共查询到20条相似文献,搜索用时 156 毫秒
1.
A symmetric two-site, one-electron model is treated within perturbation theory in electron wavefunction overlap from different
sites. The significant role of the double degeneracy of levels in the unperturbed Hamiltonian is pointed out. It is shown
that as a result of this the terms of the perturbative expansion for the correction to the energy of an unperturbed level
produce different results depending on the parity of the order. Namely, even terms give rise to a level shift (an analog of
the polaron shift in the polaron-crystal model), while odd terms result in splitting (an analog of the polaron band width).
Also, the shift of the levels decreases with increasing vibronic coupling constant by a power law, and their splitting, exponentially.
This is in full accord with the well-known results of small-radius polaron theory.
Fiz. Tverd. Tela (St. Petersburg) 39, 2159–2167 (December 1997) 相似文献
2.
This paper discusses the effect of dynamic zero-point and thermal spin-density fluctuations (SDF) on the electronic spectrum
of the nearly-ferromagnetic semiconductor FeSi. It is shown that near T=0° zero-point SDF can lead to so much splitting of
the electron states of the valence and conduction band that a “gapless” ground state arises. As the temperature increases,
the forbidden gap in the spectrum of d electrons first reappears due to suppression of zero-point fluctuations and then disappears again, as the amplitude of thermal
spin fluctuations increases. It is these transformations of the electronic spectrum that are the reason for the anomalous
changes in the magnetic susceptibility with temperature observed experimentally.
Fiz. Tverd. Tela (St. Petersburg) 40, 1437–1441 (August 1998) 相似文献
3.
V. T. Dolgopolov G. E. Tsydynzhapov A. A. Shashkin E. V. Deviatov F. Hastreiter M. Hartung A. Wixforth K. L. Campman A. C. Gossard 《JETP Letters》1998,67(8):595-601
We employ a magnetocapacitance technique to study the spectrum of the soft two-subband (or double-layer) electron system in
a parabolic quantum well with a narrow tunnel barrier at the center. In this system, when unbalanced by gate depletion, two
sets of quantum oscillations are observed at temperatures T≳30 mK: one originates from the upper electron subband in the closer-to-the-gate part of the well, and the other indicates
the existence of common gaps in the spectrum at integer fillings. For the lowest filling factors υ=1 and υ=2, both the presence of a common gap down to the point of the one-to two-subband transition and their nontrivial magnetic
field dependences point to magnetic-field-induced hybridization of electron subbands.
Pis’ma Zh. éksp. Teor. Fiz. 67, No. 8, 563–568 (25 April 1998)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
4.
M. A. Skvortsov 《JETP Letters》1998,67(2):133-139
Motivated by the recent observation of the metal-insulator transition in Si MOSFETs, a study is made of the quantum interference
correction to the conductivity in the presence of the Bychkov-Rashba spin splitting. For a small splitting, a crossover from
the localizing to antilocalizing regime is obtained. The antilocalization correction vanishes, however, in the limit of a
large separation between the chiral branches. The relevance of the chiral splitting for the 2D electron gas in Si MOSFETs
is discussed.
Pis’ma Zh. éksp. Teor. Fiz. 67, No. 2, 118–123 (25 January 1998)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
5.
P. Thalmeier 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(1):29-48
The Heavy Fermion state in UPd2Al3 may be approximately described by a dual model where two of the three U-5
f electrons are in a localized state split by the crystalline electric field into two low lying singlets with a splitting energy
Δ≃ 6 meV. The third 5
f electron has itinerant character and forms the Heavy Electron bands. Inelastic neutron scattering and tunneling experiments
suggest that magnetic excitons, the collective propagating crystal field excitations of the localized 5
f electrons, mediate superconducting (sc) pairing in UPd2Al3. A theory for this novel mechanism is developed within a nonretarded approach. A model for the magnetic exciton bands is
analyzed and compared with experiment. The sc pair potential which they mediate is derived and the gap equations are solved.
It is shown that this mechanism favors an odd parity state which is nondegenerate due to the combined symmetry breaking by
the crystalline electric field and the AF order parameter. A hybrid model including the spin fluctuation contribution to the
pairing is also discussed.
Received 22 October 2001 and Received in final form 28 February 2002 相似文献
6.
The band structure of linear chains of fullerene molecules is calculated as a function of the intermolecular π-electron overlap integral T, which increases under increasing external pressure. Chains consisting of neutral (C60) and charged (C
60
−
) molecules are studied. It is shown that there is a sharp transition from a metal (or narrow-gap semiconductor) to an insulator
(with band gap ∼1 eV)with increasing T. The proposed model makes it possible to describe the formation of solid-carbon struc-tures, containing chains of covalently
bound fullerene molecules, with different pressure-dependent semiconductor properties.
Pis’ma Zh. éksp. Teor. Fiz. 65, No. 8, 647–650 (25 April 1997) 相似文献
7.
S. G. Rautian 《Journal of Experimental and Theoretical Physics》1997,85(3):451-461
We examine the linear and cubic optical polarizations of the degenerate electron gas in spherical metallic particles. For
photon energies that are high compared to the splitting of the spectrum of electron states we use a unified approach to calculate
the dimensional (size, or quantum) and Drude parts of the polarization and the variation of energy distribution of the electrons
induced by a field.
Zh. éksp. Teor. Fiz. 112, 836–855 (September 1997) 相似文献
8.
R. N. Li A. I. Mil’shtein V. M. Strakhovenko 《Journal of Experimental and Theoretical Physics》1997,85(6):1049-1059
The helical splitting amplitudes of a high-energy photon in an external Coulomb field are found exactly with respect to Zα. Both screened and unscreened potentials are investigated. The treatment is carried out within the semiclassical approach,
which is valid for small angles between the momenta of all photons. A new representation is used for the semiclassical electronic
Green’s function. The resulting expressions are analyzed in detail for the case of transverse components of the momenta of
the final photons that are large compared with the electron mass.
Zh. éksp. Teor. Fiz. 112, 1921–1940 (December 1997) 相似文献
9.
It is predicted that resonance coupling between two discrete electron energy levels corresponding to different size-quantization
quantum numbers and different Landau quantum numbers can occur in a quantum well in a quantizing magnetic field. The resonance
coupling is due to the interaction of an electron with LO phonons and results in the formation of polaron states of a new type. It is shown that for a certain value of the magnetic
field, which depends on the splitting of the electron size-quantization levels, the absorption peak and the two-phonon resonance
Raman scattering peak split into two components, the separation between which is determined by the electron-phonon coupling
constant. The resonance coupling between size-quantization levels with the same Landau quantum numbers is also studied. The
splitting of the peaks in this case is virtually independent of the magnetic field and can be observed in much weaker fields.
The experimental observation of the effect will make it possible to determine the relative position of the electronic levels
and the electron-phonon coupling constant.
Pis’ma Zh. éksp. Teor. Fiz. 65, No. 7, 511–515 (10 April 1997) 相似文献
10.
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
11.
N. I. Alekseev 《Technical Physics》1998,43(5):535-538
The influence of the escape of fast plasma electrons on the electron distribution function (EDF) in a low-voltage cesium Knudsen
arc is discussed. It is shown that even with a large Knudsen parameter l
e
/h∼5–10 (where h is the gap and l
e
is the mean free path of electrons with energy of the order of the anode barrier) the electron flux from the plasma to the
anode is virtually identical to that calculated with a Maxwellian EDF.
Zh. Tekh. Fiz. 68, 61–64 (May 1998) 相似文献
12.
M. Kiselev F. Bouis F. Onufrieva P. Pfeuty 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(4):601-611
We study in a mean-field approximation the ordered “excitonic” states which develop around the quantum critical point (QCP)
associated with the electronic topological transition (ETT) in a 2D electron system on a square lattice. We consider the case
of hopping beyond nearest neighbors when ETT has an unusual character. We show that the amplitude of the order parameter (OP)
and of the gap in the electron spectrum increase with increasing the distance from the QCP, , where and n is an electron concentration. Such a behavior is different from the ordinary case when OP and the gap decrease when going
away from the point which is a motor for instability. We show that the chemical potential lies always inside the gap for wavevectors
in a proximity of whatever is the doping concentration. The spectrum gets a characteristic flat shape as a result of hybridization effect in
the vicinity of two different SP's. The shape of the spectrum as a function of and the angle dependence of the gap have a striking similarity with the features observed in the normal state of the underdoped
high- cuprates. We discuss also details about the phase diagram and the behaviour of the density of states.
Received 9 June 1999 相似文献
13.
We have studied the electron structure and magnetic properties of Heusler phase Co2YBi and half-Heusler phase CoYBi (Y=Mn, Cr) by using the full-potential linearized-augmented plane-wave (FLAPW) method. Co2MnBi and Co2CrBi are predicted to be half-metallic magnetism with a total magnetic moment of 6 and 5 μB, respectively, well consistent with the Slater-Pauling rule. We also predict CoMnBi to be half-metallic magnetism with a slight compression. The gap origin for Co2MnBi and Co2CrBi is due to the 3d electron splitting of Mn (Cr) and Co atoms, and the gap width depends on Co electron splitting. The atom coordination surroundings have a great influence on the electron structure, and consequently the Y site in the X2YZ structure has a more remarkable electron splitting than the X site due to the more symmetric surroundings. The investigation regarding the lattice constant dependence of magnetic moment shows that the Co magnetic moment exhibits an opposite behavior with the change of the lattice constant for Heusler and half-Heusler alloys, consequently leading to the different variation trends for total magnetic moment. The variation of total and atom magnetic moment versus lattice constant can be explained by the extent of 3d electron splitting and localization of Mn (Cr) and Co atoms for both the series of alloys. 相似文献
14.
O. S. Torosyan S. M. Yailoyan F. S. Torosyan L. M. Mkhoyan 《Physics of the Solid State》1999,41(6):934-935
Expressions are obtained for the hyperfine splitting in EPR spectra of impurity ions with electron spin 1/2 and arbitrary
nuclear spin for arbitrary anisotropy of the g-factor and hyperfine structure constants. These results generalize the previously obtained results of Weil for the case of
weakly anisotropic g-factors and hyperfine structure constants.
Fiz. Tverd. Tela (St. Petersburg) 41, 1026–1027 (June 1999) 相似文献
15.
Y. J. Wang Y. A. Leem B. D. McCombe X. -G. Wu F. M. Peeters E. D. Jones J. R. Reno X. Y. Lee H. W. Jiang 《Physica E: Low-dimensional Systems and Nanostructures》2000,6(1-4)
Electron cyclotron resonance (CR) has been studied in magnetic fields up to 32 T in two heavily modulation-δ-doped GaAs/Al0.3Ga0.7As single quantum well samples. Little effect on electron CR is observed in either sample in the region of resonance with the GaAs LO phonons. However, above the LO-phonon frequency energy ELO at B>27 T, electron CR exhibits a strong avoided-level-crossing splitting for both samples at energies close to ELO+(E2−E1), where E2, and E1 are the energies of the bottoms of the second and the first subbands, respectively. The energy separation between the two branches is large, reaching a minimum of about 40 cm−1 around 30.5 T for both samples. This splitting is due to a three-level resonance between the second LL of the first electron subband and the lowest LL of the second subband plus an LO phonon. The large splitting in the presence of high electron densities is due to the absence of occupation (Pauli-principle) effects in the final states and weak screening for this three-level process. 相似文献
16.
O. V. Volkov V. E. Zhitomirskii I. V. Kukushkin K. von Klitzing K. Eberl 《JETP Letters》1996,64(10):774-779
A study is made of the temperature dependence of the magnetooscillations of the recombination radiation of 2D electrons from
the photoexcited size-quantization subband in an isolated GaAs/AlGaAs quantum well. It is shown that at high temperatures
(T>10 K) the period of the oscillations is determined by the ratio of the intersubband energy splitting and the sum of the electron
and hole cyclotron energies. It is found that as the temperature decreases (T<5 K), a new series of oscillations (with the same period but with a larger phase shift), which are associated with the appearance
of excitonic states under the Landau levels, appears.
Pis’ma Zh. éksp. Teor. Fiz. 64, No. 10, 719–724 (25 November 1996) 相似文献
17.
S. N. Artemenko 《JETP Letters》1999,70(8):526-532
The current-voltage characteristics (IVCs) of a layered superconductor with singlet d pairing at low temperatures are calculated in the internal Josephson effect (IJE) regime. Coherent electron tunneling between
layers is assumed. A finite resistance of the superconductor in the resistive state arises because of quasiparticle transitions
through the superconducting gap near nodes. Because of charge effects the interaction of the Josephson junctions formed by
the layers does not lead to substantial differences in the shapes of different branches of the IVCs. The model describes the
basic qualitative features of the effect in high-temperature superconductors for voltages which are low compared with the
amplitude of the superconducting gap.
Pis’ma Zh. éksp. Teor. Fiz. 70, No. 8, 516–521 (25 October 1999) 相似文献
18.
V. V. Vecheslavov 《Journal of Experimental and Theoretical Physics》1999,89(1):182-187
This report is a continuation of an analysis, initiated elsewhere V.V. Vecheslavov and B. V. Chirikov, Zh. éksp. Teor. Fiz.
114, 1516 (1998) [JETP 86, 823 (1998)], of the effect of splitting of the separatrix of a nonlinear resonance for the model of standard mapping, based
on results of direct measurements of the splitting angle α(K), where K is the system parameter. Measurements were made in the previously used wide range 0.1≳α≳10−208 (1⩾K⩾0.0004), but with significantly higher relative (better than 1050) and average (∼10−55) accuracy. This procedure made it possible to substantially refine the effects observed in Ref. 1 and construct qualitatively
new empirical dependences providing reliable extrapolation of the data obtained for the angle and the invariant in the intermediate
asymptotic limit K≲10−2 beyond the limits of the investigated region. The results obtained by us can be useful for further development of the theory
of separatrix splitting and formation of the stochastic layer of a nonlinear resonance.
Zh. éksp. Teor. Fiz. 116, 336–346 (July 1999) 相似文献
19.
It is shown that d
x
2−y
2 symmetry of superconducting order due to valence bond (VB) type correlations is possible. The VB correlations are compatible
with antiferromagnetic (AF) spin order. For the two-dimensional Hubbard model with arbitrary doping, the variational method
of local unitary transformations is used to construct explicitly a uniform state with VB structure. The d-channel attraction of holes is a consequence of the modulation of hops by the populations of centers accompanying VB formation,
and the parameters of the modulation are determined variationally. The increase in the density of states at the Fermi level
accompanying AF splitting of the band, which is absent in the paramagnetic state, is important for the gap width. The gap
width and its ratio to T
c are of the order of 2Δ≃0.1t and 2Δ/kT
c≃4–4.5 with U/t≃8. The agreement between the phase diagram found and experiment is discussed.
Pis’ma Zh. éksp. Teor. Fiz. 67, No. 5, 350–355 (10 March 1998) 相似文献
20.
G. M. Gur’yanov V. N. Demidov N. P. Korneeva V. N. Petrov Yu. B. Samsonenko G. É. Tsyrlin 《Technical Physics》1997,42(8):956-960
An efficient and fast system for recording and analysis of reflection high-energy electron diffraction (RHEED) patterns is
described. The software developed for this system includes three program packages: one for operating in the single-window
mode, one for operating in the four-window mode, and one for the linear regime. Examples are given of the use of the system
for monitoring and control of growth of III–V semiconductor compounds by molecular-beam epitaxy. Using this system, we discovered
an effect wherein a periodic splitting of the RHEED peaks occurs during the growth of GaAs (100).
Zh. Tekh. Fiz. 67, 111–116 (August 1997) 相似文献