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Superconductivity from valley fluctuations and approximate SO(4) symmetry in a weak coupling theory of twisted bilayer graphene

You, Yi-Zhuang ; Vishwanath, Ashvin

npj quantum materials, 2019-04, Vol.4 (1), Article 16 [Periódico revisado por pares]

London: Nature Publishing Group

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  • Título:
    Superconductivity from valley fluctuations and approximate SO(4) symmetry in a weak coupling theory of twisted bilayer graphene
  • Autor: You, Yi-Zhuang ; Vishwanath, Ashvin
  • Assuntos: Bilayers ; Brillouin zones ; Broken symmetry ; CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY ; Coupling ; Fermi liquids ; Form factors ; Graphene ; Insulators ; Superconductivity ; Symmetry
  • É parte de: npj quantum materials, 2019-04, Vol.4 (1), Article 16
  • Notas: AC02-05CH11231
    USDOE Office of Science (SC)
  • Descrição: Abstarct The recent discovery of the Mott insulating and superconducting phases in twisted bilayer graphene has generated tremendous research interest. Here, we develop a weak coupling approach to the superconductivity in twisted bilayer graphene, starting from the Fermi liquid regime. A key observation is that near half filling, the fermiology consists of well nested Fermi pockets derived from opposite valleys, leading to enhanced valley fluctuation, which in turn can mediate superconductivity. This scenario is studied within the random phase approximation. We find that inter-valley electron pairing with either chiral (d + id mixed with p−ip) or helical form factor is the dominant instability. An approximate SO(4) spin-valley symmetry implies a near degeneracy of spin-singlet and triplet pairing. On increasing interactions, commensurate inter-valley coherence wave (IVCW) order can arise, with simultaneous condensation at the three M points in the Brillouin Zone, and a 2 × 2 pattern in real space. In simple treatments though, this leads to a full gap at fillings ± (1/2 + 1/8), slightly away from half-filling. The selection of spin-singlet or spin triplet orders, both for the IVCW and the superconductor, arise fcase corresponds to the Hundsrom SO(4) symmetry breaking terms. Mott insulators derived from phase fluctuating superconductors are also discussed, which exhibit both symmetry protected and intrinsic topological orders.
  • Editor: London: Nature Publishing Group
  • Idioma: Inglês
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  • Realização: ABCD-USP USP   Logos de Redes Sociais: Freepik

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