Single atom conductance measurements can be performed by forming nanocontacts using a scanning tunnelling microscope (STM). In the case of fully spin-polarized transport, a spin resolved conductance quantum of 0.5G0 is expected, in contrast to the value of G0 expected in normal atomic nanocontacts with one full spin degenerate open channel. A spin-resolved conductance has been observed in the experiments carried out by Neel et. al. [1] on cobalt atoms. When the cobalt atom is placed on a copper surface and contacted by a tungsten tip, a conductance of G0 is observed, whereas when it is placed on a cobalt island and contacted by a nickel tip, a conductance of 0.5G0 is observed. Here we present the results of calculations to explore the mechanism underlying this effect, investigating whether or not spin-polarized transport is actually present. These calculations were performed using the ab initio transport method SMEAGOL [2], which combines the non-equilibrium Green function formalism with the DFT implementation SIESTA [3].

[1] N. Neel, J. Kröger, and R. Berndt, Phys. Rev. Lett. (submitted).
[2] A. R. Rocha et. al., Phys. Rev. B 73, 085414 (2006). [3] J. M. Soler et. al., J. Phys. Cond. Matter 14, 2745 (2002).