Anisotropic properties of the excitation spectrum ofSr2RuO4crystals

Abstract

We have systematically investigated the totally symmetric Raman-scattering spectra of Sr 2 RuO 4 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 line-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 RuO 2 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 Ϫ1 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 RuO 2 plane below 60 cm Ϫ1 at 7 K. These anisotropic properties have been obtained for 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 ϭ0.97 K. The observed magnetic excitation suggests that the magnetic correlation is also important in understanding the mechanism of superconductivity of Sr 2 RuO 4 .

Raman scattering and optical absorption studies of an orbital ordered Ca2RuO4

“…2(a) shows the temperature dependent Raman scattering spectra of Ca 2 RuO 4 in x 0 x 0 geometry for low energy region (100-700 cm K1 ) [In comparison, we also show the spectra in zz geometry at 10 K (a dashed line) and 400 K (a dotted line)]. We can observe more than seven phonon modes in x 0 x 0 geometry at 10 K, in contrast to two phonon modes in Sr 2 RuO 4 with tetragonal I4/mmm space group [16]. It should be related with the fact that there is significant tilting and rotation of RuO 6 octahedra in Ca 2 RuO 4 while not in Sr 2 RuO 4 [13].…”

Lattice dynamics and the electron-phonon interaction inCa2RuO4

“…27 Note also that the magnitudes of the inverse asymmetry parameters, 1/|q|, in the PM insulating region of Ca 2 RuO 4 for T N < T < T MI are comparable to those in the metallic region of Sr 2 RuO 4 (Ref. 29) and La 1−x Ca x MnO 3 .…”

Lattice dynamics and electron-phonon coupling inSr2RuO4: Inelastic neutron scattering and shell-model calculations

“…Only three zone-center modes are Raman active and were observed by Udagawa et al [35,36]. The two A g -modes corresponding to the c-axis vibrations of Sr and to that of the apical oxygen are found at 5.96 and 16.49 THz, respectively, and one E g mode is found at 7.36 THz [35,36]. The corresponding frequencies determined by inelastic neutron scattering perfectly agree with these Raman results, we find the frequencies 6.02, 16.44 and 7.27 THz.…”

“…The modes in the frequency range 14-16 Thz correspond to vibrations of the apical oxygen parallel to the c axis and the highest band of phonons with frequencies above 20 THz is associated with the inplane bond-stretching vibrations. Only three zone-center modes are Raman active and were observed by Udagawa et al [35,36]. The two A g -modes corresponding to the c-axis vibrations of Sr and to that of the apical oxygen are found at 5.96 and 16.49 THz, respectively, and one E g mode is found at 7.36 THz [35,36].…”