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1.
The nature of pairing mechanism as well as transition temperature of yttrium cuprates is discussed using the strong coupling
theory. An interaction potential has been developed for the layered structure with two conducting CuO2(a–b) layers in a unit cell. The interaction potential properly takes care of electron-electron, electron-phonon and electron-plasmon
interactions. Furthermore, the electron-phonon coupling parameter (λ), the modified Coulomb repulsive parameter (μ*) and the 2D acoustic phonon (plasmon) energy as a function of oxygen deficiency is worked out. Finally, the superconducting
transition temperature (T
c) is then evaluated by using these coupling parameters and obtainedT
c = 95(92)K for Y(Yb)Ba2Cu3O7−δ
superconductors withδ = 0·0. The model parameters estimated from the layered structure approach are consistent with the strong coupling theory.
The result deduced on the variation ofT
c withδ are in fair agreement with the earlier reported data on yttrium cuprates. The analysis of the above results are discussed. 相似文献
2.
首次报道了室温和非共振条件下,分子束外延(MBE)生长的CdTe/ZnTe超晶格的喇曼散射测量和分析。观察到最低级次的CdTe和ZnTe纵光学声子限制模,并用应力和限制效应精确计算了频移,得到的ZnTe纵光学声子频移理论值与实验结果符合得较好。特别指出,当CdTe和ZnTe层厚小于2nm时,声子频移的限制效应不可忽略,对所测样品的喇曼全谱作了分析。 相似文献
3.
B. H. Armstrong 《International Journal of Thermophysics》1988,9(5):825-838
In an earlier paper, Heisenberg's uncertainty principle was invoked at the melting point T
m of crystalline solids to provide fundamental justification for Lindemann's melting law and to compute diffusion coefficients of several alkali halides. The uncertainty principle defines breakdown of Debye zone boundary (ZB) phonons as valid collective excitations when phonon energies and line widths due to anharmonicity become comparable at T
m. Upon breakdown, random, high-frequency single-particle motion or partial decoupling of crystal ions sets in. Lifetimes of these single-particle ZB motions are determined from the minimum-uncertainty product inequality by assuming that it becomes an equality at T
m for ZB phonons. The present paper addresses improved formulation of that work and extended application to ionic electrical conductivities of 18 molten alkali halides at T
m. It is shown that use of the Debye model produces an approximate lower bound to the mean free time, not the unconstrained direct estimate previouslu implied. This feature is generally reflected in results for ionic conductivities and alkali halide diffusion coefficients for which comparison experimental data were found. However, in spite of this lower-bound formulation and the simple nature of the computation, the results compare favorably with experiment. A model of random single-particle harmonic motion superimposed on the lower-frequency collective motion is proposed to account for volume expansion accompanying the partial decoupling for hard-sphere ions. Experimental comparisons for 15 alkali halides show the decoupling volume change to account largely for the total volume change of melting (in the hard-sphere approximation), yielding a closer agreement with experiment than recent calculations aimed explicitly at the total volume change.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A. 相似文献
4.
Koji Watari Hiromi Nakano Kimiyasu Sato Kazuyoshi Urabe Kozo Ishizaki Shixun Cao Katsunori Mori 《Journal of the American Ceramic Society》2003,86(10):1812-1814
The thermal conductivity of a SiC ceramic was measured as 270 W·m−1 ·K−1 at room temperature. At low temperatures ( T < 25 K), the decrease in the conductivity was proportional to T 3 on a logarithmic scale, which indicated that the conductivity was controlled by boundaries. The calculated phonon mean free path in the ceramic increased with decreased temperature, but was limited to ∼4 μm, a length almost equal to the grain size, at temperatures below 30 K. We concluded that the thermal conductivity of the ceramic below 30 K was influenced significantly by grain boundaries and grain junctions. 相似文献
5.
Warren E. Pickett 《Journal of Superconductivity》1991,4(6):397-407
The temperature dependence of the resistivity of the cuprate superconductors arising from phonon scattering is considered within standard Bloch-Gruneisen theory allowing for several different shapes of transport spectral functions
tr
2
F(). In contrast to often made comments that linear resistivity is not characteristic of electron-phonon scattering, it is shown rather that it is more difficult to get muchnonlinearity from this theory except below 50–100 K, and in this low-T regime better solutions to the Boltzmann equation might be required. The reasons for the linear behavior are clarified, and the variations to be expected from possible coupling functions are explored. Possible origins of the nonlinear resistivity seen in YBa2Cu4O8 and recently in YBa2Cu3O7 are suggested, and effects not included specifically in these calculations are discussed. It is also pointed out that phonon contributions to the energy () dependence of quasiparticles, which is a closely related consequence of electron-phonon coupling, will differ significantly from the simple
2 Fermi liquid behavior that is commonly assumed. 相似文献
6.
A. P. Litvinchuk C. Thomsen M. Cardona L. Börjesson M. Käll P. Berastegui L. -G. Johansson 《Journal of Superconductivity》1994,7(1):113-116
We report a reflectivity study of thez-polarized TO-phonons of Pr
x
Y1–x
Ba2Cu4O8 and YBa2–y
Sr
y
Cu4O8 alloys in the temperature range 10–300 K. Anomalies of the frequency and linewidth of the plane-oxygen vibration at300 cm–1 due to the opening of the superconducting gap are found to occur upon crossing the superconducting transition temperatureT
c
. Phonon self-energy effects are strongly dependent onT
c
, providing evidence for a relative shift of the gap with respect to the energy of phonon.On leave from the Institute for Semiconductor Physics, Ukrainian Academy of Sciences, 252650 Kiev-28, Ukraine. 相似文献
7.
Dovletgeldi Seyitliyev Xixi Qin Manoj K. Jana Svenja M. Janke Xiaowei Zhong Wei You David B. Mitzi Volker Blum Kenan Gundogdu 《Advanced functional materials》2023,33(21):2213021
Electron–phonon interactions play an essential role in charge transport and transfer processes in semiconductors. For most structures, tailoring electron–phonon interactions for specific functionality remains elusive. Here, it is shown that, in hybrid perovskites, coherent phonon modes can be used to manipulate charge transfer. In the 2D double perovskite, (AE2T)2AgBiI8 (AE2T: 5,5“-diylbis(amino-ethyl)-(2,2”-(2)thiophene)), the valence band maximum derived from the [Ag0.5Bi0.5I4]2– framework lies in close proximity to the AE2T-derived HOMO level, thereby forming a type-II heterostructure. During transient absorption spectroscopy, pulsed excitation creates sustained coherent phonon modes, which periodically modulate the associated electronic levels. Thus, the energy offset at the organic–inorganic interface also oscillates periodically, providing a unique opportunity for modulation of interfacial charge transfer. Density-functional theory corroborates the mechanism and identifies specific phonon modes as likely drivers of the coherent charge transfer. These observations are a striking example of how electron–phonon interactions can be used to manipulate fundamentally important charge and energy transfer processes in hybrid perovskites. 相似文献
8.
V. A. Andrianov V. P. Gor’kov V. P. Koshelets L. V. Filippenko 《Measurement Techniques》2006,49(8):830-838
The energy resolution of superconducting tunnel detectors is investigated from the point of view of the effect of recombination
and boundary losses of nonequilibrium quasiparticles. Using the x-ray fluorescence method, the dependence of the signal on
the energy of x-ray quanta is measured for Ti/Nb/Al/AlOx/Al/Nb/NbN detectors. The form of the apparatus line is also investigated. The experimental data are analyzed using the diffusion
model of tunnel detectors.
__________
Translated from Izmeritel’naya Tekhnika, No. 8, pp. 59–64, August, 2006. 相似文献
9.
THz acoustic phonons have wavelengths in the nm range and can be used as internal probes to investigate self-assemble quantum dots (QDs) structures. The interaction between delocalised acoustic phonons and an ensemble of localised electronic states yields interferences in the Raman scattering efficiency. Raman scattering interferences provide an image in reciprocal space of the electronic density and therefore allow one to probe the spatial ordering of QDs and the localisation of the electronic states. Spatial correlations functions are obtained by performing inverse Fourier transforms. Characteristic distances can be identified, provided that optical and acoustic wave reflexion effects are taken into account. 相似文献
10.
The lattice contribution to the thermal conductivity (κph) in La0.80Ca0.20 MnO3 manganites is discussed within the Debye-type relaxation rate approximation in terms of the acoustic phonon frequency and
relaxation time. The theory is formulated when heat transfer is limited by the scattering of phonons from defects, grain boundaries,
charge carriers, and phonons. The lattice thermal conductivity dominates in La–Ca–MnO manganites and is an artifact of strong
phonon-impurity and -phonon scattering mechanisms in the ferromagnetic metallic state. The electronic contribution to the
thermal conductivity (κe) is estimated following the Wiedemann–Franz law. This estimate sets an upper bound on κe, and in the vicinity of the Curie temperature (240 K) κe is about 1% of total heat transfer of manganites. Another important contribution in the metallic phase should come from spin
waves (κm). It is noticed that κm increases with a T2 dependence on the temperature. These channels for heat transfer are algebraically added and κtot develops a broad peak at about 55 K, before falling off at lower temperatures. The behavior of the thermal conductivity in
manganites is determined by competition among the several operating scattering mechanisms for the heat carriers and a balance
between electron, magnon, and phonon contributions. The numerical analysis of heat transfer in the ferromagnetic metallic
phase of manganites shows similar results as those revealed from experiments.
相似文献