1st Physical Institute, Faculty of Physics, University of Göttingen, Göttingen, Germany.
Physics of Nanosystems, Department of Physics, Ludwig-Maximilians-Universität München, Munich, Germany.
Nature. 2022 Aug;608(7922):298-302. doi: 10.1038/s41586-022-04937-1. Epub 2022 Aug 10.
Divergent density of states offers an opportunity to explore a wide variety of correlated electron physics. In the thinnest limit, this has been predicted and verified in the ultraflat bands of magic-angle twisted bilayer graphene, the band touching points of few-layer rhombohedral graphite and the lightly doped rhombohedral trilayer graphene. The simpler and seemingly better understood Bernal bilayer graphene is also susceptible to orbital magnetism at charge neutrality leading to layer antiferromagnetic states or quantum anomalous Hall states. Here we report the observation of a cascade of correlated phases in the vicinity of electric-field-controlled Lifshitz transitions and van Hove singularities in Bernal bilayer graphene. We provide evidence for the observation of Stoner ferromagnets in the form of half and quarter metals. Furthermore, we identify signatures consistent with a topologically non-trivial Wigner-Hall crystal at zero magnetic field and its transition to a trivial Wigner crystal, as well as two correlated metals whose behaviour deviates from that of standard Fermi liquids. Our results in this reproducible, tunable, simple system open up new horizons for studying strongly correlated electrons.
各向异性的态密度为探索各种关联电子物理提供了机会。在最薄的极限下，这在魔角扭曲双层石墨烯的超平坦能带、少数层菱面体石墨的能带接触点和轻掺杂菱面体三层石墨烯中已经被预测和验证。更简单且看似更容易理解的范德华双层石墨烯在中性电荷下也容易受到轨道磁性的影响，从而导致层反铁磁态或量子反常霍尔态。在这里，我们报告了在范德华双层石墨烯中电场控制的李希特跃迁和范霍夫奇点附近的一系列关联相的观察结果。我们提供了观察半金属和四分之一金属形式的斯通纳铁磁体的证据。此外，我们还确定了在零磁场下具有非平凡魏格纳-霍尔晶体及其向平凡魏格纳晶体转变的特征，以及两种行为偏离标准费米液体的关联金属。我们在这个可重复、可调谐、简单的系统中的结果为研究强关联电子开辟了新的视野。
