Manipulating Berry curvature in hBN/bilayer graphene commensurate heterostructures
Manipulating Berry curvature in hBN/bilayer graphene commensurate heterostructures
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DOI：
10.1103/physrevb.101.195406
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发表时间：
2020-05
影响因子：
3.7
通讯作者：
Afsal Kareekunnan;M. Muruganathan;H. Mizuta
中科院分区：
文献类型：
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作者：
Afsal Kareekunnan;M. Muruganathan;H. Mizuta
由于系统的非对称性而产生的Berry曲率是一种重要的物理性质，它导致了一些有趣的现象，如谷霍尔效应。在hBN包裹的双层石墨烯体系以及hBN/单层石墨烯异质结构中，已经有一些实验观察到了谷霍尔效应。虽然hBN包覆石墨烯的目的是为了改善石墨烯的电子性质，但hBN层在破坏层对称性和诱导Berry曲率方面的作用还没有明确的研究。在这项研究中，我们发现对于异质结构的公度态，hBN层的构型和取向对双层石墨烯系统中破坏层对称性的Berry曲率的极性和大小有很大的影响。此外，Berry曲率的极性和大小还可以通过施加平面外电场通过调节层不对称性来进一步操纵。然而，在hBN/单层石墨烯公度体系中，hBN层的存在破坏了亚晶格对称性，并导致Berry曲率，其大小和极性取决于hBN层的构型和取向。此外，虽然可以通过施加平面外电场来进一步调节大小，但由于亚晶格的不对称性不能随着外加电场的施加而逆转，所以极性对场的敏感性相当不敏感。
Berry curvature, which arises from the asymmetry in a system, is a paramount physical property that results in interesting phenomena such as valley Hall effect. There have been several experimental observations of valley Hall effect in hBN encapsulated bilayer graphene systems as well as hBN/single-layer graphene heterostructures. Although the intent of encapsulating graphene with hBN is to improve the electronic properties of the graphene, the effect of the hBN layer in breaking the layer symmetry and inducing Berry curvature in these systems is not studied explicitly. In this study, we show that for the commensurate state of the heterostructure, the configuration, as well as the orientation of the hBN layer, has an immense effect on the polarity as well as the magnitude of the Berry curvature in bilayer graphene system as they break the layer symmetry. Also, the polarity and the magnitude of the Berry curvature can further be manipulated with the application of an out-of-plane electric field by tuning the layer asymmetry. Whereas, in hBN/single-layer graphene commensurate systems, the presence of an hBN layer breaks the sublattice symmetry and induces Berry curvature, whose magnitude and polarity depend on the configuration and the orientation of the hBN layer. Moreover, although the magnitude can be further tuned with the application of an out-of-plane electric field, the polarity is rather insensitive to the field as the sublattice asymmetry cannot be reversed with the applied field.