共查询到20条相似文献,搜索用时 31 毫秒
1.
V. M. Svistunov V. Yu. Tarenkov A. I. D’yachenko R. Aoki 《Physics of the Solid State》1997,39(10):1572-1574
Pronounced softening of the high-frequency part of the phonon spectrum at high pressures is observed by means of tunneling
spectroscopy. As the pressure is increased, the characteristic frequencies of the spectrum at ħΩ>60 mV decrease at the rate d ln(ħΩ)/dP≈(−6.5±0.5)×10−3 kbar−1. On the other hand, hydrostatic pressure causes the low frequencies of the phonon spectrum of Bi 2223 metal oxide to shift
very slightly toward higher energies, consistent with Raman spectra.
Fiz. Tverd. Tela (St. Petersburg) 39, 1764–1766 (October 1997) 相似文献
2.
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
3.
August Yurgens Dag Winkler Nicolay Zavaritsky Tord Claeson 《Czechoslovak Journal of Physics》1996,46(Z3):1293-1294
We report on thec-axis superconducting energy gap parameter Δ
c
(T) of intrinsic Josephson tunnel junctions inBi
2
Sr
2
CaCu
2
O
8+δ (Bi2212) single crystals. Δ
c
(4.2K)≈10−13 meV, which is approximately a factor of two smaller than reported in the majority of tunneling experiments. Δ
c
(T) deviates strongly from the BCS temperature dependence. These observations may be explained by a multilayer model of Bi2212
which assumes that theBi−O layers are superconducting due to the proximity effects. The Josephson tunneling then takes place between adjacentBi−O layers while there is a strong proximity coupling betweenBi−O andCu−O layers.
The work is supported by Swedish Supercon-ductivity Consortium and NUTEK, and, in part, by Russian Foundation for Basic Research,
grant #95-02-04307 相似文献
4.
D. Shimada K. Ajiki N. Miyakawa K. Hagiwara N. Tsuda 《Zeitschrift für Physik B Condensed Matter》1991,85(1):7-14
Fine structures were observed in the tunneling conductance of a sintered Bi 2223-SnO2 junction. The structures are weaker than those of a single crystalline Bi2212. They correspond to the Raman spectrum of Bi2223 and approximately to the phonon density of states of Bi2212. The structures must therefore be phonon structures, and phonons may contribute substantially to highT
c superconductivity. Multiphonon structures are scarcely discernible. Hence we propose a new model, in place of the prior multiphonon model, to explain the rapid increase inT
c with the CuO2 layer number. 2 (21 K)=68±4 meV inT
c=98±5 K. 2 (0)/k
B
T
c is 8.1±0.9. The temperature dependence of the gap was also observed and discussed. 相似文献
5.
K. P. Meletov A. A. Maksimov I. I. Tartakovskii 《Journal of Experimental and Theoretical Physics》1997,84(1):144-150
Measurements have been made of the Raman, optical absorption, and luminescence spectra of single crystals and pellets of the
fullerite C70 at T=300 K and at pressures up to 12 GPa. The baric shift dω/dP and the Grüneisen parameters of the Raman-active intramolecular phonon modes have been determined. It has been established
that the d
ω/dP value for certain phonon modes abruptly changes at pressures of P
1≈2 GPa and P
2≈5.5 GPa, as do the half-widths of the Raman lines. These features in the Raman spectrum are associated with phase transitions
at high pressure. The baric shifts of the absorption and luminescence edges of C70 crystals have been determined and are −0.12 eV/GPa and −0.11 eV/GPa, respectively, for absorption and luminescence. The baric
shift of the absorption edge decreases significantly with increasing pressure and is −0.03 eV/GPa at 10 GPa. These data have
been used to determine the deformation potential of the fullerite C70, which is about 2.1±0.1 eV.
Zh. éksp. Teor. Fiz. 111, 262–273 (January 1997) 相似文献
6.
We have obtained a generalization of the hydrodynamic theory of vacuum in the context of general relativity. While retaining
the Lagrangian character of general relativity, the new theory provides a natural alternative to the view that the singularity
is inevitable in general relativity and the theory of a hot Universe. We show that the macroscopic source-sink motion as a
whole of ordinary (dark) matter that emerges during the production of particles out of the vacuum can be a new source of gravitational
vacuum polarization (determining the variability of the cosmological term in general relativity). We have removed the well-known
problems of the cosmological constant by refining the physical nature of dark energy associated precisely with this hydrodynamically
initiated variability of the vacuum energy density. A new exact solution of the modified general relativity equations that
contains no free (fitting) parameter additional to those available in general relativity has been obtained. It corresponds
to the continuous and metric-affecting production of ultralight dark matter particles (with mass m
0 = (ħ/c
2) $
\sqrt {12\rho _0 k}
$
\sqrt {12\rho _0 k}
≈ 3 × 10−66 g, k is the gravitational constant) out of the vacuum, with its density ρ0, constant during the exponential expansion of a spatially flat Universe, being retained. This solution is shown to be stable
in the regime of cosmological expansion in the time interval −∞ < t < t
max, when t = 0 corresponds to the present epoch and t
max= 2/3H
0
cΩ0m
≈ 38 × 109 yr at Ω0m
= ρ0/ρc ≈ 0.28 (H
0 is the Hubble constant, ρc is the critical density). For t > t
max, the solution becomes exponentially unstable and characterizes the inverse process of dark matter particle absorption by
the vacuum in the regime of contraction of the Universe. We consider the admissibility of the fact that scalar massive photon
pairs can be these dark matter particles. Good quantitative agreement of this exact solution with the cosmological observations
of SnIa, SDSS-BAO, and the decrease in the acceleration of the expansion of the Universe has been obtained. 相似文献
7.
S. S. Aplesnin 《Journal of Experimental and Theoretical Physics》1997,85(6):1196-1203
The two-dimensional Heisenberg spin-1/2 model with alternated exchange interaction along the c axis and an anisotropic distribution of the exchange interaction in the lattice, J
b/J
c=0.1, is examined. A quantum Monte Carlo method is used to calculate the phase diagrams of the antiferromagnet, the dimer
state in a plane, the value of the alternation δ of the exchange interaction, and the anisotropy Δ=1−J
xy/J
z of the exchange interaction, Δ∼δ
0.58(6). The following characteristics are calculated for Δ=0.25: the dependence of the temperature of the dimer-state-paramagnet
transition on the alternation of the exchange interaction, T
c(δ)=0.55(4)(δ−0.082(6))0.50(3), the singlet-triplet energy gap, and the dependence of the magnetization on the external field for some values of δ. The value of the exchange interaction, J
c=127 K, the alternation of the exchange interaction, δ=0.11J
c, and the correlation radius along the c axis, ξ
c≈28c, are determined. Finally, it is found that the temperature dependence of the susceptibility and the specific heat are in
good agreement with the experimental data.
Zh. éksp. Teor. Fiz. 112, 2184–2197 (December 1997) 相似文献
8.
9.
A. A. Petukhov B. E. Zhurtanov S. S. Molchanov N. D. Stoyanov Yu. P. Yakovlev 《Technical Physics》2011,56(4):520-525
The electroluminescent characteristics of an InGaAsSb/GaAlAsSb heterostructure LED emitting at 1.85 μm are studied in the
temperature range 20–200°C. It is shown that the emission power exponentially drops as P ≅ 0.4exp(2.05 × 103/T) with a rise in temperature primarily because of an increase in the Auger recombination rate. It is found that band-to-band
radiative recombination goes in parallel with recombination through acceptor levels, the latter causing the emission spectrum
to broaden. With a rise in temperature, the activation energy of the acceptor levels decreases by the law ΔE≅ 32.9 − 0.075T and the maximum of the LED’s emission spectrum shifts toward the long-wavelength range (hν
max = 0.693 − 4.497 × 10−4
T). Based on the dependence E
g
= hν
max − 0.5kT and experimental data, an expression is derived for the temperature variation of the bandgap in the In0.055Ga0.945AsSb active area, E
g
≅ 0.817 − 4.951 × 10−4
T, in the range 290 K < T < 495 K. The resistance of the heterostructure decreases exponentially with rising temperature as R
0 ≅ 5.52 × 10−2exp(0.672/2kT), while cutoff voltage U
cut characterizing the barrier height of a p−n junction decreases linearly with increasing temperature (U
cut = −1.59T + 534). It is found that the current through the heterostructure is due to the generation-recombination mechanism throughout
the temperature interval. 相似文献
10.
Chen Li-chuan A. Rabenau W. Weppner 《Applied Physics A: Materials Science & Processing》1978,17(3):233-237
The ionic and electronic conductivities of Ag2Tl6I10 single crystals have been studied as a function of crystallographic orientation and temperature from 20 to 135°C. EMF as
well as AC and DC techniques have been employed. The highly anisotropic material is predominantly an Ag+-ion conductor parallel toc-direction, with the Ag+ ions moving through linear channels that are not interconnected. The conductivity σ‖c
=1.6×10−7Ω−1cm−1 at 25°C, with an activation enthalpy for σ‖c
of 0.38 eV. The conduction perpendicular toc-direction has been found to be predominantly electronic with a value of σ⊥c
=3×10−9Ω−1cm−1 at 25°C and an activation enthalpy for σ⊥c
of 0.64 eV. This is the first observation of one-dimensional Ag+ conduction and this type of orientation-dependent change from ionic to electronic conduction.
On leave from Institute of Physics, Academia Sinica, Peking, China. 相似文献
11.
The effect of γ irradiation on the temperature hysteresis in dielectric permittivity ɛ and loss tangent tan δ of crystalline Rb2ZnBr4 has been studied in the vicinity of the incommensurate-commensurate phase transition. The ɛ(T) and tan δ(T) curves were found to exhibit anomalies in the form of maxima. Hysteresis was observed in the measured properties, including
the transition temperature T
c
(ΔT=T
c
h
−T
c
c
), in both unirradiated and irradiated samples. It is shown that, as the radiation dose increases the extent of the hysteresis
ΔT increases, the values of ɛ
max and tan δ
max at the transition point decrease, and the anomalies wash out.
Fiz. Tverd. Tela (St. Petersburg) 40, 1911–1914 (October 1998) 相似文献
12.
The dielectric nonlinearity of ferroelectric Li2−x
NaxGe4O9 (x≈0.23) crystals is measured in the neighborhood of the phase transition temperatures. The magnitude of the nonlinear coefficient
β is estimated from the shift in T
c and the reduction in ɛ
max under the influence of E
=, from the dielectric nonlinearity in the paraphase, and from the temperature dependence of P
s in crystalline Li2−x
NaxGe4O9 (x≈0.23). The resulting values of β are 1.87, 1.26, 2.17, and 1.17×10−9 (CGSE cm2)−2, respectively. The mechanism for the phase transition in crystalline Li2−x
NaxGe4O9 (x≈0.23) is discussed.
Fiz. Tverd. Tela (St. Petersburg) 41, 1070–1072 (June 1999) 相似文献
13.
The electrical resistance of the binary liquid system cyclohexane + acetic anhydride is measured, in the critical region,
both in the pure mixture and when the mixture is doped with small amounts (≈ 100 ppm) of H2O/D2O impurities.T
c
was approached to aboutt=3×10−6 wheret=(T −T
c
)/T
c
. The critical exponentb ≈ 0.35 in the fit of the resistance data to the equationdR/dT ∼t
−b
does not seem to be affected appreciably by the impurities. There is a sign reversal ofdR/dt in the non-critical region. Binary liquid systems seem to violate the universality of the critical resistivity. 相似文献
14.
E. S. Itskevich 《Journal of Experimental and Theoretical Physics》1998,86(4):805-810
A study is made of the properties of the homologous series of mercury HTSC-cuprates HgBa2Can−1CunO2n
+2+δ with n=1–8. Experiments are conducted under pressure for samples with n=1–5. The Hg-1223 and Hg-1234 phases were synthesized using a controlled high pressure chamber. The oxygen content of an initial
mixture corresponding to the Hg-1234 phase was varied by changing the composition of the initial BaO/BaO2 oxides. The dependence of the superconducting transition temperature T
c
on the lattice constant a (and, therefore, on the oxygen content) and of T
c
max
and dT
c
max
/dp on n are convex upward up to n=4, 5. The maximum values always correspond to the Hg-1223 phase. Experimental T
c
max
(n) curves for the phases with n=1–6 and dT
c
max
/dp curves for n=1–5 are compared with Anderson’s theory (the so-called RVB model). A general analysis of these results indicates that the
mercury cuprates have an ideal structure for HTSC. The Hg-1223 phase is the “champion” in this ideal structure and the critical
temperature corresponding to this phase (T
c
=135 K) is the highest at atmospheric pressure.
Zh. éksp. Teor. Fiz. 113, 1474–1483 (April 1998) 相似文献
15.
The values of the insulator gap Δ in one-dimensional systems of interacting bosons described by the Hubbard Hamiltonian are
calculated at low temperatures by the quantum world-line Monte Carlo algorithm. The dependence of Δ on the size of the system,
the temperature, and the parameters of the model is investigated. It is shown that a chain with N
a=50 sites is already sufficient to estimate the thermodynamic value of the critical quantity (t/U)c for which a transition from the insulator into the superfluid state occurs in a commensurate system. To within the computational
error, this value, (t/U)c=0.300±0.005, agrees with the value (t/U)c=0.304±0.002 obtained previously by the combined “exact diagonalization + renormalization-group analysis” method. The characteristic
Kosterlitz-Thouless behavior of the insulator gap is demonstrated near the critical region: Δ∼exp[−b(1−t/t
c)−1/2].
Pis’ma Zh. éksp. Teor. Fiz. 64, No. 2, 92–96 (25 July 1996) 相似文献
16.
Yin-Zhe Ma Yan Gong Xuelei Chen 《The European Physical Journal C - Particles and Fields》2009,60(2):303-315
We investigate the observational signatures of the holographic dark-energy models, including both the original model and a
model with an interaction term between the dark energy and dark matter. We first delineate the dynamical behavior of such
models, especially considering whether they would have a “big rip” for different parameters; then we use several recent observations,
including 182 high-quality type Ia supernovae data observed with the Hubble Space Telescope, the SNLS and ESSENCE surveys,
42 latest Chandra X-ray cluster gas mass fraction, 27 high-redshift gamma-ray burst samples, the baryon acoustic oscillation
measurement from the Sloan Digital Sky Survey, and the CMB shift parameter from the WMAP three-year result to give more reliable
and tighter constraints on the holographic dark-energy models. The results of our constraints for the holographic dark-energy
model without interaction is c=0.748−0.009+0.108, Ω
m0=0.276−0.016+0.017, and for the model with interaction (c=0.692−0.107+0.135, Ω
m0=0.281−0.017+0.017, α=−0.006−0.024+0.021, where α is an interacting parameter). As these models have more parameters than the ΛCDM model, we use the Bayesian Evidence as a model-selection criterion to make comparisons. We found that the holographic
dark-energy models are mildly favored by the observations as compared to the ΛCDM model. 相似文献
17.
The absorption spectra, fluorescence spectrum and fluorescence decay curve of Nd3+ ions in CaNb2O6 crystal were measured at room temperature. The peak absorption cross section was calculated to be 6.202×10−20 cm2 with a broad FWHM of 7 nm at 808 nm for E//a light polarization. The spectroscopic parameters of Nd3+ ions in CaNb2O6 crystal have been investigated based on Judd-Ofelt theory. The parameters of the line strengths Ω
t
are Ω
2=5.321×10−20 cm2,Ω
4=1.734×10−20 cm2,Ω
6=2.889×10−20 cm2. The radiative lifetime, the fluorescence lifetime and the quantum efficiency are 167 μs, 152 μs and 91%, respectively. The fluorescence branch ratios are calculated to be β
1=36.03%,β
2=52.29%,β
3=11.15%,β
4=0.533%. The emission cross section at 1062 nm is 9.87×10−20 cm2. 相似文献
18.
Yu. A. Simonov 《JETP Letters》2008,87(3):121-123
The dipion spectrum for the ϒ(nS) → ϒ(n′S) transition with n < 4 has the form dw/dq ∼ (phase space) |η − x|2, with x = q
2 − 4m
π2 / (ΔM)2 − 4m
π2 < q
2 ≡ M
ππ2, and ΔM = M(nS) − M(n′S). The parameter η is calculated and the spectrum is shown to reproduce the experimental data for all three types of decays:
3 → 1, 2 → 1, and 3 → 2 with η ≈ 0.5, 0, and −3, respectively.
The text was submitted by the author in English. 相似文献
19.
L. K. Aminov I. N. Kurkin S. P. Kurzin D. A. Lukoyanov I. Kh. Salikhov R. M. Rakhmatullin 《Journal of Experimental and Theoretical Physics》1997,84(1):183-189
Our studies involve measuring spin-lattice relaxation times for Nd3+ ions in yttrium-aluminum garnets over the temperature range 4–50 K at 9.25 and 36.4 GHz for different orientations of the
external magnetic field in relation to the crystallographic axes. The temperature dependence of the relaxation rate is described
by T
1
−1
=AT
n+b exp(−Δ/kT), where n varies from sample to sample, with n=1 for “perfect” samples (i.e., with the longest relaxation times). Here Δ is approximately 130 cm−1, which is the energy of the excited Kramers doublet of the neodymium ion closest to the ground state, and this makes it possible
to interpret the second term in T
1
−1
as the contribution of two-stage relaxation proceeding through the intermediate level Δ. A strong field dependence of these
processes has been discovered: when the frequency was increased fourfold, the relaxation rate increased by a factor of 10.
The effect is a specific manifestation of the degeneracy of the excited level, breaking of the symmetry of the crystalline
field due to lattice defects, and the prevalence of deformations of a certain type in the spin-lattice interaction.
Zh. éksp. Teor. Fiz. 111, 332–343 (January 1997) 相似文献
20.
Weak transitions of decuplet isobars are expanded in terms of eigen-amplitudes of the direct channel in the framework of SU(3).
Starting with the most general weak Hamiltonian and assuming intermediate states to be non-exotic, we obtain ΔI=1/2 rule for Ω− decays. Invoking of the CP invariance forbids all thepv weak processesD(10)→D(10) +P(8). Decays of the charmed multiplets are also discussed in these dynamical considerations. We obtain triplet dominance of
charm changing weak Hamiltonian for Ω*++
3 decays. 相似文献