Competing interactions of spin with charge and lattice, which are determined by spin-orbit interaction, yield rich phase diagrams of states in novel correlated-electron materials. In such materials, magnetically ordered phases are very often in direct competition with other ordered phases, as for instance a spin- or charge-ordered phase. Unfortunately, the dominant interaction that is responsible for the formation of a specific phase is most often hard to determine in thermal equilibrium, so that a fundamental understanding of the underlying competing interactions of the spin in its collective environment is out of reach using static measurements. Time-resolved spectroscopy techniques have the potential to overcome these limitations by temporally driving the material system out of equilibrium. The subsequent relaxation pathways are then determined by the spin-charge-lattice interactions, which can be studied by the use of various photoemission techniques.

In this presentation, I will demonstrate how recent developments in ultrafast light sources and photoemission detector technology have paved the way towards a completely new generation of time-resolved photoemission experiments. With this tool at hand, we can directly observe the temporal evolution of excited carriers and spins in energy, momentum space and time, providing an unprecedented insight into the fundamental energy and momentum dissipation mechanisms even in complex condensed matter.

Please contact phweb@ust.hk should you have questions about the talk.