Quantum Monte Carlo study of magnetic ordering and superconducting pairing symmetry in twisted bilayer graphene

Shi-Chao Fang; Guang-Kun Liu; Hai-Qing Lin; Zhong-Bing Huang

doi:10.1103/PhysRevB.100.115135

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Quantum Monte Carlo study of magnetic ordering and superconducting pairing symmetry in twisted bilayer graphene

Shi-Chao Fang, Guang-Kun Liu, Hai-Qing Lin, Zhong-Bing Huang

DOI 10.1103/PhysRevB.100.115135 · Physical Review B

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Abstract

To understand correlated insulating and unconventional superconducting states in twisted bilayer graphene, we perform a systematic study of spin and pairing correlations in an effective two-orbital Hubbard model, by using the ground-state constrained-path quantum Monte Carlo method. Our numerical simulations reveal that when only the on-site Hubbard U is considered, the long-range magnetic order develops for U≥3.2t at half filling. Upon doping away from half filling, an analysis based on the pairing correlations and corresponding vertex contributions identifies that pairing with the d+id symmetry is the dominant pairing channel. As the on-site Coulomb interaction is increased, both spin correlation and effective pairing interaction are enhanced simultaneously, indicating the intimate relation between magnetism and superconductivity. An inclusion of nearest neighbor Coulomb interaction V results in a suppression of the d+id superconductivity, but it can survive in the small V regime. Our findings are useful for clarifying the ongoing controversy on the superconducting pairing symmetry in twisted bilayer graphene.