Chin. Phys. B
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CN 11-5639/O4
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Chin. Phys. B  
  Chin. Phys. B--1996, Vol.5, No.3
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GENERAL

CONJUGATE POINTS ALONG NULL GEODESICS IN A CLASS OF SPACETIMES

KUANG ZHI-QUAN, LIANG CAN-BIN, WU YUE-JIANG
Acta Phys. Sin. (Overseas Edition), 1996, 5 (3): 161-169 doi: 10.1088/1004-423X/5/3/001
Full Text: [PDF 223 KB] (Downloads:329)
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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 η not confined in a t-z plane contains two pairs of segments (M,M) and (N, N) such that each point p in M(resp.N) has a unique conjugate point p along η that is located in M (resp. N) and vice versa, and what is more interesting, if p and p are conjugate points along η with p∈J+(p), then 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.
CLASSICAL AREAS OF PHENOMENOLOGY

IONS CONFINEMENT IN ELECTRON BEAM ION TRAP

LIU MING-HAI, WANG SHAN-CAI, HY XI-WEI
Acta Phys. Sin. (Overseas Edition), 1996, 5 (3): 176-184 doi: 10.1088/1004-423X/5/3/003
Full Text: [PDF 237 KB] (Downloads:427)
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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.

WHISPERING-GALLERY MODE STRUCTURE IN SEMICONDUCTOR MICRODISK LASERS AND CONTROL OF THE SPONTANEOUS EMISSION FACTOR

GUO CHANG-ZHI, CHEN SHUI-LIAN
Acta Phys. Sin. (Overseas Edition), 1996, 5 (3): 185-194 doi: 10.1088/1004-423X/5/3/004
Full Text: [PDF 286 KB] (Downloads:320)
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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.

OPTICAL BISTABILITY IN A RING CAVITY WITH A PHOTOREFRACTIVE TWO-WAVE MIXER

HONG YAN-HUA, DAI JIAN-HUA, XIE PING, ZHANG HONG-JUN
Acta Phys. Sin. (Overseas Edition), 1996, 5 (3): 195-200 doi: 10.1088/1004-423X/5/3/005
Full Text: [PDF 149 KB] (Downloads:280)
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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.

TRANSVERSE MODULATION OF BEAM PROFILES IN PUMP-PROBE CONFIGURATIONS WITH BaTiO3:Ce

XIE PING, DAI JIAN-HUA, WANG PENG-YE
Acta Phys. Sin. (Overseas Edition), 1996, 5 (3): 201-206 doi: 10.1088/1004-423X/5/3/006
Full Text: [PDF 159 KB] (Downloads:325)
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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.
ATOMIC AND MOLECULAR PHYSICS

EXTENDED SSH MODEL FOR C58B2 AND C58N2

XU QIANG, DONG JIN-MING, JIANG JIE, XING DING-YU
Acta Phys. Sin. (Overseas Edition), 1996, 5 (3): 170-175 doi: 10.1088/1004-423X/5/3/002
Full Text: [PDF 186 KB] (Downloads:277)
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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.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

SOFT-X-RAY PHOTOEMISSION STUDY OF Mn/GaP(100) INTERFACE

XU SHI-HONG, XU PENG-SHOU, LU ER-DONG, YU XIAO-JIANG, ZHANG XIN-YI, YANG FENG-YUAN
Acta Phys. Sin. (Overseas Edition), 1996, 5 (3): 207-212 doi: 10.1088/1004-423X/5/3/007
Full Text: [PDF 198 KB] (Downloads:284)
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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.

THIRD-HARMONIC COEFFICIENT IN A BILATERAL ROUGH GOLD FILM PERCOLATION SYSTEM

YE GAO-XIANG, ZHANG QI-RUI, WEN ZI-LI, JIAO ZHENG-KUAN, ZHANG XUAN-JIA, XU YU-QING
Acta Phys. Sin. (Overseas Edition), 1996, 5 (3): 213-218 doi: 10.1088/1004-423X/5/3/008
Full Text: [PDF 173 KB] (Downloads:314)
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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.

GROWTH MODE OF Cu-RICH PARTICLES ON LASER-ABLATED YBa2Cu3O7 THIN FILMS

YANG YE, LIU JUN-ZHENG, LI LIN, ZHOU YU-QING, ZHOU YUE-LIANG, CHEN ZHENG-HAO, Lü HUI-BIN, CUI DA-FU, YANG GUO-ZHEN
Acta Phys. Sin. (Overseas Edition), 1996, 5 (3): 219-224 doi: 10.1088/1004-423X/5/3/009
Full Text: [PDF 243 KB] (Downloads:360)
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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.

PREPARATION OF a-AXIS ORIENTED YBa2Cu3Ox THIN FILMS

NIE JIA-CAI, CHEN LIE, YANG TAO, GUO LI-PING, WU PEI-JUN, LIU GUI-RONG, LI LIN, ZHAO ZHONG-XIAN
Acta Phys. Sin. (Overseas Edition), 1996, 5 (3): 225-230 doi: 10.1088/1004-423X/5/3/010
Full Text: [PDF 201 KB] (Downloads:282)
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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.
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