Single-enantiomer spin polarisers in superconducting junctions

Abstract

Chiral matter acting as a spin-selective device in biased electron transport is attracting attention for the quantum-technological design of miniaturized electronics. To date, however, experimental reports on spin selectivity are not conclusive. The magnetoresistance in electron transport measurements observed for chiral materials on ferromagnets upon magnetisation reversal is proposed to result from electrostatic rather than from the sought-after chiral effects. Recent break junction studies even question the spin-dependent electron flow across single chiral molecules. Here, we avoid ferromagnetic electrodes and magnetisation reversal to provide unambiguous experimental evidence for the chirality-induced spin selectivity effect of single enantiomers. Functionalising the superconducting tip of a scanning tunnelling microscope with a manganese atom cluster gives rise to Yu-Shiba-Rusinov resonances that serve as spin-sensitive probes of the tunnelling current in junctions of single heptahelicene molecules adsorbed on a crystalline lead surface. Our key finding is the dependence of the signal strength of these states in spectroscopy of the differential conductance on the handedness of the molecule. The experiments unveil the role of the enantiomers as spin polarisers and the irrelevance of electrostatics in the chosen model system.

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