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Spontaneous isospin polarization and quantum Hall ferromagnetism in a rhombohedral trilayer graphene superlattice
Xiangyan Han(韩香岩), Qianling Liu(刘倩伶), Ruirui Niu(牛锐锐), Zhuangzhuang Qu(曲壮壮), Zhiyu Wang(王知雨), Zhuoxian Li(李卓贤), Chunrui Han(韩春蕊), Kenji Watanabe, Takashi Taniguchi, Zizhao Gan(甘子钊), and Jianming Lu(路建明)
Chin. Phys. B,
2023, 32 (11):
117201.
DOI: 10.1088/1674-1056/acddcf
Moiré superlattices in van der Waals heterostructures have recently attracted enormous interests, due to the highly controllable electronic correlation that gives rise to superconductivity, ferromagnetism, and nontrivial topological properties. To gain a deep understanding of such exotic properties, it is essential to clarify the broken symmetry between spin and valley flavors which universally exists in these ground states. Here in a rhombohedral trilayer graphene crystallographically aligned with a hexagonal boron nitride, we report various kinds of symmetry-breaking transition tuned by displacement fields (D) and magnetic fields: (i) While it is well known that a finite D can enhance correlation to result in correlated insulators at fractional fillings of a flat band, we find the correlation gap emerges before the flavor is fully filled at a positive D, but the sequence is reversed at a negative D. (ii) Around zero D, electronic correlation can be invoked by narrow Landau levels, leading to quantum Hall ferromagnetism that lifts all the degeneracies including not only spin and valley but also orbital degrees of freedom. Our result unveils the complication of transitions between symmetry-breaking phases, shedding light on the mechanisms of various exotic phenomena in strongly correlated systems.
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