Project without external funding

Time-dependent diffraction and EXAFS during laser induced ultrashort structural changes: Theory and simulations

Project Details
Project duration: 12/200606/2009

Fortsetzungsantrag im DFG-Schwerpunktprogramm 1134 "Aufklärung transienter Strukturen in kondensierter Materie mit Ultrakurzzeit-Röntgenmethoden" (3. Projektperiode)

In the third funding period our project will focus on the further description of laser induced structural changes and on some theoretical developments. We will pay particular attention to those systems which have already been studied or are planned to be studied by the experimental groups within the priority program. The concrete new problems we are going to address are:

1) Theoretical description of femtosecond laser excitation on systems which undergo volume collapse transitions (SmS and Ce). Ce an SmS exhibit a structure conserving phase transition in which the unit cell volume changes by 16% and 17%, respectively. We plan to describe the laser-induced transition from the collapsed-volume to the expanded-volume phases.

2) Determination of the time evolution of potential landscapes and of the train tensor in laser excited solids. Interpretation of the puzzling results of a recent experiment by Lindenberg et al. These experimental results on ultrafast melting questions previous existing theories about the behavior of the potential energy surfaces and bond changes and therefore poses a challenge to theoreticians. We plan to conduct extensive molecular dynamics simulations on both accurate and empirical potentials to seek for the right theoretical interpretation.

3) Study of laser excitation of trained magnetic films. When thin magnetic films (for instance Fe) grow on a substrate having a considerably different lattice constant (for instance Cu), they acquire, due to the mismatch of the lattices, a metastable and strained structure which is different from that corresponding to the bulk-solid or isolated films. We plan to investigate if femtosecond laser excitation of such films can trigger a transition from this "wrong" structure into the stable one.

Moreover, we plan to continue the investigations started during the second period and not yet concluded, namely

4) Laser excitation of coherent phonons in Bi and excitation of a Peierls transition on Bi under pressure, and inclusion of Density Functional Theory and self-consistent methods in the study of laser-induced phase transitions.

Principal Investigator

Last updated on 2017-11-07 at 13:58