Charge-transfer insulation in twisted bilayer graphene

Louk Rademaker; Paula Mellado

doi:10.1103/PhysRevB.98.235158

paper

Charge-transfer insulation in twisted bilayer graphene

arXiv:1805.05294 · doi:10.1103/PhysRevB.98.235158

Abstract

We studied the real space structure of states in twisted bilayer graphene at the `magic angle' $θ = 1.0 8^{\circ}$ . The flat bands close to charge neutrality are composed of a mix of `ring' and `center' orbitals around the AA stacking region. An effective model with localized orbitals is constructed, which necessarily includes more than just the four flat bands. Long-range Coulomb interaction causes a charge-transfer at half-filling of the flat bands from the `center' to the `ring' orbitals. Consequently, the Mott phase is a featureless spin-singlet paramagnet. We estimate the effective Heisenberg coupling that favors the singlet coupling to be $J = 3.3$ K, consistent with experimental values. The superconducting state depends on the nature of the dopants: hole-doping yields $p + i p$ -wave whereas electron-doping yields $d + i d$ -wave pairing symmetry.

arXiv comment8 pages, 6 figures. This second version contains more detailed computations on the Coulomb energy from the unequal charge distribution

Charge-transfer insulation in twisted bilayer graphene

Abstract

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