Integrated Calendar

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.

Defects in the solid state are potentially suitable candidates for nanoscale sensing and imaging. Among these, the nitrogen-vacancy (NV) center in diamond has gained wide publicity due to its long coherence time, stability and wide temperature and frequency ranges of operation. With recent reports on the sensing of electron and nuclear spins from single proteins, we attempt to go one step further to the realm of correlated spins. I will present measurements of electron spins in spin-labeled molecules both at room temperature and at low temperature. I will show that it is possible to detect the dipolar coupling between two spin labels in a doubly-labeled peptide using a scheme we call "triple electron-electron resonance". This is a necessary step towards sensing of spins in correlated-electrons
systems. Together with quantum-assisted schemes and improvements in signal readout, I will offer methods with which we can tackle challenges in chemical physics, laying out a potential platform for a spin network.

Protein-protein interactions play important roles in most cellular processes. Proteins interact through chemical and structural complementarity of their mutual binding sites. Amino acids found in physical proximity form non-covalent interactions that stabilize the complex. Here we studied the evolution of PPI interfaces applying directed in vitro evolution on a random TEM library expressed on yeast surface. Our study focused on two specific questions: 1) How plastic is a well-defined PPI interface? For that purpose the TEM library was softly selected against its high affinity binder BLIP and analyzed by deep sequencing. 2) Is it possible to evolve new PPIs? Here the monomeric TEM library was selected against TEM-WT and other proteins to create new binders. Our results show that PPI interfaces are plastic and easily formed, hence evolution must actively act to prevent promiscuous protein binding. One mechanism which seems to be applied by nature for that purpose is keeping wild type proteins below their potential stability in a way that they are easily destabilized upon mutation.