  Polyalanine molecules (PA) with an {\alpha}-helix conformation gathered
recently a lot of interest as the propagation of electrons through the chiral
backbone structure comes along with spin polarization of the transmitted
electrons. By means of scanning tunneling microscopy and spectroscopy at
ambient conditions, PA molecules adsorbed on surfaces of epitaxial magnetic
Al2O3/Pt/Au/Co/Au nanostructures with perpendicular anisotropy were studied.
Thereby, a correlation between the PA molecules ordering at the surface with
the electron tunneling across this hybrid system as a function of the substrate
magnetization orientation as well as the coverage density and helicity of the
was observed. The highest spin polarization values, P, were found for
well-ordered self-assembled monolayers and with a defined chemical coupling of
the molecules to the magnetic substrate surface, showing that the current
induced spin selectivity is a cooperative effect. Thereby, P deduced from the
electron transmission along unoccupied molecular orbitals of the helical
molecules is larger as compared to values derived from the occupied molecular
orbitals. Apparently, the larger orbital overlap is resulting in a higher
electron mobility yielding a higher P value. By switching the magnetization
direction of the Co-layer, it was demonstrated that the non-spin-polarized STM
can be used to study chiral molecules with a sub-molecular resolution, to
detect properties of buried magnetic layers and to detect the spin polarization
of the molecules from the change of the magnetoresistance of such hybrid
structures.
