共查询到20条相似文献,搜索用时 31 毫秒
1.
S. H. Ma Z. Y. Jiao X. Q. Dai Z. X. Yang 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,83(4):437-443
Ordered sulphur overlayers adsorbed on Ir(100) surface are studied with differentcoverage ranging from 0.11 to 1.0 ML. Calculations indicate that atomic S adsorbsfavourably in hollow sites, forming strong covalent bonds with the substrate surface andthe adsorption energy is nearly unchanged at lower coverages(θ S ≤ 0.50 ML). In good agreement withexperimental observations, the p(2 × 2)-S and c(2 × 2)-Sare predicted to be the most stable overlayers. The obtained surface electronic structuremodifications induced by sulphur adsorption are coverage-dependent and the results are inaccordance with the rectangular band and the Hammer-Nørskov models. Moreover, the effectof sulphur on the adsorption of CO is discussed in the p(2 × 2)?(S + CO)overlayer on Ir(100). 相似文献
2.
I. Kachaev V. Dorofeev A. Ekimov V. Gotman A. Ivashin V. Kalendarev Yu. Khokhlov M. Kholodenko V. Konstantinov V. Matveev M. Mikhasenko V. Nikolaenko A. Plekhanov D. Ryabchikov Yu. Salomatin V. Sugonyaev E. Volkov A. Zaitsev 《Physics of Atomic Nuclei》2015,78(13):1474-1477
Partial wave analysis of the π–A π+π–π– system produced by 29 GeV/cπ– beam on a beryllium target is presented. About 30 × 106 |events in the wide t′|range 0–0.8 GeV2/c 2 are collected with upgraded VES setup. The size of the data sample is 2.5 times larger than one previously analyzed by VES. Data are analyzed using formalism of the density matrix with unlimited rank. We discuss status of the a 1(1420) a 2(1700) a 3(1875) states and a structure of exotic ρ(770)π P-wave with J PC = 1-+. Parameters of a 3(1875) are estimated as M = 1985 ± 20 MeV/c 2, Γ = 200 ± 50 MeV/c 2 (preliminary). 相似文献
3.
The Higgs-strahlung production process pp → Z′ → ZH is an important process for studying the HZZ′ interaction. We take the B ? L model and the nonuniversal S U(2)1 × S U(2)2 × U(1) Y model as two examples and investigate their correction effects on ZH production at the LHC. Our numerical results show that, considering constraints on these two new physics models, the contributions of the B ? L model to the ZH production cross section are very small, while the S U(1)1 × S U(2)2 × U(1) Y model can generate significant contributions. 相似文献
4.
Raúl Enrique Félix-Medina Manuel Andrés Leyva-Lucero Salvador Meza-Aguilar Claude Demangeat 《The European Physical Journal B - Condensed Matter and Complex Systems》2018,91(4):62
Riva et al. [Surf. Sci. 621, 55 (2014)] as well as Calloni et al. [J. Phys.: Condens. Matter 26, 445001 (2014)] have studied the oxydation of Cr films deposited on Fe(001)bcc through low-energy electron diffraction, Auger electron spectroscopy and scanning tunneling microscopy. In the present work we perform a density functional approach within Quantum Expresso code in order to study structural and magnetic properties of CrO overlayers on Fe(001)bcc. The calculations are performed using DFT+U. The investigated systems include O/Cr/Fe(001)bcc, Cr/O/Fe(001)bcc, Cr0.25O0.75/Fe(001)bcc, as well as the O coverage O x /Cr/Fe(001)bcc (x = 0.25; 0.50). We have found that the ordered CrO overlayer presents an antiferromagnetic coupling between Cr and Fe atoms. The O atoms are located closer to the Fe atoms of the surface than the Cr atoms. The ground state of the systems O/Cr/Fe(001)bcc and Cr/O/Fe(001)bcc corresponds to the O/Cr/Fe(001)bcc system with a magnetic coupling c(2 × 2). The effect of the O monolayer on Cr/Fe(001)bcc changes the ground state from p(1 × 1) ↓ to c(2 × 2) and produces an enhancement of the magnetic moments. The O x overlayer on Cr/Fe(001)bcc produces an enhancement of the Cr magnetic moments. 相似文献
5.
We discuss the scenario where the X(3872) resonance is the \(c\bar c\) = χc1(2P) charmonium which “sits on” the D*0\({\bar D^0}\) threshold. We explain the shift of the mass of the X(3872) resonance with respect to the prediction of a potential model for the mass of the χc1(2P) charmonium by the contribution of the virtual D*\(\bar D\) + c.c. intermediate states into the self energy of the X(3872) resonance. This allows us to estimate the coupling constant of the X(3872) resonance with the D*0\({\bar D^0}\) channel, the branching ratio of the X(3872) → D*0\({\bar D^0}\) + c.c. decay, and the branching ratio of the X(3872) decay into all non-D*0\({\bar D^0}\) + c.c. states. We predict a significant number of unknown decays of X(3872) via two gluon: X(3872) → gluongluon → hadrons. We suggest a physically clear program of experimental researches for verification of our assumption. 相似文献
6.
E. Z. Kuchinskii N. A. Kuleeva M. V. Sadovskii 《Journal of Experimental and Theoretical Physics》2017,125(6):1127-1136
We study disorder effects upon the temperature behavior of the upper critical magnetic field in an attractive Hubbard model within the generalized DMFT+Σ approach. We consider the wide range of attraction potentials U—from the weak coupling limit, where superconductivity is described by BCS model, up to the strong coupling limit, where superconducting transition is related to Bose–Einstein condensation (BEC) of compact Cooper pairs, formed at temperatures significantly higher than superconducting transition temperature, as well as the wide range of disorder—from weak to strong, when the system is in the vicinity of Anderson transition. The growth of coupling strength leads to the rapid growth of Hc2(T), especially at low temperatures. In BEC limit and in the region of BCS–BEC crossover Hc2(T), dependence becomes practically linear. Disordering also leads to the general growth of Hc2(T). In BCS limit of weak coupling increasing disorder lead both to the growth of the slope of the upper critical field in the vicinity of the transition point and to the increase of Hc2(T) in the low temperature region. In the limit of strong disorder in the vicinity of the Anderson transition localization corrections lead to the additional growth of Hc2(T) at low temperatures, so that the Hc2(T) dependence becomes concave. In BCS–BEC crossover region and in BEC limit disorder only slightly influences the slope of the upper critical field close to T c . However, in the low temperature region Hc2 (T may significantly grow with disorder in the vicinity of the Anderson transition, where localization corrections notably increase Hc2 (T = 0) also making Hc2(T) dependence concave. 相似文献
7.
In this proceeding, we present our recent work on decay behaviors of the Pc hadronic molecules, which can help to disentangle the nature of the two Pc pentaquark-like structures. The results turn out that the relative ratio of the decays of P c + (4380) to \({\bar D *}{\Lambda _c}\) and J/ψp is very different for Pc being a \({\bar D *}{\Sigma _c}\) or \(\bar D\Sigma _c *\) bound state with \({J^P} = \frac{{{3 - }}}{2}\) And from the total decay width, we find that Pc(4380) being a \(\bar D\Sigma _c *\) molecule state with \({J^P} = \frac{{{3 - }}}{2}\) and Pc(4450) being a \({\bar D *}{\Sigma _c}\) molecule state with \({J^P} = \frac{{{5 + }}}{2}\) is more favorable to the experimental data. 相似文献
8.
A three-dimensional (3D) reconstruction of the atomic structure of the (100) surface of a 1T-TiSe2 layered dichalcogenide crystal has been performed from X-ray photoelectron and Auger electron diffraction data. The diffraction patterns of the emission of Auger electrons of Se(LMM) selenium and photoelectrons of Ti2p titanium have been considered as holographic diagrams. Being processed with the scattering pattern extraction algorithm using the maximum entropy method (SPEA-MEM), they provide individual 3D images of the nearest environment of selenium and titanium atoms in the TiSe2 lattice. Using reconstructed 3D images, the positions of 128 atoms in the 2 × 2 × 1.5-nm region of the surface layer of TiSe2 have been determined. The structure of the surface has a 1T polytype. Interatomic distances in the layer and van der Waals gap are larger than the respective parameters in the bulk of the crystal. It is assumed that titanium layers in two Se-Ti-Se upper surface structural units are displaced along the [001] axis. The structure of the surface layer can be described by a unit cell of the P3 space group with the parameters a = 3.85 Å and c = 14.4 Å. 相似文献
9.
In order to explain the fermions’ masses and mixing parameters appearing in the lepton sector of the Standard Model, one proposes the extension of its symmetry. A discrete, non-Abelian subgroup of U(3) is added to the gauge group SU(3) C × SU(2) L × U(1) Y . Apart from that, one assumes the existence of one extra Higgs doublet. This article focuses mainly on the mathematical theorems and computational techniques which brought us to the results. 相似文献
10.
N. V. Anshukova B. M. Bulychev A. I. Golovashkin L. I. Ivanova A. A. Minakov A. P. Rusakov 《Physics of the Solid State》2003,45(7):1207-1212
The temperature dependences of the specific heat C(T) and thermal conductivity K(T) of MgB2 were measured at low temperatures and in the neighborhood of T c . In addition to the well-known superconducting transition at T c ≈40 K, this compound was found to exhibit anomalous behavior of both the specific heat and thermal conductivity at lower temperatures, T≈10–12 K. Note that the anomalous behavior of C(T) and K(T) is observed in the same temperature region where MgB2 was found to undergo negative thermal expansion. All the observed low-temperature anomalies are assigned to the existence in MgB2 of a second group of carriers and its transition to the superconducting state at Tc2≈10?12 K. 相似文献
11.
We uncover the low-energy spectrum of a t-J model for electrons on a square lattice of spin-1 iron atoms with 3d xz and 3d yz orbital character by applying Schwinger-boson-slave-fermion mean-field theory and by exact diagonalization of one hole roaming over a 4 × 4 × 2 lattice. Hopping matrix elements are set to produce hole bands centered at zero two-dimensional (2D) momentum in the free-electron limit. Holes can propagate coherently in the t-J model below a threshold Hund coupling when long-range antiferromagnetic order across the d + = 3d (x + iy)z and d ? = 3d (x ? iy)z orbitals is established by magnetic frustration that is off-diagonal in the orbital indices. This leads to two hole-pocket Fermi surfaces centered at zero 2D momentum. Proximity to a commensurate spin-density wave (cSDW) that exists above the threshold Hund coupling results in emergent Fermi surface pockets about cSDW momenta at a quantum critical point (QCP). This motivates the introduction of a new Gutzwiller wavefunction for a cSDW metal state. Study of the spin-fluctuation spectrum at cSDW momenta indicates that the dispersion of the nested band of one-particle states that emerges is electron-type. Increasing Hund coupling past the QCP can push the hole-pocket Fermi surfaces centered at zero 2D momentum below the Fermi energy level, in agreement with recent determinations of the electronic structure of mono-layer iron-selenide superconductors. 相似文献
12.
Yu. G. Galitsyn D. V. Dmitriev V. G. Mansurov S. P. Moshchenko A. I. Toropov 《JETP Letters》2005,81(12):629-633
The critical exponents of the β-(2×4) → α-(2×4) reconstruction phase transition on the (001) GaAs surface are determined experimentally. It is found that the phase transition is analogous to a van der Waals transition. The critical parameters T c , P c , and Θc have been measured experimentally. The mean field theory is applied, and three-parameter isotherms are obtained that agree with the experimental results at the following values of the parameters: Est = 0.36 eV, ΔE = 0.18 eV, and E i = 0.134 eV. Precision measurements of the critical exponents β and δ are carried out. Their values β = 1/8 and δ = 15 indicate that the phase transition is truly two-dimensional. 相似文献
13.
L. G. Mamsurova K. S. Pigalskiy N. G. Trusevich A. A. Vishnev M. A. Rogova S. Yu. Gavrilkin A. Yu. Tsvetkov 《JETP Letters》2015,102(10):662-667
The magnetization M(H) in the superconducting state, dc magnetic susceptibility χ(T) in the normal state, and specific heat C(T) near the superconducting transition temperature T c have been measured for a series of fine-crystalline YBa2Cu3O y samples having nearly optimum values of y = 6.93 ± 0.3 and T c = (91.5 ± 0.5) K. The samples differ only in the degree of nanoscale structural inhomogeneity. The characteristic parameters of superconductors (the London penetration depth and the Ginzburg–Landau parameter) and the thermodynamic critical field H c are determined by the analysis of the magnetization curves M(H). It is found that the increase in the degree of nanoscale structural inhomogeneity leads to an increase in the characteristic parameters of superconductors and a decrease in H c(T) and the jump of the specific heat ΔC/T c. It is shown that the changes in the physical characteristics are caused by the suppression of the density of states near the Fermi level. The pseudogap is estimated by analyzing χ(T). It is found that the nanoscale structural inhomogeneity significantly enhances and probably even creates the pseudogap regime in the optimally doped high-T c superconductors. 相似文献
14.
We consider Ising models in two and three dimensions, with short range ferromagnetic and long range, power-law decaying, antiferromagnetic interactions. We let J be the ratio between the strength of the ferromagnetic to antiferromagnetic interactions. The competition between these two kinds of interactions induces the system to form domains of minus spins in a background of plus spins, or vice versa. If the decay exponent p of the long range interaction is larger than d + 1, with d the space dimension, this happens for all values of J smaller than a critical value Jc(p), beyond which the ground state is homogeneous. In this paper, we give a characterization of the infinite volume ground states of the system, for p > 2d and J in a left neighborhood of Jc(p). In particular, we prove that the quasi-one-dimensional states consisting of infinite stripes (d = 2) or slabs (d = 3), all of the same optimal width and orientation, and alternating magnetization, are infinite volume ground states. Our proof is based on localization bounds combined with reflection positivity. 相似文献
15.
D. A. Gorodetsky Yu. P. Mel’nik D. P. Proskurin V. A. Usenko 《Physics of the Solid State》2004,46(10):1940-1948
The structure and electronic properties of antimony on the Mo(110) surface are investigated over a wide range of coverages. In the submonolayer range, p(2×1), p(1×1), (1×3), and (1×2) adsorbate structures matched to the substrate are formed at room temperature. For coverages larger than a monolayer, three-dimensional antimony crystals whose orientation is determined by the substrate grow on the surface. Annealing of the system at temperatures higher than 1000 K leads to the formation of structures that are not observed upon condensation. The results of analyzing the electron energy-loss spectra jointly with the work function of the surface suggest the formation of surface molybdenum-antimony alloys. 相似文献
16.
Helmut Strothmann 《Zeitschrift für Physik A Hadrons and Nuclei》1966,192(1):51-62
The light output,S v by α-particles stopped in anthracene vapour has been measured as a function of vapour pressure (10–700 mm Hg) and temperature (250°C–385°C). The comparison of the results for an idealised vapour neglecting collisions with the light output,S c, from anthracene crystals by α-particles impinging parallel to thec′-axis yields the unexpected results: Sv(8.78 MeV)/Sc(8.78 MeV)=0.46±0.05 andS v(6.05 MeV)/S c(6.05 MeV)=0.57±0.08. A simple model assuming quenching by collisions of the vapour molecules could explain the observed dependence of the light output on the vapour pressure at fixed temperature. The path lengthsR v of α-particles in anthracene vapour were determined to be Rv(8.78 MeV)=(9.0±0.6) mg/cm2,R v(6.05 MeV)=(4.9±0.6) mg/cm2 and the ratio of the light output by the two different α-energiesS v(8.78 MeV)/S v(6.05 MeV)=1.42±0.2. 相似文献
17.
M. N. Magomedov 《Physics of the Solid State》2003,45(7):1213-1218
A new approach is proposed for calculating the Debye temperature of a nanocrystal in the form of an n-dimensional rectangular parallelepiped with an arbitrary microstructure and the number of atoms N ranging from 2n to infinity. The geometric shape of the system is determined by the lateral-to-basal edge ratio of the parallelepiped. The size dependences of the Debye and melting temperatures for a number of materials are calculated using the derived relationship. The theoretical curves thus obtained agree well with the experimental data. The calculated dependences of the superconducting transition temperature T c on the size d of aluminum, indium, and lead nanocrystals are also in reasonable agreement with the experimental estimates of T c (d). It is demonstrated that, as the nanocrystal size d decreases, the greater the deviation of the nanocrystal shape from an equilibrium shape (in our case, a cube), the higher the temperature of the superconducting transition T c (d). The superconducting transition temperature is calculated as a function of the thickness (diameter) of a plate (rod) with an arbitrary length. It is found that a decrease in the thickness (diameter) of the plate (rod) leads to an increase in the temperature T c (z): the looser the microstructure of the metallic nanocrystal, the higher the temperature T c (z). 相似文献
18.
S. I. Krasnosvobodtsev A. V. Varlashkin A. I. Golovashkin N. P. Shabanova 《Physics of the Solid State》2005,47(9):1600-1604
The upper critical field H c 2 (H ‖ c) of the two-band superconductor MgB2 is studied as a function of the residual resistivity ρn. It is found that the superconductor follows the standard trend: the slope-dHc2/dT of the temperature dependence of Hc2(T) increases with the number of defects. The upper critical field in the clean limit is found, and direct estimations of the parameters of carriers in the 2D σ band (including the Fermi velocity and the coherence length) are made. The contribution of the electron scattering to the magnitude of Hc2 is determined, and the mean free path of electrons in samples with various defect concentrations is estimated. The density of states of σ electrons at the Fermi level is calculated using the dependence of the slope-dHc2/dT on ρn and a band structure model. It is impossible to estimate this density of states directly, because the upper critical field is determined by the carriers of one band, whereas the resistivity depends on the carriers in both bands. 相似文献
19.
V. L. Gurtovoi S. V. Dubonos A. V. Nikulov N. N. Osipov V. A. Tulin 《Journal of Experimental and Theoretical Physics》2007,105(6):1157-1173
The obtained periodic magnetic-field dependences I c+(Φ/Φ0) and I c?(Φ/Φ0) of the critical current measured in opposite directions on asymmetric superconducting aluminum rings has made it possible to explain previously observed quantum oscillations of dc voltage as a result of alternating current rectification. It was found that a higher rectification efficiency of both single rings and ring systems is caused by hysteresis of the current-voltage characteristics. The asymmetry of current-voltage characteristics providing the rectification effect is due to the relative shifts of the magnetic dependences I c?(Φ/Φ0) = I c+(Φ/Φ0 + Δ?) of the critical current measured in opposite directions. This shift means that the position of I c+(Φ/Φ0) and I c?(Φ/Φ0) minima does not correspond to n + 0.5 magnetic flux Φ quanta, which is in direct contradiction to measured Little-Parks resistance oscillations. Despite this contradiction, the amplitude I c, an(Φ/Φ0) = I c+(Φ/Φ0) ? I c?(Φ/Φ0) of critical current anisotropy oscillations and its variations with temperature correspond to the expected amplitude of persistent current oscillations and its variations with temperature. 相似文献
20.
Yucheng Wang Gao Xianlong Shu Chen 《The European Physical Journal B - Condensed Matter and Complex Systems》2017,90(11):215
We study a one-dimensional quasiperiodic system described by the Aubry–André model in the small wave vector limit and demonstrate the existence of almost mobility edges and critical regions in the system. It is well known that the eigenstates of the Aubry–André model are either extended or localized depending on the strength of incommensurate potential V being less or bigger than a critical value V c , and thus no mobility edge exists. However, it was shown in a recent work that for the system with V < V c and the wave vector α of the incommensurate potential is small, there exist almost mobility edges at the energy E c±, which separate the robustly delocalized states from “almost localized” states. We find that, besides E c±, there exist additionally another energy edges E c′±, at which abrupt change of inverse participation ratio (IPR) occurs. By using the IPR and carrying out multifractal analyses, we identify the existence of critical regions among |E c±|?≤?|E|?≤?|E c′±| with the mobility edges E c± and E c′± separating the critical region from the extended and localized regions, respectively. We also study the system with V > V c , for which all eigenstates are localized states, but can be divided into extended, critical and localized states in their dual space by utilizing the self-duality property of the Aubry–André model. 相似文献