•J. U. Würfel¹, S. Dantscher², C. Kennerknecht², W. Pfeiffer², S. Schramm² und H. B. Weber^1
1Forschungszentrum Karlsruhe, Institut für Nanotechnologie, PO-Box 3640, D-76021 Karlsruhe
²Physikalisches Institut EP1, Universität Würzburg, Am Hubland, D-97074 Würzburg

We investigate electron transport properties of single-molecule junctions, formed by the mechanically-controlled break-junction technique. Recent experiments demonstrated that we are able to contact single molecules [1]. Here, we report on measurements carried out under illumination with a femtosecond TiSa laser system. We observe a photo-induced enlargement of the conductance. As possible mechanism a thermally induced diminishment of the contact distance is discussed and contrasted to a picture of photo-excited electrons in the leads. When diode-like molecules are used, different photo-induced conductance changes for positive and negative bias voltage are observed.

[1] Phys. Rev. Lett., 88, 176804 (2002)