Spin Selectivity in Photoelectron Transmission through Self-Assembled Monolayers of Mercurated DNA Helices

Chiral molecules have been shown to act as electron spin filters at room temperature, however the mechanisms remain elusive. Molecular spin-orbit coupling is thought to play a dominant role due to the chiral electrostatic potential that breaks inversion symmetry experienced by transmitted electrons. To test this hypothesis, we designed helical DNA molecules that contain mercury atoms bound at base-pair mismatches. By controlling the number and location of mercury atoms along the DNA axis, we manipulate the strength of the helical spin-orbit field via the heavy atom effect. Monolayers of mercurated DNA are formed on ferromagnetic substrates. Using ultraviolet photoemission spectroscopy, efficiencies of electron transmission through DNA monolayers is probed. Photoelectrons from ferromagnetic surfaces are spin polarized, while adsorbed chiral molecules act as spin filters. Thus, emission intensities and energies of the secondary-electron cutoff are compared using DNA monolayers with varying mercury content. Demonstrating control over molecular spin-orbit coupling to tune spin selectivity by chiral molecules is critical to assess their practically for spintronics applications.