Table of contents

20 March 1996, Volume 5 Issue 3 Previous issue    Next issue

GENERAL

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CONJUGATE POINTS ALONG NULL GEODESICS IN A CLASS OF SPACETIMES KUANG ZHI-QUAN (邝志全), LIANG CAN-BIN (梁灿彬), WU YUE-JIANG (吴月江) Acta Physica Sinica (Overseas Edition), 1996, 5 (3):  161-169.  DOI: 10.1088/1004-423X/5/3/001 Abstract ( 1435 )   PDF (223KB) ( 431 )   The existence and location of conjugate points along null geodesics in Taub's vacuum spacetime is investigated in detail. It is shown that every null geodesic $\eta$ not confined in a t-z plane contains two pairs of segments ($\mathcal{M}$, $\widetilde{\mathcal{M}}$) and ($\mathcal{N}$ $\widetilde{\mathcal{N}}$) such that each point p in $\mathcal{M}$(resp.$\mathcal{N}$) has a unique conjugate point $\widetilde{p}$ along $\eta$ that is located in $\widetilde{\mathcal{M}}$ (resp. $\widetilde{\mathcal{N}}$) and vice versa, and what is more interesting, if p and $\widetilde{\mathcal{p}}$ are conjugate points along $\eta$ with $\widetilde{\mathcal{p}}$∈J+(p), then $\widetilde{\mathcal{p}}$∈I+(p). This presents a realistic example illustrating that there do exist null geodesics emanating from p that can get into I+(p) before meeting a point conjugate to p. All results are generalized to a class of spacetimes.

ATOMIC AND MOLECULAR PHYSICS

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EXTENDED SSH MODEL FOR C58B2 AND C58N2 XU QIANG (徐强), DONG JIN-MING (董锦明), JIANG JIE (蒋杰), XING DING-YU (邢定钰) Acta Physica Sinica (Overseas Edition), 1996, 5 (3):  170-175.  DOI: 10.1088/1004-423X/5/3/002 Abstract ( 1628 )   PDF (186KB) ( 372 )   The extended Su-Schrieffer-Heeger model is used to study the electronic energy levels and molecular structures for two kinds of isomers of C58X2(X=B, or N). In each case we obtain two sets of stable solutions. For C58X2 (1, 2), both sets of solutions are found to be reasonable, indicating two different phases. For C58X2(1, 60 ), only one set of solutions which satisfy the central inversion symmetry is physically reasonable.

CLASSICAL AREAS OF PHENOMENOLOGY

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IONS CONFINEMENT IN ELECTRON BEAM ION TRAP LIU MING-HAI (刘明海), WANG SHAN-CAI (王善才), HY XI-WEI (胡希伟) Acta Physica Sinica (Overseas Edition), 1996, 5 (3):  176-184.  DOI: 10.1088/1004-423X/5/3/003 Abstract ( 1082 )   PDF (237KB) ( 522 )   This paper shows the evolution of density and temperature of multi-charged ions in an electron beam ion trap (EBIT). Three cases are studied: the continuous neutral gas injection, ion source injection, and evaporative cooling. The effects of the neutral gas density, axial potential, and the beam current density on the ions evolution are discussed.

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WHISPERING-GALLERY MODE STRUCTURE IN SEMICONDUCTOR MICRODISK LASERS AND CONTROL OF THE SPONTANEOUS EMISSION FACTOR GUO CHANG-ZHI (郭长志), CHEN SHUI-LIAN (陈水莲) Acta Physica Sinica (Overseas Edition), 1996, 5 (3):  185-194.  DOI: 10.1088/1004-423X/5/3/004 Abstract ( 1434 )   PDF (286KB) ( 404 )   The mode density and cross-sectional area of whispering-gallery modes of various possible polarizations existing in a microdisk cavity structure have been investigated and compared in some detail. Their variations with the disk thickness and radius have been calculated and the behavior of the spontaneous emission factor controlled by the microdisk structure have been shown. It is found that for a given microdisk thickness, the spontaneous emission factor increases with decreasing microdisk radius, but decreases after passing a maximum value, This non-monotonic behavior has never been noted before by others. The variation of spontaneous emission factor with respect to microdisk thickness also exhibits similar behavior. For a microdisk laser emitting at 1.5 μm wavelength, the enhanced spontaneous emiasion factor can barely exceed 0.2. A device configuration for improving the coupling between the whispering-gallery mode and the active region, and for leading the laser beam out of this high-Q microcavity is proposad, and its feasibility in realizing a thresholdless laser is discussed.

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OPTICAL BISTABILITY IN A RING CAVITY WITH A PHOTOREFRACTIVE TWO-WAVE MIXER HONG YAN-HUA (洪艳华), DAI JIAN-HUA (戴建华), XIE PING (谢平), ZHANG HONG-JUN (张洪钧) Acta Physica Sinica (Overseas Edition), 1996, 5 (3):  195-200.  DOI: 10.1088/1004-423X/5/3/005 Abstract ( 1112 )   PDF (149KB) ( 361 )   We observed the phenomenon of optical bistability in a ring cavity with a photorefractive two-wave mixer. The experimental results are in agreement with those of theory.

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TRANSVERSE MODULATION OF BEAM PROFILES IN PUMP-PROBE CONFIGURATIONS WITH BaTiO3:Ce XIE PING (谢平), DAI JIAN-HUA (戴建华), WANG PENG-YE (王鹏业), ZHANG HONG-JUN(张洪钧) Acta Physica Sinica (Overseas Edition), 1996, 5 (3):  201-206.  DOI: 10.1088/1004-423X/5/3/006 Abstract ( 1184 )   PDF (159KB) ( 415 )   Transverse spatial modulation of beam profiles for a probe beam counterpropagating to a pump beam in a 45°-cut BaTiO3:Ce crystal with an externally applied electric field is studied numerically studied. For the case that the direct ion of the external field makes an angle of 45° with the c-axis of the crystal, the probe beam, which propagates in the direction perpendicular to the external field and has a waist wider than that of the pump beam, can acquire deep spatial modulation. In contrast, the pump beam shows no spatial modulation but diffracts only. For the case the external field is directed opposite to the direction mentioned above, the probe beam shows much stronger spatial modulation as compared to the pump.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

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SOFT-X-RAY PHOTOEMISSION STUDY OF Mn/GaP(100) INTERFACE XU SHI-HONG (徐世红), XU PENG-SHOU (徐彭寿), LU ER-DONG (陆尔东), YU XIAO-JIANG (余小江), ZHANG XIN-YI (张新夷), YANG FENG-YUAN (杨风源) Acta Physica Sinica (Overseas Edition), 1996, 5 (3):  207-212.  DOI: 10.1088/1004-423X/5/3/007 Abstract ( 1279 )   PDF (198KB) ( 378 )   The interface formation and electronic structures of the Mn/GaP(100) interface are studied with synchrotron radiation photoemission, At the early stage of Mn deposition, Mn covers the whole GAP(100) surface. With the increase of coverage, Ga atoms can be exchanged by Mn atoms and diffuse into the Mn overLaycr. However, P atoms remain always near the interracial region. A sigaificant difference of the electronic structures is observed between the ultra-thin and the thick Mn films. The explanations for this are given in the text.

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THIRD-HARMONIC COEFFICIENT IN A BILATERAL ROUGH GOLD FILM PERCOLATION SYSTEM YE GAO-XIANG (叶高翔), ZHANG QI-RUI (张其瑞), WEN ZI-LI (文自立), JIAO ZHENG-KUAN (焦正宽), ZHANG XUAN-JIA (张宣嘉), XU YU-QING (许宇庆) Acta Physica Sinica (Overseas Edition), 1996, 5 (3):  213-218.  DOI: 10.1088/1004-423X/5/3/008 Abstract ( 1358 )   PDF (173KB) ( 413 )   In this paper, the third-harmonic coefficient in a bilateral rough Au-film percolation system deposited on the self-affine substrates is studied. It is proved experimentally that both the critical current and the film resistivity an functions of the third-harmonic coefficient yield power law critical behaviors. However, compared with flat systems, the critical exponents are significantly changed. The discussion for the universality behavior in this special system is also presented.

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GROWTH MODE OF Cu-RICH PARTICLES ON LASER-ABLATED YBa2Cu3O7 THIN FILMS YANG YE (杨晔), LIU JUN-ZHENG (刘军政), LI LIN (李林), ZHOU YU-QING (周玉清), ZHOU YUE-LIANG (周岳亮), CHEN ZHENG-HAO (陈正豪), Lü HUI-BIN (吕惠宾), CUI DA-FU (崔大复), YANG GUO-ZHEN (杨国桢) Acta Physica Sinica (Overseas Edition), 1996, 5 (3):  219-224.  DOI: 10.1088/1004-423X/5/3/009 Abstract ( 1274 )   PDF (243KB) ( 447 )   The microstructure of the laser-ablated YBa2Cu3O7 (YBCO) thin film deposited on heated (100) SrTiO3 substrate was examined by transmission electron microscope. The par-ticles on the film mainly consist of CuO and few CuYO2. Most of these non-superconducting particles nucleate on or near the surface of the film and protrude about 100-400 nm in height, A large amount of a-axis YBCO grains also exist in the film, which nucleate at the substrate surface and grow perpendicularly above the c-axis YBCO film. The YBCO thin film deposited under low oxygen pressure has very different microstructure compared with YBCO thin film deposited under high oxygen pressure.

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PREPARATION OF a-AXIS ORIENTED YBa2Cu3Ox THIN FILMS NIE JIA-CAI (聂家财), CHEN LIE (陈烈), YANG TAO (杨涛), GUO LI-PING (郭丽萍), WU PEI-JUN (吴培钧), LIU GUI-RONG (刘贵荣), LI LIN (李林), ZHAO ZHONG-XIAN (赵忠贤) Acta Physica Sinica (Overseas Edition), 1996, 5 (3):  225-230.  DOI: 10.1088/1004-423X/5/3/010 Abstract ( 1218 )   PDF (201KB) ( 359 )   The a-axis oriented YBa2Cu3Ox(YBCO) thin films could be grown on (100) SrTiO3(STO) substrates with STO buffer layers by dc and rf magnetron sputtering either by low-ering the deposition temperature, or by using a self-template technique. For the latter, the resistivity of the thin film at 290K along the substrate [001] direction is about four times larger than that in the [010] direction. The zero resistance temperatures Tc0 are 89 K in both directions. So high quality a-axis oriented YBCO thin films can be prepared by the self-template technique. Also the Tc0 increase monotonously with the reduction of the thickness of the YBCO seed layer.