排序方式: 共有21条查询结果,搜索用时 31 毫秒
1.
Knyazev Yu. V. Kazak N. V. Gavrichkov V. A. Polukeev S. I. Ovchinnikov S. G. 《JETP Letters》2022,116(8):567-573
JETP Letters - Changes in the magnetic properties of FeBO3 single crystals in the course of spin crossover occurring with increasing pressure up to 63 GPa are studied both experimentally and... 相似文献
2.
S.G. Ovchinnikov V.A. Gavrichkov M.M. Korshunov E.I. Shneyder I.A. Nekrasov Z.V. Pchelkina J. Spitaler 《Journal of magnetism and magnetic materials》2009,321(7):917-919
A review of recent results for the doping dependence of the Fermi surface and mechanism of pairing in LaSrCuO obtained within the LDA+GTB multielectron approach is given. Both magnetic and phonon contributions to the dx2-y2-gap are considered. 相似文献
3.
V. A. Gavrichkov S. G. Ovchinnikov 《Journal of Experimental and Theoretical Physics》2004,98(3):556-564
The spectral density, dispersion relations, and the position of the Fermi level for n-doped compositions based on NCO and LCO were calculated within the framework of the generalized tight binding method. As distinguished from LCO, the dielectric gap in NCO is nonlinear in character. We observe a virtual level both at the bottom of the conduction band and at the top of the valence band in both compounds. However, its position corresponds to the extreme bottom of the conduction band in LCO and is 0.1–0.2 eV above the bottom in NCO. This explains why we observe Fermi level pinning in n-LCO as the concentration of the doping component grows and reproduce its absence in NCCO at low doping values. We also found both compositions to be unstable in a narrow concentration range with respect to a nonuniform charge density distribution. The relation between the phase diagram for NCCO and the calculated electronic structure is discussed. 相似文献
4.
A. A. Borisov V. A. Gavrichkov S. G. Ovchinnikov 《Journal of Experimental and Theoretical Physics》2003,97(4):773-780
The electronic structure of p-type doped HTSC cuprates is calculated by explicitly taking into account strong electron correlations. The smooth evolution of the electronic structure from undoped antiferro-magnetic to optimally and heavily doped paramagnetic compositions is traced. For a low doping level, in-gap impurity-type states are obtained, at which the Fermi level is pinned in the low-doping region. These states are separated by a pseudogap from the valence band. The Fermi surfaces calculated for the paramagnetic phase for various concentrations of holes are in good agreement with the results of ARPES experiments and indicate a gradual change in the Fermi surface from the hole type to the electron type. 相似文献
5.
V. A. Gavrichkov S. G. Ovchinnikov I. A. Nekrasov Z. V. Pchelkina 《Journal of Experimental and Theoretical Physics》2011,112(5):860-876
The band structure, spectral intensity, and position of the Fermi level in doped p-type La1 − x
M
x/2+MnO3 manganites (M = Sr, Ca, Ba) is analyzed using the LDA + GBT method for calculating the electronic structure of systems with
strong electron correlations, taking into account antiferro-orbital ordering and using the Kugel-Khomskii ideas and real spin
S = 2. The results of the ferromagnetic phase reproduce the state of a spin half-metal with 100% spin polarization at T = 0, when the spectrum is of the metal type for a quasiparticle with one spin projection and of the dielectric type for the
other. It is found that the valence band becomes approximately three times narrower upon a transition to the paramagnetic
phase. For the paramagnetic phase, metal properties are observed because the Fermi level is located in the valence band for
any nonzero x. The dielectrization effect at the Curie temperature is possible and must be accompanied by filling of d
x
orbitals upon doping. The effect itself is associated with strong electron correlations, and a complex structure of the top
of the valence band is due to the Jahn-Teller effect in cubic materials. 相似文献
6.
Ovchinnikov S. G. Rudenko V. V. Kazak N. V. Edelman I. S. Gavrichkov V. A. 《Journal of Experimental and Theoretical Physics》2020,131(1):177-188
Journal of Experimental and Theoretical Physics - The simple lattice and magnetic structure, the high Néel temperature, the narrow antiferromagnetic resonance line of FeBO3, and the narrow... 相似文献
7.
An exact diagonalization of the Hamiltonian in the p-d model of a CuO6 cluster was used to obtain dependences on the model parameters of the lowest-energy two-hole terms: the energy difference
between the 2p orbitals of planar and apical oxygen Δ(apex)=ε(2p)−ε[2p(apex)], the crystal field parameter
, and the ratio of the distances between the copper atom and the apical and planar oxygen atoms d(apex)/d(pl). In the limit of large d(apex)/d(pl) and Δd, our model is equivalent to the three-band p-d model and, in this case, large singlet-triplet splitting Δε⩾1 eV is also observed. As the parameters decrease, a singlet-triplet crossover is observed. Two mechanisms are identified
for stabilization of the triplet term 3
B
1g
(0) as the ground state. It is shown that for realistic values of the parameters, reduction of the p-d model to the three-band model is limited by the low energies of the current excitations because of the presence of the lower
excited 3
B
1g
and 1
A
1g
cluster states. Intercluster hopping causes strong mixing of singlet and triplet states far from the G point. The results
of the calculations are compared with data obtained by angle-resolved photoelectron emission in Sr2CuO2Cl2.
Fiz. Tverd. Tela (St. Petersburg) 40, 184–190 (February 1998) 相似文献
8.
Switching from simple semiconductors to more complicated chemical compositions, we encounter mainly nonstoichiometric or undoped
compounds. Combined with other characteristic features of d(f) compounds, this can lead, together with the ordinary scattering by spin disorder in magnetic semiconductors, to an unusual
impurity contribution to the total scattering of carriers even in intrinsic semiconductors. A unique scheme for calculating
the energy structure of the conduction-band bottom of a ferromagnetic semiconductor and the temperature and field dependences
of the impurity contribution to the resistivity is proposed on the basis of a model Hamiltonian. The computed magnetoresistance
ratio is negative and has a maximum near T
c
. A qualitative comparison is made between the results and the experimental temperature dependences of the Hall mobility and
magnetoresistance ratio in the ternary semiconductor n-HgCr2Se4, which is nonstoichiometric with respect to the chalcogen. To identify previously unobserved temperature oscillations of
the resistance, a careful analysis is made of the low-temperature part of the resistance using the relations obtained.
Fiz. Tverd. Tela (St. Petersburg) 41, 68–76 (January 1999) 相似文献
9.
Critical phenomena in ethylbenzene oxidation in an acetic acid solution at high cobalt(III) concentrations (from 0.01 to 0.2 mol L−1) were studied at 60–90 °C by the gasometric (O2 absorption), spectrophotometric (CoIII accumulation), and chemiluminescence (relative concentration of radical RO2
·) methods. These phenomena are as follows: (1) increase in the oxidation rate above the theoretical limiting rate of radical
autooxidation (k
3
2[RH]2/2k
6); (2) achievement of a maximum and a sharp decrease in the oxidation rate and concentration of radical RO2
· with the further increase in the CoII concentration (existence of critical concentrations). The oxidation rate increases due to the reaction RO2
· + CoII + H+ → → ROOH + CoIII, while the inhibition effect is caused by the decay of RO2
· radical involving two cobalt(II) atoms: RO2
· + 2 CoII → R′CO + CoIII + CoII (k(70 °C) ≈ 300 L2 mol−2 s−1). The detailed scheme (through the formation of the complex RO2
·CoII) describing the conjugation of these reactions was proposed.
__________
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1823–1827, August, 2005. 相似文献
10.
A. D. Balaev V. A. Gavrichkov S. G. Ovchinnikov V. K. Chernov T. G. Aminov G. G. Shabunina 《Journal of Experimental and Theoretical Physics》1998,86(5):1026-1029
In the magnetic field range ΔH=8–60 kOe we observed and studied the anomalous oscillations in the magnetic field dependence of the resistance and magnetization
of single crystals of n-HgCr2Se4. The absence of periodicity in 1/H in the ΔH=8–20 kOe range can be explained by the non-Fermi-liquid behavior of the electron subsystem and agrees with the theory of
the de Haas-van Alphen in systems with intermediate valence. In stronger fields, ΔH=20–60 kOe, the amplitude of the fundamental harmonic decreases, with the number and amplitude of the higher-order harmonics
increasing. As a result, noise is superimposed on the signal as magnetic field strength grows. The temperature dependence
of the magnetization is the sum of the monotonic spin-wave contribution and the oscillating part.
Zh. éksp. Teor. Fiz. 113, 1877–1882 (May 1998) 相似文献