Metal–insulator transitions in layered ruthenates

We present the phenomenological systematics of a series of ruthenates, (Ca, Sr)n+1 RunO3n+1, which exhibits a rich variety of ground states. We will also discuss in some detail the physical properties of the two-dimensional Mott-transition system, Ca2−xSrxRuO4, in which the Mott insulator Ca2RuO4 evolves into the spin-triplet superconductor Sr2RuO4 by means of a band-width control.