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The particle in a symmetrical squared tangent potential well is studied by examining its Shannon information entropy and standard deviations. The position and momentum information entropy densities ρs(x), ρs(p) and probability densities ρ(x), ρ(p) are illustrated with different potential range L and potential depth U . We present analytical position information entropies Sx for the lowest two states. We observe that the sum of position and momentum entropies Sx and Sp expressed by Bialynicki-Birula–Mycielski (BBM) inequality is satisfied. Some eigenstates exhibit entropy squeezing in the position. The entropy squeezing in position will be compensated by an increase in momentum entropy. We also note that the Sx increases with the potential range L, while decreases with the potential depth U . The variation of Sp is contrary to that of Sx. 相似文献
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G.E. Grechnev A.S. Panfilov A.V. Fedorchenko V.A. Desnenko S.L. Gnatchenko V. Tsurkan J. Deisenhofer A. Loidl D.A. Chareev O.S. Volkova A.N. Vasiliev 《Journal of magnetism and magnetic materials》2012
Magnetization studies were carried out for the novel FeSe1−xTex superconductors (0≤x≤1) to investigate a behavior of the intrinsic magnetic susceptibility χ in the normal state. The magnetic susceptibility was found to increase gradually with Te content. The temperature dependencies of the magnetic susceptibility χ and its anisotropy Δχ=χ∥−χ⊥ were measured for FeSe in the temperature range 4.2–300 K, and a growth of susceptibility with temperature was revealed. For FeTe a substantial increase of χ under pressure was found. Ab initio calculations of the band structure and magnetic susceptibility have shown, that FeSe1−xTex systems are close to magnetic instability with dominating enhanced spin paramagnetism. The calculated paramagnetic susceptibility exhibits a strong dependence on the unit cell volume V and especially the height of chalcogen species from the Fe plane. With appropriate values of these parameters the calculations have reproduced the experimental data on χ(T) and χ(P) for FeSe and FeTe, respectively. 相似文献
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We study the Quantum Regge Calculus of Einstein–Cartan theory to describe quantum dynamics of Euclidean space–time discretized as a 4-simplices complex. Tetrad field eμ(x) and spin-connection field ωμ(x) are assigned to each 1-simplex. Applying the torsion-free Cartan structure equation to each 2-simplex, we discuss parallel transports and construct a diffeomorphism and local gauge-invariant Einstein–Cartan action. Invariant holonomies of tetrad and spin-connection fields along large loops are also given. Quantization is defined by a bounded partition function with the measure of SO(4)-group valued ωμ(x) fields and Dirac-matrix valued eμ(x) fields over 4-simplices complex. 相似文献
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L.M. Wang Jyh-Yi Lee H.C. Yang J.C. Chen Hsiang-Lin Liu Kun-Sheng Lu Lance Horng H.E. Horng 《Journal of magnetism and magnetic materials》2006
La0.7Sr0.3MnO3 (LSMO) tunneling magnetoresistance (TMR) junctions have been fabricated on step-edge (0 0 1) SrTiO3 substrates with a high step-edge angle. In the measurement of magnetoresistance (MR) ratio versus external magnetic field H, butterfly-like MR curves are clearly observed. The MR(H ) curves vary with θ, the angle between the applied magnetic field and the current direction in the substrate plane, showing anisotropic MR properties. A much broader MR(H) response is observed for the configuration of H perpendicular to the substrate plane. Additionally, the maxima-MR field Hp almost coincides with the coercive field Hc for θ<60° but obeys a different form from Hc(θ). The high-field junction resistance shows an intrinsic sin2θ angular dependence, while the low-field resistance shows an extrinsic cos(4θ) angular dependence. The distinctive features are mainly due to the induced magnetization anisotropy in the artificial steps of grain boundaries. 相似文献
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Temperature dependencies of magnetic susceptibility and electric resistivity of Co-based metallic glasses (MGs) of the general composition Co(72-x)Mex(Si,B)28(Me=Fe,Cr,Si:B=18:10) have been studied up to 950 K. The studied MGs were found to be ferromagnets at the room temperature and their Curie point TC ranges within 260–560 K depending on the dopant contents. At the temperatures higher than TC, a wide paramagnetic region exists. The regularities of magnetic moment variation upon Cr doping evidence a formation of antiferromagnetic clusters, which determine the anomalous behavior of resistivity. 相似文献
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Motivated by experiments in nanoscopic systems, we study a generalized Anderson, which consist of two spin degenerate doublets hybridized to a singlet by the promotion of an electron to two conduction bands, as a function of the energy separation δ between both doublets. For δ=0 or very large, the model is equivalent to a one-level SU(N) Anderson model, with N=4 and 2 respectively. We study the evolution of the spectral density for both doublets (ρ1σ(ω) and ρ2σ(ω)) and their width in the Kondo limit as δ is varied, using the non-crossing approximation (NCA). As δ increases, the peak at the Fermi energy in the spectral density (Kondo peak) splits and the density of the doublet of higher energy ρ2σ(ω) shifts above the Ferrmi energy. The Kondo temperature TK (determined by the half-width at half maximum of the Kondo peak in density of the doublet of lower energy ρ1σ(ω)) decreases dramatically. The variation of TK with δ is reproduced by a simple variational calculation. 相似文献
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Using Monte Carlo simulations with the Metropolis algorithm, we have studied the influence of crystal-field interaction on the critical behavior of magnetic spin-1 Ising film on a cubic lattice structure. The phase diagrams in the (kBTc/J,R=Js/J) plane are obtained for different values of the crystal-field interaction. We found that the special point Rsp(Rc), at which the critical temperature is independent of the film thickness N, is independent of the crystal-field interaction and that the system may exhibit a tricritical behavior. 相似文献
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Minos A. Neto J. Roberto Viana J. Ricardo de Sousa 《Journal of magnetism and magnetic materials》2012
In this work we study the critical behavior of the quantum spin-1/2 anisotropic Heisenberg antiferromagnet in the presence of a longitudinal field on a body centered cubic (bcc) lattice as a function of temperature, anisotropy parameter (Δ) and magnetic field (H ), where Δ=0 and 1 correspond the isotropic Heisenberg and Ising models, respectively. We use the framework of the differential operator technique in the effective-field theory with finite cluster of N =4 spins (EFT-4). The staggered ms=(mA−mB)/2 and total m=(mA+mB)/2 magnetizations are numerically calculated, where in the limit of ms→0 the critical line TN(H,Δ) is obtained. The phase diagram in the T−H plane is discussed as a function of the parameter Δ for all values of H∈[0,Hc(Δ)], where Hc(Δ) correspond the critical field (TN=0). Special focus is given in the low temperature region, where a reentrant behavior is observed around of H=Hc(Δ)≥Hc(Δ=1)=8J in the Ising limit, results in accordance with Monte Carlo simulation, and also was observed for all values of Δ∈[0,1]. This reentrant behavior increases with increase of the anisotropy parameter Δ. In the limit of low field, our results for the Heisenberg limit are compared with series expansion values. 相似文献
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We consider a free quantum scalar field satisfying modified dispersion relations in curved spacetimes, within the framework of Einstein–Aether theory. Using a power counting analysis, we study the divergences in the adiabatic expansion of 〈?2〉 and 〈Tμν〉, working in the weak field approximation. We show that for dispersion relations containing up to 2s powers of the spatial momentum, the subtraction necessary to renormalize these two quantities on general backgrounds depends on s in a qualitatively different way: while 〈?2〉 becomes convergent for a sufficiently large value of s , the number of divergent terms in the adiabatic expansion of 〈Tμν〉 increases with s. This property was not apparent in previous results for spatially homogeneous backgrounds. 相似文献
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The spin dynamics of the semiclassical Heisenberg model with uniaxial anisotropy, on the layered triangular lattice with antiferromagnetic coupling for both intralayer nearest neighbor interaction and interlayer interaction is studied both in the ordered phase and in the paramagnetic phase, using the Monte Carlo-molecular dynamics technique. The important quantities calculated are the full dynamic structure function S(q,ω), the chiral dynamic structure function Schi(ω), the static order parameter and some thermodynamic quantities. Our results show the existence of propagating modes corresponding to both S(q,ω) and Schi(ω) in the ordered phase, supporting the recent conjectures. Our results for the static properties show the magnetic ordering in each layer to be of coplanar 3-sublattice type deviating from 120° structure. In the presence of magnetic trimerization, however, we find the 3-sublattice structure to be weakened along with the tendency towards non-coplanarity of the spins, supporting the experimental conjecture. Our results for the spin dynamics are in qualitative agreement with those from the inelastic neutron scattering experiments performed recently. 相似文献
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We study the dynamic process of the multiple-vehicle collision when a vehicle stops suddenly in a traffic flow. We apply the optimal-velocity model to the vehicular motion. If a vehicle does not decelerate successfully, it crashes into the vehicle ahead with a residual speed. The collision criterion is presented by vi(t)/Δxi(t)→∞ if Δxi(t)→0 where vi(t) and Δxi(t) are the speed and headway of vehicle i at time t. The number of crumpled vehicles depends on the initial velocity, the sensitivity, and the initial headway. We derive the region map (or phase diagram) for the multiple-vehicle collision. 相似文献
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Sequential ballistic deposition (BD) with next-nearest-neighbor (NNN) interactions in a N -column box is viewed as a time-ordered product of (N×N)-matrices consisting of a single sl2-block which has a random position along the diagonal. We relate the uniform BD growth with the diffusion in the symmetric space HN=SL(N,R)/SO(N). In particular, the distribution of the maximal height of a growing heap is connected with the distribution of the maximal distance for the diffusion process in HN. The coordinates of HN are interpreted as the coordinates of particles of the one-dimensional Toda chain. The group-theoretic structure of the system and links to some random matrix models are also discussed. 相似文献
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W.J. Li B.C. ZhaoR. Ang W.H. SongY.P. Sun Yuheng Zhang 《Journal of magnetism and magnetic materials》2006
A series of the double-doping samples La(2+4x)/3Sr(1−4x)/3Mn1−xCuxO3(0?x?0.2) with the Mn3+/Mn4+ ratio fixed at 2:1 have been prepared. The structural, magnetic, transport properties and magnetoresistance of the series samples have been investigated. It is found that no apparent crystal structure change is introduced by Cu doping up to x=0.20. But the Curie temperature TC and magnetization M are strongly affected by Cu substitution. A remarkable magnetotransport behavior, characterized by double bumps, is observed, and an obvious low-temperature upturn is found in the range of 0.07?x?0.12. As a result, the temperature range of colossal magnetoresistance (CMR) is greatly broadened. Moreover, it is found that the room temperature magnetoresistance (MR) of double-doping samples is obviously larger that the undoped La2/3Sr1/3Mn1−xCuxO3 at 300 K, which can give a guide for the adequate selection of the room temperature CMR materials. 相似文献
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We have performed a theoretical study of the specific heat C(T), as a function of temperature, of magnetic and semiconductor quasiperiodic structures. The quasiperiodic structures considered here are constructed according to the Fibonacci, double-period and Thue–Morse quasiperiodic sequences. On one hand, we assume the magnetic structures composed of ferromagnetic films, each one described by the Heisenberg model. On the other hand, we consider semiconductor structures composed of slabs of AlN and GaN, which are characterized by the dielectric functions εA(ω) and εB(ω), and have thicknesses da and db, respectively. Our results illustrate the effects of disorder on the oscillatory behavior of the specific heat in the low temperature regime. 相似文献
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We determine the simple currents and fixed points of the orbifold theory CFT⊗CFT/Z2, given the simple currents and fixed point of the original CFT . We see in detail how this works for the SUk(2) WZW model, focusing on the field content (i.e. h -spectrum of the primary fields) of the theory. We also look at the fixed point resolution of the simple current extended orbifold theory and determine the SJ matrices associated to each simple current for SU2(2) and for the B1(n) and D1(n) series. 相似文献
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