1 State Key Laboratory for Mesoscopic Physics, School of Physics, Peking University, Beijing 100871, China; 2 Institute of Microelectronics, Chinese Academy of Sciences, Beijing 100029, China; 3 University of Chinese Academy of Sciences, Beijing 100049, China
Abstract Flat-band physics of moiré superlattices, originally discovered in the celebrated twisted bilayer graphene, have recently been intensively explored in multilayer graphene systems that can be further controlled by electric field. In this work, we experimentally find the evidence of correlated insulators at half filling of the electron moiré band of twisted monolayer-trilayer graphene with a twist angle around 1.2°. Van Hove singularity (VHS), manifested as enhanced resistance and zero Hall voltage, is observed to be distinct in conduction and valence flat bands. It also depends on the direction and magnitude of the displacement fields, consistent with the asymmetric crystal structure. While the resistance ridges at VHS can be enhanced by magnetic fields, when they cross commensurate fillings of the moiré superlattice in the conduction band, the enhancement is so strong that signatures of correlated insulator appear, which may further develop into an energy gap depending on the correlation strength. At last, Fermi velocity derived from temperature coefficients of resistivity is compared between conduction and valence bands with different displacement fields. It is found that electronic correlation has a negative dependence on the Fermi velocity, which in turn could be used to quantify the correlation strength.
Fund: J. L. acknowledges support from the National Natural Science Foundation of China (Grant No. 11974027), the National Key R&D Program of China (Grant Nos. 2019YFA0307800 and 2021YFA1400100), and Beijing Natural Science Foundation (Grant No. Z190011). C. H. acknowledges support from the National Natural Science Foundation of China (Grant No. 62275265) and Beijing Natural Science Foundation (Grant No. 4222084).
Corresponding Authors:
Jianming Lu, Chunrui Han
E-mail: jmlu@pku.edu.cn;hanchunrui@ime.ac.cn
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