In-plane and out-of-plane optical spectra of Sr₂RuO₄

In-plane (ab-plane) and out-of-plane (c-axis) optical spectra were investigated at various temperatures for Sr₂RuO₄ which is isostructural with the cuprate superconductor La_2−xSr_xCuO₄ and becomes superconducting below 1 K. The ratio of the in-plane to out-of-plane low-energy spectral weight of this compound is approximately 10², an anisotropy comparable to that of the cuprate. The temperature dependence of the c-axis spectrum suggests coherent motion of conduction carriers with strongly renormalized mass and scattering rate along the c axis at low temperatures.