Cascade of correlated phases in the vicinity of tuneable van Hove singularities in Bernal bilayer graphene

The naturally occurring Bernal bilayer graphene has a complex low-energy band structure. It hosts electric-field-controlled Lifshitz transitions where the density of states diverges. In the vicinity of these tunable van-Hove-singularities, we observe experimental signatures consistent with various interaction-driven phases, including the fractional metals of Stoner type [1, 2]. 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 field [1].

In addition, we report a novel interaction-driven behaviour in the Stoner phases in the electron-doped regime electric-field gapped Bernal bilayer graphene [2]. Specifically, we reveal that the spin- and valley-polarized phases exhibit an insulator-like temperature dependence of the conductance that challenges the conventional picture of metallic Stoner magnetism. The phases feature a nonlinear transport behaviour that is sensitive to the onsets of the Stoner orders and consistent with the emergence of exotic correlated orders beyond Stoner ferromagnetism, such as charge density waves or Wigner crystal states [2].

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

 

[1] Anna M. Seiler, Fabian R. Geisenhof, Felix Winterer, Kenji Watanabe, Takashi Taniguchi, Tianyi Xu, Fan Zhang and R. Thomas Weitz, Nature 608, 298-302 (2022)

[2] Anna M. Seiler, Martin Statz, Isabell Weimer, Nils Jacobsen, Kenji Watanabe, Takashi Taniguchi, Zhiyu Dong, Leonid S. Levitov and R. Thomas Weitz, arXiv:2308.00827 (2023)