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1.
Explicit expressions have been derived for the volume dependence of electron-phonon coupling strength (λ) and the Coulomb pseudopotential (μ*) considering the variation of Fermi momentum (κ
F) and Debye temperature (θ
D) with volume. Ashcroft’s model pseudopotential and RPA form of dielectric screening have been used for obtaining pressure
dependence of transition temperature (T
C) and the logarithmic volume derivative (Φ) of the effective interaction strength (N
0
V) for metallic glass superconductor Mg70Zn30. It has been observed that T
C of the metallic glass Mg70Zn30 decreases rapidly with increase of pressure and the superconducting phase disappears at about 30% decrease of volume, for
which the μ* curve shows a minimum and an elbow is formed in the Φ graph. 相似文献
2.
Aditya M. Vora 《Frontiers of Physics in China》2007,2(4):430-435
The theoretical investigation of the superconducting state parameters (SSP) viz. electron-phonon coupling strength λ, Coulomb pseudopotential μ*, transition temperature T
c, isotope effect exponent α and effective interaction strength N
0
V of ten Cu
C
Zr100−C
metallic glasses have been reported using Ashcroft’s empty core (EMC) model potential. Three local field correction functions
proposed by Hartree (H), Taylor (T) and Ichimaru-Utsumi (IU) are used in the current investigation to study the screening
influence on the aforesaid properties. It is observed that the electron-phonon coupling strength λ and the transition temperature T
C
are quite sensitive to the selection of the local field correction functions, whereas the Coulomb pseudopotential μ*, isotope effect exponent α and effective interaction strength N
0
V show weak dependences on local field correction functions. The T
c obtained from IU-local field correction function are found an excellent agreement with available theoretical or experimental
data. Also, the present results are found in qualitative agreement with other such earlier reported data, which confirms the
superconducting phase in metallic glasses.
相似文献
3.
Bibhuti Parida Jitendra Sahoo Namita Shadangi P. Nayak 《Indian Journal of Physics》2010,84(10):1333-1339
Here we have considered the electron-phonon interaction in the Periodic Anderson Model (PAM) to describe the temperature dependence
of resistivity in some heavy fermion (HF) systems. Since the resistivity is related to the imaginary part of the electron
self energy, the expression of the same is evaluated from electron Green function by the double time temperature dependant
Green function technique of the Zubarev type. In order to understand the effect of electron-phonon interaction in these systems,
we couple the phonons to both the f-electrons as well as to the electrons of the hybridization band of both conduction and f-electrons. The influence of various model parameters, namely, the position of 4f level E
0, the electron-phonon coupling strengths f
1(q) and f
2(q), the effecting coupling strength g = N(0)γ
02/ω
0 have been studied on the temperature dependence of resistivity in HF systems. The numerical analysis is performed for q = 0 and for finite temperature in the static limit. The analysis of the results gives satisfactorily in comparison to the
experimental observations. 相似文献
4.
Aditya M. Vora 《Central European Journal of Physics》2008,6(2):253-262
The theoretical investigations of the superconducting state parameters (SSP) viz. electron-phonon coupling strength λ, Coulomb pseudopotential μ*, transition temperature T
C
, isotope effect exponent α and effective interaction strength N
O
V of six binary La100-C
Ga
C
(C = 16, 20, 22, 24, 26 and 28 at. %) metallic glasses have been reported using Ashcroft’s empty core (EMC) model potential
for the first time. Five local field correction functions proposed by Hartree (H), Taylor (T), Ichimaru-Utsumi (IU), Farid
et al. (F) and Sarkar et al. (S) are used in the present investigation to study the screening influence on the aforesaid properties. It is observed that
the electron-phonon coupling strength λ and the transition temperature T
C
are quite sensitive to the selection of the local field correction functions, whereas the Coulomb pseudopotential μ*, isotope effect exponent α and effective interaction strength N
O
V show weak dependences on the local field correction functions. The T
C
obtained from H-local field correction function are found in qualitative agreement with available experimental data and show
almost linear nature with the concentration (C) of ‘Ga’ element. A linear T
C
equation is proposed by fitting the present outcomes for H-local field correction function, which is in conformity with other
results for the experimental data. Also, the present results are found to be in qualitative agreement with other such earlier
reported data, which confirms the superconducting phase in the metallic glasses.
相似文献
5.
Effect of heavy cation doping (Ca2+ at the A-site) on the thermal properties of perovskite LaMnO3 has been investigated using the Rigid Ion Model (RIM)). As strong electron-phonon interactions are present in these compounds,
the lattice part of the specific heat deserves proper attention. The specific heat of magnetoresistance compound La0.25Ca0.75MnO3 as a function of temperature (10 K ≤ T ≤ 300 K) is reported. Our results on specific heat are in good agreement with the measured values of specific heat at lower
temperatures. In addition, the results on the cohesive energy (ϕ), molecular force constant (f), Restrahalen frequency (ν
0), Debye temperature (Θ
D) and Gruneisen parameter (γ) are also discussed.
相似文献
6.
Our well-recognized pseudopotential is used to investigate the superconducting state parameters viz: electron-phonon coupling
strength λ. Coulomb pseudopotential μ*, transition temperature T
c, isotope effective exponent α and interaction strength N
0
V for the In1−x
Zn
x
and In1−x
Sn
x
binary alloys. We have incorporated six different types of local field correction functions, proposed by Hartree, Taylor,
Vashistha-Singwi, Ichimaru-Utsumi, Farid et al and Sarkar et al to show the effect of exchange and correlation on the aforesaid properties. Very strong influence of the various exchange
and correlation functions is concluded from the present study. The comparison with other such theoretical values is encouraging,
which confirms the applicability of our model potential in explaining the superconducting state parameters of binary mixture. 相似文献
7.
E. Cappelluti C. Grimaldi L. Pietronero 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(4):511-517
In small Fermi energy metals, disorder can deeply modify superconducting state properties leading to a strong suppression
of the critical temperature Tc. In this paper, we show that also normal state properties can be seriously influenced by disorder when the Fermi energy E
F is sufficiently small. We calculate the normal state spin susceptibility χ for a narrow band electron-phonon coupled metal
as a function of the non-magnetic impurity scattering rate . We find that as soon as is comparable to E
F, χ is strongly reduced with respect to its value in the clean limit. The effects of the electron-phonon interaction including
the nonadiabatic corrections are discussed. Our results strongly suggest that the recent finding on irradiated MgB2 samples can be naturally explained in terms of small E
F values associated with the σ-bands of the boron plane, sustaining therefore the hypothesis that MgB2 is a nonadiabatic metal.
Received 31 July 2002 / Received in final form 21 September 2002 Published online 31 December 2002 相似文献
8.
Summary The thermal conductivity of YBa2Cu3O7−δ high-T
c superconductor is analysed self-consistently on both normal and superconducting states on the base of the Bardeen-Rickayzen-Tewordt
extended theory to take into account the effects of magnetic field and superconducting fluctuations. It is shown that experimental
data are in a quantitative agreement with theory even if the number and variation intervals of adjustable parameters are substantially
reduced in comparison with previous works. Phonon relaxation rates due to different mechanisms of phonon scattering as well
as the parameters of electron-phonon interaction are estimated. It is shown that thermal conductivity in YBa2Cu3O7−δ is consistent with the BCS model with intermediate electron-phonon coupling λ=1–3 the phonon-electron and electron-phonon
relaxation times near critical temperature are evaluated to be 10−10s and 10−12s, respectively. 相似文献
9.
C M Srivastava 《Pramana》1987,29(4):L423-L428
A criterion for superconductivity in highT
c oxidic compounds is proposed based on a short range cooperative electron-phonon coupling and the Darwin interaction for Cooper
pairing. It is shown that the small polaron stabilization energy (ε
p) should be less than about 0.04 eV and the system should have a metal ion for which Darwin interaction energy is large. 相似文献
10.
In the present paper some superconducting (SC) state parameters of metals Ga, Cd and In have been studied through Harrison’s
First Principle [HFP] pseudopotential technique using McMillan’s formalism. The impact of choosing two different sets of core
energy eigenvalues viz. Herman-Skillman and Clementi (or Experimental) has been studied.
It has been observed that the choice of eigenvalues has appreciable impact on the form factor and consequently on the SC state
transition parameter viz. electron-phonon coupling strength (λ) and superconducting transition temperature T
c
. Hence the choice of suitable eigenvalues is essential for these computations. Reasonable agreement with experimental and
theoretical data have been obtained. 相似文献
11.
The spectral dependence of the electron-phonon relaxation rate γe−ph(ℏω) in metals is studied in pump-supercontinuum-probe (PSCP) experiments with femtosecond time resolution. Investigation
of this spectral dependence, which exhibits a substantial slowing of the relaxation rate γe−ph(ℏω) near the Fermi level E
F
, using the parametrization γe−ph(ℏω)∝λ〈Ω2〉 (ℏω−E
F
)2 makes it possible to determine directly the electron-phonon interaction parameter λ〈Ω2〉. The parameter λ〈Ω2〉 for YBa2Cu3O7−δ is analyzed using this method.
Pis’ma Zh. éksp. Teor. Fiz. 70, No. 5, 329–332 (10 September 1999) 相似文献
12.
Aditya M. Vora 《Central European Journal of Physics》2008,6(2):238-252
Ashcroft’s empty core (EMC) model potential is used to study the superconducting state parameters (SSPs) viz. electron-phonon
coupling strength λ, Coulomb pseudopotential μ*, transition temperature T
C
, isotope effect exponent αand effective interaction strength N
O
V of some binary metallic glasses based on the superconducting (S), conditional superconducting (S’) and non-superconducting
(NS) elements of the periodic table. Five local field correction functions proposed by Hartree (H), Taylor (T), Ichimaru-Utsumi
(IU), Farid et al. (F) and Sarkar et al. (S) are used for the first time with EMC potential in the present investigation to study the screening influence on the aforesaid
properties. The T
C
obtained from the H-local field correction function are in excellent agreement with available theoretical or experimental
data. In the present computation, the use of the pseudo-alloy-atom model (PAA) was proposed and found successful. Present
work results are in qualitative agreement with such earlier reported experimental values which confirm the superconducting
phase in all metallic glasses. A strong dependency of the SSPs of the metallic glasses on the valence ‘Z’ is identified.
相似文献
13.
N. E. Sluchanko V. V. Glushkov S. V. Demishev M. V. Kondrin N. A. Samarin V. V. Moshchalkov V. V. Brazhkin 《Journal of Experimental and Theoretical Physics》1998,86(1):190-196
The thermopower coefficient as a function of temperature, S(T), has been measured in nonequilibrium superconductors, such as Al1−x
Six substitutional solid solutions and Al-Si alloys on various decay stages. When aluminum is substituted with silicon, the contribution
to the thermopower due to phonon-drag effects, which are dominant in pure aluminum at low temperatures, is suppressed, and
low-temperature anomalies in S(T) detected in compositions near lattice instability limit are determined by the diffusion component of the thermopower. The
low-temperature anomalies in the thermopower and the notable increase in the coefficient in front of the linear term in S(T) are attributed to effects of thermopower renormalization due to the electron-phonon interaction enhancement with “soft modes”
in the face-centered cubic (FCC) lattice of Al1−x
Six solid solutions. The nature of these anomalies in S(T) is analyzed in terms of the Kaiser and Reizer-Sergeev models.
Zh. éksp. Teor. Fiz. 113, 339–351 (January 1998) 相似文献
14.
We apply the Bogoliubov compensation principle to the gauge electro-weak interaction to demonstrate the spontaneous generation
of an anomalous three-boson gauge invariant effective interaction. The non-trivial solution of the compensation equations
uniquely defines the values of the parameters of the theory and the form factor of the anomalous interaction. The contribution
of this interaction to the running EW coupling, α
ew(p
2), gives its observable value α
ew(M
W
2)=0.0374, in satisfactory agreement to the experiment. The anomalous three-boson interaction gives a natural explanation of
the well-known discrepancy in the muon g−2. The implications for EW studies at Tevatron and LHC are briefly discussed. 相似文献
15.
The exact formula of Tc’s equation and the isotope effect exponent of two-band s-wave superconductors in the weak-coupling limit are derived by considering
the influence of interband interaction. In each band, our model consists of two pairing interactions: the electron-phonon
interaction and non-electron-phonon interaction. We find that the isotope effect exponent of MgB2, α = 0.3 with Tc ≈ 40 K can be found in the weak coupling regime and interband interaction of electron-phonon shows more effect on the isotope
effect exponent than on the interband interaction of non-phonon. 相似文献
16.
Aditya M. Vora 《Central European Journal of Physics》2008,6(2):263-276
The theoretical computation of the superconducting state parameters (SSP) viz; electron-phonon coupling strength λ, Coulomb pseudopotential μ
*, transition temperature T
c
, isotope effect exponent α and effective interaction strength N
O
V of some monovalent (Cu and Au), divalent (Ca, Sr, Ba, αHg, βHg and Ra) and polyvalent (Lu, Rh, Sc, Y, La, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Ac, Th, Hf, Ru, Os, Ir, V, Ta, Pa, Cr, Mo,
U, Re, Np and Pu) amorphous metals based on the different groups of the periodic table have been carried out for the first
time using the well known Ashcroft’s empty core (EMC) model pseudopotential. Herein, we have employed five different types
of local field correction functions proposed by Hartree (H), Taylor (T), Ichimaru-Utsumi (IU), Farid et al. (F) and Sarkar et al. (S) to study the exchange and correlation effects on the present investigations. A very strong influence of all the exchange
and correlation functions have been observed in the present study. Our results are in fair agreement with documented theoretical
as well as experimental data. A strong dependency of the SSP of amorphous metals on the valency Z was found.
相似文献
17.
A detailed theoretical analysis of the experimental data obtained earlier in the studies of the tunneling spectra in the MgB2 two-band superconducting system has been performed. It is shown that most these data are well described in the generalized
two-band Bardeen-Cooper-Schrieffer theory with the constants of the intraband electron-phonon interaction that reasonably
coincide with the ab initio calculation results. It is shown that the existence of specific collective excitation in this
system induced by oscillations of the relative phase of two superconducting condensates (the Leggett mode) indicates the overestimation
of the constants of the interband electron-phonon interaction in the ab initio calculations. The dependences of the superconducting
gaps and the Leggett mode frequency on the temperature and the disorder degree in the Mg1 − x
Al
x
B2 system have been thoroughly studied. 相似文献
18.
J. K. Baria 《Czechoslovak Journal of Physics》2004,54(4):469-485
A model pseudopotential depending on an effective core radius but otherwise parameter free is used to study the interatomic
interactions, phonon dispersion curves (inq and r-space analysis), phonon density of states, mode Grüneisen parameters, dynamical elastic constants (C
11,C
12 andC
44), bulk modulus (B), shear modulus (C′), deviation from Cauchy relation (C
12–C
44), Poisson’s ratio (σ), Young’s modulus (Y), behavior of phonon frequencies in the elastic limit independent of the direction (Y
1), limiting value in the [110] direction (Y
2), degree of elastic anisotropy (A), maximum frequencyω
max, mean frequency 〈ω〉, 〈ω
2〉1/2=(〈ω〉/〈ω
−1〉)1/2, fundamental frequency 〈ω
2〉, and propagation velocities of the elastic constants in Cu, Ag, Au, Ni, Pd, and Pt. The contribution of s-like electrons
is calculated in the second-order perturbation theory for the model potential while that of d-like electrons is taken into
account by introducing repulsive short-range Born-Mayer like term. Very recently proposed screening function due to Sarkar
et al. has been used to obtain the screened form factor. The theoretical results are compared with experimental findings wherever
possible. A good agreement between theoretical investigations and experimental findings has proved the ability of our model
potential for predicting a large number of physical properties of transition metals. 相似文献
19.
The dynamics of the nonlinear excitations in a two-dimensional (2D) φ4-diatomic lattice, with nonlinear on-site electron-phonon coupling at the polarizable ion site has been presented, without
considering the self consistent phonon approximation. One of the major results obtained from our calculations is in the understanding
of continuous structural phase transition, where we have obtained the minimum in soft mode frequency at a soft mode temperatureT
s (>T
c), not at critical temperatureT
c. This occurs due to the anisotropy of such 2D systems. 相似文献
20.
K. V. Ivanin A. V. Leont’ev V. S. Lobkov G. M. Safiullin V. V. Samartsev 《Bulletin of the Russian Academy of Sciences: Physics》2012,76(3):290-294
The results from experiments employing coherent femtosecond spectroscopy in a layer of two-dimensional electron gas at the
boundary of the GaAs/AlGaAs heterojunction at room temperature are presented. The decay curves of primary femtosecond photon
echo are obtained. The decoherence time in two-dimensional electron gas depends strongly on the power of the exciting pulse
and varies from 36 to 54 fs. The dephasing time is studied for the first time as a function of the power of exciting pulses
at room temperature. It is established that this dependence obeys the law T
2 ∼ N
−0.22, which differs from the typical law T
2 ∼ N
−1 for unscreened electron-electron interaction in semiconductor crystals. Analysis shows that electron-phonon interaction plays
an important part along with electron-electron interaction. The induced spin gratings in the GaAs/AlGaAs heterostructure are
studied with an eye to their possible application in spintronics. 相似文献