Evidence of Gate-Tunable Mott Insulator in Trilayer Graphene-Boron Nitride Moir\'e Superlattice.
Evidence of Gate-Tunable Mott Insulator in Trilayer Graphene-Boron Nitride Moir\'e Superlattice.
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2018-03
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通讯作者：
Guorui Chen;Lili Jiang;Shuang Wu;Bosai Lyu;Hongyuan Li;B. L. Chittari;Kenji Watanabe;T. Taniguchi;Zhiwen Shi;Jeil Jung;Yuanbo Zhang;Feng Wang
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作者：
Guorui Chen;Lili Jiang;Shuang Wu;Bosai Lyu;Hongyuan Li;B. L. Chittari;Kenji Watanabe;T. Taniguchi;Zhiwen Shi;Jeil Jung;Yuanbo Zhang;Feng Wang
莫特绝缘体在强关联物理中起着核心作用，其中排斥库仑相互作用主导电子动能，并导致每个单元格中有一个电子占据的绝缘状态。掺杂的Mott绝缘体通常用Hubbard模型来描述，它可以引起其他相关的现象，如异常的磁性，甚至高温超导。一个可调的Mott绝缘体，其中库仑相互作用和动能之间的竞争可以在原位变化，可以为Mott物理的研究提供一个宝贵的模型系统。在这里，我们报告的ABC三层石墨烯（TLG）和六方氮化硼（hBN）异质结构与莫尔超晶格实现这样的可调莫特绝缘体。与单层石墨烯中的无质量狄拉克电子不同，原始ABC TLG中的电子的特征在于四次能量色散和大的有效质量，这有利于强关联现象。TLG/hBN异质结构中的莫尔超晶格导致栅极可调谐的窄电子能带。由于石墨烯的自旋和谷简并性，每个填充的迷你带在一个莫尔晶格位点中包含4个电子。莫特绝缘体状态出现在1/4和1/2填充，分别对应于每个站点一个电子和两个电子。此外，ABC TLG/hBN异质结构中的Mott态表现出前所未有的可调谐性：Mott带隙可以通过垂直电场原位调制，同时电子掺杂可以被栅极调谐以填充从一个Mott绝缘态到另一个Mott绝缘态的能带。我们对可调莫特绝缘体的观察为探索二维莫尔超晶格异质结构中的新型强关联现象提供了巨大的机会。
Mott insulator plays a central role in strongly correlated physics, where the repulsive Coulomb interaction dominates over the electron kinetic energy and leads to insulating states with one electron occupying each unit cell. Doped Mott insulator is often described by the Hubbard model, which can give rise to other correlated phenomena such as unusual magnetism and even high temperature superconductivity. A tunable Mott insulator, where the competition between the Coulomb interaction and the kinetic energy can be varied in situ, can provide an invaluable model system for the study of Mott physics. Here we report the realization of such a tunable Mott insulator in the ABC trilayer graphene (TLG) and hexagonal boron nitride (hBN) heterostructure with a Moir\'e superlattice. Unlike massless Dirac electrons in monolayer graphene, electrons in pristine ABC TLG are characterized by quartic energy dispersion and large effective mass that are conducive for strongly correlated phenomena. The Moir\'e superlattice in TLG/hBN heterostructures leads to narrow electronic minibands that are gate-tunable. Each filled miniband contains 4 electrons in one Moir\'e lattice site due to the spin and valley degeneracy of graphene. The Mott insulator states emerge at 1/4 and 1/2 fillings, corresponding to one electron and two electrons per site, respectively. Moreover, the Mott states in the ABC TLG/hBN heterostructure exhibit unprecedented tunablility: the Mott gap can be modulated in situ by a vertical electrical field, and at the mean time the electron doping can be gate-tuned to fill the band from one Mott insulating state to another. Our observation of a tunable Mott insulator opens up tremendous opportunities to explore novel strongly correlated phenomena in two-dimensional Moir\'e superlattice heterostructures.