Raman scattering in theRTiO3family of Mott-Hubbard insulators

Heavy-fermion formation at the metal-to-insulator transition inGd1−xSrxHeinrich1, Nidda2, Fritsch3 et al. 2001Phys. Rev. B

“…These pellets have been annealed at 1473 K under N 2 atmosphere for 15 hours and finally arc-melted under argon atmosphere. For Sr concentrations x ≤ 0.7 X-ray powder diffraction revealed the proper orthorhombically distorted GdFeO 3 perovskite structure [6]. For x > 0.7 the system attains the cubic perovskite structure like pure SrTiO 3 .…”

Phonons and magnetic excitations in the Mott insulatorLaTiO3

“…[3], neither strong background scattering nor Fano shape of the Raman lines is observed. The temperature shift of some Raman lines exhibits clear anomaly below T N : a signature for structural rearrangement.…”

“…It has been pointed out [1] that earlier Raman results of Reedyk at al. [3], where large background and Fano shape of the phonon line near 300 cm −1 have been observed, may also indicate orbital fluctuations coupled to lattice vibrations. Some recent experimental results on the temperature dependence near T N of neutron and x-ray diffraction, heat capacity and infrared spectra [4,5], however, provide evidence for noticeable deformation of TiO 6 octahedra and structural anomaly near the antiferromagnetic ordering, which indirectly supports the concept of orbital ordering.…”

“…Indeed, anomalous variation of phonon Raman intensities and linewidths has been reported at 50 K for LaTiO 3+δ/2 near the metal-to-Mottinsulator transition at 0.01 < δ < 0.04 [10]. The room temperature dc resistivity (ρ = 0.02 Ωcm) of the LaTiO 3 sample used in the Raman experiments of Reedyk et al [3] is much lower than that reported for nearly stoichiometric samples (ρ > 0.5 Ωcm [7,8]) and rather corresponds to δ = 0.04. Therefore, it is of definite interest to examine the Raman spectra of stoichiometric LaTiO 3 in a broad temperature range including Néel temperature T N .…”

“…able symmetric lines at 252 and 296 cm −1 instead of one broader asymmetric band between 220 and 300 cm −1 . Taking into account that for LaTiO 3+δ/2 one expects an increase of the electronic background, phonon line intensity and phonon line width with increasing δ [10], the puzzling "Fano shaped" band reported by Reedyk et al [3] seems to have simpler explanation as a complex band, consisting of two relatively broad symmetric lines centered at 252 and 296 cm −1 .…”