Dresden 2003 – wissenschaftliches Programm
MA 25.1: Vortrag
Donnerstag, 27. März 2003, 15:15–15:30, HSZ/04
Treating the bias voltage in calculations for spin-dependent vacuum tunneling: A model for the tunnel barrier — •Jürgen Henk and Patrick Bruno — Max-Planck-Institut für Mikrostrukturphysik, Halle (Saale)
Application of a bias voltage to a tunnel junction leads to a non-equilibrium situation which is rather difficult to be treated in full detail in first-principles calculations. An alternative to the self-consistent potential obtained by the appropriate non-equilibrium Green-functions technique is to use a model potential in the spacer region while retaining the ab-initio lead potentials.
Inspired by earlier works on surface barriers, we propose a heuristic model barrier for vacuum tunneling through a planar junction. The barrier shape is determined by several physical requirements, whereas the few free parameters are fixed by reproducing the spectral densities obtained by ab-initio calculations for semi-infinite systems. Hence, the shape of the tunnel barrier is uniquely determined for each bias voltage and lead separation.
To demonstrate the applicability of our ansatz we address the so-called zero-bias anomaly. First-principles tunneling calculations explain the absence of the zero-bias anomaly in vacuum tunneling between Co(0001) leads which was observed in recent experiments .
 H. F. Ding, W. Wulfhekel, J. Henk, P. Bruno, and J. Kirschner. Submitted to Phys. Rev. Lett.