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Polarized Raman scattering measurements on IrTe2 single crystals carried out over the 15–640 K temperature range, and across the structural phase transition, reveal different insights regarding the crystal symmetry. In the high temperature regime three Raman active modes are observed at all of the studied temperatures above the structural phase transition, rather than two as predicted by the factor group analysis for the assumed P̄3m 1 symmetry. This indicates that the actual symmetry of the high temperature phase is lower than previously thought. The observation of an additional Eg mode at high temperature can be explained by doubling of the original trigonal unit cell along the c axis and within the P̄3cl symmetry. In the low temperature regime (below 245 K) the other Raman modes appear as a consequence of the symmetry lowering phase transition and the corresponding increase of the primitive cell. All of the modes observed below the phase transition temperature can be assigned within the monoclinic crystal symmetry. The temperature dependence of the Raman active phonons in both phases is mainly driven by anharmonicity effects. The results call for reconsideration of the crystallographic phases of IrTe2. [ABSTRACT FROM AUTHOR]

We report first-principles calculations of the lattice dynamics of KNi2Se2 together with Raman scattering study. We have observed three out of four Raman-active modes predicted by factor group analysis. Calculated phonon frequencies are in good agreement with experimental findings. Contrary to its iron counterpart (KxFe2-ySe2), K0.95Ni1.86Se2 does not show vacancy ordering. [ABSTRACT FROM AUTHOR]

The vibrational properties of K0.88Fe1.63S2 were investigated using Raman spectroscopy and analyzed on the basis of peculiarities of its crystal structure. Fourteen Raman active modes, predicted by factor-group analysis, were observed and assigned, confirming Fe vacancy ordering. Phonon energy temperature dependence is fully driven by anharmonicity effects in the range of 80-300 K. High-energy Raman spectra revealed two-magnon excitations of three optical magnon branches. It is shown that the magnetic structure of this material is consistent with the high-temperature block-antiferromagnetism of K0.8Fe1.6Se2. [ABSTRACT FROM AUTHOR]

The vibrational properties of ErTe3 were investigated using Raman spectroscopy and were analyzed on the basis of peculiarities of the RTe3 crystal structure. Four Raman active modes for the undistorted structure, predicted by factor-group analysis, are experimentally observed and assigned according to diperiodic symmetry of the ErTe3 layer. By analyzing temperature dependence of the Raman mode energy and intensity, we have provided clear evidence that all Raman modes, active in the normal phase, are coupled to the charge-density waves. In addition, new modes have been observed in the distorted state. [ABSTRACT FROM AUTHOR]

Raman scattering spectra of zigzag spin chain TaFe1.25Te3 single crystal are presented in a temperature range from 80 to 300 K. Nine Raman active modes of Ag and Bg symmetry are clearly observed and assigned by probing different scattering channels, which is confirmed by lattice dynamics calculations. Temperature dependence of the Raman modes linewidth is mainly governed by the lattice anharmonicity. The only deviation from the conventional behavior is observed for Ag symmetry modes in a vicinity of the magnetic phase transition at TN≈200 K. This implies that the electron-phonon interaction weakly changes with temperature and magnetic ordering, whereas small changes in the spectra near the critical temperature can be ascribed to spin fluctuations [ABSTRACT FROM AUTHOR]

We present a study of charge density wave (CDW) ordering in CeTe3 at room temperature using a scanning tunneling microscope and Raman spectroscopy. Two characteristic CDW ordering wave vectors obtained from the Fourier analysis are assessed to be |c*-q|=4.19nm-1 and |q|=10.26nm-1 where |c*|=2π/c is the reciprocal lattice vector. The scanning tunneling spectroscopy measurements, along with inelastic light (Raman) scattering measurements, show a CDW gap Δmax of approximately 0.37 eV. In addition to the CDW modulation, we observe an organization of the Te sheet atoms in an array of alternating V- and N-shaped groups along the CDW modulation, as predicted in the literature. [ABSTRACT FROM AUTHOR]

We present the Raman scattering spectra of the BaFe2X3 (X = S, Se) compounds in a temperature range between 20 and 400 K. Although the crystal structures of these two compounds are both orthorhombic and very similar, they are not isostructural. The unit cell of BaFe2S3(BaFe2Se3) is base-centered Cmcm (primitive Pnma), giving 18 (36) modes to be observed in the Raman scattering experiment. We have detected almost all Raman active modes, predicted by factor group analysis, which can be observed from the cleavage planes of these compounds. Assignment of the observed Raman modes of BaFe2S(Se)3 is supported by the lattice dynamics calculations. The antiferromagnetic long-range spin ordering in BaFe2Se3 below TN = 255 K leaves a fingerprint both in the A1g and B3g phonon mode linewidth and energy. [ABSTRACT FROM AUTHOR]

Raman scattering spectra of the new Fe-based S = 2 spin-ladder compound BaFe2Se2O are measured in a temperature range between 15 and 623 K. All six A1g and two B1g Raman active modes of BaFe2Se2O, predicted by the factor-group analysis, have been experimentally observed at energies that are in a rather good agreement with the lattice dynamics calculation. The antiferromagnetic long-range spin ordering in BaFe2Se2O below TN = 240 K leaves a fingerprint both in the A1g and B1g phonon mode linewidth and energy. In the energy range between 400 and 650 cm-1 we have observed a magnetic excitation related structure in the form of a magnon continuum, with the peaks corresponding to the singularities in the one-dimensional density of magnon states. The onset value of magnetic continuum (2▵ S ) is found at about 437 cm-1 at 15 K. The magnetic continuum disappears at about 623 K, which led us to conclude that the short-range magnetic ordering in BaFe2Se2O exists apparently up to 2.6TN. [ABSTRACT FROM AUTHOR]