The number of conducting channels for one propagating direction is equal tothat for the other direction in ordinary quantum wires. However, they can beimbalanced in graphene nanoribbons with zigzag edges. Employing the modelsystem in which a degree of channel-number imbalance can be controlled, wecalculate the shot-noise power at zero frequency by using theBoltzmann-Langevin approach. The shot-noise power in an ordinary diffusiveconductor is one-third of the Poisson value. We show that with increasing thedegree of channel-number imbalance, the universal one-third suppression breaksdown and a highly nonuniversal behavior of shot noise appears.
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