Attosecond Electron Dynamics in Bulk Germanium

Understanding and manipulation of out-of-equilibrium quantum states is a growing area of scientific and industrial research. Modern experimental techniques are able to probe the dynamics of electrons on attosecond time scales, and time-dependent density functional theory (TDDFT) simulations allow to follow the electronic bands in real time in materials subject to intense laser pulses and assist in interpreting and understanding the experimental data. For intense laser fields, non-linear effects open new intriguing questions and novel opportunities, which are beyond the seminal yet oversimplified analytical Franz-Keldysh model. For this goal, TDDFT may provide us an acceptable trade-off between accuracy and computational cost. In particular, TDDFT has enabled the simulation of transient absorbance and reflectance maps and helped assign their features to the relevant electronic transitions in diamond and silicon. In this work, we apply numerical pump-probe experiments to study the narrow-gap bulk semiconductor germanium, whose semi-core d-levels add extra dynamical features as well as extra computational challenges. We will present our simulations of transient reflectance spectra for moderate and strong laser fields and compare our results to recent experimental findings. Also, we will present the analysis of band occupations in different parts of the Brillouin zone which allows to differentiate between interband and intraband electron motion.

Seminar realized in the framework of the funded project:

PRIN 2017RKWTMY - Attosecond transient absorption and reflectivity for the study of exotic materials (aSTAR).