Chiral-induced spin selectivity — Theoretical perspectives based on electron correlations

Chiral-induced spin selectivity, discovered about a decade ago in helical molecules, is a non-equilibrium effect that emerges from the interplay between geometrical helicity and spin-orbit interactions. Several model Hamiltonians building on this interplay have been proposed and while these can yield spin-polarized transport properties that agrees with experimental observations, they simultaneously depend on unrealistic values of the spin-orbit interaction parameters. It is likely, however, that a common deficit originates from the fact that all these models are uncorrelated, or, single-electron theories. Therefore, chiral-induced spin selectivity is, here, addressed using i) a many-body approach, which allows for non-equilibrium conditions and a systematic treatment of the correlated state, and ii) electron exchange and correlations emerging from the coupling between ionic vibrations and electrons.

In the first part it is shown that the intrinsic molecular spin-polarization increases by two orders of magnitudes, or more, compared to the corresponding result in the uncorrelated model. In addition, the electronic structure responds to varying external magnetic conditions which, therefore, enables comparisons of the currents provided for different spin-polarizations in one of the (or both) leads between which the molecule is mounted. Using experimentally feasible parameters and room temperature, the obtained normalized difference between such currents may be as large as 5 — 10 % for short molecular chains, clearly suggesting the vital importance of including electron correlations when searching for explanations of the phenomenon.

In the second part, a spin-dependent electron-phonon coupling which originates from the spin-orbit interaction is introduced, and it is shown that such electron-phonon coupling generates an exchange splitting between the spin channels in the structure. By application of these results to a model for a chiral molecular structure mounted between metallic leads, the chiral-induced spin selectivity is found to become several tens of percents using experimentally feasible parameters.

References:
i) J. Fransson, Chirality-Induced Spin Selectivity: The Role of Electron Correlations, J. Phys. Chem. Lett. 10, 7126 (2019).
ii) J. Fransson, Vibrational origin of exchange splitting and chiral-induced spin selectivity, Phys. Rev. B, 102, 235416 (2020).
iii) J. Fransson, Charge Redistribution and Spin Polarization Driven by Correlation Induced Electron Exchange in Chiral Molecules, arXiv:2130.00840.