Vol. 46, No. 4 (1997)
1997, 46 (4): 625-639. doi: 10.7498/aps.46.625
Based on the analysis of properties of protonic excitation and displacements in the hydrogen bonded molecular systems we proposed here a new model Hamiltonian and theory for studying the properties of nonlinear collective excitation and proton transfer resulting from the localized fluctuation of protons and the deformation of structure of heavy ionic sublattice owing to the protonic displacements.We give the equations of motion and corresponding solutions of solitons,discuss the features and meanings of these solutions and the advantages of our model,and explain completely motion of two kinds of defects and proton transfer in the hydrogen bonded molecular systems.
1997, 46 (4): 640-644. doi: 10.7498/aps.46.640
A group of gravitational solitons produced by plane-symmetric scalar fields is found.The singularity and energy problems of these solitons are discussed.
The most probable approach is used to treat the problem of the DLA model.The most probable distribution of the particles,the fractal dimension and the screening exponent of the DLA cluster are obtained.The results agree with the computer simulation results.
CALIBRASION OF THE ENERGY RESPONSE FOR THE SOFT X-RAY DETECTIONS ELEMENTS WITH THE BEIJING- SYNCHROTRON RADIATION FACILITY
1997, 46 (4): 650-655. doi: 10.7498/aps.46.650
Calibration of the energy response for the soft X-ray detection elements using in the ICF diagnostic are reported.The Beijing synchrotron Radiation Facility (3B1 beam line,photon energy～250—1000eV,radiation flux ～1012photon/s·mm2·mr2·0.1% band-width,beam current ～20—80mA) and target chamber of the reflectometer are used.The source intensity is monitored by AXUV-100 photodiode.The calibration of the energy response for the XRD,filter light film,Ⅱa type diamond photoconductive detector,transmission grating and soft X-ray film are given and analysed.
CLASSICAL AREA OF PHENOMENOLOGY
1997, 46 (4): 656-660. doi: 10.7498/aps.46.656
One of the main difficulties of quantum computation is that decoherence destroys the information in a quantum computer memory cell.On the basis of Rzazewski′s work,we have studied the effect of spontaneous emission on the memory cell when each memory cell is taken to be two-level atom.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
THE STATIC MAGNETIC MODE AND THE OSCILLATING ELECTRIC FIELD IN THE INTERACTION OF ELECTRO MAGNETIC FIELD WITH IONIZATION FRONT
1997, 46 (4): 661-665. doi: 10.7498/aps.46.661
Using the electromagnetic dispersion relation in the cold plasma, we research the static magnetic mode that arises in the process of interaction of electromagnetic wave with moving- ionization front driven by an intense laser and find that an oscillating electric field is excited- under a special condition. We also define the condition under which the oscillating electric field appears.
THE REFLECTION AND TRANSMISSION OF ELECTRO MAGNETIC WAVE WITH s POLARIZATION ON A MOVING FRONT OF AN UNDERDENSE PLASMA
1997, 46 (4): 666-671. doi: 10.7498/aps.46.666
The reflection and transmission on a moving plasma's front driven by an intense laser is investigated for an electromagnetic wave with s polarization. Using the boundary conditions of electromagnetic wave, we derive the formulae of the coefficients of the reflection and transmission and discuss them for some special cases.
1997, 46 (4): 672-678. doi: 10.7498/aps.46.672
The H-mode has been achieved on HT-6M Tokamak by edge ohmic heating (EOH) method. The H-mode is studied by the neutral particle measurement method. The escape particle flux decreases- during H-mode. The central neutral atoms density drop, and the central particle confinement time-- τp is increased about one times after applying the EOH.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
1997, 46 (4): 679-687. doi: 10.7498/aps.46.679
By gradually varying the bias voltage between the gold tip and the gold sample, it is observed with the scanning tunneling microscope that large bias voltages may induce atoms to diffuse on the gold tip and ofter result in an increasing of the tip length. We also observed the field emission and resonant tunneling phenomena. A mechanism based on the polarization of the tip is proposed for the field-induced atomic diffusion. Such field induced diffusion is believed to be responsible for surface modification with large bias voltage pulses.
1997, 46 (4): 688-693. doi: 10.7498/aps.46.688
Recent studies show that the so called “jump to contact” phenomenon, which often happens between a sharp tip and a flat surface in close proximity and results in formation of a neck between the two, is probably the origin of friction. By studying the phenomenon with a scanning- tunneling microscope (STM) and monitoring the conductance evolution, we have found that such necks- between the STM tip and the Pb(110) sample surface, after being stretched to a certain degree, may- shrink spontaneously till its break. The fact that surface cleanness and temperature have- significant influence on the shrinking process suggests that the process is a result of surface- diffusion of Pb atoms.
The effect of atomic disorder fluctuation on the distributions of bond lengths and electron densities for optically-excited C60 and C60 doped with alkali-metal are studied and we adopt the methods that the fluctuation is modeled by Gaussian-random parameters, and that the sample averaging is performed over a large number of independent atomic disorder configurations.The distributions of bond lengths and electron densities are shown to be the functions of the strength for the atomic dis order fluctuation,as well as the number and variety of extra charges.It is discovered:1 When the difference between the long and short bonds is 0.0044nm,the dimerization in C60 still remains when the atomic disorder fluctuation is 0—0.01nm.2 When the strength of the atomic disorder fluctuation is 0—0.00775nm,there exist polarons in C±60 and C--60; when the strength of the atomic disorder fluctuation is 0—0.00548nm,there also exist polarons in C－60,C3－60 and C±±60.
1997, 46 (4): 702-714. doi: 10.7498/aps.46.702
Simulation of crystal field levels and the barycenters are conducted, based on the fluorescence spectra of GdOBr∶Eu under ambient and high pressures. Calculated results are concide with experimental results very well. Variations of Slater and spin-orbit parameters with pressure are obtained. With pressure increasing, B40,B60 increase, B64 decreases, and B20 and B44 show some what fluctuating variations. Strength of the crystal field decreases with increasing pressure from 0GPa to about 8GPa, then increases slightly until 12GPa. Variation of spin-orbit parameter is similar to that of crystal field strength. Slater parameters Ei(i=1—3) show different variations for different i under pressures. E1∶E2∶E3 is little short of the value of hydrogenic ratio, but varies slightly with increasing pressure. To reveal physical significance in the variations of these parameters, comparison with variations with different hosts are made.
1997, 46 (4): 715-723. doi: 10.7498/aps.46.715
The strong coupling polaron in a slab of polar crystal in magnetic field is investigated by means of the extended the strong coupling variational theory of polaron. The energy and the effective mass of polaron are derived as functions of slab thickness and magnetic field. The numerical results of Cu2O slab show that the influence of magnetic field reduces the energy of polaron and enhances the energy shift of electron, and that the surface optical modes are important to polaronic effect in a thin slab and in the presence of magnetic field.
AN IMPROVEMENT IN SELF-CONSISTENT CLUSTER METHOD FOR DETERMINING THE CRITICAL POINT IN ISING SPIN SYSTEM
1997, 46 (4): 724-731. doi: 10.7498/aps.46.724
We show the equivalence between the self-consistent cluster method (SCM) and the modified cluster field method (MCFM). Based on the SCM and MCFM, we propose a new method to- calculate critical points of Ising spin system, the method is demonstrated on the two-dimension square lattice.
ENHANCEMENT OF THE REFLECTIVITY OF Co/C SOFT X-RAY MULTILAYERS AT GRAZING INCIDENCE BY THERMAL TREATMENT
1997, 46 (4): 732-739. doi: 10.7498/aps.46.732
We report a significant increase of the reflectivity of a soft X-ray Co/C multilayer at grazing incidence after low temperature annealing. By monitoring the enhancement of the first order modulation peak on annealing, the effective interdiffusion coefficient as low as -10－25ｍ2ｓ－1 has been measured,which is nearly equal to the true macroscopic interdiffusion coefficient as the modulation wavelength of the Co/C multilayer studied is well above the critical wavelength. The negative true macroscopic interdiffusion coefficient indicates that there is a tendency to phase separation in the Co-C system, which can be interpreted as the positive enthalpy of mixing calculated based on Miedema′s macroscopic atom model. The decrease of reflectivity above some anneal temperature is also discussed and explained as the competition between interfacial sharpness and roughness.
1997, 46 (4): 740-746. doi: 10.7498/aps.46.740
A theoretical and experimental study of intersubband absorption in p-type GexSi1-x/Si multiple quantum wells are presented,the calculations are performed with envelop-function approach,with full inclusion of the degeneracy and warping of the three topmost bulk valence bands described by the strain-dependent Luttinger-Kohn Hamiltonian.The Hartree potential and the exchange correlation interaction are taken into account in a self-consistent manner.And finally the absorption spectra is calculated.We contribute some absoptions observed with normal incident unpolarized infra-beam to the band-mixing of heavy,light and split-off bands in GexSi1-x/Si quantum wells.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
1997, 46 (4): 747-755. doi: 10.7498/aps.46.747
The stabilities of one-dimensional conducting polymer chains with finte lengths have been studied in the frame work of the SSH tight-binding model.Three kinds of boundary conditions have been proposed to stabilize the dimerized structure of the chains.It was found that the natural boundary condition or the end-fixed boundary condition is applicable for getting a result to fit the observed photo-absorption of polyacetylene with short (N<20) lengths.
1997, 46 (4): 756-761. doi: 10.7498/aps.46.756
In order to investigate the nature of the charge carriers in NdCeCuO system, we prepared Nd1.85-xCe0.15CaxCuO4-δ and Nd2-xCaxCuO4-δ , and studied transport properties of them. With increasing Ca concentration, the sign of Hall coefficient is changed from negative to positive. The hole state in CuO2 plane arises from the lattice distortion induced by Ca doping, which leads to the- O2p band pass through the Fermi level.
NONLINEAR THEORETICAL ANALYSIS OF THE TRANSPORT PROPERTIES OF 2-D BLOCH ELECTRON UNDER ELECTRIC AND MAGNETIC FIELD
1997, 46 (4): 762-766. doi: 10.7498/aps.46.762
Magnetic-field-induced electronic Bloch-energy-band splitting is unimportant at not very low temperature. In such cases, we analyse the Hall drifted velocities with the quasiclassical dynamic equations. The numerical solutions demonstrate a striking sudden change of each Hall drifted velocity.
1997, 46 (4): 767-774. doi: 10.7498/aps.46.767
By using the Linear Muffin-Tin Orbital (LMTO) method and synchrotron radiation photoemission,the electronic structure and surface stability of ZnSe(100) nonreconstruction surface,c(2×2) undimerized and c(2×2) dimerized reconstruction surfaces have been theoretically and- experimentally investigated.We find that ZnSe(100)c(2×2) undimerized surfaces is more stable than ZnSe(100) nonreconstruction surface and c(2×2) dimerized reconstruction surfaces, supporting the experimental results proposed by Farrell.Through discussing surface states,we have found the- difference between ZnSe(100) reconstruction surface and c(2×2) undimerized surface. The theoretical result is in good agreement with the synchrotron radiation photoemission measurements.
THE EFFECTS OF INTERVALLEY INTERACTIONS ON THE ELECTRONIC STRUCTURES IN QUANTUM WELLS Ge0.3Si0.7/Si/Ge0.3Si0.7 GROWN ON Ge0.3Si0.7(001)
1997, 46 (4): 775-782. doi: 10.7498/aps.46.775
Using the generalized k·p method based on empirical pseudopotential theory associated with boundary conditions of current density operator,the electronic bound levels are calculated for quantum wells Ge0.3Si0.7/Si/Ge0.3Si0.7 grown on Ge0.3Si0.7(001).The energy level splitting by intervalley interactions is studied in detail and the dispersions of electronic bound levels in the well plane are also discussed.
Oxygen in YBaCuO superconductor was partly substituted by Cl- in the forms of CuCl2 and BaCl2．There sults show superconductive phase can be obtained no matter CuCl2 or BaCl2 was used. Cl- coming from CuCl2 ccupies O2 site of 123 phase, while Cl- coming from BaCl2 enters O4 site. The former effects superconductivity dramaticaly and the electrical conductivity of normal state changes from metallic behaviour to semiconductive behaviour. The latter reduces Tc，but Tc keeps larger than 77K and the electrical conductivity of normal state still remains metallic behaviour. All these suggest that the oxygen on the CuO plane (O2) plays an important role in the high Tc superconductivity.
1997, 46 (4): 791-795. doi: 10.7498/aps.46.791
As impurities always plague real experiments,we report here a study on the effect of impurity on the dynamic scaling behavior of hysteresis.The model used is the two -dimensional Ising model with quenched random non-magnetic impurities.The results show that for any temperature below the critical point,there exists a corresponding critical concentration of impurities that serves as the critical point in the pure model for distinguishing the scaling behavior of hysteresis.The hysteresis loop area A,representing the dissipation per cycle,scales with the scanning rate of the external field R as A=A0+aRn, with a nearly constant n～1/3, weakly dependent on the concentration,and a finite area A0 even for vanishing small rates below the critical concentration.While above it, A0=0 and n increases significantly with the concentration. This behavior is similar to the pure system.Thus in the concentration -temperature phase diagram there is a regime within which the scaling relation and its exponent of the pure system are robust with impurities.
1997, 46 (4): 796-801. doi: 10.7498/aps.46.796
The Lax pair for the XYZ model under the open boundary condition is explicitly constructed and the general boundary K matrices are obtained.
DESCRIPTION OF RAMAN MAGNETIC RESONANCE SPECTROSCOPY IN WEAKLY COUPLED TWO-SPIN SYSTEM BY PRODUCT OPERATOR FORMALISM
1997, 46 (4): 802-812. doi: 10.7498/aps.46.802
Raman magnetic resonance (RMR) spectroscopy in weakly coupled two-spin system (C-H spin system in CHCl3 molecule) has been investigated in detail by product operator formalism and RMR experiment, where the irradiated nucleus is proton and the detected nucleus is carbon. The theoretical results predicted by product operator formalism are in good agreement with the RMR experiment in various radio-frequency offsets and irradiation strengths applied to proton, indicating that product-operator formalism has advantages over the perturbation approximation-method and eliminates limitation of the approximation method that can be only used to describe the RMR experiment under the case of weak radio frequency irradiation. The studies also show that product operator formalism is a powerful tool for examining the RMR experiments in complex spin systems. It is found that the multiple quantum transitions are much easier to be observable with small radio frequency offsets and higher signal-to-noise ratio is obtained with the moderate irradiation strengths in RMR experiment.
1997, 46 (4): 813-818. doi: 10.7498/aps.46.813
We have measured,for the first time,the low frequency (unclamped)electro-optic and piezoelectric coefficients in Ce:BaTiO3 crystals using interferometric techniques.When the piezoelectric contribution to the phase change by a beam passing through the crystals is ruled out,the unclamped electro-optic coefficients of the poled Ce:BaTiO3 single crystals are r42=1945±220pm/V and r13=11.8±1pm/V.Consequently,accurate values of the Pockels coefficients are provided for researching the photorefractive effect and theoretical study of the Ce:BaTiO3 crystal.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
SOLUTE DISTRIBUTION CHARACTERISTICS OF Pd40Ni40P20 ALLOY SOLIDIFIED IN MICROGRAVITY AND GRAVITY CONDITIONS
1997, 46 (4): 819-825. doi: 10.7498/aps.46.819
This paper studies the difference of solute distribution in microstructure of Pd40Ni40P20 alloy solidified on board a Chinese Retrievable Satellite and on the ground.Compared with those in normal gravity condition(1g),it was found that P content was lower but Pd content was higher in the primary phase,however in the eutectic region P content increased but Pd content decreased in microgravity condition(μg).By evaluating the mass transport coefficients in both cases it can be concluded that the difference in solute distribution both in 1g and μｇ conditions was due to the existence of buoyancy convection in the ground-based experiments.
1997, 46 (4): 826-832. doi: 10.7498/aps.46.826
A novel passivation film on GaAs surface has been grown by microwave sulfur glow discharge technique.Auger electron spectroscopy and Rutherford back scattering measurements show that the film is mainly composed of sulfur and gallium,and atomic ratio of gallium to sulfur is about 1∶1.From X-ray diffraction spectroscopy measurememt,GaS is identified to be hexagonal polycrystalline material.The refraction index and dielectric constant of GaS have also been determined.