Bulk valley transport and Berry curvature spreading at the edge of flat bands

Sinha, Subhajit ; Adak, Pratap Chandra ; Surya Kanthi, R. S. ; Chittari, Bheema Lingam ; Sangani, L. D. Varma ; Watanabe, Kenji ; Taniguchi, Takashi ; Jung, Jeil ; Deshmukh, Mandar M. (2020) Bulk valley transport and Berry curvature spreading at the edge of flat bands Nature Communications, 11 (1). ISSN 2041-1723

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Official URL: http://doi.org/10.1038/s41467-020-19284-w

Related URL: http://dx.doi.org/10.1038/s41467-020-19284-w


2D materials based superlattices have emerged as a promising platform to modulate band structure and its symmetries. In particular, moiré periodicity in twisted graphene systems produces flat Chern bands. The recent observation of anomalous Hall effect (AHE) and orbital magnetism in twisted bilayer graphene has been associated with spontaneous symmetry breaking of such Chern bands. However, the valley Hall state as a precursor of AHE state, when time-reversal symmetry is still protected, has not been observed. Our work probes this precursor state using the valley Hall effect. We show that broken inversion symmetry in twisted double bilayer graphene (TDBG) facilitates the generation of bulk valley current by reporting experimental evidence of nonlocal transport in a nearly flat band system. Despite the spread of Berry curvature hotspots and reduced quasiparticle velocities of the carriers in these flat bands, we observe large nonlocal voltage several micrometers away from the charge current path — this persists when the Fermi energy lies inside a gap with large Berry curvature. The high sensitivity of the nonlocal voltage to gate tunable carrier density and gap modulating perpendicular electric field makes TDBG an attractive platform for valley-twistronics based on flat bands.

Item Type:Article
Source:Copyright of this article belongs to Springer Nature Limited.
Keywords:Electronic Properties and Devices; Electronic Properties and Materials; Quantum Hall; Two-Dimensional Materials.
ID Code:117616
Deposited On:28 Apr 2021 12:15
Last Modified:28 Apr 2021 12:15

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