לוח שנה משולב

The basic motivation for our work is to understand how charge is transported on an atomic spatial and attosecond time scale. Strong-field ionization in the dipole approximation (i.e. tunnel ionization) is much faster than the group delay of the electron wavepacket (i.e. Wigner delay), whereas photoemission from atoms can typically be described by the Wigner delay - but not in all cases. For example autoionization resonances in the continuum can change the ionization delay. Moving to condensed matter we have investigated the escape time of photoemitted electrons from metal surfaces such as Ag, Au and Cu. We want to address the question about the correct escape velocity of the electons and their ability to “feel” the periodic crystal potential on a attosecond time and an atomic length scale. Our most recent experiment can confirm an upper limit of around 300 attosecond over a distance less than 2 atomic layers during which an electron can assume its effective mass. Furthermore femtosecond charge transport modulation driven by a transient electric field in the petahertz regime have been observed in diamond and can be explained by the dynamical Kranz Keldysh effect (DFKE). State-of-the-art numerical calculations reveal that only a small number of transitions give rise to the observed effects and that the more classical intra-band transitions dominate the response over inter-band transitions.

In this talk, I will discuss how coherent electromagnetic radiation at infrared and TeraHerz frequencies can be used to coherently rearrange atoms within the crystal lattice of a solid. The motion of atoms is large, and energy flows between different modes of the crystal. Such nonlinear phononics allows for the control of metal insulator transitions, magnetic phenomena, superconductivity and ferroelectricity.
I will also discuss how femtosecond x-ray beams from free electron lasers are integral to these studies, and are used to image structures during these non-equilibrium processes.