Abstract
This Perspective discusses recent experiments that bear on the chiral induced spin selectivity (CISS) mechanism and its manifestation in electronic and magnetic properties of chiral molecules and materials. Although the discussion emphasizes newer experiments, such as the magnetization dependence of chiral molecule interactions with ferromagnetic surfaces, early experiments, which reveal the nonlinear scaling of the spin filtering with applied potential, are described also. In many of the theoretical studies, one has had to invoke unusually large spin–orbit couplings in order to reproduce the large spin filtering observed in experiments. Experiments imply that exchange interactions and Pauli exclusion constraints are an important aspect of CISS. They also demonstrate the spin-dependent charge flow between a ferromagnetic substrate and chiral molecules. With these insights in mind, a simplified model is described in which the chiral molecule’s spin polarization is enhanced by a spin blockade effect to generate large spin filtering.
Highlights
This Perspective discusses recent experiments that bear on the chiral induced spin selectivity (CISS) mechanism and its manifestation in electronic and magnetic properties of chiral molecules and materials
First reported in 1999,1 the chiral induced spin selectivity (CISS) effect refers to the preferential transmission of electrons with one spin orientation over the other through chiral molecules and materials.[2]
Recent experiments are revealing that CISS, which couples the electron spin direction to the molecular frame, imparts enantiospecificity to chemical reactions[4] and to adsorption on ferromagnetic surfaces.[5−7] While spin selection rules are well-appreciated in reaction dynamics, and must be considered for molecules with unpaired electrons or electrons that are not paired within a state, the spin direction is not defined in the molecular reference frame
Summary
Iβ are the experimental measurables (e.g., current, rate constant, etc.) for spin pointing parallel or antiparallel to the electron’s velocity. A number of recent reviews related to the CISS effect are available.[8,9] Most CISS-related experiments have been performed with molecules adsorbed to surfaces,[10] which relates the spin direction to the laboratory frame that is defined by the substrate’s surface normal and/or magnetization direction. In this Perspective, we discuss recent experiments that supply a new viewpoint about the electronic and magnetic properties associated with surface-immobilized chiral molecules and their charge and spin transfer (and transport). We discuss some recent theoretical approaches, which may explain the large spin polarizations observed in experiments
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