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

Abstract

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...

Spin filtering in all-electrical three-terminal interferometers

“…This description of the helical molecule is similar to that investigated in previous works 38,39,44,45 in a two-terminal geometry, where TRS or unitraity is effectively broken, as discussed in Sec. I.…”

Spin dynamics in helical molecules with nonlinear interactions

“…A number of theoretical models have been put forward to explain the observed spin selectivity in helical molecules. Usually they rely on large SOC [4][5][6][7][8][9][10][11][12], the need for dephasing when SOC is weak [13,14], the leakage of electrons from the molecule to the environment [15], the role of the bonding of the molecule to the metallic leads that enhance the effect [16,17], or the interplay between a helicity-induced SOC and a strong dipole electric field, which is characteristic of these molecules [18] (see [19,20] for a recent review). Theoretical models usually assume rigid lattices and neglect the local deformation of the molecule about the carrier.…”

Spin-Current Induced Mechanical Torque in a Chiral Molecular Junction

“…Our calculations are performed for the range 0.01 ∼ 0.6 of α values, which are about four orders of magnitude larger. It is customary 13,14 to adopt such values for the analysis of the effect of the chiral-induced spin selectivity. 43 Figure 7 (b) exhibits the energy dependence of the spin-resolved conductance for N mol = 23 when an unpolarized electron is injected.…”

“…8,10 Since such organic molecules do not contain magnetic atoms, it has been suggested that the only possible origin of the CISS effect would be the SOI. In recent theoretical studies, the underlying physical mechanism of the spin polarization are studied for a double-stranded DNA 12 and for single-stranded molecules, 13,14 using the tight-binding model with Rashba-like SOI. Moreover, a minimal realistic model accounting for the nature of porbitals are shown to exhibit possible CISS effect.…”

“…Assuming for simplicity that the system is at zero temperature, we derive a continuity equation for the spin, based on a microscopic model Hamiltonian for chiral molecules introduced in previous publications. [12][13][14] At steady state, this equation relates the spin current to the mechanical torque acting on the chiral molecule. The dependence of this mechanical torque on the parameters of the molecule is the central issue of our discussion.…”