Anisotropic optical conductivity of Sr3Ru2O7

The optical conductivity sigma(omega) of Sr3Ru2O7 has been studied both in the ab planes, between 12 and 450 K, and along the c axis between 12 and 300 K. sigma(ab)(omega) is Drude-type but, for increasing T, it shows a crossover around 300 K to a regime with enhanced scattering rate, probably driven by a stronger coupling with the optical phonons. The spectral weight shows the imprints of strong correlations, but less pronounced than in a high-T-c material. Along the c axis, the Drude term has a much smaller plasma frequency, and a strong absorption appears at 1 eV. These findings indicate an anisotropic metallic state where electron-electron and electron-phonon interactions play a major role. This picture may be reconciled with the local-density calculations reported in the literature, which predict an insulating c axis, once those interactions are taken into account.