Insight into the Origin of Chiral-Induced Spin Selectivity from a Symmetry Analysis of Electronic Transmission

Abstract

The chiral-induced spin selectivity (CISS) effect, which describes the spin-filtering ability of diamagnetic structures like DNA or peptides having chiral symmetry, has emerged in the past years as the central mechanism behind a number of important phenomena, like long-range biological electron transfer, enantiospecific electrocatalysis, and molecular recognition. Also, CISS-induced spin polarization has a considerable promise for new spintronic devices and the design of quantum materials. The CISS effect is attributed to spin–orbit coupling, but a sound theoretical understanding of the surprising magnitude of this effect in molecules without heavy atoms is currently lacking. We are taking an essential step into this direction by analyzing the importance of imaginary terms in the Hamiltonian as a necessary condition for nonvanishing spin polarization in helical structures. On the basis of first-principles calculations and analytical considerations, we perform a symmetry analysis of the key quantities determining transport probabilities of electrons of different spin orientations. These imaginary terms originate from the spin–orbit coupling, and they preserve the Hermitian nature of the Hamiltonian. Hence, they are not related to the breaking of time-reversal symmetry resulting from the fact that molecules are open systems in a junction. Our symmetry analysis helps to identify essential constraints in the theoretical description of the CISS effect. We further draw an analogy with the appearance of imaginary terms in simple models of barrier scattering, which may help understanding the unusually effective long-range electron transfer in biological systems.

Toward a First-Principles Evaluation of Transport Mechanisms in Molecular Wires

“…[2][3][4] Moreover, approaches for exploiting the spin-polarization properties of diamagnetic helical molecules, such as proteins or DNA, have been suggested in the past, where chiral-induced spin selectivity can be used to design more efficient water-splitting or memory devices. [5][6][7][8][9][10][11] Besides potential technological applications, the field of molecular electronics is appealing due to its significance for fundamental science, offering insights into molecules under unusual circumstances. There are continuing efforts to study charge transport processes in biomolecules like peptides, enzymes and DNA, as they are of vital importance to every living organism, for example in the context of oxidative DNA damage.…”

The Importance of Spin State in Chiral Supramolecular Electronics

“…The helical symmetry displayed a much higher spin polarization than the β-strand conformation, highlighting the role of helical geometry in the CISS effect ( Maslyuk et al, 2018 ). In this sense, Herrmann et al analyzed the crucial role of the imaginary terms in the Hamiltonian matrix for nonvanishing spin polarization in helical structures ( Zöllner et al, 2020 ).…”

Orbital and spin polarizations induced by current through a helical atomic chain

“…It is interesting, however, to ask whether only the helical arrangement of atoms can produce any spin selectivity in a model with isotropic atoms connected by geometry-dependent hopping matrix elements. Numerical calculations for specific molecules have also been performed using the density functional method [40][41][42][43][44][45] and a tight-binding model [46], which will be necessary to obtain the spin-selectivity efficiency in a specific organic molecule. An alternative approach is still desirable in order to reach a common mechanism of the enhanced spin selectivity which has been observed in various helical molecules.…”