Transitions in matter triggered by intense ultrashort X-ray pulses

In my talk I will give an overview on the recent results of our theoretical investigation how the unique properties of X-ray free-electron laser (FEL) radiation can be employed to modify extended atomic or molecular assemblies, and to create new states of matter. I will discuss three topics that are related to various irradiation regimes that can be achieved, depending on the FEL pulse fluence: (i) atomic processes within laser-created plasmas, (ii) ultrafast electron kinetics in irradiated semiconductors, and (iii) radiation-induced structural changes in solids.