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1. Chirality‐induced Magnet‐free Spin Generation in a Semiconductor

   https://doi.org/10.1002/adma.202406347  

   Liu, Tianhan ; Adhikari, Yuwaraj ; Wang, Hailong ; Jiang, Yiyang ; Hua, Zhenqi ; Liu, Haoyang ; Schlottmann, Pedro ; Gao, Hanwei ; Weiss, Paul S ; Yan, Binghai ; et al ( June 2024 , Advanced Materials)

   Electrical generation and transduction of polarized electron spins in semiconductors are of central interest in spintronics and quantum information science. While spin generation in semiconductors has been frequently realized via electrical injection from a ferromagnet, there are significant advantages in nonmagnetic pathways of creating spin polarization. One such pathway exploits the interplay of electron spin with chirality in electronic structures or real space. Here, utilizing chirality‐induced spin selectivity (CISS), we demonstrate efficient creation of spin accumulation inn‐doped GaAs via electric current injection from a normal metal (Au) electrode through a self‐assembled monolayer of chiral molecules (α‐helix L‐polyalanine, AHPA‐L). The resulting spin polarization is detected as a Hanle effect in then‐GaAs, which is found to obey a distinct universal scaling with temperature and bias current consistent with chirality‐induced spin accumulation. The experiment constitutes a definitive observation of CISS in a fully nonmagnetic device structure and demonstration of its ability to generate spin accumulation in a conventional semiconductor. The results thus place key constraints on the physical mechanism of CISS and present a new scheme for magnet‐free semiconductor spintronics.

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2. Chiral Induced Spin Selectivity and Its Implications for Biological Functions

   https://doi.org/10.1146/annurev-biophys-083021-070400  

   Ron Naaman, Yossi Paltiel ( May 2022 , Annual review of biophysics)

   Chirality in life has been preserved throughout evolution. It has been assumed that the main function of chirality is its contribution to structural properties. In the past two decades, however, it has been established that chiral molecules possess unique electronic properties. Electrons that pass through chiral molecules, or even charge displacements within a chiral molecule, do so in a manner that depends on the electron’s spin and the molecule’s enantiomeric form. This effect, referred to as chiral induced spin selectivity (CISS), has several important implications for the properties of biosystems. Among these implications, CISS facilitates long-range electron transfer, enhances bio-affinities and enantioselectivity, and enables efficient and selective multi-electron redox processes. In this article, we review the CISS effect and some of its manifestations in biological systems.We argue that chirality is preserved so persistently in biology not only because of its structural effect, but also because of its important function in spin polarizing electrons. 

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3. Spin‐selective electron transmission through self‐assembled monolayers of double‐stranded peptide nucleic acid

   https://doi.org/10.1002/chir.23290  

   Möllers, Paul Valerian ; Ulku, Selma ; Jayarathna, Dilhara ; Tassinari, Francesco ; Nürenberg, Daniel ; Naaman, Ron ; Achim, Catalina ; Zacharias, Helmut ( January 2021 , Chirality)

   Monolayers of chiral molecules can preferentially transmit electrons with a specific spin orientation, introducing chiral molecules as efficient spin filters. This phenomenon is established as chirality‐induced spin selectivity (CISS) and was demonstrated directly for the first time in self‐assembled monolayers (SAMs) of double‐stranded DNA (dsDNA)¹. Here, we discuss SAMs of double‐stranded peptide nucleic acid (dsPNA) as a system which allows for systematic investigations of the influence of various molecular properties on CISS. In photoemission studies, SAMs of chiral, γ‐modified PNA show significant spin filtering of up toP= (24.4 ± 4.3)% spin polarization. The polarization values found in PNA lacking chiral monomers are considerably lower at aboutP= 12%. The results confirm that the preferred spin orientation is directly linked to the molecular handedness and indicate that the spin filtering capacity of the dsPNA helices might be enhanced by introduction of chiral centers in the constituting peptide monomers.

    

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4. Challenges in the Direct Detection of Chirality‐induced Spin Selectivity: Investigation of Foldamer‐based Donor‐acceptor Dyads

   https://doi.org/10.1002/chem.202301005  

   Privitera, Alberto ; Faccio, Davide ; Giuri, Demetra ; Latawiec, Elisabeth I. ; Genovese, Damiano ; Tassinari, Francesco ; Mummolo, Liviana ; Chiesa, Mario ; Fontanesi, Claudio ; Salvadori, Enrico ; et al ( October 2023 , Chemistry – A European Journal)

   Over the past two decades, the chirality‐induced spin selectivity (CISS) effect was reported in several experiments disclosing a unique connection between chirality and electron spin. Recent theoretical works highlighted time‐resolved Electron Paramagnetic Resonance (trEPR) as a powerful tool to directly detect the spin polarization resulting from CISS. Here, we report a first attempt to detect CISS at the molecular level by linking the pyrene electron donor to the fullerene acceptor with chiral peptide bridges of different length and electric dipole moment. The dyads are investigated by an array of techniques, including cyclic voltammetry, steady‐state and transient optical spectroscopies, and trEPR. Despite the promising energy alignment of the electronic levels, our multi‐technique analysis reveals no evidence of electron transfer (ET), highlighting the challenges of spectroscopic detection of CISS. However, the analysis allows the formulation of guidelines for the design of chiral organic model systems suitable to directly probe CISS‐polarized ET.

    

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5. Interplay of structural chirality, electron spin and topological orbital in chiral molecular spin valves

   https://doi.org/10.1038/s41467-023-40884-9  

   Adhikari, Yuwaraj ; Liu, Tianhan ; Wang, Hailong ; Hua, Zhenqi ; Liu, Haoyang ; Lochner, Eric ; Schlottmann, Pedro ; Yan, Binghai ; Zhao, Jianhua ; Xiong, Peng ( August 2023 , Nature Communications)

   Chirality has been a property of central importance in physics, chemistry and biology for more than a century. Recently, electrons were found to become spin polarized after transmitting through chiral molecules, crystals, and their hybrids. This phenomenon, called chirality-induced spin selectivity (CISS), presents broad application potentials and far-reaching fundamental implications involving intricate interplays among structural chirality, topological states, and electronic spin and orbitals. However, the microscopic picture of how chiral geometry influences electronic spin remains elusive, given the negligible spin-orbit coupling (SOC) in organic molecules. In this work, we address this issue via a direct comparison of magnetoconductance (MC) measurements on magnetic semiconductor-based chiral molecular spin valves with normal metal electrodes of contrasting SOC strengths. The experiment reveals that a heavy-metal electrode provides SOC to convert the orbital polarization induced by the chiral molecular structure tospinpolarization. Our results illustrate the essential role of SOC in the metal electrode for the CISS spin valve effect. A tunneling model with a magnetochiral modulation of the potential barrier is shown to quantitatively account for the unusual transport behavior.

    

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