Anisotropic properties of the excitation spectrum of Sr2RuO4 crystals (Tc=1.4 K) in the normal state investigated by Raman scattering -: art. no. 134520

We have systematically investigated the totally symmetric Raman-scattering spectra of Sr2RuO4 crystals in the temperature region between room temperature and 6 K. The electron-phonon interaction for the apical oxygen vibration has been experimentally investigated by a lint-shape analysis based on the Fano interference model. It has been found that the electron-phonon interaction strongly depends on not only the polarization geometry but also the phonon-propagating direction. The phonon, which travels along the RuO2 plane in the (a,a) geometry, shows the strongest electron-phonon interaction. The intensity of the broad background due to the magnetic excitation has been suppressed in the energy region less than 300 cm(-1) at low temperature. Furthermore, the anisotropic formation of the spin gap has been also observed in excitation spectra with the propagation vector parallel to the RuO2 plane below 60 cm(-1) at 7 K. These anisotropic properties have been obtained fur a crystal with a high superconductivity transition temperature of 1.4 K. The sample quality is very important, since such an anisotropic property has not been observed in the Raman spectra for samples with T-c=0.97 K. The observed magnetic excitation suggests that the magnetic correlation is also important in understanding the mechanism of superconductivity of Sr2RuO4.