Measuring the Spin-Polarization Power of a Single Chiral Molecule

A striking experimental manifestation of chirality-induced spin selectivity (CISS) in a single-molecule scanning tunneling microscopy (STM) break-junction, consisting of individual peptide molecules of well-defined chirality bridged between a magnetized STM Ni tip and an Au electrode is demonstrated. The spin-dependent single-molecule conductance of an α-helical peptide sequence of 22 amino acid (AA) residues of both L- and D-isomers were measured employing a spin-polarized version of the STM break-junction approach. During the contact process, individual peptides can spontaneously bridge between both biased electrodes via two �S terminal groups. The current was recorded for each pulling stage in the form of current versus time/displacement, and all traces displaying well-defined single-molecule plateau features were used to build a conductance histogram The observed maxima represent the most probable conductance values for the formed single-molecule contact. The strong rectification effects observed in the limit of zero voltage conductance confirm the molecular nature of the spin filtering effect, even in the absence of the electric field associated with the bias, and the huge potential of chiral filters as circuit components in spintronics devices.