The enormous brilliance of modern synchrotron radiation sources allows for illumination of hitherto unexplored corners of the nanocosmos with unprecedented spatiotemporal resolution. Examples are growth processes of thin films and nanostructures, the formation of magnetic order during self-organized growth of ultrathin layers on nanostructured templates, the coupling of magnetic metals through natively formed oxide layers etc. Nuclear resonances constitute extremely sensitive probes for the investigation of magnetic structure and dynamics.
Moreover, ensembles of resonant nuclei in solids are ideal probes to study the fascinating properties of the collective light-matter interaction. One example is the collective version of the Lamb shift that we could observe by embedding ultrathin layers of resonant 57Fe nuclei into an x-ray cavity. Cavities facilitate to realize a very accurate control of the light-matter interaction at x-ray energies. This enabled us to demonstrate one of the key phenomena of quantum optics, electromagnetically induced transparency (EIT) in the x-ray regime.