Break junctions under femtosecond laser illumination: steps towards time-resolved photocurrent spectroscopy on the nanoscale

W. Pfeiffer1, S. Dantscher1, C. Kennerknecht1, S. Schramm1, H.B. Weber2 und J.U. Würfel2
1Physikalisches Institut EP1, Universität Würzburg, 97074 Würzburg
2Forschungszentrum Karlsruhe, Institut für Nanotechnologie, D-76021 Karlsruhe

Microscopic break junctions provide fascinating possibilities to investigate microscopic charge transport phenomena. Up to now the studies are restricted to DC current measurements. Consequently, the illumination of the contact and the investigation of the resulting photocurrents opens a new field of research. Especially, ultrashort laser pulses combined with time-resolved spectroscopy could then reveal details of the charge transfer dynamics that are of utmost importance for the understanding of the conductivity in nanoscale contacts. We present first experiments on the illumination of tunnel junctions and single molecule contacts with ultrashort laser pulses (800 nm and 400 nm, 50 fs). The junctions are stable up to intensities of 108 W cm-2 and thus allow the investigation of microscopic transport in intense laser fields. The mechanisms leading to a light induced modulation of the conductance are discussed for tunnel junctions and single molecule contacts.