Unconventional topological superconductivity and phase diagram for an effective two-orbital model as applied to twisted bilayer graphene

M. Fidrysiak; M. Zegrodnik; J. Spałek

doi:10.1103/PhysRevB.98.085436

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Unconventional topological superconductivity and phase diagram for an effective two-orbital model as applied to twisted bilayer graphene

M. Fidrysiak, M. Zegrodnik, J. Spałek

DOI 10.1103/PhysRevB.98.085436 · Physical Review B

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Abstract

We consider the superconducting and Mott-insulating states for twisted bilayer graphene, modeled as a two-narrow-band system of electrons with appreciable intra-atomic Coulomb interactions. The interaction induces kinetic exchange which leads to real space, either triplet- or singlet-spin pairing, in direct analogy to heavy fermions and high-temperature superconductors. By employing the statistically consistent Gutzwiller method, we construct explicitly the phase diagram as a function of electron concentration for the spin-triplet dx2−y2+idxy paired case, as well as determine the topological edge states. The model reproduces principal features observed experimentally in a semiquantitative manner. The essential role of electronic correlations in driving both the Mott-insulating and superconducting transitions is emphasized. The transformation of the spin-triplet state into its spin-singlet analog is also analyzed, as well as the appearance of the phase-separated superconducting+Mott-insulating state close to the half-filling.