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Bulletin of Pure and Applied Sciences- Physics (Started in 1982)
eISSN: 2320-3218
pISSN: 0970-6569
Impact Factor: 6.987 (2018)
DOI: 10.5958/2320-3218
Editor-in-Chief:  Prof. Madan jee,
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Article Details

Bulletin of Pure and Applied Sciences- Physics (Started in 1982)
Year : 2018, Volume & Issue : Volume-37D, Issue-2 (July-December)
Page No. : 50-54, Article Type : Original Aticle
Article DOI : 10.5958/2320-3218.2018.00010.6 (Received on 16.03.2018, Accepted on 21.08.2018)

Quantum Pumping of Charge and Spin Currents in Graphene Nano Ribbons

Gautam Kumar Sinha1, Om Prakash Singh2
Author’s Affiliation : 1Research Scholar, University Department of Physics, J. P. University, Chapra, Bihar 841301, India. 2University Department of Physics, J. P. University, Chapra, Bihar 841301, India.

Corresponding Author : Gautam Kumar Sinha Research Scholar University Department of Physics, J. P. University, Chapra, Bihar 841301, India.,
E-Mail:-[email protected]


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.

Keywords

Nonmagnetic, graphene nanoribbons, gate voltage, spatial symmetry, charge pumping, Fermi energy, ferromagnetic, spin pumping, photon.
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