Spin Polarization from Circularly Polarized Light Induced Charge Transfer

TL;DR

This paper demonstrates how circularly polarized light can induce spin polarization in a donor-acceptor complex through charge transfer, highlighting the role of electronic symmetry and spin-orbit coupling in this process.

Contribution

It introduces a quantum mechanical model showing how chiral light excitation leads to spin polarization via charge transfer in metalloporphyrin complexes, a novel mechanism.

Findings

Spin polarization arises from selective excitation of ring currents.

Spin polarization increases with spin-orbit coupling strength.

The effect is transient, depending on dephasing rates.

Abstract

We show how a spin polarization can be generated through the photo-induced electron transfer of an achiral donor-acceptor complex following chiral light excitation. In particular, we illustrate the basic energetic and symmetry requirements for chirality induced spin selectivity where the chirality emerges from the electronic degrees of freedom following excitation with circularly polarized light. We study this effect in a simple model of a metalloporphyrin complex with an axial acceptor ligand using quantum mechanical rate theories and numerical simulations. We find that the spin polarization emerges due to the selective excitation of a ring current within the porphryin, breaking the degeneracy of the two degenerate spin states. The resultant spin polarization increases with the spin orbit coupling between the metal in the porphyrin and the axial ligand, and is transient, with a lifetime dependent on the rate of dephasing from the Jahn-Teller distortion mode. This proposed effect should be observable in spin-resolved photoemission spectroscopy.