Speaker
Description
Diverging density of states can lead to correlated phases in low dimensional systems. This includes the graphene family that hosts electric-field controlled Lifshitz transitions and concomitant van Hove singularities in the density of states. Here, we present the observation of experimental signatures consistent with various interaction-driven phases in hole-doped Bernal bilayer graphene including the fractional metals of Stoner type [1]. More prominently, we have found competing nontrivial insulating and metallic phases 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 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 [2].
[1] Anna M. Seiler, Fabian R. Geisenhof, Felix Winterer, Kenji Watanabe, Takashi Taniguchi, Tianyi Xu, Fan Zhang, 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, R. Thomas Weitz, in preparation (2023)
