Nematic superconductivity in magic-angle twisted bilayer graphene from atomistic modeling

Twisted bilayer graphene (TBG) develops large moiré patterns at small twist angles with flat energy bands hosting domes of superconductivity. The large system size and intricate band structure have however hampered investigations into the superconducting state. Here, using full-scale atomistic model...

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Bibliographic Details
Published in:Communications physics 2022-04, Vol.5 (1), p.1-11, Article 92
Main Authors: Löthman, Tomas, Schmidt, Johann, Parhizgar, Fariborz, Black-Schaffer, Annica M.
Format: Article
Language:English
Subjects:
639/766/119/1003
639/766/119/2795
Atomic properties
Bilayers
Energy bands
Energy gap
Graphene
High temperature
Interlayers
Modelling
Moire patterns
Order parameters
Physics
Physics and Astronomy
Superconductivity
Superconductors
Unit cell
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Summary:Twisted bilayer graphene (TBG) develops large moiré patterns at small twist angles with flat energy bands hosting domes of superconductivity. The large system size and intricate band structure have however hampered investigations into the superconducting state. Here, using full-scale atomistic modelling with local electronic interactions, we find at and above experimentally relevant temperatures a highly inhomogeneous superconducting state with nematic ordering on both atomic and moiré length scales. The nematic state has a locally anisotropic real-valued d -wave pairing, with a nematic vector winding throughout the moiré pattern, and is three-fold degenerate. Although d -wave symmetric, the superconducting state has a full energy gap, which we tie to a π -phase interlayer coupling. The superconducting nematicity is further directly detectable in the local density of states. Our results show that atomistic modeling is essential and also that very similar local interactions produce very different superconducting states in TBG and the high-temperature cuprate superconductors. Calculating properties of the superconducting state in magic-angle twisted bilayer graphene is complicated by the enormous number of carbon atoms in the moiré unit cell. Using a full-scale atomistic modelling approach, the authors report evidence for a fully gapped d-wave superconducting order parameter with associated nematicity arising on both the atomic- and moiré-lattice scales.
ISSN:2399-3650
2399-3650
DOI:10.1038/s42005-022-00860-z