Chirality Induced Spin Selectivity – the Photoelectron View

Abstract

In this short overview we discuss the manifestation of the chirality-induced spin selectivity (CISS) effect in photoelectron spectroscopy experiments with direct spin analysis. Various systems, from the initially investigated monolayers of molecular biosystems and organic heptahelicene to recent chirally grown solid oxide films, are evaluated. High spin polarization values of up to P = 60 % have been observed for samples at room temperature. For all classes it was shown that the longitudinal spin orientation changes sign with a change of the enantiomeric form. Recent advances allow to distinguish the contributions of electrons with different kinetic energies to the electron spin polarization, and thus to distinguish the CISS effect from bulk contributions to the spin originating from different mechanisms.

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

“…Chiral molecules have been demonstrated to behave as spin filters due to the chiral induced spin selectivity (CISS) effect, experimentally proved for a large variety of organic and inorganic systems. [2][3][4][5][6][7][8][9][10] Electrons with either spin up or down cross enantiomers at different rates depending on molecular handedness, though it is not yet understood whether this selectivity arises at the charge injection level or when the charges drift over the molecular backbone. Although featuring a much lower strength, the electrical magnetochiral anisotropy (eMChA) is closely related to CISS effect, because it implies a variation of the electrical resistance of the sample depending on the interplay between chirality and magnetic fields.…”

Chiral Induced Spin Selectivity

“…Spin-resolved photoemission of electrons through chiral molecular films or ultrathin chiral materials is often considered the “gold standard” for quantifying the CISS effect because measurement of the electron spin population is not convoluted with charge displacement currents. These studies have provided insights into the importance of molecular helicity and length, as well as substrate spin–orbit coupling ,,− on the spin-dependent electron transmission. In cognate approaches, researchers have begun to explore CISS effects indirectly, e.g., through shifts in the substrate work function , and through spin-dependent electron-induced chemical reactions …”

“…Similar studies have been carried out showing the spin selectivity of other oligonucleotides, 40 oligopeptides, 15,40 metal oxides, 39,41 and helicenes. 28 For a recent review of CISS studies using Mott polarimetry, see ref 29.…”

Role of Electrode Polarization in the Electron Transport Chirality-Induced Spin-Selectivity Effect

“…The chirality-induced spin-selectivity (CISS) effect is considered as a general name for a group of effects, characterized by a different electronic response to an external stimulus in the presence of chiral molecules. − The two central manifestations of the CISS effect are observed in photoemission experiments and transport experiments. − In photoemission experiments, electrons are photoexcited to leave a metal covered by chiral molecules, and the rate of emission depends on the polarization of the illumination (or more precisely on the relation between the polarization of the light and the chirality of the molecular layer). In transport experiments, current is passed through a metal-chiral molecule-ferromagnet (FM) junction, and the current is different depending on the FM being magnetized parallel or antiparallel to the molecular chiral axis (which is typically also the direction of current flow).…”