We investigate the nature and origin of the metal-insulator transition in ${\mathrm{Sr}}_2{\mathrm{Ru}}_{1-x}{\mathrm{Ti}}_x{\mathrm{O}}_4$ as a function of increasing Ti content $\left(x\right)$. Employing detailed core, valence, and conduction band studies with x-ray and ultraviolet photoelectron spectroscopies along with Bremsstrahlung isochromat spectroscopy, it is shown that a hard gap opens up for Ti content $⩾0.2$, while compositions with $x<0.2$ exhibit finite intensity at the Fermi energy, $E_F$. This establishes that the metal-insulator transition in this homovalent substituted series of compounds is driven by Coulomb interaction leading to the formation of a Mott gap, in contrast to transitions driven by disorder effects or band filling.

• Received 12 January 2006

DOI:https://doi.org/10.1103/PhysRevB.73.165105