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1.
S. I. Matveenko 《JETP Letters》2003,78(6):384-388
We show that many observable properties of high-temperature superconductors can be obtained in the framework of a one-dimensional self-consistent model with included superconducting correlations. Analytical solutions for spin, charge, and superconductivity order parameters are found. The ground state of the model at low hole doping is a spin-charge solitonic superstructure. Increased doping leads to a transition to the superconducting phase. There is a region of doping where superconductivity, spin density wave, and charged stripe structure coexist. The charge density modulation appears in the vicinity of vortices (kinks in the 1D model) in the superconducting state. 相似文献
2.
A. Sherman M. Schreiber 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(2):203-214
Using the method which retains the rotation symmetry of spin components in the paramagnetic state and has no preset magnetic
ordering, spectral and magnetic properties of the two-dimensional t-J model in the normal state are investigated for the ranges of hole concentrations 0 ⩽ x ⩽ 0.16 and temperatures 0.01t ⩽ T ⩽ 0.2t. The used hopping t and exchange J parameters of the model correspond to hole-doped cuprates. The obtained solutions are homogeneous which indicates that stripes
and other types of phase separation are not connected with the strong electron correlations described by the model. A series
of nearly equidistant maxima in the hole spectral function calculated for low T and x is connected with hole vibrations in the region of the perturbed short-range antiferromagnetic order. The hole spectrum has
a pseudogap in the vicinity of (0,π) and (π, 0). For x ≈ 0.05 the shape of the hole Fermi surface is transformed from four small ellipses around (±π/2,±π/2) to two large rhombuses
centered at (0, 0) and (π,π). The calculated temperature and concentration dependencies of the spin correlation length and
the magnetic susceptibility are close to those observed in cuprate perovskites. These results offer explanations for the observed
scaling of the static uniform susceptibility and for the changes in the spin-lattice relaxation and spin-echo decay rates
in terms of the temperature and doping variations in the spin excitation spectrum of the model.
Received 14 November 2002 Published online 1st April 2003
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ID="a"e-mail: alexei@fi.tartu.ee 相似文献
3.
4.
采用第一性原理方法,对BaTi2Bi2O的电子结构和磁性进行计算.非磁性态的计算结果显示:费米能级处的态密度主要来自dz2,dx2-y2和dxy三个轨道,同时费米面也主要有三部分组成,并且将其沿着矢量q1=(π/a,0,0)和q2=(0,π/a,0)平移时,第三部分费米面(沿着X-R连线)与第一部分费米面(M-A连线)嵌套明显,计算得出磁化系数χ0(q)在X点出现峰值,与峰值出现在M点的FeAs基超导体不同.上述磁化率峰值可以诱导产生自旋密度波,使得BaTi2Bi2O材料的磁性基态是bi-collinear antiferromagnetism(AF3)与blocked checkerboard antiferromagnetism(AF4)的二度简并态.随着空穴掺杂,χ0(q)的峰值降低,而电子掺杂则导致峰值变大.当自旋涨落被完全压制时,超导出现,这可以解释为什么超导只出现在空穴掺杂型化合物而非电子掺杂型. 相似文献
5.
Y. Kitaoka K. Ishida S. Ohsugi K. Fujiwara G. -q. Zheng K. Asayama 《Applied magnetic resonance》1992,3(3-4):549-596
The magnetic and superconducting properties in the high-T c cuprates have been investigated over a wide hole doping range by63Cu,17O and205Tl NMR and NQR in the lightly-doped La2?xSrxCuO4 (LSCO), the heavily-doped Tl2Ba2CuO6+y (TBCO) and the Zn-doped YBa2Cu3O7 (YBCO7). In low doping region, the large antiferromagnetic (AF) spin correlation around the zone boundary (q=Q) causes the Curie-Weiss behavior of63(1/T 1 T) associated with that of the staggered susceptibility χO(T) in LSCO. In the vicinity of the hole content whereT c has a peak, the AF spin correlation still survives, although the magnetic coherence length ξM is considerably short being presumably (ξM/a) ~ 1. The further doping destroys progressively the AF spin correlation, which is no longer present is non-superconducting TBCO compounds. These NMR evidences signify that there is an intimate relation between the presence of the AF spin correlation and the onset of the superconductivity. The local collapse of AF spin correlation is a primary cause for the unexpected strong reduction ofT c in case of the substitution of Zn impurities into the CuO2 plane. The superconducting properties clarified by NMR experiments cannot be accounted for by the conventional BCS model or other isotropic s-wave models. A d-wave model is applicable in interpreting consistently most of the NMR results, if the finite density of states at the Fermi level is taken into consideration and is associated with the pair breaking effect. There are increasing evidences that the magnetic mechanism for the superconductivity is promising in high-T c cuprates. 相似文献
6.
Artem A. Vladimirov Dieter Ihle Nikolay M. Plakida 《The European Physical Journal B - Condensed Matter and Complex Systems》2018,91(8):195
We present a spin-rotation-invariant Green-function theory for the dynamic spin susceptibility in the spin-1/2 antiferromagnetic t-J Heisenberg model on the honeycomb lattice. Employing a generalized mean-field approximation for arbitrary temperatures and hole dopings, the electronic spectrum of excitations, the spin-excitation spectrum and thermodynamic quantities (two-spin correlation functions, staggered magnetization, magnetic susceptibility, correlation length) are calculated by solving a coupled system of self-consistency equations for the correlation functions. The temperature and doping dependence of the magnetic (uniform static) susceptibility is ascribed to antiferromagnetic short-range order. Our results on the doping dependencies of the magnetization and susceptibility are analyzed in comparison with previous results for the t-J model on the square lattice. 相似文献
7.
T. Morinari 《Journal of Physics and Chemistry of Solids》2008,69(12):2960-2962
In angle-resolved photoemission spectroscopy pseudogap phenomenon in high-temperature superconductors is observed as Fermi arcs, or truncated Fermi surface. Here I argue that the hole induced chiral spin texture scenario naturally leads to Fermi arcs by including hole hopping processes. Disappearance of part of the Fermi surface is associated with the effect of the coherence factor. Suppressed spectral weight of the holes turns out to be an electron-like component which has weight near (π,0) only and has some charge instability. 相似文献
8.
The dynamics of a mobile hole in two-dimensional frustrated quantum magnets is investigated by exact diagonalization techniques. Our results provide evidence for spin-charge separation upon doping the kagome lattice, a prototype of a spin liquid. In contrast, in the checkerboard lattice, a symmetry broken valence bond crystal, a small quasiparticle peak is seen for some crystal momenta, a finding interpreted as a restoration of weak holon-spinon confinement. 相似文献
9.
A. Curir 《General Relativity and Gravitation》1981,13(5):417-423
A black hole is interpreted as an open system in the Prigogine sense. From the point of view of spin transformations, the existence of a phase transition corresponding to an extreme Kerr hole is recognized. The role played by the spin entropy into superradiance of a rotating black hole is investigated. 相似文献
10.
Doping evolution of the Fermi surface topology of Na(x)CoO(2) is studied systematically. Both local density approximation (LDA) and local spin density approximation (LSDA) predict a large Fermi surface as well as small hole pockets for doping levels x approximately 0.5. In contrast, the hole pockets are completely absent for all doping levels within LSDA+U. More importantly, we find no violation of Luttinger's rule in this system. The measured Fermi surface of Na(0.7)CoO(2) can be explained by its half-metallic behavior and agrees with our LSDA+U calculations. 相似文献
11.
We present different numerical calculations based on variational quantum Monte Carlo simulations supporting a ferromagnetic ground state for finite and small hole densities in the two-dimensional infinite-U Hubbard model. Moreover, by studying the energies of different total spin sectors, these calculations strongly suggest that the paramagnetic phase is unstable against a phase with a partial polarization for large hole densities delta approximately 0.40 with evidence for a second-order transition to the paramagnetic large doping phase. 相似文献
12.
Y. Ōno R. Bulla A.C. Hewson M. Potthoff 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(3):283-290
We have studied the critical behaviour of a doped Mott insulator near the metal-insulator transition for the infinite-dimensional
Hubbard model using a linearized form of dynamical mean-field theory. The discontinuity in the chemical potential in the change
from hole to electron doping, for U larger than a critical value U
c, has been calculated analytically and is found to be in good agreement with the results of numerical methods. We have also
derived analytic expressions for the compressibility, the quasiparticle weight, the double occupancy and the local spin susceptibility
near half-filling as functions of the on-site Coulomb interaction and the doping.
Received 15 March 2001 and Received in final form 22 May 2001 相似文献
13.
A. V. Mikheenkov A. F. Barabanov 《Journal of Experimental and Theoretical Physics》2007,105(2):347-359
Experimental data on the spin susceptibility of HTSC cuprates are reproduced on the basis of a spherically symmetric approach in the frustrated Heisenberg model. The inclusion of real and imaginary renormalizations in spin Green’s functions makes it possible to explain the evolution of spin excitation spectrum ω(q) and susceptibility spectrum χ(q, ω) in the range from insulator to optimal doping. In the low-frustration limit corresponding to the weakly doped mode, the saddle singularity of ω(q) and scaling of χ2D(ω) =∫d q Im χ(q, ω) are reproduced and an analytic expression is derived for the scaling function. In the strong frustration (optimal doping) mode, the stripe scenario is demonstrated; this leads to a peak of χ2D (ω) in the region of ω~60 meV. 相似文献
14.
A.J. Epstein H. Rommelmann M.A. Druy A.J. Heeger A.G. MacDiarmid 《Solid State Communications》1981,38(8):683-687
A detailed study of magnetic properties of [CHH(I3)y]x demonstrates that with quasi-uniform doping, the spin susceptibility is small, consistent with the soliton doping mechanism. Traditional doping techniques lead to one order of magnitude larger spin susceptibilities, and to a nonuniform dopant distribution. We present a simple model which accounts for the observed susceptibility based on the effect of a radial variation of y within the (CH)x fibrils. 相似文献
15.
A new mechanism for the pairing in cuprate superconductors ia proposed and studied by using the mean-field approximations. A hybridieation singlet pair is formed by media of strong hybridization between a d hole on Cu site and a p doped hole with opposite spin on the nearest-neighbor O site in the CuO2 plane. The transition temperature can be found to reach a peak around δ~0.1-0.3 and the ratio of energy gap to Tc has a maximum 4.0. This is in good agreement with experiments. The specific heat jump as a function of doping fraction δ, the upper critical field and the coherence length, are obtained. 相似文献
16.
Guodong Tang Chipui Tang Xiaonong Xu Yun He Li Qiu Liya Lv Zhihe Wang Youwei Du 《Solid State Communications》2010,150(35-36):1706-1709
The magnetothermopower have been studied in Lu-doped Ca3?xLuxCo4O9+δ. A strong magnetic field suppression of thermopower indicates large spin entropy contribution. The magnetothermopower for doped samples are overall enhanced compared with that for undoped Ca3Co4O9+δ, providing an experimental evidence for the enhancement of spin entropy. Magnetic results confirm that Co4+ concentration is reduced by Lu doping. We suggest that the reduction in Co4+ concentration results in the enhanced spin entropy. 相似文献
17.
The effect of doping of rare earth Pr3+ ion as a replacement of Sm3+ in Sm0.5Sr0.5MnO3 is investigated. Temperature dependent dc and ac magnetic susceptibility, resistivity, magnetoresistance measurements on chemically synthesized (Sm0.5−xPrx)Sr0.5MnO3 show various unusual features with doping level x=0.15. The frequency independent ferromagnetic to paramagnetic transition at higher temperature (∼191 K) followed by a frequency dependent reentrant magnetic transition at lower temperature (∼31 K) has been observed. The nature of this frequency dependent reentrant magnetic transition is described by a critical slowing down model of spin glasses. From non-linear ac susceptibility measurements it has been confirmed that the finite size ferromagnetic clusters are formed as a consequence of intrinsic phase separation, and undergo spin glass-like freezing below a certain temperature. There is an unusual observation of a 2nd harmonic peak in the non-linear ac susceptibility around this reentrant magnetic transition at low temperature (∼31 K). Arrott plots at 10 and 30 K confirm the existence of glassy ferromagnetism below this low temperature reentrant transition. Electronic- and magneto-transport measurements show a strong magnetic field—temperature history dependence and strong irreversibility with respect to the sweeping of magnetic field. These results are attributed to the effect of phase separation and kinetic arrest of the electronic phase in this phase separated manganite at low temperatures. 相似文献
18.
J. Altmann W. Brenig A.P. Kampf 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(3):429-433
We have investigated the evolution of the electronic properties of the t-t'-U Hubbard model with hole doping and temperature. Due to the shape of the Fermi surface, scattering from short wavelength spin
fluctuations leads to strongly anisotropic quasi-particle scattering rates at low temperatures near half-filling. As a consequence,
significant variations with momenta near the Fermi surface emerge for the spectral functions and the corresponding ARPES signals.
At low doping the inverse lifetime of quasiparticles on the Fermi surface is of order varying linearly in temperature from energies of order t down to a very low energy scale set by the spin fluctuation frequency while at intermediate doping a sub-linear T-dependence is observed. This behavior is possibly relevant for the interpretation of photoemission spectra in cuprate superconductors
at different hole doping levels.
Received 31 July 2000 相似文献
19.
Schlottmann P 《Physical review letters》2000,84(7):1559-1562
The low-temperature properties of a magnetic impurity of spin S interacting with an electron gas via anisotropic spin exchange are studied via Bethe's ansatz. For S>1/2 the impurity is only partially compensated at T = 0, leaving an effective spin that is neither integer nor half integer. The entropy has an essential singularity at H = T = 0, and the susceptibility and the specific heat follow power laws of H and T with nonuniversal exponents, which are the consequence of a quantum critical point. The results for the generalization to an arbitrary number of channels are also reported. 相似文献
20.
Based on a variational approach, we propose that there are two kinds of low-energy states in the t-J-type models at low doping. In a quasiparticle state an unpaired spin bound to a hole with a well-defined momentum can be excited with spin waves. The resulting state shows a suppression of antiferromagnetic order around the hole with the profile of a spin bag. These spin-bag states with spin and charge or hole separated form a continuum of low-energy excitations. Very different properties predicted by these two kinds of states explain a number of anomalous results observed in the exact diagonalization studies on small clusters up to 32 sites. 相似文献