Cited by 680Topological Materials and PhenomenaGraphene research and applications2D Materials and Applications

Topological valley transport at bilayer graphene domain walls

Ju, Long, Shi, Zhiwen, Nair, Nityan, Lv, Yinchuan, Jin, Chenhao, Velasco, Jairo, Ojeda-Aristizabal, Claudia, Bechtel, Hans A. +4 more·2015·Nature

Abstract

Electron valley, a degree of freedom that is analogous to spin, can lead to novel topological phases in bilayer graphene. A tunable bandgap can be induced in bilayer graphene by an external electric field, and such gapped bilayer graphene is predicted to be a topological insulating phase protected by no-valley mixing symmetry, featuring quantum valley Hall effects and chiral edge states. Observation of such chiral edge states, however, is challenging because inter-valley scattering is induced by atomic-scale defects at real bilayer graphene edges. Recent theoretical work has shown that domain walls between AB- and BA-stacked bilayer graphene can support protected chiral edge states of quantum valley Hall insulators. Here we report an experimental observation of ballistic (that is, with no scattering of electrons) conducting channels at bilayer graphene domain walls. We employ near-field infrared nanometre-scale microscopy (nanoscopy) to image in situ bilayer graphene layer-stacking domain walls on device substrates, and we fabricate dual-gated field effect transistors based on the domain walls. Unlike single-domain bilayer graphene, which shows gapped insulating behaviour under a vertical electrical field, bilayer graphene domain walls feature one-dimensional valley-polarized conducting channels with a ballistic length of about 400 nanometres at 4 kelvin. Such topologically protected one-dimensional chiral states at bilayer graphene domain walls open up opportunities for exploring unique topological phases and valley physics in graphene.

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Crossref · 10.1038/nature14364

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  • The propagating directions of an edge state for K and K′ valleys are exactly opposite at both AB-type and BA-type domain walls, demonstrating valley-chirality and locking of valley-polarized edge states to one propagating direction in the absence of inter-valley scattering.

    “It is seen that the propagating directions of an edge state for K and K′ valleys are exactly opposite, no matter at an AB-type or BA-type domain wall. This is a manifestation of valley-chirality of the valley-Hall effect, in other words, the valley-polarized edge states are locked to one propagating direction in the absence of inter-valley scattering14,20.”

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Authors
Ju, L., Shi, Z., Nair, N., Lv, Y., Jin, C., Velasco, J., Ojeda-Aristizabal, C., Bechtel, H. A., Martin, M. C., Zettl, A., Analytis, J., & Wang, F.
Affiliations
  • University of California, Berkeley (US)
  • Lawrence Berkeley National Laboratory (US)
Corresponding author
Wang, Feng
Venue
Nature
Published
2015-04
Volume
520
Issue
7549
Pages
650-655
ISSN
  • 0028-0836 (ISSN-L)
  • 1476-4687
OpenAlex
W1996794882
Cited by
680
References
33
Citations by year
2026: 31 · 2025: 59 · 2024: 58 · 2023: 56 · 2022: 61 · 2021: 74 · 2020: 80 · 2019: 75 · 2018: 77 · 2017: 58 · 2016: 37 · 2015: 14
FWCI
31.51
Type
journal article
Language
en
Open access
closed
Locations
  • Nature (publishedVersion)
  • PubMed (publishedVersion)
Topics
  • Physical Sciences › Physics and Astronomy › Atomic and Molecular Physics, and Optics › Topological Materials and Phenomena
  • Physical Sciences › Materials Science › Materials Chemistry › Graphene research and applications
  • Physical Sciences › Materials Science › Materials Chemistry › 2D Materials and Applications
Keywords
bilayer graphene, domain walls, valley transport, valley polarization, quantum valley Hall effect, chiral edge states, topological insulators, ballistic transport, field-effect transistors, valley physics

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