Topological valley currents via ballistic edge modes in graphene superlattices near the primary Dirac point
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Abstract: Graphene on hexagonal boron nitride (hBN) can exhibit a topological phase via mutual crystallographic alignment. Recent measurements of nonlocal resistance (Rnl) near the secondary Dirac point (SDP) in ballistic graphene/hBN superlattices have been interpreted as arising due to the quantum valley Hall state. We report hBN/graphene/hBN superlattices in which Rnl at SDP is negligible, but below 60 K approaches the value of h/2e2 in zero magnetic field at the primary Dirac point with a characteristic decay length of 2 μm. Furthermore, nonlocal transport transmission probabilities based on the Landauer-Büttiker formalism show evidence for spin-degenerate ballistic valley-helical edge modes, which are key for the development of valleytronics.
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Funder: China Scholarship Council (CSC); doi: https://doi.org/10.13039/501100004543
Funder: Fundacja na rzecz Nauki Polskiej (Foundation for Polish Science); doi: https://doi.org/10.13039/501100001870
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Narodowe Centrum Nauki (National Science Centre) (UMO-2017/24/T/ST3/00501)
Royal Society (EP/P026311/1)
RCUK | Engineering and Physical Sciences Research Council (EPSRC) (EP/P026311/1)