Quantum transport theory for nanostructures with Rashba spin-orbital interaction

The experiment that the high spin selectivity and the length-dependent spin polarization are observed in double-stranded DNA [Science 331, 894 (2011)], is elucidated by considering the combination of the spin-orbit coupling, the environment-induced dephasing, and the helical symmetry. We show that the spin polarization in double-stranded DNA is significant even in the case of weak spin-orbit coupling, while no spin polarization appears in single-stranded DNA. Furthermore, the underlying physical mechanism and the parameters-dependence of the spin polarization are studied.PACS numbers: 87.14.gk, 87.15.Pc, Molecular spintronics, by combining molecular electronics with spintronics to manipulate the transport of electron spins in organic molecular systems, is regarded as one of the most promising research fields and is now attracting extensive interest [1][2][3][4], owing to the long spin relaxation time and the flexibility of organic materials. Unconventional magnetic properties of molecular systems reported in organic spin valves and magnetic tunnel junctions, are attributed to the hybrid states in the organicmagnetic interfaces [5][6][7][8][9] and to single-molecule magnet [4]. Organic molecules would not be suitable candidates for spin-selective transport because of their nonmagnetic properties and weak spin-orbit coupling (SOC) [10].However, very recently, Göhler et al. reported the spin selectivity of photoelectron transmission through selfassembled monolayers of double-stranded DNA (dsDNA) deposited on gold substrate [11]. They found that wellorganized monolayers of the dsDNA act as very efficient spin filters with high spin polarization at room temperature for long dsDNA, irrespective of the polarization of the incident light. The spin filtration efficiency increases with increasing length of the dsDNA and contrarily no spin polarization could be observed for single-stranded DNA (ssDNA). These results were further substantiated by direct charge transport measurements of single ds-DNA connected between two leads [12]. Although several theoretical models were put forward to investigate the spin-selective properties of DNA molecule based on single helical chain-induced Rashba SOC [13,14], the models neglect the double helix feature of the dsDNA and are somewhat inconsistent with the experimental results that the ssDNA could not be a spin filter. Until now the underlying physical mechanism remains unclear for high spin selectivity observed in the dsDNA [15,16].In this Letter, a model Hamiltonian, including the small environment-induced dephasing, the weak SOC, and the helical symmetry, is proposed to investigate the quantum spin transport through the ssDNA and dsDNA connected to nonmagnetic leads. We interpret the experimental results that the electrons transmitted through the dsDNA exhibit high spin polarization, the spin filtration efficiency will be enhanced by increasing the DNA length, and no spin polarization appears for the ssDNA. The physical mechanism arises from the combination of the dephasing, the S...

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“…By taking a unitary transformation with the operator U (l) = e (imα/ 2 ) l σ ⊥ dl [24], H ss is transformed into…”

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confidence: 99%

Spin-Selective Transport of Electrons in DNA Double Helix

Guo¹,

Sun²

2012

Phys. Rev. Lett.

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307

476

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“…It is realized, when the ratio of QPC length to width L/W ≈ 1 and the QPC confinement energy (in our case in z-direction) is comparable to the spin splitting energy introduced by the Rashba effect. The Rashba effect inside QPCs is then written in the form of tight-binding Hamiltonian [6] as two hopping matrix elements between the dot and the leads: t α -"direct", spin-conserved tunneling and t α SO -"indirect" spin-flip tunneling, mediated by inter-subband mixing:…”

Section: Modelmentioning

confidence: 99%

Spin Dependent Fano Resonances in a Rashba System with Coulomb Interactions

Stefański

2011

Acta Phys. Pol. A

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The effects of interplay of interference of quantum mechanical electron waves and their mutual Coulomb interactions are investigated in the device composed of interacting quantum dot attached to polarized leads via quantum point contacts with the Rashba interaction. The Zeeman-split dot sub-levels form two interfering channels and as a result spin dependent Fano resonances arise in the conductance through the system. The Coulomb repulsion between the channels modifies the width and shape of the Fano resonances as compared to the non-interacting case. We formulate the Fano expression dependent on the dot's occupancy regulated by the Coulomb interactions.

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“…It is then convenient to eliminate the a x -term by a unitary transformation on the dot fermions [20],…”

Section: Modelmentioning

confidence: 99%