Institute for Electronic Structure Dynamics

Femtoslicing Spectroscopy

Ultrafast magnetism and photoinduced phase transitions in solids probed by X-rays

Materials with complex phase diagrams like magnetic compounds exhibit macroscopic functionalities that may be used in future electronic or storage devices to make them faster, smaller, and more energy efficient. The aim of our research is the understanding and control of these functionalities on a fundamental microscopic level. To this end, we explore the complex interplay between materials’ spin, orbital, charge, and lattice degrees of freedom upon photo-excitation on an ultrafast timescale. An excellent tool to probe these in a time-resolved manner are ultrashort soft X-ray pulses. Soft X-rays allow probing the materiel response in a highly selective and local manner. In particular spectroscopy employing circular polarized X-rays is unique sensitive to spin and orbital magnetic moments.

With the BESSY II Femtoslicing Facility we have established a unique storage ring based source of ultrashort soft X-ray pulses. As the only fs soft X-rays source providing circular polarization in a wide photon energy range, this facility has been instrumental in understanding magnetic effects on ultrashort time scales. Even today, very few such sources exist while ours provides a unique experimental environment for time-resolved X-ray absorption spectroscopy, X-ray magnetic circular dichroism and for other photon-in-photon-out techniques like (resonant) soft X-ray (magnetic) scattering, and (resonant) soft X-ray (magnetic) reflectivity. The materials’ response on a 100 fs time scale provides insight into the coupling of various degrees of freedom and our suite of methods and instrumentation allows investigating a large variety of complex materials. 

Probing the magnetic degree of freedom by ultrashort soft X-ray pulses upon photoexcitation.