共查询到20条相似文献,搜索用时 15 毫秒
1.
Shigenori Tanaka 《Physica C: Superconductivity and its Applications》1994,220(3-4):341-346
A semiempirical method for the calculation of the bond ionicity, which is applicable even to extremely anisotropic systems such as copper-oxide superconductors, is proposed as a generalization of the Phillips-Van Vechten-Levine scheme. The value of the ionicity calculated for oxides generally tends to increase as the crystal strain becomes more tensile. It is characteristic of cuprate superconductors that the values of the ionicity are high compared with other 3d transition-metal oxides. Also significant are the extremely high ionicities in the direction normal to the CuO2 planes and the relatively high covalencies of the intraplanar bonds. These crystal-chemical characteristics may be intimately related to the remarkable insulator-to-metal transition and the associated high-Tc superconductivity in the layered copper-oxide systems. 相似文献
2.
Koya Aoi Wolfgang Dieterich Peter Fulde 《Zeitschrift für Physik A Hadrons and Nuclei》1974,267(3):223-228
We investigate the possible occurrance of partially depaired states in superconducting intercalated layered systems. Those states are discussed as a possible explanation of the high critical fields found in some of these materials. It is shown that the Chandrasekhar-Clogston limit does not apply to those states mentioned above and that the maximum field compatible with superconductivity is a sensitive function of the shape of the Fermi surface. Mean free path and spin-orbit effects on the partially depaired state are investigated. An experiment is proposed to decide between the partially depaired state and a large spin-orbit scattering rate as possible explanations for the large critical fields. 相似文献
3.
The newly discovered iron-based high temperature superconductors have demonstrated rich physical properties. Here we give a brief review on the recent studies of the upper critical field and its anisotropy in a few typical series of the iron-based superconductors (FeSCs). In spite of their characters of a layered crystal structure, all the FeSCs possess an extremely large upper critical field and a weak anisotropy of superconductivity, being unique among the layered superconductors. These particular properties indicate potential applications of the FeSCs in the future. Based on the experimental facts of the FeSCs, we will discuss the possible mechanisms of pair breaking in high magnetic fields and its restrictions on the theoretical analysis of the superconducting pairing mechanisms. 相似文献
4.
Michael Kolbe Burkhard Beckhoff Michael Krumrey Gerhard Ulm 《Applied Surface Science》2005,252(1):49-52
X-ray reflectometry is the method of choice to determine the thickness of nanolayered systems with small uncertainties. In view of known limitations of this method for extremely thin or laterally inhomogeneous layers we compared X-ray reflectometry with fundamental parameter based X-ray fluorescence analysis using synchrotron radiation in the radiometry laboratory of the PTB. The results of both methods for a set of sample systems with transition metal layers of various thicknesses deposited on silicon wafers were compared and showed a good agreement within their respective uncertainties. For the investigation of layered systems both methods are very appropriate and, in addition, can give complementary information about the layers. Thus, the density is determined by X-ray reflectometry, and X-ray fluorescence analysis gives information about trace elements within the layers and the layer homogeneity. 相似文献
5.
R. Kotyński 《Opto-Electronics Review》2010,18(4):366-375
Metal-dielectric layered stacks for imaging with sub-wavelength resolution are regarded as linear isoplanatic systems — a
concept popular in Fourier optics and in scalar diffraction theory. In this context, a layered flat lens is a one-dimensional
spatial filter characterised by the point spread function. However, depending on the model of the source, the definition of
the point spread function for multilayers with sub-wavelength resolution may be formulated in several ways. Here, a distinction
is made between a soft source and hard electric or magnetic sources. Each of these definitions leads to a different meaning
of perfect imaging. It is shown that some simple interpretations of the PSF, such as the relation of its width to the resolution
of the imaging system are ambiguous for the multilayers with sub-wavelenth resolution. These differences must be observed
in point spread function engineering of layered systems with sub-wavelength sized PSF. 相似文献
6.
Gruyters M 《Physical review letters》2005,95(7):077204
The magnetic behavior of CoO nanoparticles and layered CoO/ferromagnetic (FM) structures has been investigated by magnetization and hysteresis loop measurements. In the amorphous CoO, a large uncompensation of spins is found that is closely related to spin-glass-like behavior below a freezing temperature T(F) approximately 215-220 K. The spin-glass-like phase may be described by the de Almeida-Thouless line for Ising spin systems. The exchange bias in the layered CoO/FM structures is explained by the spin-glass-like state in the nanoparticles constituting the CoO film. 相似文献
7.
Layered complex networks 总被引:2,自引:0,他引:2
8.
K.S. Challagulla 《哲学杂志》2013,93(14):1197-1222
A micromechanical model based on the asymptotic homogenization technique has been developed to predict the complete elastic, dielectric and piezoelectric properties of a general 2-2 layered piezoelectric composite where the constituent phases are elastically anisotropic and piezoelectrically active. Two classes of layered piezoelectric composites (i.e. longitudinally and transversely layered) are considered in two widely different ceramic- and polymer-based systems and their effective properties are obtained in the limits of both large-volume (i.e. bulk) and small-volume (i.e. thin-film) systems. It is demonstrated that: (i) in the bulk, ceramic–ceramic layered composite system, the elastic, piezoelectric, and dielectric properties of the composites vary linearly with volume fraction of the second phase, while in the bulk ceramic–polymer layered composite system, the corresponding properties vary non-linearly with volume fraction of the second phase; (ii) in the prismatic (thin-film) layered piezoelectric composite system, the non-vanishing, effective elastic, piezoelectric and dielectric properties vary linearly with the volume fraction of the second phase for both the longitudinally and transversely layered composite structures in the ceramic–ceramic and the ceramic–polymer composite systems; (iii) the ceramic–polymer piezoelectric layered composites that incorporate a low density polymeric phase with lower acoustic impedance generally exhibit enhanced piezoelectric coupling constants and lowered acoustic impedance; (iv) the longitudinally layered composites exhibit higher piezoelectric coupling constants and lower acoustic impedance compared to that of the transversely layered composites; and (v) the best combination of properties for applications such as hydrophones (i.e. the highest piezoelectric coupling constants and the lowest acoustic impedance) is obtained in the ceramic–polymer, longitudinally layered, thin-film, piezoelectric composites. 相似文献
9.
Periodic oscillations in transmission decay of anderson localized one-dimensional dielectric systems
Ghulinyan M 《Physical review letters》2007,99(6):063905
It is well recognized that the transmittance of Anderson localized systems decays exponentially on average with sample size, showing large fluctuations brought up by extremely rare occurrences of necklaces of resonantly coupled states, possessing almost unity transmission. We show here that in a one-dimensional (1D) random photonic system with resonant layers these fluctuations appear to be very regular and have a period defined by the localization length xi of the system. We stress that necklace states are the origin of these well-defined oscillations. We predict that in such a random system efficient transmission channels form regularly each time the increasing sample length fits so-called optimal-order necklaces and demonstrate the phenomenon through numerical experiments. Our results provide new insight into the physics of Anderson localization in random systems with resonant units. 相似文献
10.
11.
Alexander Vinokurov Victor Farafonov Vladimir Il’in 《Journal of Quantitative Spectroscopy & Radiative Transfer》2009,110(14-16):1356-1368
A separation of variables method based on expansions of the electromagnetic fields in terms of spherical wave functions is expanded at nonspherical (axisymmetric) particles with a rather large number of layers. Commonly used alternative approaches to systems of linear algebraic equations relative to unknown field expansion coefficients for layered particles are considered in some detail. The SVM code developed is compared with the EBCM, GMT and DDA codes designed for multilayered scatterers and some numerical results obtained for nonspherical scatterers with up to 100 layers are presented as illustrations. 相似文献
12.
J. Banys J. Macutkevic V. Samulionis A. Brilingas Yu. Vysochanskii 《Phase Transitions》2013,86(4):345-358
Investigation results of dielectric and ultrasonic properties of layered CuInP2S6 crystals are presented. At low frequencies, dielectric spectra are highly influenced by the high ionic conductivity with the activation energy of 7357.4?K (0.635?eV). The high-frequency part of the spectra is determined by relaxational soft mode. The critical slowing down and Debye-type dispersion show the order–disorder type of the phase transition. The temperature dependence of the relaxational soft mode and dielectric contribution show a quasi-one-dimensional behaviour. Ultrasonic velocity exhibits critical slowing down which is accompanied by attenuation peaks in the phase transition region. Layered CuInP2S6 crystals have extremely large elastic nonlinearity in the direction perpendicular to layers. The nonlinear elastic parameters substantially increases at the PT temperature. 相似文献
13.
The potential electrostatic energy of a charge near the surface of a metal with a metal or a dielectric coating (adsorbate), on the interface between metal (semimetal) and insulator (electrolyte) and in layered thin-film sandwich-type systems (MIS structures) has been calculated. The influence of the metal and the dielectric epitaxial coatings of the metal surface upon the interaction of charges is investigated. Taking into account the spatial dispersion effects, it is shown that in thin films surrounded by a medium with a large dielectric constant, the Coulomb repulsion between electrons decreases. 相似文献
14.
15.
Based on the effective medium theory, the triangular ground plane cloak can be realized by thin layered systems. Two solutions of parameter setting of the layered cloak are suggested to demonstrate the invisibility performance of a hybrid incoming wave. The hybrid parameters are derived from the equivalent of both anisotropies of permittivity and permeability to the alternating layers. The performance of the designed layered cloak is validated by both TM and TE wave simulations with near-field distributions and average scattering power outflows on an observation semicircle. From the simulation results, the layered cloak with both hybrid parameters and improved hybrid parameters can reflect the incoming TM/TE waves in a specular direction, and the latter behaves with a better overall invisibility performance. 相似文献
16.
S. Fritzsche 《Phase Transitions》2013,86(2-3):169-190
Some less known methods are described for the analysis of trajectories of guest molecules in porous solids. Such trajectories can be calculated by Molecular Dynamics (MD) computer simulations in order to analyze the interrelations between the structure and the particle behaviour including collective phenomena. Some results obtained with these methods for diffusing methane in zeolites of type LTA are presented. An analytical potential model for LTA type zeolites is given that make extremely long runs or simulations of large lattice regions for systems with rigid lattice possible. Such runs are necessary e.g. to examine questions as the influence of extented lattice defects or the fractal behaviour of the partical trajectories. 相似文献
17.
Recently pattern formation in layered structures, showing complicated superimposed patterns, has been modeled by coupling two Turing systems linearly, i.e., passively, such that the characteristic length scales of the independent systems are well separated. Here we propose a model of two non-linearly coupled Turing systems to study pattern formation in layered membrane-like structures, where the coupling plays an active role and changes the kinetics of the uncoupled systems. Extensive numerical simulations show that non-linear coupling generates a number of new regular patterns different from the ones observed earlier with linearly coupled systems. Some of them turn out to be superimposed patterns with different length scales, but many are not. Also, contrary to the linear coupling case, the strength of the non-linear coupling is found to play an important role in the formation and selection of patterns. 相似文献
18.
V. S. Rusakov I. A. Sukhorukov A. M. Zhankadamova K. K. Kadyrzhanov 《Moscow University Physics Bulletin》2012,67(3):263-268
A physical model of thermally induced processes of diffusion and phase formation in layered metal-metalloid systems is offered. The software for the model is created, which allows one to quantitatively describe the kinetics of these processes under arbitrary modes of annealing. The results of theoretical computations are compared with the data of experimental studies of a 57Fe:O+ layered implantation system using the methods of M?ssbauer spectroscopy. The agreement between the numerical and experimental results indicates that the nature of phase transformations in the investigated system is determined by a change in the local concentration of the metalloid during its interstitial diffusion and corresponds to peculiarities of the phase equilibrium diagram of the Fe-O binary system. 相似文献
19.
We report on the dynamics of resonant energy transfer in monodisperse, mixed-size, and energy-gradient (layered) assemblies of CdSe nanocrystal quantum dots. Time-resolved and spectrally resolved photoluminescence directly reveals the energy-dependent transfer rate of excitons from smaller to larger dots via electrostatic coupling. The data show a rapid (0.7-1.9 ns) energy transfer directly across a large tens-of-meV energy gap (i.e., between dots of disparate size), and suggest that interdot energy transfer can approach picosecond time scales in structurally optimized systems. 相似文献
20.
《Physica C: Superconductivity and its Applications》2002,360(1-2):140-158
Physics of layered systems is studied from the crystal structure point of view. The relationships between structural and superconducting properties are discussed, and particular attention is paid to the layered structure. We discuss the possible role of inequivalent layers and charge transfer interlayer redistribution. By taking into account the modified charge transfer approach a workable model that provides a possibility for comparison of the structural, electronic, chemical factors etc., for the occurrence of superconductivity of layered systems is considered. The present paper analyzes the possible applications of the inequivalent layer model to the mercurocuprate family and provides rationalization to the experimentally observed nonmonotonic “bell”-shaped dependence of critical temperature of a number of layers in the elementary cell. 相似文献