Vol. 35, No. 4 (1986)
1986, 35 (4): 419-432. doi: 10.7498/aps.35.419
The pseudo-symmetry often occurs in the crystal structures. The types of pseudo-symmetry may be classified into three categories, i.e. enantiomorphous, translational and those based on other symmetry elements. The present paper discussed some possible translational types in detail, and derived the elements of the pseudo-symmetry for the low symmetry crystal systems (74 space groups). A number of examples show that the pseudo-symmetry is universally exist. Finally, the compatibility between the pseu-do and inberent symmetry groups is also discussed.
1986, 35 (4): 433-442. doi: 10.7498/aps.35.433
In this paper we analyze the topological obstruction in gauge group cohomology. By means of ?ech-de Rham double complex, we have used the region subdivision method to go over each order obstructions of operation d-1, and each order cocycle is connected with the index Z, so the global topological meaning of cocycle for gauge group has been-clarified.
THE TWO WINDOW FOURIER TRANSFORM TECHNIQUE AND ITS APPLICATION IN THE SPECTRUM ANALYSIS OF QUANTUM OSCILLATIONS
1986, 35 (4): 443-450. doi: 10.7498/aps.35.443
The conventional Fourier transform methods were found to give an inadequately accurae and complete spectrum of the quantum oscillation frequencies for some materials with complicated Fermi surface such as IV-VI compounds in the distorted phase. Because of this problem, the early de Haas-van Alphen data of SnTe could not be interpreted properly. The ‘two window Fourier transform'technique was developed, and it solved this problem successfully in the Fermi surface measurements of Pb1-xSnxTe and SnTe. In this technique, the spectrum analysis are performed twice for each set of data by using two different windows, refered as ‘strong window' and ‘weak window' respectively, so as to increase the signal to noice ratio and to detect components with weaker strength and to resolve neighbouring components of similar strength. Hence higher detectability and resolvability and better accuracy can be achieved. The analysis results of the pseudo-SdH simulation signal, consisting of 10 components with different amplitude, show that the error in frequency of the spectrum is less than 1%.
1986, 35 (4): 451-458. doi: 10.7498/aps.35.451
The refractive index including linear and nonlinear terms, the zero dispersion wavelength and their relation to the temperature have been calculated by using semi-classical method. The theoretical results are consistent with experiment results.
TEMPORAL AND SPECTRAL FEATURE OF THE 3(ω0)/2 SPATIALLY FINE STRUCTURES IN LASER IRRADIATED PLANAR TARGETS
1986, 35 (4): 459-466. doi: 10.7498/aps.35.459
Both temporally and Spectrally resolved fine structures of 90° lateral 3/2ω0 harmo-nic emission were experimentally observed. The existence of 3/2ω0 harmonic filaments isattributed to the 3/2ω0 harmonic radiation emitted from neighborhood of the bottom ofmoving filament, about nc/4 away from it. The double hump structure with intensered hump of laterally emitted 3/2ω0 spectrum can also be explained by Doppler correc-tion besides the thermal correction due to fast moving TPD process occuring in the unstable filaments. Estimation of both red and blue shifts using our simple model is wellconsistent with experimental results. Experiments showed that the 3/2ω0 emission wasobviously suppressed by using broad band laser owing to more uniform illumination on the target surface and broad band effect. These may be promissing for superhot electron suppression.
STUDIES OF FOURIER-TRANSFORM ANALYSIS METHOD FOR ENERGY-DEPENDENT PHOTOELECTRON DIFFRACTION (II)——THE SYSTEMS OF Se-Ni (111) AND S-Ni(111)
1986, 35 (4): 467-474. doi: 10.7498/aps.35.467
Direct Fourier-transform analysis method for energy-dependent photoelectron-dif-fraction curves of P(2×2) and (31/2×31/2) Se or S on Ni(lll) system has been studied. From calculations for different adsorption sites and different beams, their influence on Fourier peak positions and related layer spacing modification values △n has been analysed and their relation to atom spacing discussed in some detail.
1986, 35 (4): 475-481. doi: 10.7498/aps.35.475
The magnetic structure and anomalous behavior of the temperature dependence of magnetization at low temperatures for amorphous NdxT1-x(T=Fe, Co, Ni) thin films are discussed. It has been observed that the sudden drop of magnetization is at about 20 K, and the temperature corresponding to the sudden drop on the magnetization curves does not change with composition, we suggested that as the neodymium component exceeded a certain amount, in the ground state the asperomagnetic and the speromagnetie structures may coexist for these amorphous alloys. The sudden drop of magnetization at about 20K may be explained by the phase transition between the speromagne-tism and paramagnetism. The critical composition of neodymium component for eoexi-stance of these magnetic structures approximately corresponds to x≥0.45, 0.20 and 0.08 for Nd-Fe, Nd-Co and Nd-Ni amorphous thin films, respectively.
COMPUTER SIMULATION OF THE STRUCTURE OF AMORPHOUS ALLOY Ni64B36 (I)——THE CHEMICAL SHORT RANGE ORDER IN THE ALLOY
1986, 35 (4): 482-488. doi: 10.7498/aps.35.482
The structure of the metallic glass Ni64B36 is simulated by a computer model which consists of two different size spheres. We calculate the partial radial distribution functions, the angular distribution functions and the homogeneity of the model, and discuss the chemical short-range order of the structure. All the results show that in the transiion metal-metalloid glasses, the relative distribution of the metalloid atoms is an important characteristic of the chemical short-range order, this can be characterized by the site rc of the first split peak of the metalloid-metalloid distribution function.
1986, 35 (4): 489-496. doi: 10.7498/aps.35.489
The M?ssbauer spectra, the magnetic properties, neutron diffraction and X-ray pho-toelectron spectra of pure and Co coated α-Fe2O3 have been measured. It is found that the Morin transition temperature of α-Fe2O3 is influenced and the eoercivity is increased obviously by Co coating. We suggest that a fine structure (single ion) anisotropy energy constant Kfs would be decreased by Co coating, this could explain the experimental results.
1986, 35 (4): 497-504. doi: 10.7498/aps.35.497
The structure and ionic conduction of glasses in system LiF-LiCI-B2O3, especially the role of F- ion in network of glasses and the influence of F-, Cl-, Li+ ions on conductivity have been studied by B-NMR and infrared spectra. For glasses in system LiF-LiCl-B2O3, the boron changes from triangular [BO3] to tetrahedron [BO3F] configuration with increasing LiF content, and F- ion participates in network formation. Therefore the network of glasees expands layer into space, and the glasses form three-dimensional network structure containing [BO3F] unit. The Cl- ion exists in network in a state separated from network and plays the role of loosening network, so that it is effective for conductivity. The Li+ ion is the conductive phase, it gives the major contribution to conductivity. The ionic conductivity of glasses in this system increases with increasing LiF and LiCl content, and is 6.12×10-4Ω-1·cm-1 at 300℃.
1986, 35 (4): 505-511. doi: 10.7498/aps.35.505
In this work, the phase relations of LaNi5-xSix(x≤1.25) have been studied by means of X-ray powder diffraction method and DTA method, and the hydrogen absorption properties of the samples have been measured using gas-gathering method. The α-phase (LaNi5) and the new discovered ternary compound LaNi4Si (β) forms a eutectic system. The eutectic reactionis α+β(?)1170℃/ L. The eutectic point is at x=0.96. In the single phase area of a-phase, the lattice parameter a de-creases and c increases with the substitution of Si, The ternary compound LaNi4Si belongs to orthorhqmbic system with lattice parameters a = 8.382?, b = 5.210?, c = 3.989?. The measured density is 7.59 g/cm3. There are two formula unit per unit cell. Possible space groups are D2h5,C2v2,C2v4. The hydrogen quantities absorbed by the La1-ySiyNi5 samples decrease rapidly with Si content increasing. The absorbed hydrogen quantities of La-Ni5-xSix samples vary slowly with the Si content and the plateau pressures decrease. The formation free energy of LaNi4.8Si0.2H6.5 is 475 cal/mol H2. Si substitution increased the stability of hydrides. The new compound LaNi4Si has reversible hydrogen absorption and desorption properties with formation of hydride LaNi4SiH3.6.
The electronic structure of ScH2 and HfH2 have been calculated by using the self-consistent LMTO-ASA method, without placing an extra muffin-tin sphere at the octahedral site in the fcc lattice to make a correction for muffin-tin potential. In the case of ScH2, the result is in good agreement with that of Peterman and Harmon and the photoemission data, the only discrepancy is the position of T2, which is located below the Fermi level rather than above it, therefore, the occupancy of proton in the octahedral site is quite possible. The general feature of the calculated density of states of HfH2 is in reasonable agreement qualitatively with the photoemission data. The electronic charge within the hydrogen sphere is about 1.2-1.3.
In this paper, we describe the results of the equilibrium ESE and the LESE measurements in B- or P-doped a-Si1-xCx:H films at 77 K. To our knowledge, this is the first observation of the ESE of holes in the valence band tail for the films. The present LESE result shows that B-doping does not reduce the total density of dangling bonds including D+ and D-, although it improves the photoconductivity in a-Si1-xCx :H.
In this paper, the fundamental theory of FTER-Q switch resonator is developed. The resonator is composed of many optical elements, it cannot be solved by the conventional method. Combining matrix optics with integral equations of diffractions of optical resonator, we obtain a theoretical solution, which gives out a lot of quantities, such as Fre-snel number, diffration losses, resonace frequency and its interval, etc., that can be compared with the result of parallel plane resonator.
1986, 35 (4): 529-534. doi: 10.7498/aps.35.529
This paper describes a new method for performing Mellin transform. The principle of design of hologrophic lens and the method for making binary computer-generated holograms are given. A 1-dimensional Mellin transform with sixteen sampling spots is performed by the experiment. The method can be directly extended to the 2-dimensio ual case.
1986, 35 (4): 535-539. doi: 10.7498/aps.35.535
A theoretical model for resonance absorption initiated by self-focusing filamenta-tion is proposed on the base of experiments of the 2ω0 time resolved spectrum and recent experiments of 3ω0/2 filamentation, as well as slow ion emission. A number of aspects of previously obtained experimental results may well be explained.
1986, 35 (4): 540-544. doi: 10.7498/aps.35.540
Superconducting lead film is driven into the non-equilibrium state by tunnel injection of quasi-particles. There are two kinds of zero resistance state under the same injection level, depending upon the sample history. With the help of double tunnel injection, we found one of them is in the homogeneous non-equilibrium superconducting state and the other in the N-S inhomogeneous one.
1986, 35 (4): 545-548. doi: 10.7498/aps.35.545
Superconducting Sn films are driven into the non-equililbrium state by tunnel injection of quasi-particles. The voltage across the films starts to appear when injection current increase to a certain value. Near the transition temperature of the Sn films, Tc, the corresponding resistance increase rapidly with increasing temprature. The behavior is similar to the resistance of the normal-superconductor interface. But, the observed effect is orders of magnitude larger than N-S interface resistance and the value of resistance will decrease suddenly, even vanish, when the injection current increases to a higher threshold value I".
1986, 35 (4): 549-552. doi: 10.7498/aps.35.549
The Tc formula, derived in the previous papers of this series, is examined by comparing the Tc values, calculated from it, either with the numerical solutions of the Elia-shberg equation or with the experimental values of various superconductors. The agreement between them are satisfactory for superconductors with small λ.
1986, 35 (4): 553-555. doi: 10.7498/aps.35.553
We have generalized second Noether's theorem to the case in which the action integral is not invariant under the infinitesimal transformation involving arbitrary funetions, and we give some application for the massive Yang-Mills fields.
1986, 35 (4): 556-560. doi: 10.7498/aps.35.556
Last year we reported the theoretic calculation for two-photon ionization of alkali metal and noble gas atoms on the basis of Hartree-Slater self eonsistant theory. In this paper, we extend the application of the program to calculate two-photon excitation cross section of any atoms.In the calculation, we separate the transition matrix element into the resonance term and nonresonant background. For the resonance part, the possible coupling of intermediate states are taken into account and experimental results are used to remove the error of calculated energy level. On the other hand, the nonresonant background term can be obtained by solving an inhomogeneous differential equation.The two-photon excitation cross sections of Hg atom are calculated as an example,and some discussios is given.