Vol. 47, No. 6 (1998)
We introduce a kind of quantum pure statessupergaussan pure states, in which the coordinate probability density distribution is between the gaussian distribution and rectangle distribution. Some properties of quantum mechanics, squeezing, higher-order squeezing and Shannon's entropy in this state are studied. The relation between squeezing and Shannon's entropy is also discussed.
The energy-level shifts of hydrogen spectrum in the curved space-time caused by the strong short laser pulse are studied. It is shown that under the present conditions of high-power laser pulse, the magnitude of the energy-level shifts of highly excited hydrogen atom will be observable.
1998, 47 (6): 897-905. doi: 10.7498/aps.47.897
Singular-spectrum analysis(SSA) is essentially a linear method based on the covariance matrix which reflects the structrue of the linear dependence. Numerical experience, however,led several authors to express some doubts about reliability of SSA in the attractor reconstruction.In this paper,based on higher-order cumulants which are blind to any kind of Gaussian process and can be used for analyzing the nonlinear correlation, a new notion of higher-order singular-spectrum analysis(H-SSA) is proposed.We illustrate our technique with numerical data from Hénon map,Logistic map and Lorenz model,and show that H-SSA is robust to reconstruction delay,embedding dimension and sampling time,and to the effect of the additive noise.
1998, 47 (6): 906-915. doi: 10.7498/aps.47.906
The cellular automaton models for one-dimensional traffic flow problems are considered.Starting with a microscopic relation for the updating rule describing the occupancy on each site of the road,a macroscopic evolution relation for the average speed of cars can be obtained by carrying out statistical averages.Mean field equations are obtained by considering the asymptotic form of the evolution relation.This gives the average car speed in the long time limit as a function of the car density.The evolution relation is a nonlinear mapping between the average speeds at two consecutive time steps.The mean field results can be obtained by studying the attractors of the mapping.The approach is applied to the study of the model recently proposed by Fukui and Ishibashi.Our calculations show that for models in which the maximum speed of each car is M,a decoupling scheme retaining correlations up to M+1 sites can be applied to the calculation of spatial correlations involving more than M+1 sites. Exact results are obtained using our approach for models without random delay.For models with random delay,results are in good agreement with the simulation results.
1998, 47 (6): 916-921. doi: 10.7498/aps.47.916
The emission time extracted from two-particle relative-momentum correlation functions has been studied as a function of the spatial extent of the source for 40Ar+197Au reaction at 25MeV/u.Reduction of ～50% in the mass number of the source has a very small effect on the calculated correlation functions and the extracted emission time.For the cases of short emission time τ(τ≤100fm/c),use of a smaller nuclear density would lead to somewhat smaller assignment for τ;therefore,these τ values extracted in the normal nuclear density can be taken as upper limits of τ values.For the cases of long emission time (τ≥300fm/c),the emission times do not vary with the size of the source and these τ values can be taken as the real values.
ATOMIC AND MOLECULAR PHYSICS
STUDY OF MULTIPHOTON SELECTIVE EXCITATION OF DIATOMIC MOLECULES IN INTENSE LASER FIELDS BY USING THE QUADRATIC ANHARMONIC MODEL
1998, 47 (6): 922-930. doi: 10.7498/aps.47.922
In this letter,we use the quadratic algebraic Hamiltonian that represents a non-rotating Morse oscillator to study the state-selective excitation of a diatomic molecule placed in the intense laser field of an infrared laser.The selective transition probabilities of HF molecule and the averaged absorb energies are calculated.
CLASSICAL AREA OF PHENOMENOLOGY
EFFECT OF FINITE BANDWIDTHS OF LASER FIELDS ON ELECTROMAGNETICALLY INDUCED TWO-PHOTON TRANSPARENCY AND ABSORPTION ENHANCEMENT
1998, 47 (6): 931-937. doi: 10.7498/aps.47.931
The effects of finite bandwidths of laser fields and Doppler broadening on electromagnetically induced two-photon transparency and absorption enhancement in a four-level system have been discussed in this paper.The optimum experimental arrangement of this system for reducing the Doppler effects of the three laser fields has been obtained by the calculation results.
COMPUTER SIMULATION OF THE THERMAL FLOW INSIDE THE HIGH PRESSURE CELL(Ⅱ) CALCULATING RESULTS AND ANALYSIS
1998, 47 (6): 938-944. doi: 10.7498/aps.47.938
The static and non-steady distributions of temperature inside a high static pressure cell were calculated numerically by using the method provided by our previous work for different pressure media and heating elements. The results of numerical calculation for static and non-steady distribution of temperatures are all agree with the approximate analytic results. The thermal conductivity of pyrophyllite obtained from the experimental slope of maximal value of the temperature versus heating power is in agree with the special thermal conductive experimental value.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
1998, 47 (6): 945-951. doi: 10.7498/aps.47.945
We have investigated theoretically and experimentally the impurity-free vacancy induced disordering for GaAs/AlGaAs double quantum well laser structure grown by MBE with capped SiO2 by repid thermal annealing. The position of the photoluminescence peaks, due to the n=1 electron to heavy-hole transition, was measured before and after annealing the samples. As a result, the samples annealed rapidly show blue shift in the position of photoluminescence peaks and the magnitude of shift increases with increasing temperature. We analyzed theoretically the Al-Ga interdiffusion process in GaAs/AlGaAs quantum well structure and the experimental energy shifts were compared with a theoretical model to obtain the diffusion coefficient of aluminum into the quantum well at different temperatures and the activation energy of aluminum diffusion process. The aluminum diffusion coefficient in the sample annealed at 950 ℃ for 30 s is 6.6×10-16 cm2/s. The activation energy found is 5.0 eV.
1998, 47 (6): 952-959. doi: 10.7498/aps.47.952
By using plan-view and cross-sectional transmission electron microscopies and Rutherford backscattering and channeling spectroscopy technologies, the secondary defect in MeV P+-implanted Si and the effect of self-ion irradiation on them have been investigated. The experimental results showed that the depths of secondary defect peaks are a little bit larger than the mean projected ranges measured and those computed by using program TRIM. The results also pointed out that the self-ion irradiation onto the MeV P+-implanted Si with a suitable energy and dose before annealing can reduce the secondary defect formation. But if the self-ion irradiation is applied after the annealing, the effects will be contrary. The physical reason of these has been discussed. Furthermore, the critical dose of the secondary-defect occurring in Si+- and P+-implanted Si have been presented, and the relation of the critical dose with the ion-implantation energy has been also discussed.
1998, 47 (6): 960-964. doi: 10.7498/aps.47.960
We report a method of carbon nanotube and nano-polyhedron growth in graphite surface by 60keV Ar+ ion beam bombardment. High resolution transmission electron microscopy (HRTEM) reveals that the nanostructures range from ～20nm to ～0.4μm in size and the distance between carbon layers in multilayer walls is 0.34nm. Based on HRTEM images, we propose a growth model of “combined carbon polyhedron”.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
INFLUENCE OF Cu DOPING IN Mn SITES OF La-Ca-Mn-O SYSTEM ON MAGNETORESISTANCE EFFECT AT LIQUID NITROGEN
1998, 47 (6): 965-969. doi: 10.7498/aps.47.965
We studied the influence of Cu doping in Mn sites of single phase bulk materials La2/3Ca1/3Mn1-xCuxOy on their magnetoresistance effect at liquid nitrogen in experiment. We find that, for the best doped sample (x≈0.15), it shows great magnetoresistance effect clearly. Moreover, the main variation of the magnetoresistance is under the field below 1T. The MR ratio rises up to ～5×104% when the field is increased to 6T. It increases three orders of magnitude compared with samples deviated from the best doping.
1998, 47 (6): 970-977. doi: 10.7498/aps.47.970
The results of a theoretical study of the electronic structure of the Ⅱ-Ⅵ compound ZnTe are presented. The bulk electronic structure is described by the nearest neighbor tight binding formalism. Using the scattering theory method, we have obtained wavevector-resolved surface densities of states and the surface band structure. There are no surface states in the gap. Surface states and resonances in the valence band and conduction band regions show resemblance with those of relaxed(110) surface of Ⅲ-Ⅴ compounds and the Ⅱ-Ⅵ compounds. The results are in good agreement with other theoretical studies.
Si+ ION IMPLANTATION INFLUENCE ON PHOTOLUMINESCENCE IN Si1-xGex/Si QUANTUM WELLS GROWN BY MOLECULAR BEAM EPITAXY
1998, 47 (6): 978-984. doi: 10.7498/aps.47.978
Ion implantation and annealing have been used to switch the luminescence in Si1-xGex/Si quantum wells from a band-edge exciton process to a broad well below the band edge. The damage introduced by silicon ion implants, which leads to the formation of the platelets correlated with broad band luminescence, is related to the track of an implanted ion and the recoiled atoms in the quantum well structures. The activation energy for defect clusters is about 0.1eV, which is larger compared with the activation energy of ～0.05 eV for interstitial atoms. This indicates that the defect clusters is responsible for the deep broad photoluminescence in early MBE samples.
1998, 47 (6): 985-989. doi: 10.7498/aps.47.985
The structure of a single vortex in a superconductor with s+id symmetry is given employing a recently developed Ginzburg-Landau theory by the method of relaxation iteration.We also studied the variation of respective components s and d with the temperature and magnetic field.Finally,we give the curve of the upper critical field along with transition temperature in mixed wave consideration.Our result is in qualitative agreement with the experiment data.
1998, 47 (6): 990-996. doi: 10.7498/aps.47.990
X-ray diffraction patterns and thermomagnetic curves show that all compounds are almost of single phase.All ErFe11-xCoxTi compounds (x=0—11) crystallize in the ThMn12-type structure.Substitution of Co for Fe leads to an increase of Curie temperature and a monotonic decrease of lattice constants.The composition dependence of saturation moments exhibits a maximum at about x=3. The easy magnetization direction (EMD) at room temperature,for x≤4, is along the c-axis, for 6≤x≤9,is perpedicular to the c-axis, while for further increasing x, it goes back to the c-axis. The interesting change of EMD of ErFe11-xCoxTi compounds may result from the preferential occupation of Co and the different contribution to the magnetocrystalline anisotropy from different transition-metal sites.For all ErFe11-xCoxTi compounds, a spin reorientation occurs below the Curie temperature.A tentative phase diagram for ErFe11-xCoxTi compounds has been given.
MAGNETOOPTIC EFFECTS AND PROPERTIES OF MAGNETOSTATIC WAVE PROPAGATION IN YIG-GGG WAVEGUIDE UNDER INCLINED BIAS MAGNETIC FIELD
1998, 47 (6): 997-1005. doi: 10.7498/aps.47.997
It is shown by calculation that,in contrast to the usual situation of a perpendicular bias magnetic field,an inclined bias magnetic field enhances Faraday effect,and leads to modification to the properties such as the resonant frequency and the bandwidth of magnetostatic wave in magnetic waveguide.Making appropriate use of such properties,it is possible to greatly increase the magnetooptic (MO) Bragg diffraction efficiency and to improve the characteristics of guided-wave MO Bragg devices.
1998, 47 (6): 1006-1011. doi: 10.7498/aps.47.1006
The In-substituted system,(La2/3Ca1/3)(Mn(3-2x)/3In2x/3)O3(x=0.00，0.10，0.15),was synthesized by solid-state reaction method.Its temperature dependence of electrical resistance and magnetoresistance (H=0,1.6T) and field dependence of magnetoresistance were measured by the four-probe method.It was found that when x increases,both the peak of the electrical resistivity and the peak of magnetoresistance move to lower temperatures.However,the cusp is broadened by In-substitution.The authors suggested that the variation of the proportion of In3+ ions leads to the change of manganese valence and the magnetic moments,as well as magnetic structure of the (La2/3Ca1/3)(Mn(3-2x)/3In2x/3)O3 system.Such phenomena weaken the ferromagnetic double exchange effect.
1998, 47 (6): 1012-1017. doi: 10.7498/aps.47.1012
The influence of the particle size and the magnetic deposite on the giant magnetoresistance (GMR) was investigated.Based on the free electron model and spin-dependent scattering theory,the self-energy of the conduction electrons in the granular film system was calculated.In the computing course,we connected the spin-scattering terms with the macroquantity,and abtained the formalism of GMR vs.concentration and GMR vs.size.The simulation curves show that increasing the magnetic concentation and decreasing the particle size can enhance the GMR.
STUDY ON CYCLOTRON RESONANCE SPECTRA OF TWO-DIMENSIONAL ELECTRON GASES IN PSEUDOMORPHIC InxGa1-xAs/In0.52Al0.48As HETEROJUNCTIONS
1998, 47 (6): 1018-1025. doi: 10.7498/aps.47.1018
The electron effective masses, scattering time and mobilities near the Fermi level for the lowest two subbands of the two-dimensional electron gases in a pseudomorphic In0.80Ga0.20As/In0.53Ga0.47As/In0.52Al0.48AsHEMT structure are determined by fitting the cyclotron resonance spectra. The significant enhancement of the electron effective masses, resulting from the conduction band nonparabolicity and the wave function penetration, is observed. The evident subband dependencies of the electron scattering time and mobilities dominated by the alloy scattering and ionized impurities scattering are also discussed.
1998, 47 (6): 1026-1032. doi: 10.7498/aps.47.1026
Raman spectra of the metamict and annealing recrystallization fergusonite and brocenite, found in Baiyunobo mineral deposit in China, have been measured and discussed. The spectra give three well defined characteristic band regions. The bands in the regions 840 to 600cm-1 and 340 to 280cm-1 are assigned to NbO3-4 tetrahedron stretching and bending vibrations, respectively. While the frequencies observed below 200cm-1 are due to the external modes of the NbO3-4 and lanthanide ions. The dependence of Raman frequencies on the structure and composition of the metamict and annealing recrystallization fergusonite group minerals shows that the Raman spectra are valuable for reflecting the structure distortion of the minerals. Additionally, the strong visible photoluminescence from annealing recrystallization is observed when 514.5 or 488.0nm laser line is used as excitation source, whereas metamic fergusonite group minerals exhibit no visible photoluminescence, or weak one.
1998, 47 (6): 1033-1040. doi: 10.7498/aps.47.1033
The nanocrystalline silicon embedded in silicon dioxide has been successfully prepared by post heat treatment for SiOx∶H.We have found that each strong photoluminescence spectrum from a-SiOx∶H consists of two Gaussian components.One is a main broad peak which redshifts with the increase of annealing temperature and the other is a shoulder remaining at about 835 nm.In conjunction with infrared and micro-Raman spectra,the possible origins of the two bands are discussed.The peaks around 850 nm after annealing at 1170℃ are associated with the precipitation of nanocrystalline silicon,and this supports the quantum confinement effect.
Presence of a K adlayer will promote nitridation of GaAs(100) surfaces at room temperature, as is evidenced by photoemission measurements. Following exposure of K/GaAs to pure nitrogen, there appear remarkable variations in both valence band and core level spectra, i.e., recovery of work function to a certain extent, emergence of the N2p peak in the valence band spectra and creation of chemically shifted Ga2p and As2p components in the core level spectra. For the three different K coverages we studied (1/4, 1/2 and 1ML), the 1ML one shows the strongest promotion effect.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
1998, 47 (6): 1047-1051. doi: 10.7498/aps.47.1047
Cubic C3N4 was synthesized on glass and silicon wafers by using low-pressure plasma enhanced chemical vapor deposition and silicon nitride interlayer technology.The crystalline structure was investigated by transmission electron microscopy (TEM),and this material has body centered cubic symmetrical structure.The lattice parameter a=0.536 nm determined by TEM is comparable to theoretical data 0.53973nm.The C1s and N1s binding energies are 285.01 and 398.60eV respectively,and the nitrogen content of the film is up to 42.96%,determined by X-ray photoelectron spectroscopy (XPS).The thin films on glass are transparent to light in the visible and near infrared region,and at 400 nm there appears strong light absorption.
A NEW WAY OF MAKING BUCKY ONION BY THERMAL DECOMPOSITION OF SiC NANOMETER POWDERS UNDER HIGH-TEMPERATURE AND VACUUM
1998, 47 (6): 1052-1056. doi: 10.7498/aps.47.1052
Bucky onions have been produced by decomposing SiC nanometer powders under high- temperature and vacuum. Transmission electron microscope and high resolution electron microscope observations show that when SiC particles decompose completely, they transform into quasi-spherical hollow carbon particles and onion-like particles composed of concentric graphitic shells. When SiC particles decompose incompletely, they become compound particles, which are composed of β-SiC in particles and of quasi-concentric graphitic shells on surface of particles. The results suggest that the traditional idea that planar graphite is the most stable form of pure carbon would then have to be seriously discussed.