Crossover from Room-temperature Double-channel Ballistic Transport to Single-channel Ballistic Transport in Zigzag Graphene Nanoribbons

摘要

Very recently, it was demonstrated explicitly that a zigzag graphenenanoribbon (GNR) exhibits a crossover of conductance from G0 to G0/2 withincreasing the length (G0 = 2e2/h is the quantum of conductance) even atroom-temperature [Baringhaus, et al. Nature 506, 349 (2014)]. Such a result ispuzzling as none of previous theories seem to match the experimentalobservations. Here, we propose a model to explain the crossover fromdouble-channel to single-channel ballistic transport in zigzag GNR. The sp3distortion of carbon atoms at the GNR edges induces a large spin-orbit couplingon the edges atoms, which enhances spin-flip scattering of edge states of thezigzag GNR. With sufficient spin-flip scattering, the wave-function of edgestates becomes a superposition of the spin-up and spin-down components. Thenthe coupling of the two edges becomes important. This removes the edge degreeof freedom in the zigzag GNR and results in the evolution of the conductancefrom G0 to G0/2 with increasing the length.