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1.
Crystalline (cr-) Dyag [CsC] structure] orders antiferro-magnetically with T N≅60K; amorphous (am-) DyAg ferro-magnetically with T C≈-18K. We measured the longitudinal field (LF) μ +SR relaxation functions G ZZ(t) for 5K<T<300K using surface muons. In the paramagnetic state. cr-DyAg gives an exponential G ZZ (t) in the relaxation rate rising first slowly then more rapidlynear T N; no decoupling is observed in LF up to 0.4T. In the ordered state we see a Lorentzian Kubo-Toyabe G ZZ(t), becoming nearly static at the lowest temperatures. Its static width is very narrow (Δ≈-7 MHz), and full dceoupling is
achieved here in 0.1 T. On approaching T N, the fluctuation rate and the static width increase mootonically bt the field distribution remains Loratzian. A LF of 0.4T
is then insufficient to quench the fast exponential relaxation. In paramagnetic am-DyAg, the μ + depolarization is always much faster then in cr-DyAg. At lower temperatures it is better described by a root-exponential
than an exponential G ZZ(t). Below T C an exponentially relaxing signal with 1/3 amplitude is seen. The decoupling effect of LF up to 0.4T was negligible at all
temperatures. 相似文献
2.
Measurements have been made of the Hall coefficient R 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 of R were also obtained at room temperature and these were in good agreement with earlier published work. The values of R 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 on c, 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 that R is proportional to an anisotropy parameter A, defined as A=〈 τ
2( k)〉/〈 τ( k)〉 2, where τ( k) represents the relaxation time of an electron in a state k, 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
by τ
ss
α1/ c(1− c) and τ
sd
α1/ c
2(1− c) respectively. Following Plate we have assumed that τ
ss is isotropic and that τ
sd is anisotropic, leading to an overall anisotropic relaxation time for impurity scattering. We then find the parameter A increases approximately linearly with silver content, in accordance with our experimental results. 相似文献
3.
Accumulated photon echoes have been used to investigate the mechanisms of optical dephasing in CaF 2 crystals activated by Nd 3+ ions. Tunable picosecond laser radiation, which permits the selective excitation of various Nd 3+ optical centers in the 4
I
9/2→ 4
G
5/2, 2
G
7/2 transition, is used. The optical phase relaxation times measured at temperatures from 9 to 50 K permit determination of the
homogeneous widths of the transitions between the low-lying 4
I
9/2 Stark level and three excited 4
G
5/2, 2
G
7/2 levels, and calculation of the constants of the inter-Stark relaxation transitions in the ground and excited multiplets for
the rhombic N and M Nd 3+ centers in CaF 2 crystals. An analysis of the temperature dependence of the homogeneous linewidth of the transitions between low-lying Stark
levels of the ground and excited states shows that the mechanism of optical dephasing in the crystals investigated is described
well by direct relaxation processes with resonant inter-Stark absorption of one phonon in the ground and excited states. At
T=9 K, the homogeneous linewidth Γ h in CaF 2 crystals is almost an order of magnitude smaller than Γ h in disordered CaF 2-YF 3 crystals. This difference can be attributed to the significantly greater spectral phonon density of states in disordered
crystals.
Zh. éksp. Teor. Fiz. 113, 278–290 (January 1998) 相似文献
4.
The effect of a polarized conduction-electron cloud back on a magnetic impurity dissolved in a metal is studied. It is shown
that at a temperature T
c
much higher than the Kondo temperature the system becomes unstable against symmetry breaking and that a state with 〈 S
z
〉 ≠ 0 is established. The behavior of 〈 S
z
〉 is derived for all temperatures and magnetic fields except for a very narrow region around T
c
and for very low temperatures. The minute role of Kondo-type processes in establishing the symmetry-broken state is pointed
out.
Pis’ma Zh. éksp. Teor. Fiz. 66, No. 3, 184–189 (10 August 1997)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
5.
The dielectron widths of ψ(4040), ψ(4160), and ψ(4415), and their ratios are shown to be in good agreement with experiment, if in all cases the S-D mixing with a large mixing angle θ ≅ 34° is taken. Arguments are presented why continuum states give small contributions to the wave functions at the origin.
We find that the Y (4360) resonance, considered as a pure 3 3
D
1 state, would have very small dielectron width, Γ
ee
( Y (4360)) = 0.060 keV. On the contrary, for large mixing between the 4 3
S
1 and 3 3
D
1 states with the mixing angle θ = 34.8°, Γ
ee
( ψ(4415)) = 0.57 keV coincides with the experimental number, while a second physical resonance, probably Y (4360), has also a rather large Γ
ee
( Y (∼4400)) = 0.61 keV. For the higher Y (4660) resonance, considered as a pure 5 3
S
1 state, we predict the dielectron width Γ
ee
( Y (4660)) = 0.70 keV, but it becomes significantly smaller, namely 0.31 keV, if the mixing angle between the 5 3
S
1 and 4 3
D
1 states has the characteristic value θ = 34°. The mass and dielectron width of the 6 3
S
1 charmonium state are calculated.
The text was submitted by the authors in English. 相似文献
6.
The properties and temperature behavior of the π and σ bound states are studied in the framework of the nonlocal model with
a separable interaction kernel, based on the quark Dyson-Schwinger and meson Bethe-Salpeter equations. M
π( T), f
π( T), M
σ( T), and Γ σ → ππ( T) are considered above and below the deconfinement and chiral restoration transitions.
Talk at the Round-Table Discussion “Searching for a Mixed Phase of Strongly Interacting Matter at the JINR Nuclotron,” Dubna,
July 7–9, 2005.
The text was submitted by the authors in English. 相似文献
7.
Resistivity ρ and the Hall coefficient R
H at atmospheric pressure in the temperature range of 77–400 K and the dependences of these parameters (ρ( P) and R
H( P)) and magnetic susceptibility (χ( P)) on hydrostatic pressures of up to P ≤ 7 GPa at 300 K in p-InAs〈Mn〉 single crystals was investigated. The baric coefficients of the ionization energy of Mn impurity centers and the
pressure dependence of the dielectric constant ɛ( P) were determined. 相似文献
8.
Intervalley electron scattering by phonons in (AlAs) 1(GaAs) 3(001) superlattices is studied using the pseudopotential method and a phenomenological model of the bonding forces. The deformation
potentials between the conduction band extrema of the superlattice involving short-and long-wavelength phonons are calculated.
It is shown that the mixing of states from the zinc-blende L valleys plays a greater role in intervalley scattering in a superlattice than the Γ- X mixing. In particular, due to L-L mixing, the Γ- X
3 transitions, analogous to Γ- L transitions in zinc blende, have higher intensities than the analogues of Γ- X transitions (Γ 1- M
5 and (Γ 1-Γ 3 transitions). The deformation potentials averaged over the scattering channels in the superlattice agree with the corresponding
potentials in a solid solution, but all transitions in the superlattice have higher intensities for the lower states. 相似文献
9.
Calculations of the complex elastic moduli Ĉ( T) in dilute Cr alloys are compared to measurements of the velocity and damping of sound near T
N and at high temperatures T> T
N ( T
N — Néel temperature). The thermodynamic calculation is based on the covalent bond model of 3 d ions in a state with different numbers n of covalent electrons. The parameters A
ij
(n)
of indirect exchange between the ions of the i and j sublattices are expressed in terms of the covalent bond energy Γ
ij
(n)
. The stability of the charge and spin density waves (CDWs and SDWs) is found by a variational method and is determined by
the dispersion of Γ
ij
(n)
and by the Coulomb parameters U
n. For a small structural vector Q the phase diagram contains a superantiferromagnetic phase (SAFM) at temperatures T
N< T≲2 T
N. The peak of the defect |Δ E( T)| of the modulus and of the sound damping Δ h( T
N) near the first-order SDW-SAFM transition is determined by the structure of the transitional domain. Measurements of the
anomalous growth of E( T) at temperatures T> T
N make it possible to determine the magnetostriction constants λ( T) of Ce alloys in the SAFM phase on the basis of the SAFM theory.
Fiz. Tverd. Tela (St. Petersburg) 41, 1467–1472 (August 1999) 相似文献
10.
The relaxation times of excited states of arsenic dopant in germanium at cryogenic temperatures T < 15 K have been experimentally studied by the optical pump-probe method using radiation of a free-electron laser. Two variants of the excitation of impurity centers have been used in the experiment: (i) from the 1s(A1) ground state of the dopant and (ii) from the 1s(T2) first excited state having a finite thermal population. In the former variant, it has been shown that the decay times of the 2p0 and 3p± states are about 0.8 and 0.6 ns, respectively. In the latter variant, a single measurement can simultaneously provide the relaxation times of two 2p± and 1s(T2) states about 0.6 and no more than 0.16 ns, respectively. The data obtained have indicated the possibility of forming population inversion and the gain of terahertz radiation at the 2p± → 1s(T2) and 2p0 → 1s(T2) transitions at the optical excitation of the mentioned impurity centers. 相似文献
11.
The longitudinal μ
+-spin relaxation rate has been measured on a high-purity spherical α-iron single crystal at temperatures T down to 20 mK and in applied magnetic fields B
appl parallel to 〈111〉 up to 3 T. Only above 1 K can the data be satisfactorily described by one rate constant Г. At 1 T≤ B
appl≤2 T and 50 mK≤ T≤300 mK, oscillations (“wiggles”) were in addition superimposed on the longitudinal relaxation. A qualitative understanding
of the measurements may be achieved in terms of the increasing influence of internal stresses on μ
+ diffusion as the temperature is lowered. 相似文献
12.
We study the effects of time delay on the normalized correlation function C( s) and the associated relaxation time T
c
for a bistable system with correlations between multiplicative and additive white noises under the condition of small time
delay. Using the projection operator method, the expressions of T
c
and C( s) are obtained. Based on numerical computations, it is found that the delay time τ slows down the rate of fluctuation decay of dynamical variable for the presence of positive feedback intensity ( ∈ > 0), while speeds up the rate of fluctuation decay of dynamical variable for the presence of negative feedback intensity
( ∈ < 0). The effects of the delay time τ on the T
c
and C( s) are entirely opposite for ∈ 〉 0 and ∈ < 0.
相似文献
13.
A pronounced step-like (kink) behavior in the temperature dependence of resistivity ρ( T) is observed in the optimally doped Sm 1.85Ce 0.15CuO 4 thin films around T
sf = 87 K and attributed to the manifestation of strong-spin fluctuations induced by Sm 3+ moments with the energy ħω sf = k
B
T
sf ≃ 7 meV. The experimental data are found to be well fitted by the residual (zero-temperature) ρ res, electron-phonon ρ e-ph( T) = AT, and electron-electron ρ e-e( T) = BT
2 contributions in addition to the fluctuation-induced contribution ρ sf( T) due to thermal broadening effects (of the width ω sf). According to the best fit, the plasmon frequency, impurity scattering rate, electron-phonon coupling constant, and Fermi
energy are estimated as ω p = 2.1 meV, τ
0
−1
= 9.5 × 10 −14 s −1, λ = 1.2, and E
F = 0.2 eV, respectively.
The text was submitted by the authors in English. 相似文献
14.
The nucleon electromagnetic form factors G
E
P
(q 2), G
M
P
(q 2) and the axial-vector form factor G A(q 2) are studied in a relativistic model of independent quarks confined by an equally mixed scalar-vector square root potential V
q( r)=1/2(1+ γ
0)( ar
1/2+ ν
0) taking into account the appropriate centre-of-mass corrections. The respective root-mean-square radii associated with G
E
P
(q 2) and G
A
(q 2) come out as [〈 r
2〉
E
P
] 1/2=0.86 fm and 〈 r
A
2
〉 1/2=0.88 fm. Restoration of chiral symmetry in this model is discussed to derive the pion-nucleon form factor G
πNN(q 2) and consequently the pion-nucleon coupling constant is obtained as g
πNN(q 2)=12.81 as compared to g
πNN(q 2) exp⋍13. 相似文献
15.
Results for the one-loop calculation of the decay width Γ( H→ ggZ) in the standard model with Higgs boson masses in the range 115 GeV< m
H
<2 m
W
are presented. We find that among all the helicity amplitudes contributing to the width only those for which the gluons have
the same polarization and the Z is longitudinally polarized contribute in any significant way. The calculation includes all contributions from the second
and third generations, and kinematic cuts to enhance the H→ ggZ signal. Compared to the width of H→ gg, we find Γ( H→ ggZ)/Γ( H→ gg)≲10 −4. 相似文献
16.
The spectral dependence of the electron-phonon relaxation rate γ e−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 γ e−ph(ℏω) near the Fermi level E
F
, using the parametrization γ e−ph(ℏω)∝λ〈Ω 2〉 (ℏω− E
F
) 2 makes it possible to determine directly the electron-phonon interaction parameter λ〈Ω 2〉. The parameter λ〈Ω 2〉 for YBa 2Cu 3O 7−δ is analyzed using this method.
Pis’ma Zh. éksp. Teor. Fiz. 70, No. 5, 329–332 (10 September 1999) 相似文献
17.
We use the data on the pressure (up to P=1.5 GPa) and field (up to H=17 kOe) dependence of the Hall coefficient and the resistivity at 77.6 and 300 K in p-CdSnAs 2〈Cu〉 to calculate the effective kinetic characteristics of the charge carriers, the density and mobility of the conduction
electrons and the holes of the deep acceptor and valence bands, in an interval of excess-acceptor densities N
ext ranging from 10 10–10 17 cm −3. We establish that in a heavily doped semiconductor with a deep impurity band at the tail of the density of states of the
intrinsic band, with unequal donor and acceptor densities, a a heavily doped and fully compensated semiconductor state is
realized under hydrostatic compression. The threshold value of the pressure that initiates the transition into such a state,
P
c, depends on the extent to which the impurity band is populated. In p-CdSnAs 2〈Cu〉 at N
ext= N
A, where N
A is the density of deep acceptors, and T⩽77.6 K the value of P
c amounts to 10 −4 GPa. As the population of the deep acceptor band grows, P
c increases and in the limit becomes infinite. We discuss the special features of the electrophysical properties of p-CdSnAs 2〈Cu〉 arising from the absence of an energy gap between the states of the conduction band and those of the deep acceptor band.
Zh. éksp. Teor. Fiz. 111, 562–574 (February 1997) 相似文献
18.
The effect of smooth interface potential on the electron tunneling in the GaAs/AlAs(111) structures with thin layers is studied using the pseudopotential method. The transition region between the structure components
is represented by a half-period of the hexagonal (GaAs)
3(AlAs) 3
(111) superlattice. It is shown that the allowance for the smooth potential results in a decrease in the Γ-L-mixing, Fano-resonance
narrowing, and disappearance of interface states at the GaAs/AlAs(111) interface as compared to the abrupt-interface model. The shifts of the lowest Γ-and L-resonances observed for the structures
with the layer thickness <2 nm amount to ∼0.1 eV, which is in good agreement with the behavior of levels in quantum wells.
The transmission coefficient of electrons with the energies 0–0.5 eV above the GaAs conduction-band bottom obtained by multivalley calculation is close to that calculated with allowance for the lowest conduction
band states Γ
1
(1)
and Γ
1
(2)
of superlattice and Γ
1 and L
1 of binary crystals. This indicates that a two-valley superlattice model of the smooth GaAs/AlAs(111) interface can be developed.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 7–13, July, 2007. 相似文献
19.
An analysis is made of the relation between accurate formulas for the coefficients of turbulent diffusion D
T and the alpha effect α
T for a magnetic field in the Lagrange and Euler representations. It is shown that the quadratic term with respect to α
T in the diffusion coefficient derived by Moffatt and Kraichnan is incorrect and should be dropped. First, a numerical solution
of the nonlinear equation (DIA equation) for the Green function is presented, describing the transport of a magnetic field
for the case of incompressible, uniform, isotropic, steady-state turbulence possessing helicity. These solutions are used
to calculate the steady-state coefficients D
T and α
T for various values of the parameters ξ
0= u
0
σ
0/ R
0, a= H
0/ u
0
2
p
0, σ
0/ σ
1, and R
0/ R
1, where u
0, σ
0, and R
0 are the characteristic velocity, lifetime, and scale of the turbulent pulsations, and H
0, σ
1, and R
1 are similar values describing the helicity of the medium h(1,2)=〈 u(1)· (∇× u(2))〉, and the parameter α characterizes the degree of helicity. The DIA values of D
T and α
T and the self-consistent values of these quantities calculated using the Green tensor in the diffusion approximation are in
qualitative agreement. It is shown that the coefficient of turbulent diffusion is always positive for all the types of turbulence
studied. Nonsteady-state values of D
T( t) and α
T( t) calculated by a self-consistent method are given.
Zh. éksp. Teor. Fiz. 112, 1312–1331 (October 1997) 相似文献
20.
The dependence of the intrinsic line width Γ of electron and hole states due to inelastic scattering on the wave vector k
∥ in the occupied surface state and the first image potential state on the Cu(111) and Ag(111) surfaces has been calculated
using the GW approximation, which simulates the self-energy of the quasiparticles by the product of the Greens’s function
and the dynamically screened Coulomb potential. Different contributions to the relaxation of electron and hole excitations
have been analyzed. It has been demonstrated that, for both surfaces, the main channel of relaxation of holes in the occupied
surface states is intraband scattering and that, for electrons in the image potential states, the interband transitions play
a decisive role. A sharp decrease in the intrinsic line width of the hole state with an increase in k
∥ is caused by a decrease in the number of final states, whereas an increase in Γ of the image potential state is predominantly
determined by an increase of its overlap with bulk states. 相似文献
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