Regensburg 2010 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 25: Surface Magnetism / Magnetic Imaging I

MA 25.7: Vortrag

Donnerstag, 25. März 2010, 11:45–12:00, H23

Nonequilibrium effects in spin inelastic tunneling spectroscopy — •Björn Sothmann and Jürgen König — Universität Duisburg-Essen and CeNIDE, 47048 Duisburg, Germany

In a recent experiment, Hirjibehedin et al. [1] measured the differential conductance of a single iron atom absorbed on a substrate using an STM tip. While the observed steps could be explained [2] in terms of inelastic tunneling processes exciting the atom out of its ground state, an explanation for the nonmonotonic conductance behaviour as a function of bias voltage is missing.

Here we develop a generalized theory which takes into account nonequilibrium spin occupations using a master equation approach. We find that the conductance overshoots at the inelastic steps and drops to its equilibrium values afterwards. This behaviour can be explained by bias-dependent spin occupations. Furthermore, we show that the experimentally observed absence of these overshoots at certain spin excitations can be ascribed to a spin-dependent relaxation mechanism. Finally, we discuss that the nonequilibrium effects also give rise to a super-Poissonian current noise.

[1] C. Hirjibehedin et al., Science 317, 1199 (2007).

[2] J. Fernández-Rossier, Phys. Rev. Lett. 102, 256802 (2009).