# Dresden 2003 – wissenschaftliches Programm

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# MA: Magnetismus

## MA 25: Spinabh

ängige Transportph

änomene I

### 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 [1].

[1] H. F. Ding, W. Wulfhekel, J. Henk, P. Bruno, and J. Kirschner. Submitted to Phys. Rev. Lett.