Regensburg 2007 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 41: Metal-insulator transitions
HL 41.1: Talk
Thursday, March 29, 2007, 12:45–13:00, H13
Ultrafast Insulator-Metal Transition in Vanadium Dioxide: Coherent Lattice Dynamcis and Electronic Correlations — •Rupert Huber1, Carl Kübler1, Henri Ehrke1, Rene Lopez2,3, Andrej Halabica2, Richard Haglund2, and Alfred Leitenstorfer1 — 1Fachbereich Physik, Universität Konstanz, 78464 Konstanz, Deutschland — 2Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235, USA — 3Department of Physics and Astronomy, University of North Carolina, Chapel Hill, North Carolina 27599, USA
Multi-THz pulses are employed to directly monitor the femtosecond transient behavior of the most important order parameter of the insulator-to-metal phase transition in VO2: the conductivity. Excitation with near infrared light pulses of a duration of 12 fs launches ultrafast dynamics of the ion lattice and the electronic system. Two-dimensional multi-THz measurements allow for a spectral discrimination of structural and electronic contributions revealing their subtle interplay. We find fingerprints of coherent modulations of mid infrared phonons and self-trapping of excitons induced by impulsively excited structural distortions. Wave packet motion at a frequency of 6 THz associated with excitation of V-V dimers is observed. For pump fluences beyond a temperature-dependent threshold, a structurally assisted electronic delocalization emerges within a fraction of the V-V oscillation period.