Layered Ruthenium Oxides: From Band Metal to Mott Insulator

Abstract

We present results of the first optical and angle-resolved photoemission study on a layered ruthenium oxide system with various Ca/Sr substitution levels. Using two-plane $({\mathrm{Sr}}_{1-x}{\mathrm{Ca}}_x{)}_3{\mathrm{Ru}}_2{\mathrm{O}}_7$ and one-plane ${\mathrm{Ca}}_2{\mathrm{RuO}}_4$ crystals we were able to study evolution of the electronic properties in a range from a band metal $\left({\mathrm{Sr}}_3{\mathrm{Ru}}_2{\mathrm{O}}_7\right)$ to a “bad” metal $\left({\mathrm{Ca}}_3{\mathrm{Ru}}_2{\mathrm{O}}_7\right)$ to a Mott-Hubbard insulator $\left({\mathrm{Ca}}_2\mathrm{Ru}{\mathrm{O}}_4\right)$. Apart from a Mott-Hubbard metal-insulator transition (MIT), we have uncovered a qualitative change of the electronic properties at a critical $x=0.33\mathrm{}$. We suggest that the latter is a result of a quantum phase transition into an antiferromagnetic phase that precedes the real Mott-Hubbard MIT.