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Baby skyrmions in Chern ferromagnets and topological mechanism for spin-polaron formation in twisted bilayer graphene

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  • Eslam Khalaf

    (Harvard University
    The University of Texas at Austin)

  • Ashvin Vishwanath

    (Harvard University)

Abstract

The advent of moiré materials has galvanized interest in the nature of charge carriers in topological bands. In contrast to conventional materials with electron-like charge carriers, topological bands allow for more exotic possibilities where charge is carried by nontrivial topological textures, such as skyrmions. However, the real-space description of skyrmions is ill-suited to address the limit of small skyrmions and to account for momentum-space band features. Here, we develop a momentum-space approach to study the formation of the smallest skyrmions – spin polarons, formed as bound states of an electron and a spin flip – in topological ferromagnets. We show that, quite generally, there is an attraction between an electron and a spin flip that is purely topological in origin, promoting the formation of spin polarons. Applying our results to twisted bilayer graphene, we identify a range of parameters where spin polarons are formed and discuss their possible experimental signatures.

Suggested Citation

  • Eslam Khalaf & Ashvin Vishwanath, 2022. "Baby skyrmions in Chern ferromagnets and topological mechanism for spin-polaron formation in twisted bilayer graphene," Nature Communications, Nature, vol. 13(1), pages 1-11, December.
  • Handle: RePEc:nat:natcom:v:13:y:2022:i:1:d:10.1038_s41467-022-33673-3
    DOI: 10.1038/s41467-022-33673-3
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    References listed on IDEAS

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    1. Xiaomeng Liu & Zeyu Hao & Eslam Khalaf & Jong Yeon Lee & Yuval Ronen & Hyobin Yoo & Danial Haei Najafabadi & Kenji Watanabe & Takashi Taniguchi & Ashvin Vishwanath & Philip Kim, 2020. "Tunable spin-polarized correlated states in twisted double bilayer graphene," Nature, Nature, vol. 583(7815), pages 221-225, July.
    2. Yuan Cao & Valla Fatemi & Shiang Fang & Kenji Watanabe & Takashi Taniguchi & Efthimios Kaxiras & Pablo Jarillo-Herrero, 2018. "Unconventional superconductivity in magic-angle graphene superlattices," Nature, Nature, vol. 556(7699), pages 43-50, April.
    3. Xiaobo Lu & Petr Stepanov & Wei Yang & Ming Xie & Mohammed Ali Aamir & Ipsita Das & Carles Urgell & Kenji Watanabe & Takashi Taniguchi & Guangyu Zhang & Adrian Bachtold & Allan H. MacDonald & Dmitri K, 2019. "Superconductors, orbital magnets and correlated states in magic-angle bilayer graphene," Nature, Nature, vol. 574(7780), pages 653-657, October.
    4. Petr Stepanov & Ipsita Das & Xiaobo Lu & Ali Fahimniya & Kenji Watanabe & Takashi Taniguchi & Frank H. L. Koppens & Johannes Lischner & Leonid Levitov & Dmitri K. Efetov, 2020. "Untying the insulating and superconducting orders in magic-angle graphene," Nature, Nature, vol. 583(7816), pages 375-378, July.
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