Vol. 43, No. 2 (1994)
1994-01-20
GENERAL
1994, 43 (2): 169-174.
doi: 10.7498/aps.43.169
Abstract +
In this paper a method of direct derivation for the universal R matrix of quantum group Uq(SU(1，1)) is given. It is simple and efficient for quantum groups of low rank at least. By the application of the R matrix obtained, the explicit expression for Casimir invariant of the above guantum group is given. As an application, the second order Casimir operator is rederived as well.
1994, 43 (2): 175-184.
doi: 10.7498/aps.43.175
Abstract +
By imposing conformally broken constraints on SL(2,R) WZNW model, we obtain a new classical completely integrable system which contains the famous sinh-Gordon system as a special case. The integrability of this extended sink-Gordon system is exhibited by the existence of the Lax pair with spectral parameters. And its funda-mental .Poisson-Lie brackets can be ultralocalized, corresponding classical r-matrix depends on two spetral parameters and satisfies the classical Yang-Baxter equation. After a suitable automorphic transformation of the loop algebra on which the above Lax pair takes value, such an ultralocalized r-matrix can be classified to the so-cal-led trigonometric type of r-matrices depending essentially on one spectral parameter.
1994, 43 (2): 185-190.
doi: 10.7498/aps.43.185
Abstract +
On the basis of the study in Ref [4],we construct the dressing transformations of the fundamental variables and show the dressing symmetry of the constrained system (extended sinh -Gordon equations). Finally, we discuss the ultralocalizable-criterion of an arbitrary 2D integrable model.
1994, 43 (2): 191-197.
doi: 10.7498/aps.43.191
Abstract +
The one-dimensional biquadratic map is studied by means of symbolic dynamics in two parameter plane. The skeleton of superstable orbits and the joints in the kne-ading plane have been constructed. A criterion of the existence of topological chaos has been given according to the topological entropy.
NUCLEAR PHYSICS
1994, 43 (2): 198-204.
doi: 10.7498/aps.43.198
Abstract +
Since the equilibrium composition of strange matter is crucial to the accurate calculation of its neutrino energy loss rates, we determine the composition by using the thermodynamic potentials (per unit volume) of the strange matter, and find that the electron abundance decreases with the strong interaction coupling constant or ba-ryon density. After deriving the formula of neutrino energy loss rates of the strange matter, we study the cooling of a homogeneous strange star with a thin crust in detail, and compare it with that of a neutron star. We conclude that the surface temperature of a young strange star is much less than that of a young neutron star of the same age, so one can distinguish between a strange star and a neutron star.
ATOMIC AND MOLECULAR PHYSICS
1994, 43 (2): 205-210.
doi: 10.7498/aps.43.205
Abstract +
By using the theory of configuration-interaction, we ireade a analysis of the effect of configuration interaction on the autoionization rates and branch ratios of the configurations 2p53s3l(l=0，1，2) for the Nalike Cu ion. It is shown that the autoionization rates in all the three configurations are changed substantially when the configuration-interaction are included in comparing with the calculations in single-configuration approxmation, and the branch ratios increase both in the configuration 2p53s3d and in 2p53s3p but decrease in the configuration 2p53s2.
CLASSICAL AREA OF PHENOMENOLOGY
1994, 43 (2): 211-218.
doi: 10.7498/aps.43.211
Abstract +
The theoretical analysis of two-photon photoacoustic effect is presented. The wave equation of two-photon photoacoustic efffct is derived. And the general expre-ssion of two-photon photoacoustic effect is given.
1994, 43 (2): 219-224.
doi: 10.7498/aps.43.219
Abstract +
The solution for the equations of atomic density matrix is obtained, without resorting to any approximation, in the Ξ-type of three-level system with lower-level coherence. The conditions on pumping are analyzed in the strong-coherence case for lasing without inversion and the saturation term is derived.
1994, 43 (2): 225-232.
doi: 10.7498/aps.43.225
Abstract +
Nonlinear simulation of the entropy-like quantity is given to the equilibrium electrons in a free-electron laser with reversed guide field. Results indicate that the quality of the electron beam may be better than the oae in the case of positive guide field. However, the quality of the beam is spoiled at the antiresonance. The concl-usions from the entropy-like quantity principally coincide with the experiment made by the MIT researchers.
1994, 43 (2): 233-238.
doi: 10.7498/aps.43.233
Abstract +
Dynamic processes of the modelocked laser based on a auxiliary coupled cavity containing a nonlinear frequency-doubling crystal has been systematically studied in this paper. And, the specific formulas of the output pulse width of this modelocked laser in instantaneously dynamic equilibrium are given. Moreover, the results of nu-merical analysis and calculation show that its modelocking output properties are su-perior to that of the laser modelocked by an intracavity frequency-doubling crystal.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
1994, 43 (2): 239-247.
doi: 10.7498/aps.43.239
Abstract +
Coupling between atmospheric gravity waves and plasma interchange instability in the equatorial ionosphere is studied. The interchange instability is saturated at a small amplitude by nonlinear effects if there are not any external geophysical distu-rbances to influence it. It is shown that the gravity waves can initiate the interchange instability under some conditions. The initiated instability grows to an amplitude of 50% even larger and forms plasma bubbles if the amplitude of the seed ,gravity waves is large enough. The present theory shows physical mechanism for producing large scale equatorial spread F and explains a lot of ionospheric observations.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
1994, 43 (2): 248-252.
doi: 10.7498/aps.43.248
Abstract +
The C60 single crystals up to mm-size were grown. X-ray diffraction result shows that C60 single crystal is of fcc structure, with lattice parameter of 1.413 nm. An abrupt change of conductivity (at 251K) related to the phase transition shows that C60 single crystal is of high purity and homogeneity. A drop of activation energy around 274K was observed. This activation energy drop may be an indication of another phase transition.
1994, 43 (2): 253-257.
doi: 10.7498/aps.43.253
Abstract +
We study a tight binding model Hamiltonian of the one-dimensional Bravais lat-tice. This Hamiltonian contains one impurity energy site and two hopping constants between this site and its two nearest neighbours. The formation and properties of the localized states of this model is analysed by virtue of the Green function method.
1994, 43 (2): 258-266.
doi: 10.7498/aps.43.258
Abstract +
Hanis theory of precipitate growth controlled by diffusion is demonstrated by studying the growth of the oxygen precipitates at high temperature with two-step heat treatment. And the nucleation of the oxygen precipitates is disussed according to Ham's theory tantatively.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
1994, 43 (2): 267-273.
doi: 10.7498/aps.43.267
Abstract +
By using a modified self-consistent variation method, we have calculated the subband structures of n-type inversion layer in p-type HgCdTe NIS (metal-insulator-semiconductor) devices, obtained the ground subband energy E0 and its dependence on both the doping concentration in bulk HgCdTe and the surface electron concent-ration in the inversion layer. In the treament, the influence of non-parabolic band structure due to the interaction between the conduction band and the valence band, the Zener tunneling, the resonant states and the screening effect of the surface electric field have been considered. A simple and useful formula for calculating gro-and state energy E0 has been presented. The calculated results show good agreement with experimental data.
1994, 43 (2): 274-281.
doi: 10.7498/aps.43.274
Abstract +
By using STS, combined with STM imaging, the STS spectra d(lnI)/d(lnV) -eV were measured point by point along a line on the surface of a single crystal graphite. The local density of states (LDOS) around the Fermi level EF obtained from the spectra showed basically an agreement with that of theoretical calculation. By plotting the energy positions of the LDOS peaks around EF with respect to the measurement positions, the spatial variations of the energy band of graphite close to EF were shown. With a discussion of the local electronic structure around the ine-quivalent A, B type atoms on the surface, a simple model calculation for the spatial variations of the energy band was conducted and that showed an agreement with the experimental results. By comparison of the results, the site of A type atoms on the graphite surface, which did not appear in the STM image, was determined.
1994, 43 (2): 282-288.
doi: 10.7498/aps.43.282
Abstract +
A new type of AlxGa1-xAs/GaAs beterojunction based on Si δ-doping has been fabricated by MBE method. We measured the magnetoresistances, mobility and Hall resistance of the 2-D electron gas at the junction in a transvers magnetic field from 0.3 to 30K. Using Fourier-transform analysis, the distribution of electrons and their effective masses for each subband are determined. which
are ｍ0*／ｍ0＝０．０７３，ｍ1*／ｍ0＝０．０６８. With the decreasing of temperature，the electrons in each subband increase continuously. We observed abnormal peaks in magnetoresistance wben magnetic field was scanned from 0 to 7T at 0.3K.
1994, 43 (2): 289-296.
doi: 10.7498/aps.43.289
Abstract +
A single frequency admittance spectroscopy technique is introduced for determining the band discontinuity on Si/GexSi1-x/Si single quantum well (SQW). By using this method, the more accurate experimental results can be obtaind from a single frequency admittance spectrum. For an alloy with composition x=0.33，we get the activation energy Ea＝0.20eV. In order to obtain the value of the band offset，it is necessary to determine the position of Fermi level which depends on the dopam concentration inside and outside the well, the band offset of hetero-interface and temperature. By solving Poisson equation, we get the energy band diagram and Fermi level of the test sample. It is shown that the Fermi level lies about 40 meV above the top of valance band in the well. And due iv the carrier transfer at the hetero-interface, the carrier concentration (about ２×１０17ｃｍ－３) in the well is one order large than dopant concentration(1×１０16ｃｍ－３). The energy bands at two sides of the interfaces are bent by about 0.006 eV in the well and O.11eV in the barrier, hence the valance band offset can be calculated as 0.16eV. The accuracy of this technique can also be verified from reconstruction of C-T and G-T curves by cumputer simulation.
1994, 43 (2): 297-302.
doi: 10.7498/aps.43.297
Abstract +
The temperature coefficient of resistivity (TCR) of Pd thin film with different thicknesses and annealled at different tempertures has been investigated. The experi-mental results indicated that the TCR value of thin films is much smaller than that of bulk material and it also depcnds on grain size of the thin films. It was found that the TCR is higher for larger grain size. The result is explained readily by using the two-fluid model.
1994, 43 (2): 303-307.
doi: 10.7498/aps.43.303
Abstract +
The phonon vibration characteristics of the Bi2Sr2-xBaxCuOy (x=0, 0.2，0.4) single crystal samples was studied by using Raman scattering measurement. The exp-erimental results show that in the Raman spectra of the Bi2Sr2-xBaxCuOy system the typical phonon vibrational modes mainly appear in the frequency range of 196, 282-310, 460, 625 and 660cm-1, and the intensities of the 196, 282-310, 625, and 660 cm-1 lines enhance with increasing Ba content x. In previous work, we have studied the influence of Ba-doping on the incommensurate modulation structure of the 2201 phase. On the basis of those results, in this article we analyze the relation of the incommensurate modulation structure and phonon vibration characteristics emphatically, thus point out that the intensifying of the superstructure modulation (i.e. the decr-ease of modulation period) changes the symmetry of the unit cell seriously so that the phonon Raman activity of the unit cell varies obviously.
1994, 43 (2): 308-314.
doi: 10.7498/aps.43.308
Abstract +
Ba-doping effects on the superconducting properties in the Bi2Sr2-xBaxCaCu2Oy single crystals (0≤x≤0.15) and polycrystalline samples (0≤x≤0.3) have been studied. The results show that Ba２＋ enters the superconducting phase with a solubi-lity limit. For 2212 phase single crystals, the length of c-axis and the supercondu-cting transition temperature Tc both increase with increasing Ba content. For slowly cooled sintered samples, Tc is significantly increased by Ba doping, whereas for quenched samples Tc is little affected. Changes in Tc with Ba doping have been explained by changes in the hole concentration.
1994, 43 (2): 315-321.
doi: 10.7498/aps.43.315
Abstract +
In this article, it is revealed that the Ba substitution intensifies the incommens-urate modulation of the Bi-2201 phase, namely the wavelengths of the modulation along b and c directions show obvious decrease. The study of superconductivity of the Ba-doped 2201 shows that the appropriate substitution of Ba for Sr (x≤0.2) can raise the Tc of 2201 phase, but as x exceeds 0.3, Tc decreases sharply, simult-aneously accompanied with the superconductor-insulator. transition In addition, the characteristic feature of electronic structure of the Ba-doped 2201 phase is also stu-died by use of the XPS and UPS spectra. Based on all these experimental resuits, the relation between incommensurate modulation structure, electronic structure and superconductivity for the Bi-2201 phase are discussed comprehensively, indicating that the replacement of Ba２＋ for Sr２＋ intensifies the mismatch between Bi-O layers and perovskite blocks. and the enhancement of this mismatch influences the symme-try of Cu-O2 planes seriously, just for this reason the variation of electronic state of Cu3d takes place (i.e. the degree of the coulomb correlation of the Cu3d electr-ons tends to be intensifled). In the process of Ba-doping, just due to the variation of Cu3d electrons, the 2201 phase undergoes a superconducting-insulating phase tran-sition.
1994, 43 (2): 322-326.
doi: 10.7498/aps.43.322
Abstract +
The magnetocaloric effect of several ferrite specimens, with magnetoplumbite structure, spinel structure, garnet structure and perovskite structure respectirely, have been studied experimentally. The effect of substitution of non-magnetic ions on Cu-rie temperature and magnetic entropy are also reported.
1994, 43 (2): 327-331.
doi: 10.7498/aps.43.327
Abstract +
Several samples of Cu1-xSnx series were obtained by mechanical alloying, including η-Cu6Sn5 alloy which are difficult to prepare by melting method. XRD results show that the solid solution with nanometer size is formed which including definite alloy phase in each ball milling sample. M?ssbauer spectra indicate that the Sn-rich-phase and the Cu-rich phase exist besides the alloy phase. We suggest that in the process of the ball milling, the crystallites of Cu and Sn are nanometerized, at first, and then the interdiffusion of the two kinds of atoms takes place and finally the solid solution is formed including the alloy phase, the α-Sn-rich phase and the fcc-Cu-rich phase.
1994, 43 (2): 332-339.
doi: 10.7498/aps.43.332
Abstract +
The infrared divergence response theory is applied to reorientational relaxation process of Al3+-hole in α-quartz containing Al impurity to study the behaviour of low temperature dielectric relaxation loss properties in this system. Our calculation results showed that the single phononassisted tunneling process makes the main contribution to the dielectric loss for T10 K, the thermally activated relaxation process dominates the dielectric loss; as for 6.5 K < T<10 K, the dielectric loss is the superposition of the two relaxation process. It is pointed out that for the same relaxation unit, different relaxation process may have different infrared divergence response. The ultrasonic relaxation loss properties induced by the same relaxation unit is also discussed.
1994, 43 (2): 340-344.
doi: 10.7498/aps.43.340
Abstract +
In this paper, a technique of proton elastic backscattering (EBS) in the energy range of 1.5-2.5MeV is proposed for the measurement of the total contents of oxy-gen in the films. The accuracy is better than 5% for the film thickness between less than hundreds nm to a few microns.
