Instrumentation development

We are coordinating the Röntgen-Ångström Cluster (RÅC) consortium Soft-XPCS with the goal to enable and perform fast soft X-ray photon correlation spectroscopy (soft XPCS) experiments. In particular, we want to provide instrumentation and methodological developments at MAX IV and PETRA III to perform XPCS at soft X-ray resonances on time scales ranging from seconds down to a few nanoseconds and on length scales from several 100 nm down to a few nm. With this development, we aim to explore thermal dynamics, field and current-induced motion and fluctuations after laser excitation in complex magnetic materials, including skyrmion systems, magnetic metamaterials, lanthanides, and nickelates.

We develop ultrafast x-ray scattering methods at the European X-ray Free Electron Laser in Hamburg to study the motion of electrons, spins and lattice atoms at their ultimate timescales. Such studies also reveal the intricate coupling of the different degrees of freedom of matter. For instance, we recently discovered the formation of non-equilibrium spin textures of the ultimate smallest size formed in FePt nanoparticles as they are used in magnetic data storage media. Laser heating in so-called heat assisted magnetic recording (HAMR) is used to heat magenta bits above their magnetic ordering temperature. Cooling the bits down in an applied magnetic field writes magnetic information. In the future we plan to develop this technique further to study the motion of hydrogen atoms in metals as it is relevant for future hydrogen storage applications.

Ever since the discovery of the photoeffect by Einstein has photoemission spectroscopy become one of the most powerful tools to probe the propagation of electrons in molecules and solids. We develop time-resolved photoemission spectroscopy with high temporal (~100 fs) and spectral (~20 meV) resolution based on table-top lasers and free electron lasers. The angular resolution of modern electron spectrometers enables us to probe so-called quasiparticle scattering events in quantum materials as they proceed in real time. The figure illustrates this for the scattering of electrons with a blue momentum to states characterized by the green momentum value. We plan to extend this technique to the probing of molecular orbitals in organic photovoltaic materials and in plasmonic nanostructures.