Quantum Pumping of Charge and Spin Currents in Graphene Nano Ribbons
Journal Title: Bulletin of Pure and Applied Sciences Sec. D – Physics - Year 2018, Vol 37, Issue 2
Abstract
We have studied the case of nonmagnetic leads in which only part of the graphene nano ribbons is subjected to an ac gate voltage to break the left-right spatial symmetry. It was shown that peaks of the negative (positive) charge pumping current appear at the Fermi energies around the energy maximums (minimums) of the sub-bands in the ac field free region of the graphene nano ribbon. In the case of ferromagnetic leads with the lead magnetizations being antiparallel in order to break the left-right symmetry. It was found that a pure spin current can be achieved when the whole graphene nanoribbon was under an ac gate voltage. It was also found that peaks in the negative spin pumping current at the Fermi energies around the energy maximums of the majority spin sub-bands in the ferro-magnetic leads. We have shown that the pumping current increases monotonically with the ac field strength due to the enhanced photon-assisted transmissions. We found that at low ac field frequency, the pumping currents exhibited non-monotomic frequency dependence. This is due to the competition of the weakened photon assisted transmissions and the increasing energy space of the states contributing to the pumping current. AT high frequency, the pumping current decreased monotonically with increasing frequency because the ac field became in effective in existing photons. Our results showed that the Fermi energies corresponding to peaks are influenced by the energy level shifting in the ac field free region, but independent of that in the ac field applied region.
Authors and Affiliations
Gautam Kumar Sinha
Keywords
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- EP ID EP528861
- DOI 10.5958/2320-3218.2018.00010.6
- Views 172
- Downloads 0
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