Topological valley currents via ballistic edge modes in graphene superlattices near the primary Dirac point
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jats:titleAbstract</jats:title>jats:pGraphene on hexagonal boron nitride (hBN) can exhibit a topological phase via mutual crystallographic alignment. Recent measurements of nonlocal resistance (jats:italicR</jats:italic>jats:subnl</jats:sub>) 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 jats:italicR</jats:italic>jats:subnl</jats:sub> at SDP is negligible, but below 60 K approaches the value of jats:italich</jats:italic>/2jats:italice</jats:italic>jats:sup2</jats:sup> 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.</jats:p>
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2399-3650
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European Commission (656485)
Engineering and Physical Sciences Research Council (EP/P026311/1)