Unusual Spin Polarization in the Chirality-Induced Spin Selectivity

Single-molecule junctions map the interplay between electrons and chirality

The interplay of electrons with a chiral medium has a diverse impact across science and technology, influencing drug separation, chemical reactions, and electronic transport1-30. In particular, electron-chirality interactions can significantly affect charge and spin transport in chiral conductors, making them highly appealing for spintronics. However, an atomistic mapping of different electron-chirality interactions remains elusive. Here, we find that helicene-based single-molecule junctions behave as a combined magnetic-diode and spin-valve device. This dual-functionality enables the identification of an atomic-scale coexistence of different electron-chirality interactions: the magnetic-diode behavior is attributed to an interaction between electron's angular momentum in a chiral medium and magnetic fields, whereas the spin-valve functionality is ascribed to an interaction between the electron's spin and a chiral medium. This work uncovers the coexistence of electron-chirality interactions at the atomic-scale, identifies their distinct properties, and demonstrates how integrating their functionalities can broaden of the available methods for spintronics.

Magnetochiral charge pumping due to charge trapping and skin effect in chirality-induced spin selectivity

Chirality-induced spin selectivity (CISS) generates giant spin polarization in transport through chiral molecules, paving the way for novel spintronic devices and enantiomer separation. Unlike conventional transport, CISS magnetoresistance (MR) violates Onsager's reciprocal relation, exhibiting significant resistance changes when reversing electrode magnetization at zero bias. However, its underlying mechanism remains unresolved. In this work, we propose that CISS MR originates from charge trapping that modifies the electron tunneling barrier and circumvents Onsager's relation, distinct from previous spin polarization-based models. Charge trapping is governed by the non-Hermitian skin effect, where dissipation leads to exponential wavefunction localization at the ferromagnet-chiral molecule interface. Reversing magnetization or chirality alters the localization direction, changing the occupation of impurity/defect states in the molecule (i.e., charge trapping) - a phenomenon we term magnetochiral charge pumping. Our theory explains why CISS MR can far exceed the ferromagnet spin polarization and why chiral molecules violate the reciprocal relation but chiral metals do not. Furthermore, it predicts exotic phenomena beyond the conventional CISS framework, including asymmetric MR induced by magnetic fields alone (without ferromagnetic electrodes), as confirmed by recent experiments. This work offers a deeper understanding of CISS and opens avenues for controlling electrostatic interactions in chemical and biological systems through the magnetochiral charge pumping.

Spin conductances and magnetization production in chiral molecular junctions

Motivated by experimental reports on chirality induced spin selectivity, we investigate a minimal model that allows us to calculate the charge and spin conductances through helical molecules analytically. The spin-orbit interaction is assumed to be non-vanishing on the molecule and negligible in the reservoirs (leads). The band structure of the molecule features four helical modes with spin-momentum locking that are analogous of edge-currents in the quantum spin Hall effect. While charge is conserved and therefore the charge current is independent of where it is measured-reservoirs or molecule-our detailed calculations reveal that the spin currents in the left and right leads are equal in magnitudes but with opposite signs (in linear response). We predict that transport currents flowing through helical molecules are accompanied by a spin accumulation in the contact region with the same magnetization direction for source and drain. Furthermore, we predict that the spin-conductance can be extracted directly from measuring the (quasi-static) spin accumulation-rather than the spin current itself, which is very challenging to obtain experimentally.

Transverse Spin Selectivity in Helical Nanofibers Prepared without Any Chiral Molecule

In the last decade, chirality-induced spin selectivity (CISS) has undergone intensive study. However, there remain several critical issues, such as the microscopic mechanism of CISS, especially transverse CISS where electrons are injected perpendicular to the helix axis of chiral molecules, quantitative agreement between experiments and theory, and at which level the molecular handedness is key to the CISS. Here, we address these issues by performing a combined experimental and theoretical study on conducting polyaniline helical nanofibers which are synthesized in the absence of any chiral species. Large spin polarization is measured in both left- and right-handed nanofibers for electrons injected perpendicular to their helix axis, and it will be reversed by switching the nanofiber handedness. We first develop a theoretical model to study this transverse CISS and quantitatively explain the experiment. Our results reveal that our theory provides a unifying scheme to interpret a number of CISS experiments, quantitative agreement between experiments and numerical calculations can be achieved by weak spin-orbit coupling, and the supramolecular handedness is sufficient for spin selectivity without any chiral species.

A chemical perspective on the chiral induced spin selectivity effect

This review discusses opportunities in chemistry that are enabled by the chiral induced spin selectivity (CISS) effect. First, the review begins with a brief overview of the seminal studies on CISS. Next, we discuss different chiral material systems whose properties can be tailored through chemical means, with a special emphasis on hybrid organic-inorganic layered materials that exhibit some of the largest spin filtering properties to date. Then, we discuss the promise of CISS for chemical reactions and enantioseparation before concluding.

Magneto-electrochemical method for chiral recognition of amino acid enantiomers

Chiral recognition of enantiomers with identical mirror-symmetric molecular structures is important for the analysis of biomolecules, and it conventionally relies on stereoselective interactions in chiral chemical environments. Here, we develop a magneto-electrochemical method for the enhanced detection of chiral amino acids (AAs), that combines the advantages of the high sensitivity of electrochemiluminescent (ECL) biosensors and chirality-induced effects under a magnetic field. The ECL difference between L- and D-enantiomers can be amplified over 35-fold under a field of 3.5 kG, and the chiral discrimination can be achieved in dilute AA solutions down to the nM level. The field-dependent ECL and chronocoulometry measurements suggest that chiral AAs can lock the spins on their radicals and thus enlarge the ECL change under applied magnetic fields (magneto-ECL, MECL), which explains the field-enhanced chiral discrimination of AA enantiomers. Finally, a detailed protocol is demonstrated for the identification of unknown AA solutions, in which the species, chirality and concentration of AAs can be determined simultaneously from the 2D plots of the ECL and MECL results. This work benefits the development of field-assisted detection methods and represents a promising and universal strategy for the comprehensive analysis of chiral biomolecules.

Chiral multiferroicity in two-dimensional hybrid organic-inorganic perovskites

Chiral multiferroics offer remarkable capabilities for controlling quantum devices at multiple levels. However, these materials are rare due to the competing requirements of long-range orders and strict symmetry constraints. In this study, we present experimental evidence that the coexistence of ferroelectric, magnetic orders, and crystallographic chirality is achievable in hybrid organic-inorganic perovskites [(R/S)-β-methylphenethylamine]2CuCl4. By employing Landau symmetry mode analysis, we investigate the interplay between chirality and ferroic orders and propose a novel mechanism for chirality transfer in hybrid systems. This mechanism involves the coupling of non-chiral distortions, characterized by defining a pseudo-scalar quantity, ξ = p ⋅ r ( p represents the ferroelectric displacement vector and r denotes the ferro-rotational vector), which distinguishes between (R)- and (S)-chirality based on its sign. Moreover, the reversal of this descriptor's sign can be associated with coordinated transitions in ferroelectric distortions, Jahn-Teller antiferro-distortions, and Dzyaloshinskii-Moriya vectors, indicating the mediating role of crystallographic chirality in magnetoelectric correlations.

Structural and Electronic Chirality in Inorganic Crystals: from Construction to Application

Chirality represents a fundamental characteristic inherent in nature, playing a pivotal role in the emergence of homochirality and the origin of life. While the principles of chirality in organic chemistry are well-documented, the exploration of chirality within inorganic crystal structures continues to evolve. This ongoing development is primarily due to the diverse nature of crystal/amorphous structures in inorganic materials, along with the intricate symmetrical and asymmetrical relationships in the geometry of their constituent atoms. In this review, we commence with a summary of the foundational concept of chirality in molecules and solid states matters. This is followed by an introduction of structural chirality and electronic chirality in three-dimensional and two-dimensional inorganic materials. The construction of chirality in inorganic materials is classified into physical photolithography, wet-chemistry method, self-assembly, and chiral imprinting. Highlighting the significance of this field, we also summarize the research progress of chiral inorganic materials for applications in optical activity, enantiomeric recognition and chiral sensing, selective adsorption and enantioselective separation, asymmetric synthesis and catalysis, and chirality-induced spin polarization. This review aims to provide a reference for ongoing research in chiral inorganic materials and potentially stimulate innovative strategies and novel applications in the realm of chirality.

Colossal anisotropic absorption of spin currents induced by chirality

The chiral induced spin selectivity (CISS) effect, in which the structural chirality of a material determines the preference for the transmission of electrons with one spin orientation over that of the other, is emerging as a design principle for creating next-generation spintronic devices. CISS implies that the spin preference of chiral structures persists upon injection of pure spin currents and can act as a spin analyzer without the need for a ferromagnet. Here, we report an anomalous spin current absorption in chiral metal oxides that manifests a colossal anisotropic nonlocal Gilbert damping with a maximum-to-minimum ratio of up to 1000%. A twofold symmetry of the damping is shown to result from differential spin transmission and backscattering that arise from chirality-induced spin splitting along the chiral axis. These studies reveal the rich interplay of chirality and spin dynamics and identify how chiral materials can be implemented to direct the transport of spin current.

Hybrid mesoporous electrodes evidence CISS effect on water oxidation

Controlling product selectivity is essential for improving the efficiency of multi-product reactions. Electrochemical water oxidation is a reaction of main importance in different applications, e.g., renewable energy schemes and environmental protection, where H2O2 and O2 are the two principal products. In this Communication, the product selectivity of electrochemical water oxidation was controlled by making use of the chiral induced spin selectivity (CISS) effect at mesoporous-TiO2 on the molecule-modified Au substrate. Our results show a decrease in H2O2 formation when using chiral hetero-helicene molecules adsorbed on the Au substrate. We propose a mechanism for this kinetic effect based on the onset of CISS-induced spin polarization on the Au-helicene chiral interface. We also present a new tunable substrate to investigate the CISS mechanism.

Wireless Magnetoelectrochemical Induction of Rotational Motion

Electromagnetically induced rotation is a key process of many technological systems that are used in daily life, especially for energy conversion. In this context, the Lorentz force-induced deviation of charges is a crucial physical phenomenon to generate rotation. Herein, they combine the latter with the concept of bipolar electrochemistry to design a wireless magnetoelectrochemical rotor. Such a device can be considered as a wet analog of a conventional electric motor. The main driving force that propels this actuator is the result of the synergy between the charge-compensating ion flux along a bipolar electrode and an external magnetic field applied orthogonally to the surface of the object. The trajectory of the wirelessly polarized rotor can be controlled by the orientation of the magnetic field relative to the direction of the global electric field, producing a predictable clockwise or anticlockwise motion. Fine-tuning of the applied electric field allows for addressing conducting objects having variable characteristic lengths.

Mechanism for Electrostatically Generated Magnetoresistance in Chiral Systems without Spin-Dependent Transport

Significant attention has been drawn to electronic transport in chiral materials coupled to ferromagnets in the chirality-induced spin selectivity (CISS) effect. A large magnetoresistance (MR) is usually observed, which is widely interpreted to originate from spin (dependent) transport. However, there are severe discrepancies between the experimental results and the theoretical interpretations, most notably the apparent failure of the Onsager reciprocity relations in the linear response regime. We provide an alternative mechanism for the two terminal MR in chiral systems coupled to a ferromagnet. For this, we point out that it was observed experimentally that the electrostatic contact potential of chiral materials on a ferromagnet depends on the magnetization direction and chirality. The mechanism that we provide causes the transport barrier to be modified by the magnetization direction, already in equilibrium, in the absence of a bias current. This strongly alters the charge transport through and over the barrier, not requiring spin transport. This provides a mechanism that allows the linear response resistance to be sensitive to the magnetization direction and also explains the failure of the Onsager reciprocity relations. We propose experimental configurations to confirm our alternative mechanism for MR.

Spin-Dependent Destructive and Constructive Quantum Interference Associated with Chirality-Induced Spin Selectivity in Single Circular Helix Molecules

Chirality-induced spin selectivity (CISS) effect in straight helical molecules has received intense studies in past decade; however, the CISS effect in circular helical molecules (CHMs) has still rarely been explored. Here, we have constructed single CHMs having chirality-induced spin-orbit coupling (SOC) and connected by two nonmagnetic leads and successfully gained the required conditions for CISS effect occurring in CHMs for the first time. Our results uncover that only when the CHMs form a closed loop and when the lattice positions are coupled asymmetrically with both leads does the CISS effect occur. More importantly, the CISS-associated spin-dependent destructive and constructive quantum interference (QI) together with their phase transition appears in CHMs. The combination of CISS effect and spin-dependent QI phenomena opens up a new door to understand the underlying physics of the CISS effect in helical molecules.

Monopole-like orbital-momentum locking and the induced orbital transport in topological chiral semimetals

The interplay between chirality and topology nurtures many exotic electronic properties. For instance, topological chiral semimetals display multifold chiral fermions that manifest nontrivial topological charge and spin texture. They are an ideal playground for exploring chirality-driven exotic physical phenomena. In this work, we reveal a monopole-like orbital-momentum locking texture on the three-dimensional Fermi surfaces of topological chiral semimetals with B20 structures (e.g., RhSi and PdGa). This orbital texture enables a large orbital Hall effect (OHE) and a giant orbital magnetoelectric (OME) effect in the presence of current flow. Different enantiomers exhibit the same OHE which can be converted to the spin Hall effect by spin-orbit coupling in materials. In contrast, the OME effect is chirality-dependent and much larger than its spin counterpart. Our work reveals the crucial role of orbital texture for understanding OHE and OME effects in topological chiral semimetals and paves the path for applications in orbitronics, spintronics, and enantiomer recognition.

Magnetic field-enhanced redox chemistry on-the-fly for enantioselective synthesis

Chemistry on-the-fly is an interesting concept, extensively studied in recent years due to its potential use for recognition, quantification and conversion of chemical species in solution. In this context, chemistry on-the-fly for asymmetric synthesis is a promising field of investigation, since it can help to overcome mass transport limitations, present for example in conventional organic electrosynthesis. Herein, the synergy between a magnetic field-enhanced self-electrophoretic propulsion mechanism and enantioselective redox chemistry on-the-fly is proposed as an efficient method to boost stereoselective conversion. We employ Janus swimmers as redox-active elements, exhibiting a well-controlled clockwise or anticlockwise motion with a speed that can be increased by one order of magnitude in the presence of an external magnetic field. While moving, these bifunctional objects convert spontaneously on-the-fly a prochiral molecule into a specific enantiomer with high enantiomeric excess. The magnetic field-enhanced self-mixing of the swimmers, based on the formation of local magnetohydrodynamic vortices, leads to a significant improvement of the reaction yield and the conversion rate.

Spin-Selective Oxygen Evolution Reaction in Chiral Iron Oxide Nanoparticles: Synergistic Impact of Inherent Magnetic Moment and Chirality

Electron spin polarization is identified as a promising avenue for enhancing the oxygen evolution reaction (OER), which is the bottleneck that limits the energy efficiency of water-splitting. Here, we report that both ferrimagnetic (f-Fe3O4) and superparamagnetic iron oxide (s-Fe3O4) catalysts can exhibit external magnetic field (Hext)-induced OER enhancement, and the activity is proportional to their intrinsic magnetic moment. Additionally, the chirality-induced spin selectivity (CISS) effect was utilized in synergy with Hext to get a maximum enhancement of up to 89% improvement in current density (at 1.8 V vs RHE) with a low onset potential of 270 mV in s-Fe3O4 catalysts. Spin polarization and the resultant spin selectivity suppress the production of H2O2 and promote the formation of ground state triplet O2 during the OER. Furthermore, the design of chiral s-Fe3O4 with synergistic spin potential effect demonstrates a high spin polarization of ∼42%, as measured using conductive atomic force microscopy (c-AFM).

Achiral dipoles on a ferromagnet can affect its magnetization direction

We demonstrate the possibility of a coupling between the magnetization direction of a ferromagnet and the tilting angle of adsorbed achiral molecules. To illustrate the mechanism of the coupling, we analyze a minimal Stoner model that includes Rashba spin-orbit coupling due to the electric field on the surface of the ferromagnet. The proposed mechanism allows us to study magnetic anisotropy of the system with an extended Stoner-Wohlfarth model and argue that adsorbed achiral molecules can change magnetocrystalline anisotropy of the substrate. Our research aims to motivate further experimental studies of the current-free chirality induced spin selectivity effect involving both enantiomers.

Nonequilibrium Magneto-Conductance as a Manifestation of Spin Filtering in Chiral Nanojunctions

It is generally accepted that spin-dependent electron transmission may appear in chiral systems, even without magnetic components, as long as significant spin-orbit coupling is present in some of its elements. However, how this chirality-induced spin selectivity (CISS) manifests in experiments, where the system is taken out of equilibrium, is still debated. Aided by group theoretical considerations and nonequilibrium DFT-based quantum transport calculations, here we show that when spatial symmetries that forbid a finite spin polarization in equilibrium are broken, a net spin accumulation appears at finite bias in an arbitrary two-terminal nanojunction. Furthermore, when a suitably magnetized detector is introduced into the system, the net spin accumulation, in turn, translates into a finite magneto-conductance. The symmetry prerequisites are mostly analogous to those for the spin polarization at any bias with the vectorial nature given by the direction of magnetization, hence establishing an interconnection between these quantities.

Enantiopure Dinaphtho[2,3-b:2,3-f]thieno[3,2-b]thiophenes: Reaching High Magnetoresistance Effect in OFETs

Chiral molecules are known to behave as spin filters due to the chiral induced spin selectivity (CISS) effect. Chirality can be implemented in molecular semiconductors in order to study the role of the CISS effect in charge transport and to find new materials for spintronic applications. In this study, the design and synthesis of a new class of enantiopure chiral organic semiconductors based on the well-known dinaphtho[2,3-b:2,3-f]thieno[3,2-b]thiophene (DNTT) core functionalized with chiral alkyl side chains is presented. When introduced in an organic field-effect transistor (OFET) with magnetic contacts, the two enantiomers, (R)-DNTT and (S)-DNTT, show an opposite behavior with respect to the relative direction of the magnetization of the contacts, oriented by an external magnetic field. Each enantiomer displays an unexpectedly high magnetoresistance over one preferred orientation of the spin current injected from the magnetic contacts. The result is the first reported OFET in which the current can be switched on and off upon inversion of the direction of the applied external magnetic field. This work contributes to the general understanding of the CISS effect and opens new avenues for the introduction of organic materials in spintronic devices.

A Theoretical Analysis of the Differential Chemical Reaction Results Caused by Chirality Induction

The theory of electron spin has been proposed for a century, but the study of quantum effects in biological molecules is still in its infancy. Chirality-induced spin selectivity (CISS) is a very modern theory that can explain many biochemical phenomena. In this paper, we propose a new theoretical model based on CISS theory and quantum chemistry theory, which can well explain the theoretical explanation of the chiral selectivity of chiral proteins. Moreover, this theory can predict the spin state of corresponding chiral molecules. Taking the L-DOPA and AADC enzymes as examples, this theoretical model elucidates the AADC enzyme's chiral catalysis selectivity and successfully predicts the spin state of L-DOPA and D-DOPA's valence electrons.

Spin-induced electron transmission through metal-organic chiral crystals

Metal-organic Co(II)-phenylalanine crystals were studied and were found to possess magnetic properties and long-range spin transport. Magnetic measurements confirmed that in the crystals there are antiferromagnetic interactions between Co(II) and the lattice. The metal-organic crystals (MOCs) also present the chirality-induced spin selectivity (CISS) effect at room temperature. A long-range spin polarization is observed using a magnetic conductive-probe atomic force microscope. The spin polarization is found to be in the range of 35-45%.

Efficient Spin-Selective Electron Transport at Low Voltages of Thia-Bridged Triarylamine Hetero[4]helicenes Chemisorbed Monolayer

The Chirality Induced Spin Selectivity (CISS) effect describes the capability of chiral molecules to act as spin filters discriminating flowing electrons according to their spin state. Within molecular spintronics, efforts are focused on developing chiral-molecule-based technologies to control the injection and coherence of spin-polarized currents. Herein, for this purpose, we study spin selectivity properties of a monolayer of a thioalkyl derivative of a thia-bridged triarylamine hetero[4]helicene chemisorbed on a gold surface. A stacked device assembled by embedding a monolayer of these molecules between ferromagnetic and diamagnetic electrodes exhibits asymmetric magnetoresistance with inversion of the signal according to the handedness of molecules, in line with the presence of the CISS effect. In addition, magnetically conductive atomic force microscopy reveals efficient electron spin filtering even at unusually low potentials. Our results demonstrate that thia[4]heterohelicenes represent key candidates for the development of chiral spintronic devices.

Self-Sustained Rotation of Lorentz Force-Driven Janus Systems

Rotation is an interesting type of motion that is currently involved in many technological applications. In this frame, different and sophisticated external stimuli to induce rotation have been developed. In this work, we have designed a simple and original self-propelled bimetallic Janus rotor powered by the synergy between a spontaneous electric and ionic current, produced by two coupled redox reactions, and a magnetic field, placed orthogonal to the surface of the device. Such a combination induces a magnetohydrodynamic vortex at each extremity of the rotor arm, which generates an overall driving force able to propel the rotor. Furthermore, the motion of the self-polarized object can be controlled by the direction of the spontaneous electric current or the orientation of the external magnetic field, resulting in a predictable clockwise or anticlockwise motion. In addition, these devices exhibit directional corkscrew-type displacement, when representing their displacement as a function of time, producing time-space specular behavior. The concept can be used to design alternative self-mixing systems for a variety of (micro)fluidic equipment.

Examining the Effects of Homochirality for Electron Transfer in Protein Assemblies

Protein voltammetry studies of cytochrome c, immobilized on chiral tripeptide monolayer films, reveal the importance of the electron spin and the film's homochirality on electron transfer kinetics. Magnetic film electrodes are used to examine how an asymmetry in the standard heterogeneous electron transfer rate constant arises from changes in the electron spin direction and the enantiomer composition of the tripeptide monolayer; rate constant asymmetries as large as 60% are observed. These findings are rationalized in terms of the chiral induced spin selectivity effect and spin-dependent changes in electronic coupling. Lastly, marked differences in the average rate constant are shown between homochiral ensembles, in which the peptide and protein possess the same enantiomeric form, compared to heterochiral ensembles, where the handedness of the peptide layer is opposite to that of the protein or itself comprises heterochiral building blocks. These data demonstrate a compelling rationale for why nature is homochiral; namely, spin alignment in homochiral systems enables more efficient energy transduction.

Chiral-induced spin selectivity in biomolecules, hybrid organic-inorganic perovskites and inorganic materials: a comprehensive review on recent progress

The two spin states of electrons are degenerate in nonmagnetic materials. The chiral-induced spin selectivity (CISS) effect provides a new strategy for manipulating electron's spin and a deeper understanding of spin selective processes in organisms. Here, we summarize the important discoveries and recent experiments performed during the development of the CISS effect, analyze the spin polarized transport in various types of materials and discuss the mechanisms, theoretical calculations, experimental techniques and biological significance of the CISS effect. The first part of this review concisely presents a general overview of the discoveries and importance of the CISS effect, laws and underlying mechanisms of which are discussed in the next section, where several classical experimental methods for detecting the CISS effect are also introduced. Based on the organic and inorganic properties of materials, the CISS effect of organic biomolecules, hybrid organic-inorganic perovskites and inorganic materials are reviewed in the third, fourth and fifth sections, especially the chiral transfer mechanism of hybrid materials and the relationship between the CISS effect and life science. In addition, conclusions and prospective future of the CISS effect are outlined at the end, where the development and applications of the CISS effect in spintronics are directly described, which is helpful for designing promising chiral spintronic devices and understanding the natural status of chirality from a new perspective.

A Group-Theoretic Approach to the Origin of Chirality-Induced Spin-Selectivity in Nonmagnetic Molecular Junctions

Spin-orbit coupling gives rise to a range of spin-charge interconversion phenomena in nonmagnetic systems where certain spatial symmetries are reduced or absent. Chirality-induced spin-selectivity (CISS), a term that generically refers to a spin-dependent electron transfer in nonmagnetic chiral systems, is one such case, appearing in a variety of seemingly unrelated situations ranging from inorganic materials to molecular devices. In particular, the origin of CISS in molecular junctions is a matter of an intense current debate. Here, we derive a set of geometrical conditions for this effect to appear, hinting at the fundamental role of symmetries beyond otherwise relevant quantitative issues. Our approach, which draws on the use of point-group symmetries within the scattering formalism for transport, shows that electrode symmetries are as important as those of the molecule when it comes to the emergence of a spin-polarization and, by extension, to the possible appearance of CISS. It turns out that standalone metallic nanocontacts can exhibit spin-polarization when relative rotations which reduce the symmetry are introduced. As a corollary, molecular junctions with achiral molecules can also exhibit spin-polarization along the direction of transport, provided that the whole junction is chiral in a specific way. This formalism also allows the prediction of qualitative changes of the spin-polarization upon substitution of a chiral molecule in the junction with its enantiomeric partner. Quantum transport calculations based on density functional theory corroborate all of our predictions and provide further quantitative insight within the single-particle framework.

Chiral-Induced Spin Selectivity and Non-equilibrium Spin Accumulation in Molecules and Interfaces: A First-Principles Study

Electrons moving through chiral molecules are selected according to their spin orientation and the helicity of the molecule, an effect known as chiral-induced spin selectivity (CISS). The underlying physical mechanism is not yet completely understood. To help elucidate this mechanism, a non-equilibrium Green's function method, combined with a Landauer approach and density functional theory, is applied to carbon helices contacted by gold electrodes, resulting in spin polarization of transmitted electrons. Spin polarization is also observed in the non-equilibrium electronic structure of the junctions. While this spin polarization is small, its sign changes with the direction of the current and with the handedness of the molecule. While these calculations were performed with a pure exchange-correlation functional, previous studies suggest that computationally more expensive hybrid functionals may lead to considerably larger spin polarization in the electronic structure. Thus, non-equilibrium spin polarization could be a key component in understanding the CISS mechanism.