Friday 17 May 2024
Correlated phases in the vicinity of tunable van Hove singularities in Bernal bilayer graphene
Anna Seiler (ETH)

The bandstructure of naturally occurring Bernal bilayer graphene exhibits four linearly dispersed Dirac cones [1] but changes drastically when large electric displacement fields are applied across the two layers. Here, tunable van Hove singularities lead to the emergence of complex correlated states. We observe experimental signatures consistent with various interaction-driven phases, including the fractional metals of Stoner type [2, 3]. More prominently, we find competing nontrivial insulating and metallic phases at hole doping that exhibit intriguing temperature dependences and nonlinear I-V characteristics at zero magnetic fields [2].

In addition, we report a novel interaction-driven behaviour in the Stoner phases in the electron-doped regime of biased Bernal bilayer graphene. Specifically, we find that the spin- and valley-polarized Stoner phases in this regime exhibit an insulator-like temperature dependence of the conductance. This unexpected behaviour challenges the conventional picture of metallic Stoner magnetism in this system. Furthermore, we find these Stoner phases feature a nonlinear transport behaviour that is sensitive to the onsets of the Stoner orders. These results suggest the emergence of exotic correlated orders beyond Stoner ferromagnetism, such as charge density waves or Wigner crystal states [3].

Overall, our results exemplify rich interacting physics in a simple multilayer graphene system without twist.

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You can download the slides of the presentation here (in pdf).

References:
[1] Anna M. Seiler, Nils Jacobsen, Martin Statz, Noelia Fernandez, Francesca Falorsi, Kenji Watanabe, Takashi Taniguchi, Zhiyu Dong, Leonid S. Levitov and R. Thomas Weitz, Nat. Commun. 15, 3133 (2024)
[2] Anna M. Seiler, Fabian R. Geisenhof, Felix Winterer, Kenji Watanabe, Takashi Taniguchi, Tianyi Xu, Fan Zhang, R. Thomas Weitz, Nature 608, 298-302 (2022)
[3] Anna M. Seiler, Martin Statz, Isabell Weimer, Nils Jacobsen, Kenji Watanabe, Takashi Taniguchi, Zhiyu Dong, Leonid S. Levitov, R. Thomas Weitz, arXiv:2308.00827 (2023)