Raman Investigation of the Layered Manganese Perovskite La1.2Sr1.8Mn2O7

1997 ◽  
Vol 494 ◽  
Author(s):  
D. B. Romero ◽  
V. B. Podobedov ◽  
A. Weber ◽  
J. P. Rice ◽  
J. F. Mitchell ◽  
...  
Keyword(s):  
Critical Temperature ◽  
Raman Scattering ◽  
Temperature Dependence ◽  
Raman Spectra ◽  
Anomalous Behavior ◽  
Spectral Features ◽  
Long Wavelength ◽  
Manganese Perovskite

ABSTRACTWe report the results of a detailed polarization and temperature dependence study of the Raman scattering from La1.2Sr1.8Mn2O7. The Raman spectra reveal three general spectral features. First, there are sharp peaks due to long-wavelength optic phonons. Phonons, attributed to the distortion of the MnO6 octahedra, reveal an anomalous behavior which correlates with the transition from a paramagnetic-insulating (PI) to a ferromagnetic-metallic (FM) phase at a critical temperature Tc. Second, there is an electronic continuum that is suppressed for ω < 500 cm−1 at T ≪ Tc. Third, broad peaks between 400 cm1 to 800 cm−1 seen in the PI state, surprisingly, disappear in the FM state. The implications of these results are discussed.

Raman Scattering Studies on Superconducting YBa2Cu3O7−x, Semiconducting YBa2Cu3O6+x, and Possible Impurity Phases

1987 ◽  
Vol 99 ◽  
Author(s):  
A. Mascarenhas ◽  
H. Katayama-Yoshlda ◽  
S. Geller ◽  
J. I. Pánkové ◽  
S. K. Debt
Keyword(s):  
Critical Temperature ◽  
Raman Scattering ◽  
Temperature Dependence ◽  
Phonon Mode ◽  
Group Analysis ◽  
Factor Group ◽  
Anomalous Temperature Dependence ◽  
Anomalous Temperature ◽  
Mode Softening ◽  
Characteristic Lines

ABSTRACTA Raman spectroscopie investigation of specimens of superconducting YBa2Cu3O7−x and semiconducting YBa2Cu3O6+x indicates that in the range 100 to 700 cm-1, the characteristic lines of the superconductor at 13 K, are at 150, 338, 441, 507, 590, and 644 cm-1. Comparison of the Ranan spectra of the superconductor and the semiconductor indicates a mode stiffening of the pair at 338 and 441 cm-1, hut a mode softening of the pair at 507 and 590 cm-1. A factor group analysis leads to a tentative assignment of the Raman and infrared allowed modes. At temperatures 12K < T < 180K the Raman spectra of the superconductor indicate that the phonon mode at 338 cm-1 has an anomalous temperature dependence below the superconducting critical temperature (Tc).

A Study of the Temperature-Dependence of Low-Frequency, Raman-Active Phonons in Stage-2 Graphite-K and Graphite-Rb Intercalation Compounds

1982 ◽  
Vol 20 ◽  
Author(s):  
J. Giergiel ◽  
P. C. Eklund ◽  
R. Al-Jishi ◽  
G. Dresselhaus
Keyword(s):  
Phase Transitions ◽  
Raman Scattering ◽  
Temperature Dependence ◽  
Raman Spectra ◽  
Lattice Dynamics ◽  
Low Frequency ◽  
Frequency Region ◽  
Intercalation Compounds ◽  
Dynamics Model ◽  
Scattering Study

ABSTRACTWe report results from a Raman scattering study of stage 2 Graphite-Rb and Graphite-K in the low frequency region (ω < 150 cm-1) as a function of temperature (80K < T < 300K). Four features are seen in the 80K spectra and are interpreted in terms of a Born– von Kármán lattice dynamics model. The temperature-dependence of the Raman spectra is discussed in connection with reported phase transitions in stage 2 alkalimetal graphite compounds.

Evaluation of Raman Scattering in La1-xMxMnO3 Single Crystals Due to Structural and Magnetic Transitions

1997 ◽  
Vol 494 ◽  
Author(s):  
V. B. Podobedovm ◽  
A. Weber ◽  
D. B. Romero ◽  
J. P. Rice ◽  
H. D. Drew
Keyword(s):  
Raman Scattering ◽  
Single Crystals ◽  
Raman Spectra ◽  
Phonon Scattering ◽  
Strong Dependence ◽  
Low Frequency ◽  
Anomalous Behavior ◽  
Magnetic Phase Transitions ◽  
Raman Mode ◽  
Jahn Teller

ABSTRACTThe study of doped and undoped La1-xMxMnO3 single crystals (x = 0 to x = 0.3) in the temperature range from 5 K to 423 K is reported. The activity of phonon vibrational modes in optical spectra is analyzed and a comparison to experimental Raman data is presented. Different contributions from optical phonons to the Raman scattering process are discussed. It is shown that both the value of doping and temperature have a significant influence on Raman features, and these are strongly affected by structural and magnetic phase transitions. Due to the symmetry present in distorted lanthanum manganese compounds their Raman spectra were found to contain comparable contributions from first- and second-order phonon scattering. The common features related to both the reduction of the Jahn-Teller (JT) distortion and the temperature-induced phase transition were found in the Raman spectra of La1-xMxMnO3 crystals. An anomalous behavior of the low-frequency Raman mode in doped systems was found and explained in terms of the temperature-dependent ionic radius of the La/Sr ion sites. It was found that the strong dependence of the Ag Raman mode on the value of doping may serve as a useful tool for optical characterization of La1-xMxMnO3 compounds, including the inhomogeneity of the surface.

scholarly journals Resonance and antiresonance in Raman scattering in GaSe and InSe crystals

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
M. Osiekowicz ◽  
D. Staszczuk ◽  
K. Olkowska-Pucko ◽  
Ł. Kipczak ◽  
M. Grzeszczyk ◽  
...  
Keyword(s):  
Raman Scattering ◽  
Temperature Effect ◽  
Band Gap ◽  
Raman Spectra ◽  
Quantum Interference ◽  
Optical Band Gap ◽  
Phonon Coupling ◽  
Phonon Modes ◽  
Electron Phonon Coupling ◽  
Resonant Raman

AbstractThe temperature effect on the Raman scattering efficiency is investigated in $$\varepsilon$$ ε -GaSe and $$\gamma$$ γ -InSe crystals. We found that varying the temperature over a broad range from 5 to 350 K permits to achieve both the resonant conditions and the antiresonance behaviour in Raman scattering of the studied materials. The resonant conditions of Raman scattering are observed at about 270 K under the 1.96 eV excitation for GaSe due to the energy proximity of the optical band gap. In the case of InSe, the resonant Raman spectra are apparent at about 50 and 270 K under correspondingly the 2.41 eV and 2.54 eV excitations as a result of the energy proximity of the so-called B transition. Interestingly, the observed resonances for both materials are followed by an antiresonance behaviour noticeable at higher temperatures than the detected resonances. The significant variations of phonon-modes intensities can be explained in terms of electron-phonon coupling and quantum interference of contributions from different points of the Brillouin zone.

scholarly journals Cooper Pair-Like Systems at High Temperature and their Role on Fluctuations Near the Critical Temperature

1998 ◽  
Vol 12 (29n31) ◽  
pp. 3216-3219 ◽  
Author(s):  
M. Ausloos ◽  
S. Dorbolo
Keyword(s):  
Phase Transition ◽  
Electrical Resistivity ◽  
High Temperature ◽  
Critical Temperature ◽  
Oxygen Diffusion ◽  
Cooper Pair ◽  
Anomalous Behavior ◽  
Anomalous Effect ◽  
Linear Temperature ◽  
Ybco Sample

A logarithmic behavior is hidden in the linear temperature regime of the electrical resistivity R(T) of some YBCO sample below 2T c where "pairs" break apart, fluctuations occur and "a gap is opening". An anomalous effect also occurs near 200 K in the normal state Hall coefficient. In a simulation of oxygen diffusion in planar 123 YBCO, an anomalous behavior is found in the oxygen-vacancy motion near such a temperature. We claim that the behavior of the specific heat above and near the critical temperature should be reexamined in order to show the influence and implications of fluctuations and dimensionality on the nature of the phase transition and on the true onset temperature.

Temperature dependence of Raman scattering from 4H-SiC with hexagonal defects

2011 ◽  
Vol 99 (1) ◽  
pp. 011912 ◽  
Author(s):  
R. Han ◽  
B. Han ◽  
D. H. Wang ◽  
C. Li
Keyword(s):  
Raman Scattering ◽  
Temperature Dependence

Temperature dependence of overtone intensity in raman scattering by liquids

1967 ◽  
Vol 10 (5) ◽  
pp. 41-44
Author(s):  
L. S. Stal'makhova ◽  
N. K. Sidorov ◽  
V. I. Kuryshin
Keyword(s):  
Raman Scattering ◽  
Temperature Dependence

Temperature dependence of the Raman spectra of single-wall carbon nanotubes

2000 ◽  
Vol 76 (15) ◽  
pp. 2053-2055 ◽  
Author(s):  
H. D. Li ◽  
K. T. Yue ◽  
Z. L. Lian ◽  
Y. Zhan ◽  
L. X. Zhou ◽  
...  
Keyword(s):  
Carbon Nanotubes ◽  
Temperature Dependence ◽  
Raman Spectra ◽  
Single Wall Carbon Nanotubes ◽  
Single Wall Carbon
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