68 research outputs found
Anomalous Enhancement of the Boltzmann Conductivity in Disordered Zigzag Graphene Nanoribbons
We study the conductivity of disordered zigzag graphene nanoribbons in the
incoherent regime by using the Boltzmann equation approach. The band structure
of zigzag nanoribbons contains two energy valleys, and each valley has an
excess one-way channel. The crucial point is that the numbers of conducting
channels for two propagating directions are imbalanced in each valley due to
the presence of an excess one-way channel. It was pointed out that as a
consequence of this imbalance, a perfectly conducting channel is stabilized in
the coherent regime if intervalley scattering is absent. We show that even in
the incoherent regime, the conductivity is anomalously enhanced if intervalley
scattering is very weak. Particularly, in the limit of no intervalley
scattering, the dimensionless conductance approaches to unity with increasing
ribbon length as if there exists a perfectly conducting channel. We also show
that anomalous valley polarization of electron density appears in the presence
of an electric field.Comment: 10 pages, 3 figure
Nonuniversal Shot Noise in Disordered Quantum Wires with Channel-Number Imbalance
The number of conducting channels for one propagating direction is equal to
that for the other direction in ordinary quantum wires. However, they can be
imbalanced in graphene nanoribbons with zigzag edges. Employing the model
system in which a degree of channel-number imbalance can be controlled, we
calculate the shot-noise power at zero frequency by using the
Boltzmann-Langevin approach. The shot-noise power in an ordinary diffusive
conductor is one-third of the Poisson value. We show that with increasing the
degree of channel-number imbalance, the universal one-third suppression breaks
down and a highly nonuniversal behavior of shot noise appears.Comment: 10 pages, 3 figure
Probe-configuration dependent dephasing in a mesoscopic interferometer
Dephasing in a ballistic four-terminal Aharonov-Bohm geometry due to charge
and voltage fluctuations is investigated. Treating two terminals as voltage
probes, we find a strong dependence of the dephasing rate on the probe
configuration in agreement with a recent experiment by Kobayashi et al. (J.
Phys. Soc. Jpn. 71, 2094 (2002)). Voltage fluctuations in the measurement
circuit are shown to be the source of the configuration dependence.Comment: 4 pages, 3 figure
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