Gate-tunable topological valley transport in bilayer graphene

By Mengqiao Sui, Guorui Chen, Liguo Ma, Wen-Yu Shan, Dai Tian, Kenji Watanabe, Takashi Taniguchi, Xiaofeng Jin, W. Yao, Di Xiao and 1 more. Nature Physics, 2015

349 citations recorded by the source corpus.

Bilayer graphene can host topological currents that are robust against defects and are associated with the electron valleys. It is now shown that electric fields can tune this topological valley transport over long distances at room temperature. Valley pseudospin, the quantum degree of freedom characterizing the degenerate valleys in energy bands1, is a distinct feature of two-dimensional Dirac materials1,2,3,4,5. Similar to spin, the valley pseudospin is spanned by a time-reversal pair of states, although the two valley pseudospin states transform to each other under spatial inversion. The breaking of inversion symmetry induces various valley-contrasted physical properties; for instance, valley-dependent topological transport is of both scientific and technological interest2,3,4,5. Bilayer graphene is a unique system whose intrinsic inversion symmetry can be controllably broken by a perpendicular electric field, offering a rare possibility for continuously tunable topological valley transport. We used a perpendicular gate electric field to break the inversion symmetry in bilayer graphene, and a giant nonlocal response was observed as a result of the topological transport of the valley pseudospin. We further showed that the valley transport is fully tunable by external gates, and that the nonlocal signal persists up to room temperature and over long distances. These observations challenge the current understanding of topological valley transport in a gapped system, and the robust topological transport may lead to future valleytronic applications.

Subfields: Atomic and Molecular Physics, and Optics, Materials Chemistry

View Paper: https://www.semanticscholar.org/paper/f959567eff4d612f436d80a994214a5bbf3a2f90