Pseudogap formation of four-layer BaRuO${}_3$ and its electrodynamic response changes

Abstract

We investiaged the optical properties of four-layer BaRuO${}_3$, which shows a fermi-liquid-like behavior at low temperature. Its optical conductivity spectra clearly displayed the formation of a pseudogap and the development of a coherent peak with decreasing temperature. Temperature-dependences of the density $n$ and the scattering rate $1/\ddot{I}„$ of the coherent component were also derived. As the temperature decreases, both $n$ and $1/\ddot{I}„$ decrease for four-layer BaRuO${}_3$. These electrodynamic responses were compared with those of nine-layer BaRuO${}_3$, which also shows a pseudogap formation but has an insulator-like state at low temperature. It was found that the relative rates of change of both $n$ and $1/\ddot{I}„$ determine either metallic or insulator-like responses in the ruthenates. The optical properties of the four-layer ruthenate were also compared with those of other pseudogap systems, such as high $T_c$ cuprates and heavy electron systems.

7 figures. submitted to Phys. Rev. B