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1.
R. V. Kuz’menko A. V. Ganzha O. V. Bochurova É. P. Domashevskaya J. Schreiber S. Hildebrandt S. Mo E. Peiner 《Physics of the Solid State》1999,41(4):654-659
A study is reported of the structure of photoreflectance (PR) spectra in the vicinity of the E
0 transition from thin (d=1–5 μm) n-GaAs and n-InP films (n=1016–1017 cm−3) grown epitaxially on Si(001) substrates. A quantitative analysis of the spectra involving multi-component fitting shows
that the electronic optical transition from the {3/2;±1/2} subband provides a dominant contribution to the intermediate-field
electromodulation component in both systems. The splitting observed in the GaAS/Si PR spectra near the main peak are accounted
for not by the strain-induced valence-band splitting but rather by a spectral superposition of the intermediate-field component
due to the {3/2;±1/2} subband with a low-energy excitonic component. The analytically established transition energy E
0
3/2;±1/2
is used to calculate biaxial strains in epitaxial films.
Fiz. Tverd. Tela (St. Petersburg) 41, 725–731 (April 1999) 相似文献
2.
The nucleon electromagnetic form factorsG
E
P
(q2),G
M
P
(q2) and the axial-vector form factor GA(q2) are studied in a relativistic model of independent quarks confined by an equally mixed scalar-vector square root potentialV
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 withG
E
P
(q2) and G
A
(q2) 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 factorG
πNN(q2) and consequently the pion-nucleon coupling constant is obtained asg
πNN(q2)=12.81 as compared tog
πNN(q2)exp⋍13. 相似文献
3.
4.
Rolf Rentzsch Ch. Reich A. N. Ionov V. Ginodman I. Shlimak P. Fozooni M. J. Lea 《Physics of the Solid State》1999,41(5):757-760
We present a critical review of the present state of the critical exponent puzzle of the metal-insulator transition of doped
semiconductors with emphasis on the role of meso-and macroscopic inhomogeneity caused by the disorder of intended or unintended
acceptors and donors in crystals. By using both isotopic engineering and neutron transmutation doping (NTD) of germanium we
found for low compensations (at K=1.4 and 12%) that the critical exponents of the localization length and the dielectric constant are nearly ν=1/2 and ζ=1, which double for medium compensations (at K=38 and 54%) to ν=1 and ζ=2, respectively.
Fiz. Tverd. Tela (St. Petersburg) 41, 837–840 (May 1999)
Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor. 相似文献
5.
S. V. Grigor’ev S. A. Klimko S. V. Maleev A. I. Okorokov V. V. Runov R. Kampmann H. Eckerlebe 《JETP Letters》1997,66(1):56-61
The magnetic phase transition in the Invar alloy Fe70Ni30 is investigated by means of small-angle neutron scattering over a wide range of momentum transfer. This method was used to
measure two magnetic correlation lengths R
c
1 and R
c
2 which coexist in the alloy above the phase transition temperature T
c
. The critical correlations with correlation length R
c
1 are described well by an Ornstein-Zernicke expression, and the critical correlations with the second correlation length,
an order of magnitude larger than R
c
2, are described well by a squared Ornstein-Zernicke expression. The temperature dependences obtained for the correlation
lengths R
c
1 and R
c
2 satisfy the power law R
c
∼((T−T
c
)/T
c
) −υ with critical exponents υ1=0.65±0.05 and υ2=1.3±0.1 for the shorter and longer scales, respectively.
Pis’ma Zh. éksp. Teor. Fiz. 66, No. 1, 53–57 (10 July 1997) 相似文献
6.
J. Becker H.G. Andresen J.R.M. Annand K. Aulenbacher K. Beuchel J. Blume–Werry Th. Dombo P. Drescher M. Ebert D. Eyl A. Frey P. Grabmayr T. Großmann P. Hartmann T. Hehl W. Heil C. Herberg J. Hoffmann J.D. Kellie F. Klein K. Livingston M. Leduc M. Meyerhoff H. Möller Ch. Nachtigall A. Natter M. Ostrick E.W. Otten R.O. Owens S. Plützer E. Reichert D. Rohe M. Schäfer H. Schmieden R. Sprengard M. Steigerwald K.-H. Steffens R. Surkau Th. Walcher R. Watson E. Wilms 《The European Physical Journal A - Hadrons and Nuclei》1999,6(3):329-344
The electric form factor of the neutron GEn has been determined in double polarized exclusive 3
He(e,e'n) scattering in quasi–elastic kinematics by measuring asymmetries A
⊥, A
∥ of the cross section with respect to helicity reversal of the electron, with the nuclear spin being oriented perpendicular
to the momentum transfer q in case of A⊥ and parallel in case of A∥. The experiment was performed at the 855 MeV c. w. microtron MAMI at Mainz. The degree of polarization of the electron beam
and of the gaseous 3
He target were each about 50%. Scattered electrons and neutrons were detected in coincidence by detector arrays covering large
solid angles. Quasi–elastic scattering events were reconstructed from the measured electron scattering angles ϑe, φe and the neutron momentum vector p
n
′ in the plane wave impulse approximation. We obtain the result <G
En>(0.27 < Q2c2/GeV2 < 0.5)= 0.0334 ± 0.0033stat± 0.0028syst which is averaged over the indicated range of Q
2, the squared momentum transfer. This G
En value is significantly smaller than measured from the D(e,e'n) reaction under similar kinematical conditions. To what extent final state interactions in 3He quench the G
En result is subject of calculations currently in progress elsewhere.
Received: 29 April 1999 相似文献
7.
The static conductivity σ(E) and photoconductivity (PC) at radiation frequencies ħω=10 and 15 meV in Si doped with shallow impurities (density N=1016−6×1016 cm−3, ionization energy ε1≃45 meV) with compensation K=10−4−10−5 in electric fields E=10–250 V/cm are measured at liquid-helium temperatures T. Special measures are taken to prevent the high-frequency part of the background radiation (ħω>16 meV) from striking the
sample. It is found that the conductivity σ(E) is due to carrier motion along the D
− band, which is filled with carriers under the influence of the field E. In fields E<E
q
(E
q
≃100–200 V/cm) the carrier motion consists of hops along localized D
− states in a 10–15 meV energy band below the bottom of the free band (energy ε=ε1); for E>E
q
carriers drift along localized D
− states with energy ε∞ε1−10 meV. An explanation is proposed for the threshold behavior of the field dependence of the photo-and static conductivities.
Pis’ma Zh. éksp. Teor. Fiz. 66, No. 4, 232–236 (25 August 1997) 相似文献
8.
B. A. Strukov E. P. Ragula S. Yu. Stefanovich I. V. Shnaidshtein S. V. Arkhangel’skaya A. Onodera 《Physics of the Solid State》1998,40(7):1193-1195
The specific heat of the ceramic and the permittivity of a single-crystal sample of LaBSiO5, a new ferroelectric in the stilwellite family, were measured in a temperature range which includes the phase transition
point (T
C=140 °C). The excess entropy of the phase transition ΔS=1.05 J/mol · K and the Curie-Weiss constant C
C-W=3.2×103 K were determined. The results indicate that the phase transition in this crystal is of a “mixed” nature and exhibits features
of a displacement-type transition and an order-disorder transition.
Fiz. Tverd. Tela (St. Petersburg) 40, 1310–1312 (July 1998) 相似文献
9.
S. S. Murzin 《JETP Letters》1998,67(3):216-221
The conductance of doped n-GaAs films is studied experimentally as a function of magnetic field and temperature in strong magnetic fields right up to
the quantum limit (ħωc = E
F). The Hall conductance G
xy is virtually independent of temperature T until the transverse conductance G
xx is quite large compared with e
2/h. In strong fields, when G
xx becomes comparable to e
2/h, G
xy starts to depend on T. The difference between the conductances G
xx at the two temperatures 4.2 and 0.35 K depends only weakly on the magnetic field H over a wide range of magnetic fields, while the conductances G
xx themselves vary strongly. The results can be explained by quantum corrections to the conductance as a result of the electron-electron
interaction in the diffusion channel. The possibility of quantization of the Hall conductance as a result of the electron-electron
interaction is discussed.
Pis’ma Zh. éksp. Teor. Fiz. 67, No. 3, 201–206 (10 February 1998) 相似文献
10.
We report on the first observation and studies of a weak delocalizing logarithmic temperature dependence of the conductivity,
which causes the conductivity of the 2D metal to increase as T decreases down to 16 mK. The prefactor of the logarithmic dependence is found to decrease gradually with density, to vanish
at a critical density n
c
, 2∼2×1012 cm−2, and then to have the opposite sign at n>n
c
,2. The second critical density sets the upper limit on the existence region of the 2D metal, whereas the conductivity at the
critical point, G
c
,2∼120e
2/h, sets an upper (low-temperature) limit on its conductivity.
Pis’ma Zh. éksp. Teor. Fiz. 68, No. 6, 497–501 (25 September 1998)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
11.
A study is reported of the anomalous broadening of Mn2+ EPR lines on the high-temperature side of the paraelectric-incommensurate phase transition in Rb2ZnCl4 crystals. It is shown that the resonant-line broadening is inhomogeneous and due to the contribution of low-frequency fluctuations
corresponding to the central peak in the elementary-excitation spectrum. The data obtained have permitted us to obtain the
critical correlation-length exponent ν=0.64±0.02 corresponding to the 3d XY model of Heisenberg.
Fiz. Tverd. Tela (St. Petersburg) 41, 122–125 (January 1999) 相似文献
12.
T. T. Basiev A. Ya. Karasik V. V. Fedorov K. W. Ver Steeg 《Journal of Experimental and Theoretical Physics》1998,86(1):156-163
Accumulated photon echoes have been used to investigate the mechanisms of optical dephasing in CaF2 crystals activated by Nd3+ ions. Tunable picosecond laser radiation, which permits the selective excitation of various Nd3+ 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 Nd3+ centers in CaF2 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 Γh in CaF2 crystals is almost an order of magnitude smaller than Γh in disordered CaF2-YF3 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
13.
EPR and the method of dielectric losses have been used to investigate Fe3+ centers of axial and orthorhombic symmetry in KTaO3 single crystals. The EPR spectrum of orthorhombic-symmetry Fe3+ obtained in the 8-mm wavelength range at T=77 K is described by the spin-Hamiltonian
with parameters g
x=1.98, g
y=2.01, g
z=2.00, D=0.43 cm−1, and E=5.87×10t-2 cm−1. From the dielectric measurement data we have obtained the following parameters of the relaxation of the orthorhombic Fe3+ centers in KTaO3: characteristic relaxation frequency τ
0
−1
=2.33×1012 Hz and activation energy E
a=0.044 eV. A model of the orthorhombic Fe3+ center in KTaO3 is discussed within the framework of the kinetic parameters obtained.
Fiz. Tverd. Tela (St. Petersburg) 39, 861–864 (May 1997) 相似文献
14.
A. V. Anan’ev Yu. I. Zhdanov A. P. Gerashchenko K. N. Mikhalev S. V. Verkhovskii E. Yu. Medvedev K. A. Okulova N. I. Chebotaev V. N. Goshchitskii 《JETP Letters》1998,67(3):182-188
The spin-spin relaxation rate 63
T
2
−1
of 63Cu nuclei in CuO2 layers is measured in the normal and superconducting states of the compound YBa2Cu3O6.9 (T
c
onset
=94 K) subjected to radiation-induced disordering by a fast-neutron flux Φ to T
c
onset
=68 K (Φ=7×1018 cm−2) and T
c
onset
<4 K (Φ=12×1018 cm−2). It is found that as the structural disorder increases, the contribution of the indirect spin-spin interaction 63
T
2G
−1
, which is related to the value of the spin susceptibility at the boundary of the Brillouin zone of the copper planes χs(q={π/a; π/a}), decreases slightly at the transition to the superconducting state for the initial sample and remains unchanged for the
weakly disordered sample. This behavior of the short-wavelength contribution to the spin susceptibility attests to the stability
of the x
2−y
2 symmetry of the energy gap against structural disorder, in accordance with proposed theoretical models of Cooper pairing
for high-T
c cuprates.
Pis’ma Zh. éksp. Teor. Fiz. 67, No. 3, 172–177 (10 February 1998) 相似文献
15.
The impurity photoconductivity spectra of uncompensated silicon at liquid-helium temperatures under conditions of strongly
suppressed background radiation (background) are studied in different electric fields E. It is established that the delocalization arising in the D
− band as E increases is not associated with any changes of the fluctuation potential and is due to the direct action of the field E. A delocalization band of finite width appears abruptly at a critical value E
c
(∼100 V/cm) of E. The critical field E
c
increases with the density of charged centers in the sample.
Pis’ma Zh. éksp. Teor. Fiz. 65, No. 1, 56–59 (10 January 1997) 相似文献
16.
We have discovered that the extrinsic photoconductivity spectrum of doped, uncompensated crystalline Si at liquid-helium temperatures
is qualitatively different in electric fields E above a critical value E
c
. Specifically, the red edge of the photoconductivity, associated with photoionization of a neutral impurity, is shifted strongly
to lower frequencies. This result is explained by the appearance of a mobility threshold in the D
−-band (upper Hubbard band) and the shift of this threshold as E increases.
Pis’ma Zh. éksp. Teor. Fiz. 63, No. 2, 89–94 (25 January 1996) 相似文献
17.
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
18.
Dielectric properties of ceramic samples of Sr1−x
PbxTiO3 solid solutions for x varying from 0 to 0.3 have been studied. The ferroelectric phase transition in this system has been established to persist
down to x=0.005. Within the x values of 0.002 to 0.05, the ferroelectric transition temperature is shown to follow the relation T
c=A(x−x
c)1/2, with A=440 K and x
c=0.002.
Fiz. Tverd. Tela (St. Petersburg) 39, 714–717 (April 1997) 相似文献
19.
Yu.N. Lobach A.D. Efimov A.A. Pasternak 《The European Physical Journal A - Hadrons and Nuclei》1999,6(2):131-140
Lifetimes of excited states in 110Cd have been measured by the Doppler shift attenuation method in the reaction (α,2nγ) at E
α= 25 MeV. Lifetime values for 8 states and lifetime limits for 3 states were obtained. The band structures of 110Cd have been interpreted in terms of a modified version of the interacting boson model (IBM + 2 q.p.). The calculations explain
well the excitation energies and electromagnetic transition probabilities up to J
π= 16+, except for the 10+
1 state. The structural features are discussed in terms of collective and two quasiparticle excitations.
Received: 20 March 1999 / Revised version: 28 May 1999 相似文献
20.
We introduce a new 2-parameter family of sigma models exhibiting Poisson–Lie T-duality on a quasitriangular Poisson–Lie group
G. The models contain previously known models as well as a new 1-parameter line of models having the novel feature that the
Lagrangian takes the simple form , where the generalised metric E is constant (not dependent on the field u as in previous models). We characterise these models in terms of a global conserved G-invariance. The models on G=SU
2 and its dual G
* are computed explicitly. The general theory of Poisson–Lie T-duality is also extended, notably the reduction of the Hamiltonian
formulation to constant loops as integrable motion on the group manifold. The approach also points in principle to the extension
of T-duality in the Hamiltonian formulation to group factorisations D=G⋈M, where the subgroups need not be dual or connected to the Drinfeld double.
Received: 22 August 1999 / Accepted: 4 February 2000 相似文献