Probing Chirality-Induced Spin Selectivity in Photoemission

The interaction between electrons and chiral molecules can be electron spin- and enantio-selective; this effect is referred to as chirality-induced spin selectivity (CISS). CISS manifests itself in a magnetoresistance across molecular junctions as well as in the spin polarization of photo-electrons emitted from surfaces functionalized with layers of chiral molecules [1,2,3].

In this talk, I will summarize select spin-resolved photoemission measurements [1] performed in our lab in recent years. We demonstrate that full monolayers of heptahelicenes and helical tetra-pyrroles, respectively, can generate a significant photo-electron spin polarization exceeding P = 30% [3]. Moreover, by measuring the spin polarization of photoelectrons emitted from these surfaces as a function of the sample temperature and the surface coverage, we explore the potential impact of the substrate material, of molecular vibrations, and of intermolecular interactions on the mechanism underlying CISS.

One exciting emerging application of CISS is the control of the electron spin during electrochemical reactions. Spin-selective catalysis allows to control and enhance the chemical selectivity and efficiency of spin-dependent reactions such as electrochemical water splitting [4]. While CISS is experimentally established in only in chiral molecules, similar characteristics have more recently been identified in chiral solid-state materials such as chiral transition metal oxide layers [4,5]. Here, I will also present photoemission data from 5 nm to 50 nm thin cupric oxide layers, and will discuss how the spin-selective properties of these layers could arise from two distinct chirality-related mechanisms [5].

References:

[1] P. V. Möllers, H. Zacharias et al., Isr. J. Chem. 62, e202200062 (2022)

[2] P. V. Möllers, H. Zacharias et al., Chirality 33, 93–102 (2021)

[3] P. V. Möllers, H. Zacharias et al., J. Phys. Chem. Lett. 15, 9620−9629 (2024)

[4] K. B. Ghosh, P. V. Möllers et al., J. Phys. Chem. C 123, 3024–3031 (2019)

[5] P. V. Möllers, H. Zacharias et al., ACS Nano 16, 12145−12155 (2022)