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1.
We study the effect of fluctuations on the ac conductivity of a layered superconductor for c-axis electromagnetic wave polarization. The fluctuation contributions of different physical nature and sign (paraconductivity,
Maki-Thompson anomalous contribution, one-electron density-of-states renormalization) are found to be suppressed by the external
field at different characteristic frequencies (ω
AL∼T-T
c
, ω
MT∼max{T-T
c
,τ
ϕ
−1
}, ω
DOS∼min{T, τ
−1}). As a result, the appearance of a nonmonotonic frequency dependence (pseudogap) in the infrared optical conductivity of
high-temperature superconductor is predicted.
Pis’ma Zh. éksp. Teor. Fiz. 64, No. 6, 397–401 (25 September 1996)
Department of Theoretical Physics Moscow Institute of Steel and Alloys.
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
2.
Measurements have been made of the Hall coefficientR of some alloys of silver in palladium over the temperature range 1°K to 120°K. The alloys contain between ∼1 and ∼10 at.-%
silver. Values ofR were also obtained at room temperature and these were in good agreement with earlier published work. The values ofR are negative in all the alloys, and |R| increases both on reducing the temperature and increasing the silver concentration,c. Below ∼10°K, |R| becomes independent of temperature but shows a linear dependence onc, increasing by a factor of 2.5 over the concentration range measured.
This increase is too great to be accounted for in terms of band structure changes alone, so we have examined the effects of
anisotropic impurity scattering. To a first approximation it can be shown thatR is proportional to an anisotropy parameterA, defined asA=〈τ
2(k)〉/〈τ(k)〉2, whereτ(k) represents the relaxation time of an electron in a statek, and 〈〉 is an average over the Fermi surface. In palladium we assume that the majority of the current is carried by the s-electrons.
In the presence of silver impurities these electrons can be scattered into s-states or d-states with relaxation times given
byτ
ss
α1/c(1−c) andτ
sd
α1/c
2(1−c) respectively. FollowingPlate we have assumed thatτ
ss is isotropic and thatτ
sd is anisotropic, leading to an overall anisotropic relaxation time for impurity scattering. We then find the parameterA increases approximately linearly with silver content, in accordance with our experimental results. 相似文献
3.
For the first time submillimetric microwaves (λ<1 mm) are used to observe Azbel' Kaner cyclotron resonance in metals. The very high frequency used (typicallyF≅400 GHz) gives a large value ofωτ (typically 500) and therefore very sharp peaks. The fundamental resonance fieldH
c=m
*
cω/e is rather high (typically 200 KG), so subharmonicsH
c/n can be observed at many values ofH in the field region 0–27 KG. If relatively few electrons participate in the resonance and ifω
cτ≧50 (ω
c=eH/m
*
c,τ relaxation time) thenChambers has shown that the line shapes are independent of relaxation time while the fractional linewidthΔH/H varies as l/ωτ. For the belly orbit in pure copper the conditions of Chambers' theory are satisfied forH≧20 KG parallel to [111] axis.m
* is a minimum andτ=1.8×10−10 s. 相似文献
4.
A new mechanism of a “Coulomb explosion,” where ions are accelerated by the electric field separating charges at the magnetic
Debye radius r
B∼B/4πen
e, is proposed on the basis of a nonquasineutral model of electronic vortices in a magnetic field. It is shown by means of
numerical calculations that in the process of acceleration of the ions a collisionless shock wave, whose front has an effective
width of the order of δ∼r
B, determined by the breakdown of quasineutrality, is formed in a time of the order of ω
pi
−1
, where ωpi is the ion plasma frequency. The origin of such explosive dynamics is the formation of “holes” in the electron density at
characteristic times of the order of ω
pe
−1
(ωpe is the electronic plasma frequency) as a result of the generation of electronic vorticity by the Weibel instability of an
electromagnetic wave. Calculations for a laser pulse with intensity J∼6×1018 W/cm2 show that the ions expand in the radial direction with velocities up to 3.5×108 cm/s.
Pis’ma Zh. éksp. Teor. Fiz. 70, No. 10, 669–674 (25 November 1999) 相似文献
5.
Plasma parameters in the upgraded Trimyx-M Galathea 总被引:1,自引:0,他引:1
A. I. Morozov A. I. Bugrova A. M. Bishaev A. S. Lipatov M. V. Kozintseva 《Technical Physics》2007,52(12):1546-1551
Results are presented from measurements of the plasma parameters in the upgraded Trimyx-M Galathea. After the barrier magnetic
field and the energy of the injected hydrogen plasma bunch were increased to B
bar ∼ 0.1 T and W
0 ≈ 200 J, respectively, the following plasma parameters were achieved: the density n ∼ 5 × 1013 cm−3, the plasma confinement time τ* = 800–900 μs, the elergy of the confined plasma W
1 ∼ 100 J, the ratio of the plasma pressure to the barrier magnetic pressure β
0 ∼ 0.2, the electron temperature T
e
∼ 20 eV, and the ion temperature T
i
∼ 2T
e
. The maximum time during which the plasma density decreased e-fold, τ
p
, was found to be 300 μs at B
bar = 0.1 T, which agrees with the classical transport model. 相似文献
6.
The nonadiabatic corrections to the self-energy part Σs(q, ω) of the phonon Green’s function are studied for various values of the phonon vectors q resulting from electron-phonon interactions. It is shown that the long-range electron-electron Coulomb interaction has no
direct influence on these effects, aside from a possible renormalization of the corresponding constants. The electronic response
functions and Σs(q, ω) are calculated for arbitrary vectors qand energy ω in the BCS approximation. The results obtained for q=0 agree with previously obtained results. It is shown that for large wave numbers q, vertex corrections are negligible and Σs(q, ω) possesses a logarithmic singularity at ω=2Δ, where Δ is the superconducting gap. It is also shown that in systems with nesting, Σs(Q, ω) (where Q is the nesting vector) possesses a square-root singularity at ω=2Δ, i.e., exactly of the same type as at q=0. The results are used to explain the recently published experimental data on phonon anomalies, observed in nickel borocarbides
in the superconducting state, at large q. It is shown, specifically, that in these systems nesting must be taken into account in order to account for the emergence
of a narrow additional line in the phonon spectral function S(q, ω)≈−π
−1 Im D
s
(q, ω), where D
s
(q, ω) is the phonon Green’s function, at temperatures T<T
c
.
Zh. éksp. Teor. Fiz. 115, 1799–1817 (May 1999) 相似文献
7.
A. A. Snarskii K. V. Slipchenko I. V. Bezsudnov 《Journal of Experimental and Theoretical Physics》1998,86(4):811-814
An exact relation for the realization-averaged effective conductivities in the fractal region is found for two-dimensional
randomly inhomogeneous media. It has the form {σ
e
(τ,L)~× {1/σ
e
(−τ,L)~−1=σ
e
2
(τ=0, L≫ξ), where ξ is the correlation length (the self-averaging scale), L is the size of the system, τ=(p-p
c
)/p
c
, and p
c
is the percolation threshold. For L≫ ξ, the system is self-averaged, and the relation transforms into the Dykhne reciprocity relation, A. M. Dykhne, Zh. éksp. Teor.
Fiz. 59, 110 (1970) [Sov. Phys. JETP 32, 63 (1971)] σ
e
(τ)σ
e
(−τ])=σ
e
2
(τ=0)= σ
1
σ
2. A similar relation is obtained for media with an exponentially broad distribution of local conductivities, as well as for
individual realizations of some deterministic structures.
Zh. éksp. Teor. Fiz. 113, 1484–1490 (April 1998) 相似文献
8.
A strong resonant interaction of a two-level atom with a dielectric microsphere is studied on the basis of quantum electrodynamics.
The initial condition considered is one in which the atom is initially excited and the resonant mode of the microsphere has
been excited by a single photon. The spectrum of two emitted photons depends strongly on the method used to excite the microsphere,
i.e., on the spatial distribution of the photon energy. The most characteristic feature of the two-photon fluorescence spectrum
is a strong energy correlation of the emitted photons. This correlation is expressed in the fact that the energies of the
emitted photons are related by the equation of an ellipse (ω+ω
2−2ω
vA
)2+3(ω
1−ω
2)2= 4Ω
Rabi
2
. The relation between the results obtained and the predictions of the theory of dressed states is discussed.
Pis’ma Zh. éksp. Teor. Fiz. 70, No. 3, 192–197 (10 August 1999) 相似文献
9.
An investigation is reported of stimulated two-photon emission by Bose-condensed excitons accompanied by a coherent two-exciton
recombination, i.e., by simultaneous recombination of two excitons with opposite momenta leaving unchanged the occupation
numbers of exciton states with momenta p≠0. Raman light scattering (RLS) accompanied by a similar two-exciton recombination (or production of two excitons) is also
analyzed. The processes under consideration can occur only if a system contains Bose condensate, so their detection can be
used as a new method to reveal Bose condensation of excitons. The recoil momentum, which corresponds to a change in the momentum
of the electromagnetic field in the processes, is transferred to phonons or impurities. If the recoil momentum is transmitted
to optical phonons with frequency ω
0
s
, whose occupation numbers are negligible, and the incident light frequency satisfies ω<2Ω, where Ω_=Ω−ω
0
s
is the difference frequency and Ω is the light frequency corresponding to the recombination of an exciton with zero momentum,
stimulated two-photon emission and RLS with coherent two-exciton recombination give rise to a line at 2Ω_ −ω and an anti-Stokes component at ω+2Ω_, respectively. For ω2Ω_ the RLS spectrum contains Stokes and anti-Stokes components at frequencies ω±2Ω_, whereas stimulated two-photon emission is impossible. Formulas for the cross sections at finite temperatures are obtained
for the processes under consideration. Our estimates indicate that a spectral line at 2Ω_−ω, corresponding to the stimulated two-photon emission accompanied by coherent optical phonon-assisted two-exciton recombination
can be experimentally detected in Cu2O.
Zh. éksp. Teor. Fiz. 115, 1353–1376 (April 1999) 相似文献
10.
A. M. Satanin S. V. Khor’kov V. V. Skuzovatkin 《Journal of Experimental and Theoretical Physics》1997,85(2):351-359
We study the effect of a weak nonlinearity in media on the linear regime of current flow in two-dimensional periodic structures
with two equal component concentrations. We find that the asymptotic behavior of the electric field and current as functions
of the distance between the angles in heterogeneous media is determined by the parameter h=σ
2/σ
1 (here σ
1 and σ
2 are the linear conductivities of the cells) and the external magnetic field B. This dependence leads to divergence of the higher-order moments of field and current at certain critical values h
c and B
c and to divergence of the response functions related to the higher-order moments. For square cells the effective nonlinear
conductivity diverges at h⩽h
c, with
. For structures of general shape we find the dependence of h
c on the angles and the external magnetic field. We show that for a given structure the linear regime of current flow in the
system can be reversibly transformed into a nonlinear one by varying the magnetic field strength. The critical field B
c is approximately determined from the condition ω
c
τ∼1, where ω
c and τ
−1 are, respectively, the cyclotron frequency and the collision rate. Finally, we discuss the feasibility of detecting these
effects experimentally.
Zh. éksp. Teor. Fiz. 112, 643–660 (August 1997) 相似文献
11.
A magnetized, low-β plasma in pure toroidal configuration is formed and extensively studied with ion mass as control parameter. Xenon, krypton
and argon plasmas are formed at a fixed toroidal magnetic field of 0.024 T, with a peak density of ∼1011 cm−3, ∼4 × 1010 cm −3 and ∼2 × 1010 cm −3 respectively. The experimental investigation of time-averaged plasma parameter reveals that their profiles remain insensitive
to ion mass and suggests that saturated slab equilibrium is obtained. Low-frequency (LF) coherent fluctuations (ω < ω
ci) are observed and identified as flute modes. Here ω
ci represents ion cyclotron frequency. Our results indicate that these modes get reduced with ion mass. The frequency of the
fluctuating mode decreases with increase in the ion mass. Further, an attempt has been made to discuss the theory of flute
modes to understand the relevance of some of our experimental observations. 相似文献
12.
Suleyman Cabuk 《Central European Journal of Physics》2012,10(1):239-252
The nonlinear optical properties of some ABO3 materials (BaTiO3, KNbO3, LiTaO3 and LiNbO3) are studied by density functional theory (DFT) in the local density approximation (LDA) expressions based on first-principle
calculations. Our goals are to give the details of the calculations for linear and nonlinear optical properties, including
the linear electro-optic (EO) tensor for some ABO3 structures with oxygen octahedral structures using first-principles methods. These results can then be used in the study
of the physics of ferroelectrics, specifically, we present calculations of the second harmonic generation response coefficient
X
ijk
(2) (−2ω, ω, ω) over a large frequency range for ABO3 crystals. The electronic linear EO susceptibility X
ijk
(2) (−ω, ω,0) is also evaluated below the band gap. These results are based on a series of the LDA calculations using DFT. Results for
X
ijk
(2) (−ω, ω,0) are in agreement with experiments below the band gap. The results are compared with the theoretical calculations and the
available experimental data. 相似文献
13.
B. -A. Gradwohl A. Grayevski N. Kaplan F. N. Gygax A. Schenck A. J. Van der Wal 《Hyperfine Interactions》1986,31(1-4):319-323
Longitudinal μSR measurements were performed on a single crystal sphere of DyAl2 in the range 4K≤T≤300 K (i.e. both in the ferromagnetic and paramagnetic phases). Contrary to previous reports the dynamic
depolarization rate does not diverge near TC≌65 K. Rather a well defined peak in the depolariation rate is observed around 95 K with 1/T1 (95 K)∼4 μsec−1. The depolariztion rate above TC is field independent in the range 0≤Bext≤2.5 kG. The observed behavior may be accounted for by assuming that the effective correlation time τ is given by τ−=τ
4f
−1
+τ
diffusion
−1
. The field independence requires that τeff<2·10−11. The peak in 1/T1 could then reflect a slowing down in μ+. 相似文献
14.
E. Yu. Loktionov A. V. Ovchinnikov Yu. Yu. Protasov D. S. Sitnikov 《Bulletin of the Lebedev Physics Institute》2010,37(3):82-84
Optical gas-dynamic processes occurring in polymeric targets ((CH2O)
n
, (C2F4)
n
) exposed to ultrashort laser pulses (τ
0.5 ∼ 45 − 70 fs; λ
I,II,III
= 266, 400, 800 nm; and E/S ∼ 0.1 − 40 J/cm2 at r
0 ∼ 20 μm) were studied under normal conditions and in vacuum (p ∼ 10−2 Pa). The dynamics of the mass flow from the target surface (m′ ∼ 10−5 − 10−4 g/J) was studied and the spectral-energy thresholds of laser ablation, the electron density distribution (n
e
∼ 1014 − 1018 cm−3), the mass-averaged velocity of the material flow from the target surface (∼ 103 m/s), and the chemical composition and average temperature in the near-surface plasma formation (T ∼ 5000 K) were determined using interference microscopy, emission spectroscopy, and shadowgraphy. 相似文献
15.
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
16.
V. I. Tsebro O. E. Omel’yanovskii E. F. Kukovitskii N. A. Sainov N. A. Kiselev D. N. Zakharov 《Journal of Experimental and Theoretical Physics》1998,86(6):1216-1219
Bulk samples of carbon multilayer nanotubes with the structure of nested cones (fishbone structure) suitable for transport
measurements, were prepared by compressing under high pressure (∼25 kbar) a nanotube precursor synthesized through thermal
decomposition of polyethylene catalyzed by nickel. The structure of the initial nanotube material was studied using high-resolution
transmission electron microscopy. In the low-temperature range (4.2–100 K) the electric resistance of the samples changes
according to the law ln R ∝ (T
0/T)1/3, where T
0∼7 K. The measured magnetoresistance is quadratic in the magnetic field and linear in the reciprocal temperature. The measurements
have been interpreted in terms of two-dimensional variable-range hopping conductivity. It is suggested that the space between
the inside and outside walls of nanotubes acts as a two-dimensional conducting medium. Estimates suggest a high value of the
density of electron states at the Fermi level of about 5×1021 eV−1 cm−3.
Zh. éksp. Teor. Fiz. 113, 2221–2228 (June 1998) 相似文献
17.
K.C. Chung C.S. Wang A.J. Santiago J.W. Zhang 《The European Physical Journal A - Hadrons and Nuclei》2001,12(2):161-167
The parameters of the σ-ω-ρ model in the relativistic mean-field theory with nonlinear σ-meson self-interaction are determined
by nuclear-matter properties, which are taken as those extracted by fits to data based on nonrelativistic nuclear models.
The values of the relevant parameters are C
σ
2∼ 94, C
ω
2∼ 32, C
ρ
2∼ 26, b∼ - 0.09, c∼ 1, and the σ-meson mass m
σ∼ 370 MeV, while the value of the calculated nuclear- surface thickness is t∼ 1.4 fm. The field system is shown to be stable, since the σ-meson self-interaction energy is a lower bound in this whole
parameter region with positive c. On the other hand, the effective nucleon mass M* is larger than 0.73M, if the symmetry incompressibility Ks is assumed to be negative and the nuclear-matter incompressibility K0 is kept less than 300 MeV.
Received: 27 June 2001 / Accepted: 5 October 2001 相似文献
18.
The complex time method is used to show that length l
C
of formation of processes involving emission of photons and production of pairs in a constant external field can be determined
correctly and that the resultant values of l
C
have not only qualitative, but also quantitative meaning. Analysis based on the complex time method makes it possible to
express the amplitudes of processes in the form of rapidly converging integrals. It is found that the radiation formation
length for low-energy (soft) photons decreases upon an increase in the radiation frequency in accordance with the familiar
law l
C
∼ ω−1/3, while for higher frequencies, this dependence changes to l
C
∼ ω−1/2. The formulas derived for l
C
make it possible to indicate the accuracy with which this quantity can be treated as the radiation formation length. 相似文献
19.
20.
D. E. Feldman 《JETP Letters》1999,70(2):135-140
The random field and random anisotropy N-vector models are studied with the functional renormalization group in 4−ε dimensions. The random anisotropy Heisenberg (N=3) model has a phase with an infinite correlation length at low temperatures and weak disorder. The correlation function
of the magnetization obeys a power law 〈m(r
1)m(r
2)〉∼|r
1−r
2|− 0.62ε. The magnetic susceptibility diverges at low fields as χ∼H
−1+0.15ε. In the random field N-vector model the correlation length is finite at arbitrarily weak disorder for any N>3.
Pis’ma Zh. éksp. Teor. Fiz. 70, No. 2, 130–135 (25 July 1999)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献