Raman studies of lanthanum cuprate superconductors

Anharmonicity and Weak Mode Assignment in La2-xSrxCuO4with Oxygen Isotopic Substitution

“…In the xx polarization several strong and weak modes have been observed. The energies of these peaks are in agreement with the ones observed in previous reports [2][3][4]. All peaks observed in the zz polarization were present also in the xx spectra, except for the La/Sr mode at ≈ 227 cm −1 , which disappears in the xx scattering configuration.…”

“…Two modes at ≈ 220 cm −1 and ≈ 320 cm −1 in the first order spectra that appear only in the xx spectra, are shifted due to the oxygen isotopic substitution and therefore involve vibrations of the oxygen atoms [5]. This is in agreement with Weber et al [3], who suggested that these modes are due to oxygen vibrations in the xy planes.…”

“…In this polarization configuration four modes are Raman active and it is easily observed that three of them are shifted due to the oxygen isotopic substitution and therefore mostly involve vibrations of the oxygen atoms. Only the phonon at ≈ 227 cm −1 which is not shifted with the substitution of 16 O by 18 O has been attributed to the vibrations of the La (or La/Sr in La 2−x Sr x CuO 4 ) atoms [2,3].…”

Synthesis, structural and electrical characterizations of LaSrCu0.4Al0.6O4−δ

“…In addition, other studies on single crystals have shown a strong forbidden line in one case and, in another case, evidence for Raman scattering from antiferromagnetic spin waves, which are two-dimensional correlations in The Cu-0 planes [22,25]. The presence of such effects certainly further complicates the spectral analysis of polycrystalline samples and among others our LaSrAl 0.6-Cu 0.4 O 4-d. We do not intend to detail in our case its vibrational study.…”

“…We shall not give a detailed assignment here, but we intend as far as possible to distinguish between the bands corresponding to the motions of Al-O octahedra and those associated with Cu-O. The peaks associated with the vibrations of the apical oxygen atoms along the c axis are observed at the region between 425 and 439 cm -1 [22,23]. In addition, a lower frequency band at 160 cm -1 is assigned by analogy with LaSrAlO 4 to La/Sr vibrations in the ab-plane [25] and those at the region between 291 and 313 cm -1 to the same type of vibration of oxygen atoms, as mentioned in the literature [26].…”