Electron and phonon dynamics in photoexcited solids

Pump-probe experiments are now widely used to study the electronic and structural changes in solids following laser excitation. Most of classical spectroscopies (optical spectroscopy, X ray diffraction, Raman scattering, Photoemission, ..) have been extended to perform time resolved measurements with a ~10 fs time resolution. These experiments allow to study photoinduced phase transition[1,2], ultrafast demagnetization processes or coherent phonon generation mechanisms[3]. Since experimental results are usually difficult to interpret, there is a need to develop new approaches based on ab-initio calculations or modelsto deepen our understanding of out equilibrium processes probed by such experiments.

The aim of this thesis is to perform ab-initio calculations and to develop new tools in order to understand the time resolved experiments performed on bismuth in the optical or THz range of frequencies. The goal of these calculations is to understand the dynamics of electrons and phonons in such a system. One step in this direction has already been achieved very recently [4,5,6].

The second aspect of this thesis concerns the computation of thermal diffuse scattering in equilibrium and non-equilibrium situations. The first step is to write a code in order to compute the thermal diffuse scattering and to test this code on gold which has been studied by means of time resolved electron diffraction experiments[7]. This system, while very simple, is very fascinating because of the bond hardening observed upon increasing the laser fluence. Applications to more complex systems are also envisaged.

Candidate profile:
The Phd thesis is shared between Université de Rennes (Prof. B. Arnaud) and the Université catholique de Louvain (Prof. X. Gonze), in the form of a "co-tutelle”, which means that diplomas from the two universities will be obtained. It is a nice opportunity to gain experience in two different and complementary environments. The candidate must show evidence of interest in computational modeling and is expected to have taken lectures in quantum mechanics, statistical physics and condensed matter physics. The knowledge of Fortran 90 or of another programming language is expected.

Send us a letter of motivation, a complete CV, the list of courses followed in master and the corresponding ratings, before June 26, 2015, at noon.

B. Arnaud ([email protected]) IPR, université de Rennes I, France

X. Gonze ([email protected]) IMCN , Université catholique de Louvain, Belgique

[1] E. Collet et al , Science 300, 612 (2003)

[2] M. Lorenc et al , Phys. Rev. Lett. 103 028301 (2009)

[3]H.J. Zeiger et al., Phys. Rev. B45, 768 (1992).

[4] Y. Giret, A. Gellé and B. Arnaud, Phys. Rev. Lett. 106, 155503 (2011).

[5] E. Papalazarou et al, Phys. Rev. Lett. 108, 256808 (2012).

[6] B. Arnaud and Y. Giret, Phys. Rev. Lett. 110, 016405 (2013).

[7] R. Ernstorfer et al, Science 323, 1033 (2009).