Theory of insulating phase and superconductivity in twisted bilayer graphene

ORAL

Abstract

A correlated insulating phase and superconductivity have been recently observed in twisted bilayer graphene (tBG). We study theoretically these two phases in both the weak and strong coupling limit. In the weak coupling limit, using the random phase approximation, we find various possible combinations of density wave phases and pairing symmetries [1]. In the strong coupling limit, the insulating phase is anti-ferromagnetically (AFM) ordered, like in monolayer graphene [2]. However, we find there is no local magnetic moment in this AFM phase due to the special form of Wannier functions. Using the spin-fermion model, we find attractive electron-electron interaction mediated by the critical AFM fluctuations. This attractive interaction leads to chiral d+id superconductivity. Using a finite size tight-binding model, we show explicitly the existence of edge Majorana modes.

[1] E Laksono et al., Solid State Communications 282, 38-44 (2018)
[2] HK Tang et al., Science 361 (6402), 570-574 (2018)

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Presenters

  • Xingyu Gu

    Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Department of Physics, National University of Singapore

Authors

  • Xingyu Gu

    Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Department of Physics, National University of Singapore

  • Evan Laksono

    Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Department of Physics, National University of Singapore

  • Chuan Chen

    Department of Physics, National University of Singapore, National University of Singapore

  • Jia Ning Leaw

    Department of Physics, National University of Singapore, National University of Singapore

  • Nimisha Raghuvanshi

    Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Department of Physics, National University of Singapore

  • Shaffique Adam

    Department of Physics and Centre for Advanced 2D Materials, National University of Singapore, Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Department of Physics, National University of Singapore, Yale-NUS College, National University of Singapore