to WSe${}_2$
• Magic-Angle Twisted Symmetric Trilayer Graphene as Topological Heavy Fermion Problem
• Kondo Phase in Twisted Bilayer Graphene -- A Unified Theory for Distinct Experiments
• Stabilizing fluctuating spin-triplet superconductivity in graphene via induced spin-orbit coupling
• Phase diagram of twisted bilayer graphene at filling factor $\nu =\pm 3$
• TBG as Topological Heavy Fermion: II. Analytical approximations of the model parameters
• Euler Obstructed Cooper Pairing: Nodal Superconductivity and Hinge Majorana Zero Modes
• Spin-orbit coupling-enhanced valley ordering of malleable bands in twisted bilayer graphene on WSe2
• Twist-angle dependent proximity induced spin-orbit coupling in graphene/topological insulator heterostructures
• Evolution from quantum anomalous Hall insulator to heavy-fermion semimetal in magic-angle twisted bilayer graphene
• Quantum Hall Superconductivity from Moir{é} Landau Levels
• Scaling theory of intrinsic Kondo and Hund's rule interactions in magic-angle twisted bilayer graphene
• Tunable superconductivity and Möbius Fermi surfaces in an inversion-symmetric twisted van der Waals heterostructure
• Displacement-field-tunable superconductivity in an inversion-symmetric twisted van der Waals heterostructure

Cited by in corpus (7)

• Intravalley spin-polarized superconductivity in rhombohedral tetralayer graphene
• Evolution of Superconductivity in Twisted Graphene Multilayers
• Quantum-geometric dipole: a topological boost to flavor ferromagnetism in flat bands
• Topological phases, van Hove singularities, and spin texture in magic-angle twisted bilayer graphene in the presence of proximity-induced spin-orbit couplings
• Increasing the proximity induced spin-orbit coupling in bilayer graphene/WSe${}_2$ heterostructures with pressure
• Flat-band projected versus fully atomistic twisted bilayer graphene
• Quantum Monte Carlo study of magnetism and chiral d+id-wave superconductivity in twisted bilayer graphene