Spin Filtering in Chiral Quantum Dot Assemblies

Chiral molecules have recently attracted attention due to their capacity to act as room temperature spin filters without the need for strong magnetic fields. Chiral signatures have been identified in quantum dots (QDs) coated with chiral ligands using circular dichroism (CD). These CD signals are intrinsic to the QDs. The CD signals are dependent on QD size, and so may be tuned. Chiral QD assemblies are covalently tethered to ferromagnetic substrates. We engineer a system with two spin-selective processes: charge transport through the chiral ensemble and charge injection into the magnetized substrate. The combination of these processes enables quantitative analyses of spin filtering through chiral QD assemblies as a function of various experimental parameters. We compare fluorescence lifetime asymmetry in chiral QD ensembles with varying QD size and tether length. Shorter fluorescent lifetimes corresponds to lower barriers to charge transfer through the chiral ensemble and into the substrate. By measuring fluorescent lifetime asymmetry, we quantitatively determine the spin-filtering efficiency, and thereby the practicality of incorporating chiral QDs into spintronic devices as spin-polarized electron sources.