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Phase Separation in a Spin Density Wave State of Twisted Bilayer Graphene

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Abstract

Twisted bilayer graphene at the so-called magic twist angle θ ∼ 1° is theoretically studied. In the absence of interaction between electrons, the system under study is characterized by four almost degenerate flat bands near the Fermi level. The electron-electron interaction lifts this degeneracy and stabilizes a certain order parameter in the system. We assume that the arising order parameter corresponds to a spin density wave. The evolution of such spin density wave state upon doping is analyzed. It is shown that, in the doping range where this order parameter exists, the homogeneous state of the system can be unstable to phase separation. Namely, the doping dependence of the chemical potential is nonmonotonic, which is consistent with recent experiments. Phases in the inhomogeneous state are characterized by an even number (ν = 0, ±2, ±4) of electrons per supercell. This allows explaining some features in the behavior of the conductivity of the doped system.

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Acknowledgments

We are grateful to the Joint Supercomputer Center, Russian Academy of Sciences, for access to the computing resources.

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Authors and Affiliations

  1. Institute for Theoretical and Applied Electrodynamics, Russian Academy of Sciences, Moscow, 125412, Russia

    A. O. Sboychakov, A. V. Rozhkov, K. I. Kugel & A. L. Rakhmanov

  2. Skolkovo Institute of Science and Technology, Skolkovo Innovation Center, Moscow, 143026, Russia

    A. V. Rozhkov

Authors
  1. A. O. Sboychakov
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  2. A. V. Rozhkov
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  3. K. I. Kugel
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  4. A. L. Rakhmanov
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Corresponding author

Correspondence to A. O. Sboychakov.

Additional information

Russian Text © The Author(s), 2020, published in Pis’ma v Zhurnal Eksperimental’noi i Teoreticheskoi Fiziki, 2020, Vol. 112, No. 10, pp. 693–699.

Funding

This work was supported by the Russian Foundation for Basic Research (project nos. 19-02-00421 and 19-52-50015).

Translated by K. Kugel

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Sboychakov, A.O., Rozhkov, A.V., Kugel, K.I. et al. Phase Separation in a Spin Density Wave State of Twisted Bilayer Graphene. Jetp Lett. 112, 651–656 (2020). https://doi.org/10.1134/S0021364020220130

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  • DOI: https://doi.org/10.1134/S0021364020220130

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