Quantum Hall resistances of a multiterminal top-gated graphene device

Four-terminal resistances, both longitudinal and diagonal, of a locally gated graphene device are measured in the quantum-Hall (QH) regime. In sharp distinction from previous two-terminal studies [ J. R. Williams et al. Science 317 638 (2007); B. Özyilmaz et al. Phys. Rev. Lett. 99 166804 (2007)], asymmetric QH resistances are observed, which provide information on reflection as well as transmission of the QH edge states. Most quantized values of resistances are well analyzed by the assumption that all edge states are equally populated. Contrary to the expectation, however, a 5/2 transmission of the edge states is also found, which may be caused by incomplete mode mixing and/or by the presence of counterpropagating edge states. This four-terminal scheme can be conveniently used to study the edge-state equilibration in locally gated graphene devices as well as monolayer and multilayer graphene hybrid structures.