▎ 摘　　要

We show a large magnetoresistance (MR) effect in a graphene heterostructure consisting of a metallic and semiconductor-type armchair-graphene-nanoribbon. In the heterostructure, the transmission across the first subband of the semiconducting armchair-graphene-nanoribbon and metallic armchair-graphene-nanoribbon is forbidden under zero magnetic-field, due to the orthogonality of the wavefunctions. A finite magnetic-field introduces the quantum hall-like effect, which distorts the wavefunctions. Thus, a finite transmission occurs across the heterojunction, giving rise to a large MR effect. We study the dependence of this MR on temperature and electron energy. Finally, we design a magnetic-field-effect-transistor which yields a MR of close to 100% (85%) at low (room) temperature. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4765364]