Pairing symmetry of twisted bilayer graphene: a phenomenological synthesis

Abstract

One of the outstanding questions in the study of twisted bilayer graphene -- from both experimental and theoretical points of view -- is the nature of its superconducting phase. In this work we perform a comprehensive synthesis of existing experiments, and argue that experimental constraints are strong enough to allow the structure of the superconducting order parameter to be nearly uniquely determined. In particular, we argue that the order parameter is nodal, and is formed from an admixture of spin-singlet and spin-triplet Cooper pairs. This argument is made on phenomenological grounds, without committing to any particular microscopic model of the superconductor. Existing data is insufficient to determine the orbital parity of the order parameter, which could be either p-wave or d-wave. We propose a way in which the measurement of Andreev edge states can be used to distinguish between the two.

arXiv comment10+12 pages; 3+5 figures; v3: highlighted result of STM conductance calculation

References in corpus (56)

• Magic-angle graphene superlattices: a new platform for unconventional superconductivity
• Correlated Insulator Behaviour at Half-Filling in Magic Angle Graphene Superlattices
• Tuning superconductivity in twisted bilayer graphene
• Emergent ferromagnetism near three-quarters filling in twisted bilayer graphene
• Superconductors, Orbital Magnets, and Correlated States in Magic Angle Bilayer Graphene
• Intrinsic quantized anomalous Hall effect in a moiré heterostructure
• Evidence of Ising pairing in superconducting NbSe${}_2$ atomic layers
• Magic Angle Spectroscopy
• Two Dimensional Ising Superconductivity in Gated MoS${}_2$
• Tunable Phase Boundaries and Ultra-Strong Coupling Superconductivity in Mirror Symmetric Magic-Angle Trilayer Graphene
• Tunable Correlated Chern Insulator and Ferromagnetism in Trilayer Graphene/Boron Nitride Moiré Superlattice
• Imaging Electronic Correlations in Twisted Bilayer Graphene near the Magic Angle
• Charge-Order and Broken Rotational Symmetry in Magic Angle Twisted Bilayer Graphene
• Superconductivity protected by spin-valley locking in ion-gated MoS2
• Evidence of Gate-Tunable Mott Insulator in Trilayer Graphene-Boron Nitride Moiré Superlattice
• Origin of Mott insulating behavior and superconductivity in twisted bilayer graphene
• Strange metal in magic-angle graphene with near Planckian dissipation
• Hamiltonian approach to the transport properties of superconducting quantum point contacts
• Untying the insulating and superconducting orders in magic-angle graphene
• Electric field tunable unconventional superconductivity in alternating twist magic-angle trilayer graphene
• Cascade of electronic transitions in magic-angle twisted bilayer graphene
• Cascade of Phase Transitions and Dirac Revivals in Magic Angle Graphene
• Decoupling superconductivity and correlated insulators in twisted bilayer graphene
• Nearly Flat Chern Bands in Moiré Superlattices
• Faithful Tight-binding Models and Fragile Topology of Magic-angle Bilayer Graphene
• Nematicity and Competing Orders in Superconducting Magic-Angle Graphene
• Evidence for unconventional superconductivity in twisted bilayer graphene
• Chern Insulators and Topological Flat-bands in Magic-angle Twisted Bilayer Graphene
• Superconductivity without insulating states in twisted bilayer graphene stabilized by monolayer WSe${}_2$
• A mechanism for anomalous Hall ferromagnetism in twisted bilayer graphene
• Strong coupling phases of partially filled twisted bilayer graphene narrow bands
• Half and quarter metals in rhombohedral trilayer graphene
• Detection of a Cooper-Pair Density Wave in Bi${}_2$Sr${}_2$CaCu${}_2$O${}_{8+x}$
• Ground State and Hidden Symmetry of Magic Angle Graphene at Even Integer Filling
• The Unusual Superconducting State of Underdoped Cuprates
• Andreev bound states in high-$T_c$ superconducting junctions
• Magic Angle Hierarchy in Twisted Graphene Multilayers
• Tuning electron correlation in magic-angle twisted bilayer graphene using Coulomb screening
• Twisted Bilayer Graphene IV. Exact Insulator Ground States and Phase Diagram
• Hofstadter subband ferromagnetism and symmetry broken Chern insulators in twisted bilayer graphene
• Entropic evidence for a Pomeranchuk effect in magic angle graphene
• Twisted Bilayer Graphene Aligned with Hexagonal Boron Nitride: Anomalous Hall Effect and a Lattice Model
• Ferromagnetism in narrow bands of moiré superlattices
• Charged Skyrmions and Topological Origin of Superconductivity in Magic Angle Graphene
• Quantum critical behavior in magic-angle twisted bilayer graphene
• Theories for the correlated insulating states and quantum anomalous Hall phenomena in twisted bilayer graphene
• Gate-Defined Josephson Junctions in Magic-Angle Twisted Bilayer Graphene
• Highly Tunable Junctions and Nonlocal Josephson Effect in Magic Angle Graphene Tunneling Devices
• Theory of tunneling conductance for normal metal/insulator/triplet superconductor junctions
• Coulomb screening and thermodynamic measurements in magic-angle twisted trilayer graphene
• Correlated insulators, semimetals, and superconductivity in twisted trilayer graphene
• In-plane critical magnetic fields in magic-angle twisted trilayer graphene
• Pairing in graphene-based moiré superlattices
• D-wave superconductivity in doped Mott insulators
• Strange metal behavior of the Hall angle in twisted bilayer graphene
• Spin-polarized superconductivity: order parameter topology, current dissipation, and multiple-period Josephson effect

Cited by in corpus (38)

• Spin-Orbit Enhanced Superconductivity in Bernal Bilayer Graphene
• Superconductivity and strong interactions in a tunable moiré quasiperiodic crystal
• Quantum textures of the many-body wavefunctions in magic-angle graphene
• Superconductivity and correlated phases in non-twisted bilayer and trilayer graphene
• Superconductivity in Twisted Double Bilayer Graphene Stabilized by WSe${}_2$
• Superconductivity from electronic interactions and spin-orbit enhancement in bilayer and trilayer graphene
• Stabilizing fluctuating spin-triplet superconductivity in graphene via induced spin-orbit coupling
• Nodal band-off-diagonal superconductivity in twisted graphene superlattices
• Electron spin resonance and collective excitations in magic-angle twisted bilayer graphene
• Electron-phonon coupling and competing Kekulé orders in twisted bilayer graphene
• Andreev Reflection in Scanning Tunneling Spectroscopy of Unconventional Superconductors
• Junctions and superconducting symmetry in twisted bilayer graphene
• Andreev reflection spectroscopy in strongly paired superconductors
• Vestigial singlet pairing in a fluctuating magnetic triplet superconductor: Applications to graphene moiré systems
• Topological flat bands, valley polarization, and interband superconductivity in magic-angle twisted bilayer graphene with proximitized spin-orbit couplings
• Nonlocal Moments in the Chern Bands of Twisted Bilayer Graphene
• Approximate symmetries, insulators, and superconductivity in continuum-model description of twisted WSe${}_2$
• Nematic versus Kekulé phases in twisted bilayer graphene under hydrostatic pressure
• Tunable superconductivity and Möbius Fermi surfaces in an inversion-symmetric twisted van der Waals heterostructure
• Probing the order parameter symmetry of two-dimensional superconductors by twisted Josephson interferometry
• Role of the Berry curvature on BCS-type superconductivity in two-dimensional materials
• Intrinsic non-magnetic ${\varphi }_0$ Josephson junctions in twisted bilayer graphene
• Disorder-dependent superconducting pairing symmetry in doped graphene
• Eliashberg Theory and Superfluid Stiffness of Band-Off-Diagonal Pairing in Twisted Graphene
• Superconductivity in a Topological Lattice Model with Strong Repulsion
• Insulators at Fractional Fillings in Twisted Bilayer Graphene Partially Aligned to Hexagonal Boron Nitride
• Topological Kondo effect with spinful Majorana fermions
• Local condensation of charge-$4e$ superconductivity at a nematic domain wall
• Nematic superconductivity from selective orbital pairing in Ba(Fe1-xMx)2As2 (M = Co, Ni) single crystals
• Supercurrent-induced Anomalous Thermal Hall Effect as a New Probe to Superconducting Gap Anisotropy
• Tunneling spectra of impurity states in unconventional superconductors
• Probing superconductivity with tunneling spectroscopy in rhombohedral graphene
• Topological two-band electron-hole superconductors with $d$-wave symmetry: Absence of Dirac quasiparticle annihilation in magic-angle twisted trilayer graphene
• The role of electromagnetic gauge-field fluctuations in the selection between chiral and nematic superconductivity
• Momentum-resolved spectroscopy of superconductivity with the quantum twisting microscope
• Displacement-field-tunable superconductivity in an inversion-symmetric twisted van der Waals heterostructure
• Optical and Raman selection rules for odd-parity clean superconductors
• Mean-field Modelling of Moiré Materials: A User's Guide with Selected Applications to Twisted Bilayer Graphene