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A valley valve and electron beam splitter

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Science  07 Dec 2018:
Vol. 362, Issue 6419, pp. 1149-1152
DOI: 10.1126/science.aao5989

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Making a practical valleytronics device

Two-dimensional materials with a hexagonal lattice, such as graphene, have two distinct “valleys” in their band structure. Researchers in the emerging field of valleytronics hope that these valley degrees of freedom can be exploited as information carriers, but making valleytronic devices is tricky. Li et al. created chiral valley Hall states on the boundary between oppositely gated regions of bilayer graphene. They then guided these so-called kink states through their sample using spatially modulated gating, demonstrating right and left turns, as well as a valley valve function.

Science, this issue p. 1149

Abstract

Developing alternative paradigms of electronics beyond silicon technology requires the exploration of fundamentally new physical mechanisms, such as the valley-specific phenomena in hexagonal two-dimensional materials. We realize ballistic valley Hall kink states in bilayer graphene and demonstrate gate-controlled current transmission in a four-kink router device. The operations of a waveguide, a valve, and a tunable electron beam splitter are demonstrated. The valley valve exploits the valley-momentum locking of the kink states and reaches an on/off ratio of 8 at zero magnetic field. A magnetic field enables a full-range tunable coherent beam splitter. These results pave a path to building a scalable, coherent quantum transportation network based on the kink states.

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