CISS

Experimental Studies into Chiral Induced Spin Selectivity

Group Members: Brian Bloom, Simon Wei, Emil Wierzbinski

Collaborators: David Beratan (Duke), Ron Naaman (Weizmann Institute)

University of Pittsburgh | Department of Chemistry

In collaboration with research groups in Germany and Israel, we are examining the nature of the Chiral Induced Spin Selectivity (CISS) effect. When electrons move through a chiral molecule (or structure) the electron current generates an effective magnetic field, B, that acts on the electrons’ intrinsic magnetic moment. Thus, a preference exists for electrons with one magnetic moment direction to pass through the chiral molecule (or structure). We are examining the magnitude of the CISS effect I) for chiral metal oxide films and II) for ultrathin peptide films.

I) We are collaborating with the group of Prof Zacharias (Muenster) to examine the spin polarization of electrons through copper oxide films. The image below shows electrochemical results for the growth of chiral copper oxide films.

II) We are collaborating with the group of Prof Naaman (Weizmann Inst) to examine the spin polarization of electrons tunneling through oligopeptide films on metal electrodes as a function of the peptide’s helical geometry, amino acid composition, and length. In a recent report, we showed how the spin filtering is manifest in photoemission, electrochemistry, and molecular conductance measurements.

Figure 1: Panel A shows a plot of the copper oxide film thickness (thickness was determined by AFM and by ellipsometry) as a function of deposition time- for both the D and L enantiomers. Panel B shows cyclic voltammetry data that displays an enantioselective response for the tartrate oxidation. Note that D-CuO films give the opposite response.

The image shows different measures of the spin selectivity displayed for a 14 amino acid alpha-helical peptide. The left most data are obtained by photoemission spectroscopy, the data in the center panel are obtained by cyclic voltammetry, and the data on the right were obtained by conductive atomic force microscopy.