Chiral molecular films as electron polarizers and polarization modulators

We report on spin transport along double-helical molecular systems by considering various contact configurations and asymmetries between the two helical strands in the regime of completely coherent charge transport. Our results reveal that no spin polarization appears in two-terminal molecular devices when coupled to one-dimensional electrodes. The same holds in the case of finite-width electrodes if there is a bottleneck of one single site in the system electrode-molecule-electrode. Then, additional dephasing is necessary to induce spin-filtering effects. In contrast, nonzero spin polarization is found in molecular devices with multiple terminals or with two finite-width electrodes, each of them connected to more than one site of the molecule. The magnitude of spin polarization can be enhanced by increasing the asymmetry between the two strands. We point out that the spin-filtering effects could emerge in double-helical molecular devices at low temperature without dephasing by a proper choice of the electrode number and the connection between the molecule and the electrodes.

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“…These studies were extended in Ref. [11] to include decoherence effects within the framework of scattering theory.…”

Section: Introductionmentioning

confidence: 99%

Contact effects in spin transport along double-helical molecules

et al. 2014

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“…Additionally, the CISS effect opens new opportunities for using chiral molecules in spintronic applications and could provide a deeper understanding of the spin effects in biological processes. For the above reasons, there has been considerable interest in the spin transport along various chiral systems including dsDNA (8)(9)(10)(11), single-stranded DNA (ssDNA) (12)(13)(14)(15), and carbon nanotubes (16). However, no spin selectivity was measured in the ssDNA above the experimental noise (5).…”

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confidence: 99%

Spin-dependent electron transport in protein-like single-helical molecules

Guo

Sun

2014

Proc. Natl. Acad. Sci. U.S.A.

198

249

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We report on a theoretical study of spin-dependent electron transport through single-helical molecules connected by two nonmagnetic electrodes, and explain the experiment of significant spin-selective phenomenon observed in α-helical protein and the contradictory results between the protein and single-stranded DNA. Our results reveal that the α-helical protein is an efficient spin filter and the spin polarization is robust against the disorder. These results are in excellent agreement with recent experiments [Mishra D, et al. (2013) S pintronics is a multidisciplinary field that manipulates the electron spin transport in solid-state systems and has been receiving much attention among the physics, chemistry, and biology communities (1-4). Recent experiments have made significant progress in this research field, finding that doublestranded DNA (dsDNA) molecules are highly efficient spin filters (5-7). This chiral-induced spin selectivity (CISS) is surprising because the DNA molecules are nonmagnetic and their spin-orbit couplings (SOCs) are small. Additionally, the CISS effect opens new opportunities for using chiral molecules in spintronic applications and could provide a deeper understanding of the spin effects in biological processes. For the above reasons, there has been considerable interest in the spin transport along various chiral systems including dsDNA (8-11), single-stranded DNA (ssDNA) (12-15), and carbon nanotubes (16). However, no spin selectivity was measured in the ssDNA above the experimental noise (5).Very recently, spin-dependent electron transmission and electrochemical experiments were performed on bacteriorhodopsinan α-helical protein of which the structure is single helicalembedded in purple membrane which was physisorbed on a variety of substrates (17). It was reported by means of two distinct techniques that the electrons transmitted through the membrane are spin polarized, independent of the experimental environments, implying that this α-helical protein can exhibit the ability of spin filtering. Meanwhile, a chiral-based magnetic memory device was fabricated by using self-assembled monolayer of another α-helical protein called polyalanine (18). All of these results seem to be inconsistent with previous experiments' conclusions that the single-stranded helical molecules, such as ssDNA, may not polarize the electrons (5). We note that the electron transport/transfer has been widely investigated in many proteins (19)(20)(21)(22)(23)(24)(25)(26). However, to our knowledge, the underlying physics is still unclear for spin-selective phenomenon observed in the α-helical protein and for the contradictory behaviors between the protein and the ssDNA.In this paper, we propose a model Hamiltonian to explore the spin transport through single-helical molecules connected by two nonmagnetic electrodes, and provide an unambiguous physical mechanism for efficient spin selectivity observed in the protein and for the contrary experimental results between the protein and the ssDNA. Our results reveal that t...

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“…Studies based on scattering theory at the level of the Born approximation, 16,17 including spin-orbit coupling (SOC) derived from a helically shaped potential. This approach can be closely related to the experiments in Ref.…”

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confidence: 99%

Modeling Spin Transport in Helical Fields: Derivation of an Effective Low-Dimensional Hamiltonian

et al. 2013

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This study is devoted to a consistent derivation of an effective model Hamiltonian to describe spin transport along a helical pathway and in presence of spin-orbit interaction, the latter being induced by an external field with helical symmetry. It is found that a sizeable spin polarization of an unpolarized incoming state can be obtained without introducing phase breaking processes. For this, at least two energy levels per lattice site in the tight-binding representation are needed. Additionally, asymmetries in the effective electronic-coupling parameters as well as in the spin-orbit interaction strength must be present to achieve net polarization. For a fully symmetric system -in terms of electronic and spin-orbit couplings-no spin polarization is found. The model presented is quite general and is expected to be of interest for the treatment of spindependent effects in molecular scale systems with helical symmetry.

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Chiral molecular films as electron polarizers and polarization modulators

Cited by 137 publications

References 17 publications

Contact effects in spin transport along double-helical molecules

Contact effects in spin transport along double-helical molecules

Spin-dependent electron transport in protein-like single-helical molecules

Modeling Spin Transport in Helical Fields: Derivation of an Effective Low-Dimensional Hamiltonian

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