Effect of screening on the long-wavelength optical phonons in La1.85Sr0.15CuO4

1992 ◽  
Vol 70 (5) ◽  
pp. 352-356
Author(s):  
Chellam Ramakrishnan ◽  
K. Navaneethakrishnan ◽  
N. Krishnamurthy
Keyword(s):  
Coulomb Potential ◽  
Lattice Dynamics ◽  
Wavelength Region ◽  
Coulomb Field ◽  
Longitudinal Optical ◽  
Charge Carriers ◽  
Optical Phonons ◽  
Coupling Coefficients ◽  
Long Wavelength ◽  
Rigid Ion Model

The lattice dynamics of La1.85Sr0.15CuO4 are studied with a rigid-ion model that takes into account the anisotropic screening of the Coulomb field by the charge carriers. The coupling coefficients for the screened potential are obtained using a generalized Ewald transformation that incorporates the Thomas–Fermi screening function. From the calculated phonons in the long-wavelength region it can be seen that the screening considerably reduces the longitudinal optical–transverse optical splitting of the polar modes. The nonpolar modes do not exhibit any changes in their behaviour with respect to that in the unscreened Coulomb potential.

Lattice dynamics of thallium iodide

1988 ◽  
Vol 66 (7) ◽  
pp. 630-632 ◽  
Author(s):  
C. Haridass ◽  
R. Sundararajan ◽  
N. Krishnamurthy
Keyword(s):  
Crystal Structure ◽  
Shell Model ◽  
Satisfactory Agreement ◽  
Lattice Dynamics ◽  
Optical Phonons ◽  
Long Wavelength ◽  
Potential Parameters

The long-wavelength optical phonons in orthorhombic TlI are calculated employing a shell model and transferring the potential parameters from cubic TlI and TlBr. Satisfactory agreement between experimental Raman and infrared phonons suggests that the change in the crystal structure alone is the main reason for the redistribution of phonons in the cubic to orthorhombic transition.

scholarly journals Влияние наночастиц серебра на фотодетектирующие свойства нанокомпозита TiO-=SUB=-2-=/SUB=-/оксид графена

2020 ◽  
Vol 128 (9) ◽  
pp. 1337
Author(s):  
Е.В. Селиверстова ◽  
Н.Х. Ибраев ◽  
А.Ж. Жумабеков
Keyword(s):  
Pure Titanium ◽  
Wavelength Region ◽  
Charge Carriers ◽  
Nanocomposite Material ◽  
Nanocomposite Films ◽  
Long Wavelength ◽  
Photoelectric Properties ◽  
Current Voltage ◽  
Mobility Of Charge Carriers ◽  
Current Voltage Characteristics

The effect of silver nanoparticles on the optoelectronic and photoelectric properties of a nanocomposite material based on graphene oxide (GO) and TiO2 was studied. The data of electron microscopy and Raman spectroscopy have shown that, the formation of a TiO2-GO nanocomposite material occurs during hydrothermal synthesis. The absorption spectrum of the nanocomposite is shifted to the long-wavelength region relative to the absorption of TiO2. The current–voltage characteristics of photodetector based on TiO2-GO nanocomposite films were increased by 2 and 7.5 times relative to pure titanium dioxide without and with the addition of Ag nanoparticles, respectively. The optoelectronic parameters of the devices were also increased, which is associated with growth in the mobility of charge carriers in nanocomposite films.

Photoconductivité dans l'alliage GaAsxSb1−x en présence d'un champ magnétique

1974 ◽  
Vol 52 (8) ◽  
pp. 743-747 ◽  
Author(s):  
A. Filion ◽  
E. Fortin
Keyword(s):  
Magnetic Fields ◽  
Band Gap ◽  
Effective Mass ◽  
Alloy Composition ◽  
Longitudinal Optical ◽  
Optical Phonons ◽  
Champ Magnétique

The intrinsic photoconductivity of several samples of the alloy GaAsxSb1−x has been studied at 4.2 K in the presence of magnetic fields of up to 65 kG. Values for the band-gap, the reduced effective mass of the carriers, the energy of the longitudinal optical phonons across the alloy composition are deduced from the measurements.

Rigid ion model of lattice dynamics - A re-evaluation

1971 ◽  
Vol 9 (3) ◽  
pp. 185-189 ◽  
Author(s):  
K.V. Namjoshi ◽  
S.S. Mitra ◽  
J.F. Vetelino
Keyword(s):  
Lattice Dynamics ◽  
Rigid Ion Model

Long-wavelength lattice vibrations of Ag3In5Se9 and Ag3In5Te9 single crystals — An inversion of LO- and TO-mode frequencies

2016 ◽  
Vol 30 (18) ◽  
pp. 1650229 ◽  
Author(s):  
Nizami Mamed Gasanly
Keyword(s):  
Refractive Index ◽  
Single Crystals ◽  
Longitudinal Optical ◽  
Absorption Index ◽  
Energy Losses ◽  
Optical Parameters ◽  
Lattice Vibrations ◽  
Frequency Range ◽  
Long Wavelength ◽  
Optical Modes

Infrared (IR) reflectivities are registered in the frequency range of 50–2000 cm[Formula: see text] for Ag3In5Se9 and Ag3In5Te9 single crystals grown by Bridgman method. Three infrared-active modes are detected in spectra. The optical parameters, real and imaginary parts of the dielectric function, the function of energy losses, refractive index, absorption index and absorption coefficient were calculated from reflectivity experiments. The frequencies of transverse and longitudinal optical modes (TO and LO modes) and oscillator strength were also determined. The bands detected in infrared spectra were tentatively attributed to various vibration types (valence and valence-deformation). The inversion of LO- and TO-mode frequencies of the sandwiched pair was observed for studied crystals.

Combining the deep Earth and lithospheric gravity field to study the density structure of the upper mantle

2021 ◽  
Author(s):  
Bart Root ◽  
Javier Fullea ◽  
Jörg Ebbing ◽  
Zdenek Martinec
Keyword(s):  
Gravity Field ◽  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Field Data ◽  
Wavelength Region ◽  
Density Structure ◽  
Long Wavelength ◽  
Global Gravity ◽  
Deep Earth

<p>Global gravity field data obtained by dedicated satellite missions is used to study the density distribution of the lithosphere. Different multi-data joint inversions are using this dataset together with other geophysical data to determine the physical characteristics of the lithosphere. The gravitational signal from the deep Earth is usually removed by high-pass filtering of the model and data, or by appropriately selecting insensitive gravity components in the inversion. However, this will remove any long-wavelength signal inherent to lithosphere. A clear choice on the best-suited approach to remove the sub-lithospheric gravity signal is missing. </p><p>Another alternative is to forward model the gravitational signal of these deep situated mass anomalies and subtract it from the observed data, before the inversion. Global tomography provides shear-wave velocity distribution of the mantle, which can be transformed into density anomalies. There are difficulties in constructing a density model from this data. Tomography relies on regularisation which smoothens the image of the mantle anomalies. Also, the shear-wave anomalies need to be converted to density anomalies, with uncertain conversion factors related to temperature and composition. Understanding the sensitivity of these effects could help determining the interaction of the deep Earth and the lithosphere.</p><p>In our study the density anomalies of the mantle, as well as the effect of CMB undulations, are forward modelled into their gravitational potential field, such that they can be subtracted from gravity observations. The reduction in magnitude of the density anomalies due to the regularisation of the global tomography models is taken into account. The long-wavelength region of the density estimates is less affected by the regularisation and can be used to fix the mean conversion factor to transform shear wave velocity to density. We present different modelling approaches to add the remaining dynamic topography effect in lithosphere models. This results in new solutions of the density structure of the lithosphere that both explain seismic observations and gravimetric measurements. The introduction of these dynamic forces is a step forward in understanding how to properly use global gravity field data in joint inversions of lithosphere models.</p>

scholarly journals UV Spectroscopy of the Novalike Variable TT Arietis

1982 ◽  
Vol 69 ◽  
pp. 453-454
Author(s):  
W. Wargau ◽  
H. Drechsel ◽  
J. Rahe ◽  
G. Klare ◽  
B. Wolf ◽  
...  
Keyword(s):  
Uv Spectroscopy ◽  
Wavelength Region ◽  
Apparent Magnitude ◽  
Long Wavelength ◽  
Dwarf Nova ◽  
Tt Ari ◽  
Visual Brightness

TT Ari was detected by Strohmeier et al. (1957) and is classified as a novalike variable. It was hitherto unclear whether TT Ari is a special type of dwarf nova (Warner, 1976) or an old nova (Cowley et al., 1975). Our group obtained a total of four IUE spectra between 1979 and 1981 in the short and long wavelength region. The first spectrum was taken in July 1979, when the system had a visual brightness of 11.3 magnitudes. The following two IUE observations in November 1980 revealed TT Ari in the lowest optical state (V = 14m.3) observed so far. The fourth spectrum was obtained during the rise to maximum in January 1981, when the system had an apparent magnitude of V = 11m.8. From this behavior, Krautter et al. (1981) concluded that TT Ari is a dwarf nova with extremely extended standstills as they are typical for Z Cam stars.

Raman studies of the decay of the longitudinal optical phonons in wurtzite GaN and AlxGa1-xN

2000 ◽  
Author(s):  
Kong-Thon F. Tsen ◽  
David K. Ferry ◽  
Stephen M. Goodnick ◽  
A. Salvador ◽  
Hadis Morkoc
Keyword(s):  
Longitudinal Optical ◽  
Optical Phonons

scholarly journals Method of obtaining and studying the optical properties of carbon quantum dots.

2019 ◽  
Vol 19 (3) ◽  
pp. 226-229
Author(s):  
S.D. Bardasevska ◽  
I.M. Budzulyak ◽  
S.I. Budzulyak ◽  
B.I. Rachiy ◽  
R.V. Ilnytskyi ◽  
...  
Keyword(s):  
Raw Materials ◽  
Wavelength Region ◽  
Short Wave ◽  
Carbon Quantum Dots ◽  
Long Wavelength ◽  
Plant Raw Materials ◽  
Wave Region ◽  
Exciton Mechanism ◽  
Short Wave Region ◽  
Kinetics Of

The proposed method of synthesis of CQDs on the basis of nanoporous carbon obtained from plant raw materials. It is established that in the short-wave region a band is registered, which is due to the exciton mechanism of recombination, whereas in the long-wavelength region it is related to the state of defects. The kinetics of PL extinction is not strictly exponential, which most likely indicates the distributed nature of fading from individual emitters.

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