Recent observations of considerable spin polarization in photoemission from metal surfaces through monolayers of chiral molecules were followed by several efforts to rationalize the results as the effect of spin-orbit interaction that accompanies electronic motion on helical, or more generally strongly curved, potential surfaces. In this paper we (a) argue, using simple models, that motion in curved force-fields with the typical energies used and the characteristic geometry of DNA cannot account for such observations; (b) introduce the concept of induced spin filtering, whereupon selectivity in the transmission of the electron orbital angular momentum can induce spin selectivity in the transmission process provided there is strong spin-orbit coupling in the substrate; and (c) show that the spin polarizability in the tunneling current as well as the photoemission current from gold covered by helical adsorbates can be of the observed order of magnitude. Our results can account for most of the published observations that involved gold and silver substrates, however recent results obtained with an aluminum substrate can be rationalized within the present model only if strong spin-orbit coupling is caused by the built-in electric field at the molecule-metal interface.
We present a theoretical study, based on density functional theory and tight binding modeling, of the electronic structure and spin transport properties of silicon nanoparticles with adsorbed bismuth atoms. We find the bismuth atoms to form clusters separated by quantum tunnel barriers. We predict strong spin filtering by these nanostructures in the high conductance regime when the source and drain leads are connected to the same bismuth cluster and in the low conductance regime when the source and drain leads are connected to different bismuth clusters. We relate the spin filtering to a symme…
Interplay between motion of nuclei and excited electrons in molecules plays a key role both in biological and artificial nanomachines. Here we provide a detailed analysis of coupling between quantized librational modes (librons) and charged excited states (trions) on single phthalocyanine dyes adsorbed on a surface. By means of tunnelling electron-induced electroluminescence, we identify libronic progressions on a μeV energy range in spectra of chirally adsorbed phthalocyanines, which are otherwise absent from spectra of symmetrically adsorbed species. Experimentally measured libronic spectra …
Polyalanine molecules (PA) with an α-helix conformation gathered recently a lot of interest as the propagation of electrons through the chiral backbone structure comes along with spin polarization of the transmitted electrons. By means of scanning tunneling microscopy and spectroscopy at ambient conditions, PA molecules adsorbed on surfaces of epitaxial magnetic Al2O3/Pt/Au/Co/Au nanostructures with perpendicular anisotropy were studied. Thereby, a correlation between the PA molecules ordering at the surface with the electron tunneling across this hybrid system as a function of the substrate m…
Using first-principles calculations, we investigate the electronic structures and binding properties of nicotine and caffeine adsorbed on single-walled carbon nanotubes to determine whether CNTs are appropriate for filtering or sensing nicotine and caffeine molecules. We find that caffeine adsorbs more strongly than nicotine. The different binding characteristics are discussed by analyzing the modification of the electronic structure of the molecule-adsorbed CNTs. We also calculate the quantum conductance of the CNTs in the presence of nicotine or caffeine adsorbates and demonstrate that the i…
When an electron passes through a chiral molecule there is a high probability for a correlation between the momentum and spin of the charge, thus leading to spin polarized current. This phenomenon is known as the chiral induced spin selectivity (CISS) effect. One of the most surprising experimental results recently demonstrated is that magnetization reversal in a ferromagnet (FM) with perpendicular anisotropy can be realized solely by chemisorbing a chiral molecular monolayer without applying any current or external magnetic field. This result raises the currently open question of whether this…
The spintronic properties of curved nanostructures derived from two-dimensional topological insulators (2DTI's) are explored theoretically with density functional theory-based (DFT) calculations and tight-binding models. We show that curved geometries make it possible to manipulate electron spins in ways that are not available for planar 2DTI devices. We predict that, unlike planar 2DTI devices, curved 2DTI-related nanostructures can function as highly effective {\em two}-terminal spin filters even in the absence of magnetic fields. We construct a generalization to curved geometries of our pre…
We analyze the problem of electronic transmission through different regions of a graphene sheet that are characterized by different types of connections between the Dirac points. These valley symmetry breaking Hamiltonians might arise from electronic self-interaction mediated by the dielectric environment of distinct parts of the substrate on which the graphene sheet is placed. We show that it is possible to have situations in which we can use these regions to select or filter states of one desired chirality.
Spin filtering is an essential operation in spintronics that allows creation and detection of spin polarized carriers. Transition metal ferromagnets are used as spin filters in most cases, though their spin filtering efficiency is only around ~50%, thereby limiting the efficiency of spintronic devices. Recently, chiral systems such as DNA have been shown to exhibit efficient spin filtering, a phenomenon often dubbed as "chirality induced spin selectivity" (CISS). In this work, we consider single wall carbon nanotubes helically wrapped with single stranded poly-T DNA. By magnetoresistance measu…
We theoretically analyze spin filtering in two-terminal systems, induced by the spin-orbit interaction (SOI), as a possible origin of the ``chirality-induced spin selectivity'' (CISS) effect observed experimentally in chiral molecules, such as DNA. Due to Bardarson's theorem, spin filtering cannot be realized in a molecule containing one orbital-channel. However, when two orbitals are involved, SOI can induce spin filtering in a molecule coupled to two terminals without braking time-reversal symmetry. In particular, we provide an example of a $4 \times 4$ reflection matrix for a spinful electr…
Non-equilibrium angular momentum selectivity and filtering in chiral carbon nanotubes
School of Engineering, Mackenzie Presbyterian University（麦肯锡福音大学工程学院）；MackGraphe Graphene and Nanomaterials Research Institute, Mackenzie Presbyterian University（麦肯锡福音大学MackGraphe石墨烯与纳米材料研究所）；Departamento de Física, Universidade Federal do Ceará（塞阿拉联邦大学物理系）
The functionality of many biological systems depends on reliable electron transfer with minimal heating. Unlike man-made electric circuits, nature realizes electron transport via insulating chiral molecules. Here we include spin into the analysis of tunneling through these molecules, and demonstrate its importance for efficient transport. We show that the helical geometry induces robust spin filtering accompanied by, and intimately related to, strongly enhanced transmission. Thus, we resolve two key questions posed by transport measurements through organic molecules, demonstrating their common…
Chiral-induced spin selectivity (CISS), whereby helical molecules polarize the spin of electrical current, is an intriguing effect with potential applications in nanospintronics. In this nascent field, the study of paramagnetic chiral molecules, which could introduce another degree of freedom in the control of the spin transport, remains so far unexplored. To address this challenge, herein, we propose the use of self-assembled monolayers of helical lanthanide-binding peptides. In order to elucidate the effect of the paramagnetic nuclei, monolayers of the peptide coordinating paramagnetic or di…
We show that the interplay between chiral tunneling and spin-momentum locking of helical surface states leads to spin amplification and filtering in a 3D Topological Insulator (TI). Chiral tunneling across a TI pn junction allows normally incident electrons to transmit, while the rest are reflected with their spins flipped due to spin-momentum locking. The net result is that the spin current is enhanced while the dissipative charge current is simultaneously suppressed, leading to an extremely large, gate tunable spin to charge current ratio (~20) at the reflected end. At the transmitted end, t…
Spin-momentum locking in topological insulators and materials with Rashba-type interactions is an extremely attractive feature for novel spintronic devices and is therefore under intense investigation. Significant efforts are underway to identify new material systems with spin-momentum locking, but also to create heterostructures with new spintronic functionalities. In the present study we address both subjects and investigate a van der Waals-type heterostructure consisting of the topological insulator Bi$_{2}$Se$_{3}$ and a single Se-Ta-Se triple-layer (TL) of H-type TaSe$_{2}$ grown by a nov…
Unlike the two-terminal device, in which the time-reversal invariant spin-orbit interaction alone cannot polarize the spins, such a polarization can be generated when electrons from one source reservoir flow into two (or more) separate drain reservoirs. We present analytical solutions for two examples. First, we demonstrate that the electrons transmitted through a "diamond" interferometer into two drains can be simultaneously fully spin-polarized along different tunable directions, even when the two arms of the interferometer are not identical. Second, we show that a single helical molecule at…
Singlet fission (SF) process, where a singlet exciton decays into a pair of spin one exciton states which are in the total spin singlet state, is one of the possible channels for multiple exciton generation (MEG). In chiral single-wall carbon nanotubes (SWCNTs) efficient SF is present within the solar spectrum energy range which is shown by the many-body perturbation theory (MBPT) calculations based on the density functional theory (DFT) simulations. We calculate SF exciton-to-biexction decay rates ${\rm R}_{1\to 2}$ and biexciton-to-exction rates ${\rm R}_{2\to1}$ in the (6,2), (6,5), (10,5) …
We analyze spin scattering in ballistic transport of electrons through a ripple at a normal incidence of an electron flow. The model of a ripple consists of a curved graphene surface in the form of an arc of a circle connected from the left-hand and right-hand sides to two flat graphene sheets. At certain conditions the curvature induced spin-orbit coupling creates a transparent window for incoming electrons with one spin polarization simultaneously with a backscattering of those with opposite polarization. This window is equally likely transparent for electrons with spin up and spin down that…
Characterizing distinct electron wave packets is a basic task for solid-state electron quantum optics with applications in quantum metrology and sensing. A important circuit element for this task is a non-stationary potential barrier than enables backscattering of chiral particles depending on their energy and time of arrival. Here we solve the quantum mechanical problem of single-particle scattering by a ballistic constriction in an fully depleted quantum Hall system under spatially uniform but time-dependent electrostatic potential modulation. The result describes electrons distributed in ti…
The strength of the spin-orbit interaction relevant to transport in a low dimensional structure depends critically on the relative geometrical arrangement of current carrying orbitals. Recent tight-binding orbital models for spin transport in DNA-like molecules, have surmised that the band spin-orbit coupling arises from the particular angular relations between orbitals of neighboring bases on the helical chain. Such arrangement could be probed by inducing deformations in the molecule in a conductive probe AFM type setup, as it was recently reported by Kiran, Cohen and Naaman\cite{Kiran}. Here…
The adsorption of the chiral molecule lactate on the intrinsically chiral noble metal surfaces Pt(321), Au(321) and Ag(321) is studied by Density Functional Theory calculations. We use the oPBE-vdW functional which includes van der Waals forces on an ab initio level. It is shown that the molecule binds via its carboxyl and the hydroxyl oxygen atoms to the surface. The binding energy is larger on Pt(321) and Ag(321) than on Au(321). An analysis of the contributions to the binding energy of the different molecular functional groups reveals that the deprotonated carboxyl group contributes most to…
Conformational isomers are stereoisomers that can interconvert over low potential barriers by rotation around a single bond. However, such bond rotation is hampered by geometrical constraints when molecules are adsorbed on surfaces. Here we show that the adsorption of 4,4'-bis(4-carboxyphenyl)-6,6'-dimethyl-2,2'-bipyridine molecules on surfaces leads to the appearance of pro-chiral single-molecules on NiO(001) and to enantiopure supramolecular domains on Au(111) surfaces containing the $transoid$ molecule conformation. Upon additional Fe adatom deposition, molecules undergo a controlled interc…
Interplay of spin-orbit coupling and magnetic chirality: Multidirectional spin polarization in a helical antiferromagnet
School of Vocational Studies and Applied Sciences, Gautam Buddha University（古特木佛陀大学职业与应用科学学院）；Department of Physics, Adamas University（亚当斯大学物理系）；Physics and Applied Mathematics Unit, Indian Statistical Institute（印度统计学院物理与应用数学单元）
Complex oxide heterointerfaces and van der Waals heterostructures present two versatile but intrinsically different platforms for exploring emergent quantum phenomena and designing new functionalities. The rich opportunity offered by the synergy between these two classes of materials, however, is yet to be charted. Here, we report an unconventional nonlinear optical filtering effect resulting from the interfacial polar alignment between monolayer MoS$_2$ and a neighboring ferroelectric oxide thin film. The second harmonic generation response at the heterointerface is either substantially enhan…
Non-collinear chiral antiferromagnets like Mn3Sn and Mn3Ge are known to show gigantic anomalous Hall response depending on the orientation of their inverse chiral magnetic order of Mn atoms in Kagome layers. Here we study the stability of such magnetic order in the absence of external magnetic fields on the basis of stochastic Landau-Lifshitz-Gilbert equation for a simplified two-dimensional model of these materials. We find that even without external magnetic fields, the ordered state is, once formed, highly stable against thermal fluctuations. Moreover, we show that if Mn spins are well conf…
Nature creates electrons with two values of the spin projection quantum number. In certain applications, it is important to filter electrons with one spin projection from the rest. Such filtering is not trivial, since spin-dependent interactions are often weak, and cannot lead to any substantial effect. Here we propose an efficient spin filter based upon scattering from a two-dimensional crystal, which is made of aligned point magnets. The polarization of the outgoing electron flux is controlled by the crystal, and reaches maximum at specific values of the parameters. In our scheme, polarizati…
Motivated by the discovery of the quantum anomalous Hall effect in Cr-doped \ce{(Bi,Sb)2Te3} thin films, we study the generic states for magnetic topological insulators and explore the physical properties for both magnetism and itinerant electrons. First-principles calculations are exploited to investigate the magnetic interactions between magnetic Co atoms adsorbed on the \ce{Bi2Se3} (111) surface. Due to the absence of inversion symmetry on the surface, there are Dzyaloshinskii-Moriya-like twisted spin interactions between the local moments of Co ions. These nonferromagnetic interactions twi…
