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Chin. Phys. B  
  Chin. Phys. B--1995, Vol.4, No.7
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CLASSICAL AREAS OF PHENOMENOLOGY

SQUEEZING PROPERTIES OF THE RADIATION FIELD IN THE INTERACTION OF SQUEEZED VACUUM WITH TWO TWO-LEVEL ATOMS THROUGH TWO-PHOTON TRANSITION

SONG TONG-QIANG, FENG JIAN, WANG WEN-ZHENG, XU JING-ZHI
Acta Phys. Sin. (Overseas Edition), 1995, 4 (7): 481-488 doi: 10.1088/1004-423X/4/7/001
Full Text: [PDF 200 KB] (Downloads:295)
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We study the squeezing and the amplitude-squared squeezing of radiation field in the interaction of squeezed vacuum state with two two-level atoms, and discuss the effects of the relative value of two atom-field coupling constants on them. The numerical results show that the presence of one additional atom introduces noatrivival cooperative effects into the squeezing and the amplitude-squared squeezing of radiation field.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

SOLITON EXCITATIONS INA DIATOMIC LATTICE WITH NONLINEAR ON-SITE POTENTIAL

HUANG GUO-XIANG
Acta Phys. Sin. (Overseas Edition), 1995, 4 (7): 489-499 doi: 10.1088/1004-423X/4/7/002
Full Text: [PDF 251 KB] (Downloads:246)
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We consider the soliton excitations in a diatomic chain with nonlinear on-site potential based on a quell-discreteness approximation, Different from the theoretical approach devel-oped before, our method is valid in the whole Brillouin zone of phonons. The gap solitons observed recently in a nonlinear diatomic pendulum lattice can be well explained qualita-tively. It is also shown that if the wave number of the carrier wave is near the edge of the Brillouin zone, the results coinside with that of Kivshar and Flytzanis about the gap solitons in diatomic lattices when the difference of mass between two kinds of atoms becomes small.

TWO-DIMENSIONAL LOCALIZED VIBRATIONAL MODES AROUND A POLARON WITH THE NEXT-NEAREST-NEIGHBOR HOPPING INTERACTIONS

LI ZHAN-JIE, YAO KAI-LUN
Acta Phys. Sin. (Overseas Edition), 1995, 4 (7): 500-504 doi: 10.1088/1004-423X/4/7/003
Full Text: [PDF 143 KB] (Downloads:287)
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We have calculated the vibrational modes around a polaron to test the effects of the next-nearest-neighbor hopping interactions on the localized medes within a framework of the two-dimensional mode. The results show that: (1) For a negative polaron, eleven localized modes have been found, compared with ten modes obtained on a previous work without non-nearest neighbor hopping. (2) For a positive polaron, two additional localized modes occur. (3) The localization of localized modes are strengthened and their frequencies move after turning on the next-nearest-neighbor hopping interactions.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

MAGNON EXCITATION OF QUASI-ONE-DIMENSIONAL ORGANIC FERROMAGNET

WANG YU-QING, XIONG YUAN-SHENG, YI LIN, YAO KAI-LUN
Acta Phys. Sin. (Overseas Edition), 1995, 4 (7): 505-509 doi: 10.1088/1004-423X/4/7/004
Full Text: [PDF 117 KB] (Downloads:303)
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A new quasi-one-dimensional organic ferromagnet model is proposed. Magnon excitations for finite and infinite on-site repulsion of electrons on main carbon chain are investigated. It is found that the lowest branch of spectrum preserves the characteristics of the ferromagnetic magnon. It is also shown that with increasing of the on-site repulsion energy, the itinerant π-electrons become tightly localized.

ELECTRONIC ENERGY SPECTRUM STRUCTURE OF THE TWO-DIMENSIONAL FIBONACCI QUASILATTICES WITH THREE KINDS OF ATOMS AND ONE KIND OF BOND LENGTH

YANG XIANG-BO, LIU YOU-YAN
Acta Phys. Sin. (Overseas Edition), 1995, 4 (7): 510-522 doi: 10.1088/1004-423X/4/7/005
Full Text: [PDF 314 KB] (Downloads:266)
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After establishing the method of constructing a class of two-dimensional Fibonacci quasi-lattices, by means of a decomposition-decimation method based on the renormalization-group technique, we have studied the rule. of energy spectrum splitting for the two-dimensional Fibonacci quasilattices in the framework of single-electron tight-binding on-site model. Analytic results show that there are only six kinds of clusters and the electronic energy band consists of nine subbands.

PHOTOLUMINESCENCE STUDY OF GaAs/AlGaAs QUANTUM WELL HETEROSTRUCTURE INTERFACES

YUAN ZHI-LIANG, XU ZHONG-YING, XU JI-ZONG, ZHENG BAO-ZHEN, LUO CHANG-PING, YANG XIAO-PING, ZHANG PENG-HUA
Acta Phys. Sin. (Overseas Edition), 1995, 4 (7): 523-530 doi: 10.1088/1004-423X/4/7/006
Full Text: [PDF 219 KB] (Downloads:341)
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Photoluminescence (PL) ia used to study the interface properties of GaAs/AlGaAs quan-tum well (QW) heterostructures prepared by molecular beam epitaxy with growth interrup-tion (GI). The discrete luminescence lines observed for the sample with GI are assigned to the splitting of the heavy-hole exciton associated with heterointerface islands with the lateral size greater than excjton diameter and mean height less than one monolayer, and the spectra have the Gaussian lineshapes. The results strongly support the microroughness model. We also study the temperature dependence of the exciton energies and find that excitons are localized at the interface roughness at low temperature even in the sample with GI, The lateral size of the microroughness of the GI sample is estimated to be less than 5nm from the exciton localization energy.

DOPING BEHAVIOR AND ELECTRICAL ACTIVATION OF CARBON IN GaAs

YAN BEI-PING, LUO JIN-SHENG, ZHANG QI-LIN
Acta Phys. Sin. (Overseas Edition), 1995, 4 (7): 531-535 doi: 10.1088/1004-423X/4/7/007
Full Text: [PDF 136 KB] (Downloads:270)
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Heavily C-doped GaAs films, grown by metalorganic chemical vapor deposition with CCl4 as external carbon source, have been studied by Hall-effect measurements, high-resolution double-crystal X-ray diffraction, and secondary-ion-mass spectroscopy (SIMS). Comparison among X-ray diffraction and Hall-effect measurements and SIMS results indicates that carbon is preferentially incorporated as acceptor on As lattice sites and electrical activation rate achieves 100%. There is no evidence of carbon incorporated on Ga sites as donors and incorporated on interstitial lattice sites.

THERMOELECTRIC POWER OF A LOCAL PAIR MODEL AND ITS APPLICABILITY TO YBa2Cu3O7

ZHANG LI-YUAN, GE JIU-YUAN
Acta Phys. Sin. (Overseas Edition), 1995, 4 (7): 536-541 doi: 10.1088/1004-423X/4/7/008
Full Text: [PDF 185 KB] (Downloads:276)
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A formula of thermoelectric power (TEP) for the local pair model has been derived. It has been found that from Tc to about 125K the TEP data of YBa2Cu3O7 (Y-123) can be described by this formula. We have also found that the formula of the diffusion thermoelec-tricity in the free electron approximation can be used to express the TEP data of Y-123 in the region of 220 to about 300 K. It seems that a general transition occurs in the intermediate temperature region, that is from the regime in which the local pair subsystem is dominating to the regime in which the itinerant carrier subsystem is dominating.

SPECIFIC HEAT OF A HEISENBERG SYSTEM WITH FINITE SIZE

SUN JI-RONG, WEI YU-NIAN, PU FU-CHO
Acta Phys. Sin. (Overseas Edition), 1995, 4 (7): 542-549 doi: 10.1088/1004-423X/4/7/009
Full Text: [PDF 220 KB] (Downloads:296)
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Based upon the spin wave theory, the influence of the size of a three-dimensional Heisenberg system on its thermodynamic properties was studied. It is found that the specific heat increases due to the finite size and free surface of the system. For a magnetic film with finite thickness, the interaction of spin waves was also discussed. There exist three additional scattering processes, namely, the scattering between spin waves with wave-vectors parallel to the surface of the film (two-dimensional spin wave), the scattering between two and three-dimensional waves, and the scattering between those waves with the same component in the direction along the thickness of the film. As a result, the T4 term, arising from the coupling of spin waves, in the expression of the specific heat of the system, splite into three parts proportional to T5/2,T7/2 and T4, respectively. Here T is the temperature.
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