Regensburg 2004 – scientific programme
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HL: Halbleiterphysik
HL 4: Ultrakurzzeitph
änomene
HL 4.8: Talk
Monday, March 8, 2004, 12:00–12:15, H13
How fast is the insulator-to-metal transition in VO2? — •T. Dekorsy1, A. Cavalleri2, H.H. Chong2, J.C. Kiefer3, and R.W. Schoenlein2 — 1Forschungszentrum Rossendorf, 01314 Dresden — 2Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA — 3Universite du Quebec, INRS energie et materiaux, Varennes, Quebec
We investigate the photo-induced insulator-to-metal transition in VO2, a strongly correlated semiconductor with monoclinic structure. The insulator-to-metal transition (Tc= 341 K) is initiated by photo-doping of holes into the correlated valence band with high-power femtosecond laser pulses. Experiments with time-resolutions ranging from the 100-fs regime down to 10-fs reveal a minimum time constant for the phase transition to be accomplished of approximately 75 fs. This observation gives evidence for a temporal bottleneck of the phase transition since an atomic rearrangement and symmetry increase for the formation of the high-temperature metal phase has to take place. Femtosecond excitation of VO2 with low power laser pulses reveals the excitation of low-energy coherent phonons which have displacements along the coordinates relevant for the phase transition. Interestingly the observed temporal bottleneck coincides with half the period of these phonons. Our findings demonstrate a new approach for the investigation of the interplay between atomic and electronic structure on ultrashort time scales.