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O: Fachverband Oberflächenphysik

O 27: Time-Resolved Spectroscopy II

O 27.4: Vortrag

Dienstag, 26. Februar 2008, 12:00–12:15, MA 043

Ultrafast laser-induced phase transitions in group-V elements — •Nils Huntemann, Eeuwe S. Zijlstra, and Martin E. Garcia — Theoretische Physik, Fachbereich Naturwissenschaften, Universität Kassel, Heinrich-Plett-Str. 40, 34132 Kassel, Germany

A number of pressure-induced phase transitions exist in Arsenic, Antimony, and Bismuth [U. Häussermann et al., J. Am. Chem. Soc. 124, 15359 (2002)]. These transitions occur in thermodynamical equilibrium. In the last years different nonthermal, ultrafast structural changes have been induced in solids by means of femtosecond laser pulses [See, for example, A. Cavalleri et al., Phys. Rev. Lett. 87, 237401 (2001)]. These structural transitions take place under extreme nonequilibrium conditions, primarily because laser light interacts very strongly with electrons but not with ions, and secondarily because the electrons thermalize relatively slowly with the ions (typically on a timescale of roughly 10 ps). As a consequence, laser-driven phase transitions are induced while the electrons are very hot, but the ions are still cold.

Based on first-principles electronic structure calculations we explored the possibility of inducing nonthermal structural changes in the above-mentioned group-V elements by ultrashort laser pulses. For this purpose, we determined the potential energy surface (electronic free energy) as a function of the lattice parameters and atomic coordinates for different electronic temperatures, which simulates the ultrafast laser heating of the electrons.