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Volume 18 Issue 6
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Original Articles
Rational SU(N) Gaudin Model
CAO Jun-Peng, HOU Bo-Yu, YUE Rui-Hong
Chin. Phys. Lett. 2001, 18 (6): 715-717 .  
Abstract   PDF(pc) (209KB) ( 359 )
We propose the eigenstates and eigenvalues of Hamiltonians of the rational SU(N) Gaudin model based on the quasi-classical limit of the SU(N) chain under the periodic boundary condition. Using the quantum inverse scattering method, we also obtain the eigenvalues of the generation function of the rational SU(N) Gaudin model.

Quantum Computation by Pairing Trapped Ultracold Ions
FENG Mang, ZHU Xi-Wen, GAO Ke-Lin, SHI Lei
Chin. Phys. Lett. 2001, 18 (6): 718-720 .  
Abstract   PDF(pc) (190KB) ( 393 )
Superpositional wave function oscillations for the implementation of quantum algorithms modify the desired interference required for the quantum computation. We propose a scheme with trapped ultracold ion-pairs being qubits to diminish the detrimental effect of the wave function oscillations, which is applied to the two-qubit Grover's search. It can be also found that the qubits in our scheme are more robust against the decoherence caused by the environment, and the model is scalable.
Quantum Binary Symmetric Channels
CHEN Xiao-Yu, QIU Pei-Liang
Chin. Phys. Lett. 2001, 18 (6): 721-723 .  
Abstract   PDF(pc) (177KB) ( 735 )
Quantum binary symmetric channels are defined via the invariance of fidelity under unitary transformations of the input density operators. In this definition, they not only include the most studied case of the depolarizing channel but also other channels. We investigate the character of the latter and find the maximum of the coherent information to estimate the capacities of the channels.
Quantum Motion of Atoms in a Magnetic Waveguide
LIU Xia-Ji, LI Dai-Jun, WANG De-Zhong, HUANG Hu, LI Shi-Qun, WANG Yu-Zhu
Chin. Phys. Lett. 2001, 18 (6): 724-726 .  
Abstract   PDF(pc) (279KB) ( 345 )
Based on the magnetic atomic guidance model proposed in our previous paper [Opt. Commun. 160(1999)72], the quantum motion of atoms in a magnetic tube is discussed in detail. The non-adiabatic loss of atoms as result of spin-flip transition and the adiabatic condition for keeping atoms in the guidable state are also analysed. The result shows that the atoms can be guided in the magnetic waveguide with a higher guiding efficiency by choosing suitable parameters of the magnetic tube.
Generalized Synchronization of Phase Differences in Three Lasers
ZHU Shi-Qun, LUO Xiao-Qin, FANG Jian-Xing
Chin. Phys. Lett. 2001, 18 (6): 727-730 .  
Abstract   PDF(pc) (901KB) ( 363 )
A linear array of three identical lasers that are coupled mutually in space is investigated theoretically by integration of the laser equations. It is shown that the generalized synchronization of phase differences in the laser fields appears with intermediate coupling when the laser intensities are totally chaotic and chaotically synchronized. Both intensities and phase differences are totally chaotic at smaller coupling constants. The lasers are also changed from coherent light to incoherent one when the couplings between lasers are decreased.
Approximate Scaling Behaviour of Local Spectral Density of States at Relatively Weak Perturbation: a Schematic Shell Model
Chin. Phys. Lett. 2001, 18 (6): 731-733 .  
Abstract   PDF(pc) (336KB) ( 383 )
For a schematic shell model, we show numerically that, contrary to the behaviour of eigenfunctions, the shapes of the so-called local spectral density of states become close to their forms at extremely strong perturbation (after rescaling) even when the perturbation is relatively weak. The same phenomenon is also found for the random version of the schematic shell model. We suggest that this property of the local spectral density of states may be common to models in which the Hamiltonian matrices in independent particle states have a banded and regular structure.

Break-Up of Three-Frequency KAM Tori: Determination of the Critical Parameters
ZHOU Ji-Lin, Bam-Bi HU, SUN Yi-Sui
Chin. Phys. Lett. 2001, 18 (6): 734-736 .  
Abstract   PDF(pc) (307KB) ( 519 )
With a four-dimensional symplectic map we study numerically the break-up of three-frequency Kolmogorov-Arnold-Moser (KAM) tori. The locations and stabilities of a sequence of periodic orbits, whose winding numbers approach the irrational winding number of the KAM torus, are examined. The break-up of quadratic frequency tori is characterized as the exponential growth of the residue means of the convergent periodic orbits. Critical parameters of the break-up of tori with different winding numbers are calculated, which shows that the spiral mean torus is the most robust one in our model.
Magnetization Reversal Processes in Pt/Co Multilayers Studied by Magnetic Force Microscope
ZHANG Zhen-Rong, LIU Hong, HAN Bao-Shan
Chin. Phys. Lett. 2001, 18 (6): 737-739 .  
Abstract   PDF(pc) (1453KB) ( 425 )
We have studied the magnetic reversal process of the magnetron sputtered Pt/Co multilayers by using magnetic force microscope with in situ bias magnetic fields. In thin films magnetic reversal is usually dominated either by domain nucleation or by domain wall motion. In our experiments, a series of magnetic images in situ captured in the same area indicates that the magnetic reversal in Pt/Co multilayers is dominated by domain nucleation, in stead of domain wall motion. In addition, the local demagnetized curve was obtained by using the bearing analysis of the domains in the series of magnetic images.
Thermo-field Dynamics of the Casimir Effect and Its Quantum Deformation
JING Hui, XIE Bing-Hao, CHEN Jing-Ling
Chin. Phys. Lett. 2001, 18 (6): 740-742 .  
Abstract   PDF(pc) (186KB) ( 319 )
The Casimir effect of the deformed cavity field at finite temperature is investigated by generalizing the thermo field dynamics formalism into q-deformed version. It has been shown that the impact of q-deformation on the Casimir force only manifests in the finite temperature case and the expression for the ideal pure vacuum remains unchanged, which just coincides with the suggestions of Man’ko et al. [Phys. Lett. A 176(1993 173] about the nature of q-oscillators as the nonlinear vibrations of electromagnetic field.
Calculation of the π Meson Electromagnetic Form Factor
WANG Zhi-Gang, WAN Shao-Long, WANG Ke-Lin
Chin. Phys. Lett. 2001, 18 (6): 743-745 .  
Abstract   PDF(pc) (254KB) ( 360 )
The modified flat-bottom potential (MFBP) is given by the combination of the flat-bottom potential with considerations for the infrared and ultraviolet asymptotic behaviour of the effective quark-gluon coupling. The π meson electromagnetic form factor is calculated in the framework of coupled Schwinger-Dyson equation and Bethe-Salpeter equation in simplified impulse approximation (dressed vertex) with MFBP. All our numerical results give good fit to experimental values.
Remeasurement of the Half-Life of 79Se with the Projectile X-Ray Detection Method
JIANG Song-Sheng, HE Ming, DIAO Li-Jun, GUO Jing-Ru, WU Shao-Yong
Chin. Phys. Lett. 2001, 18 (6): 746-749 .  
Abstract   PDF(pc) (329KB) ( 485 )
Remeasurement of the half-life of 79Se has been carried out with the projectile x-ray detection (PXD) in accelerator mass spectrometry. We made two major improvements over our earlier 79Se half-life determination [Nucl. Instrum. Methods B 123 (1997) 403]. Fristly, the PXD technique has been used for separation of 79Se and 75Se from 79Br and 75As isobars respectively. Secondly, the half-life of 79Se has been measured relative to the known precise half-life of 75Se (119.79 ± 0.04d). A more reliable half-life of 79Se measured with the PXD technique is (2.95 ± 0.38)x105y, about a factor of one lower than the previous value, 1.1 x 106y. The problems in the previous measurement are discussed.
Well-Deformed Oblate K Isomers Induced by Oblate Intruder States
XU Fu-Rong
Chin. Phys. Lett. 2001, 18 (6): 750-752 .  
Abstract   PDF(pc) (351KB) ( 482 )
With configuration-constrained potential energy surfaces, it has been found that the neutron-deficient Z ≈ 82 nuclei can have well-deformed oblate K isomers which are formed by exciting quasiparticles to the proton i13/2 and h9/2 oblate intruder orbitals. To achieve the configuration constrained calculations, the maximum-overlap method of wavefunctions is proposed. In the present calculations of quasiparticle states, quadrupole pairings are included. The observed Kπ = 11-1 isomer in 188Pb is confirmed to be oblately deformed, with energy consistent with the experiment. Some low-lying oblate isomeric states are predicted for 187Tl.
Production of Light Nuclei from 36Ar and 40Ar Fragmentation at About 60 MeV/Nucleon
FANG De-Qing, SHEN Wen-Qing, FENG Jun, CAI Xiang-Zhou, MA Yu-Gang, ZHANG Hu-Yong, HU Peng-Yun, ZHAN Wen-Long, GUO Zhong-Yan, XIAO Guo-Qing, LI Jia-Xing, WANG Meng, WANG Jian-Feng, NING Zhen-Jiang, WANG Jin-Chuan, WANG Jian-Song, WANG Quan-Jin, CHEN Zhi-Qiang
Chin. Phys. Lett. 2001, 18 (6): 753-755 .  
Abstract   PDF(pc) (426KB) ( 418 )
Fragments produced in the reactions of 69 MeV/nucleon 36Ar and 55 MeV/nucleon 40Ar on a Be target have been measured experimentally. The isotopic distributions from fragmentation reaction for both projectiles are reproduced by using a modified statistical abrasion-ablation model. Strong isospin effect exhibits in the isotopic distributions produced in 36Ar and 40Ar fragmentation. Experimental evidence is seen for the disappearance of the isospin effect in fragmentation reaction.
Directed and Elliptic Flow in 112Sn+112Sn Collisions
ZHANG Hu-Yong, MA Yu-Gang, YU Li-Ping, SHEN Wen-Qing, CAI Xiang-Zhou, FANG De-Qing, ZHONG Chen, HAN Ding-Ding
Chin. Phys. Lett. 2001, 18 (6): 756-758 .  
Abstract   PDF(pc) (388KB) ( 303 )
The directed and elliptic flow in collisions of 112Sn+112Sn at energies from 35 to 90 MeV/nucleon are studied in an isospin-dependent quantum molecule dynamics model. With increasing incident energy, the directed flow rises from negative to positive. Its magnitude depends on the nuclear equation of state (EOS). However, the elliptic flow decreases with increasing incident energy and its magnitude is not very sensible to EOS. Systematic studies of the impact parameter dependence and the cluster mass dependence are also performed. The study of directed flow at intermediate energies thus provides a means of extracting the information on the nuclear equation of state.
Measurement and Correction of K-Shell Ionization Cross Sections for Copper and Gallium by Electron Impact
ZHOU Chang-Geng, AN Zhu, LUO Zheng-Ming
Chin. Phys. Lett. 2001, 18 (6): 759-760 .  
Abstract   PDF(pc) (267KB) ( 641 )
The K-Shell ionization cross sections of Cu and Ga are measured by electron impact and the data of Ga are reported for the first time. The method of a thin chemical compound target with a thick substrate is formally used in the experiment. The influence of electrons reflected from the substrate is corrected by means of a calculation of electron transport.
Relativistic Calculation of Dielectronic Recombination on the C4+ Ground State
LIU Yong, ZOU Yu, FANG Quan-Yu, XU Ya-Qiong
Chin. Phys. Lett. 2001, 18 (6): 761-763 .  
Abstract   PDF(pc) (366KB) ( 443 )
The relativistic multichannel theory has been applied and a nonperturbative formula adopted to calculate the dielectronic recombination cross section due to ΔN=1 resonances for the ground state C4+. The first-order approximation is adopted for the radiative process and a correction based on the isolated resonance approximation is used for the very narrow resonances to include the radiation width. The convoluted cross section is in agreement within 5% with that of observation for resonances with n ≤ 5. For n=6 and 7, the integral cross section is overestimated by a factor of 6 and 4, respectively. According to our calculation, the Rydberg cut-off due to field ionization should be at a principal quantum number higher than that given by Mannervik et al. A Small relativistic effect is noticed at intrashell resonance.
Statistical Parameters for Hydrogen Bonding Networks: One Component
WANG Hai-Jun, HONG Xiao-Zhong, ZHAO Min, BA Xin-Wu
Chin. Phys. Lett. 2001, 18 (6): 764-766 .  
Abstract   PDF(pc) (278KB) ( 342 )
Based on the analysis of network structures formed by hydrogen bonds as the sol-gel phase transition takes place in a single component hydrogen bonding system, the theory of reversible gelation is applied to calculate some statistical parameters that determine many physical and chemical properties of the networks. Then the numerical simulation of the number of active chains and dangling chains, the number of effective cross-linkages, the number of active and dangling mers and the modulus as a function of conversion are undertaken.

A Modified Perturbation Method of Electromagnetic Scattering from a Rough Surface by Considering the Effect of the Curvature
GUO Li-Xin, WU Zhen-Sen, ZHANG Min
Chin. Phys. Lett. 2001, 18 (6): 767-770 .  
Abstract   PDF(pc) (342KB) ( 776 )
A modified perturbation method of electromagnetic scattering from a rough surface is presented, in which the effect of the curvature of the surface is taken into account based on the conventional small perturbation method. The problem of scattering error by the conventional small perturbation method at grazing angle is solved. Compared with a set of measured data, the numerical results of the backscattering radar cross section show that this modified perturbation method is validity for small, moderate and grazing angle incidence.
Generation of the Stigmatic Beam with Orbital Angular Momentum
GAO Chun-Qing, WEI Guang-Hui, Horst WEBER
Chin. Phys. Lett. 2001, 18 (6): 771-773 .  
Abstract   PDF(pc) (452KB) ( 448 )
The stigmatic beam with orbital angular momentum is generated by transforming the Hermite-Gaussian beam of a diode-pumped Nd:YAG laser through a rotated cylindrical optical system. Behind the transformation optics the output beam has an intensity distribution of ring shape and a twist phase. The beam transformation is theoretically calculated and the result has been confirmed in the experiments.
Application of Laser Magnetic Resonance Spectroscopy to the Measurement of Electric Dipole Moment of Free Radicals
LIU Yu-Yan, , GUO Yuan-Qing, HUANG Guang-Ming, LIN Jie-Li, DUAN Chuan-Xi, LI Feng-Yan, LI Jin-Rui
Chin. Phys. Lett. 2001, 18 (6): 774-775 .  
Abstract   PDF(pc) (225KB) ( 404 )
An intracavity CO laser magnetic resonance spectrometer with homogeneous dc electric field applied via a pair of parallel Stark plates in the absorption cell is used to measure the electric dipole moments of free radicals. Taking advantage of high sensitivity and high resolution of this technique and the Stark effect, highly-resolved saturated absorption spectra of v = 1-0 transition of 15N16O in the ground state X2II3/2 have been successfully observed in the presence of a low electric field. The electric dipole moment of NO in the electronic ground state is determined as μ = 0.1566 ± 14 D (Debye) from the analysis of the observed spectra, confirming that, combined with the Stark field, the laser magnetic resonance technique can be an effective and reliable approach for the precise measurement of electric dipole moments of free radicals, especially the unstable ones.
Spatiotemporal Instability of Ultrashort Pulses in Dispersive Self-Focusing Media
WEN Shuang-Chun, FAN Dian-Yuan
Chin. Phys. Lett. 2001, 18 (6): 776-778 .  
Abstract   PDF(pc) (388KB) ( 610 )
Spatiotemporal instability in dispersive self-focusing media is
investigated on the basis of a modified nonlinear Schrödinger equation (NLSE) beyond the slowly varying envelope approximation. It is found that, for both normal and anomalous dispersions, space-time focusing may lead to the appearance of new temporal instability regions for some range of spatial frequencies. The physical origin of the new instability regions lies in the part of space-time coupling related to the fourth-order dispersion. Furthermore, space-time focusing shrinks the instability regions and slightly reduces the maximum growth rates of the original spatiotemporal instability gain spectra obtained from the standard NLSE.
Nonlinear Optical Absorption of Glassy Thin Films Containing InSb Nanocrystals
ZHU Kai-Gui, SHAO Qing-Yi, SHI Jian-Zhong
Chin. Phys. Lett. 2001, 18 (6): 779-781 .  
Abstract   PDF(pc) (343KB) ( 388 )
Nonlinear optical absorption of glassy thin films containing InSb nanocrystals was measured by Z-scan technique using Gaussian beam of He-Ne laser (632.8 nm). Both two-photon and saturation absorptions were observed in the composite thin films containing InSb nanocrystals with different average sizes. An enhanced nonlinear optical coefficient was achieved.

External Electro-optic Sampling Utilizing an Asymmetric Fabry-Pérot Film of Poled Electro-optical Polymer
CHEN Kai-Xin, YANG Han, ZHANG Da-Ming, ZHANG Hong-Bo, YI Mao-Bin
Chin. Phys. Lett. 2001, 18 (6): 782-784 .  
Abstract   PDF(pc) (299KB) ( 687 )
External electro-optic sampling has been first demonstrated using a poled electro-optical polymer asymmetric Fabry-Pérot film, placed freely on the indium-tin oxide coplanar waveguide transmission line and used as electro-optic probe tip. Only one laser beam is required due to the fact that the asymmetric Fabry-Pérot film is utilized to convert the phase modulation to amplitude modulation. A 1.2 GHz microwave signal is sampled, and the voltage sensitivity about 2mV/√Hz is obtained. The results are promising for technical applications in the high-speed electronic devices and monolithic microwave integrated circuits research.
Stop Gaps and Single Defect States of Acoustic Waves in Two-Dimensional Lattice of Liquid Cylinders
WU Fu-Gen, LIU Zheng-You, LIU You-Yan
Chin. Phys. Lett. 2001, 18 (6): 785-787 .  
Abstract   PDF(pc) (395KB) ( 445 )
The acoustic wave band structures and single defect states of the two-dimensional periodic composite media of water (mercury)cylinders with circular cross section in mercury (water) host was studied by using the plane-waves method and supercell calculations. We find that the numbers of the gaps in the first 50 bands vs filling fraction have the similar results as gap/midgap ratio of the lowest gap in the period systems. Only one band gap exhibits in wide range of filling fraction, and several defect states are created inside the band gaps in single defect system. The influences of filling fraction and defect radius on the band structure are investigated.
Current Sheet Formation in Weakly Ionized Plasmas
JI Hai-Sheng, LI Xiao-Qing, SONG Mu-Tao,
Chin. Phys. Lett. 2001, 18 (6): 788-789 .  
Abstract   PDF(pc) (216KB) ( 355 )
Using the two fluid model, the problem of two-dimensional steady-state magnetic reconnection in incompressible resistive weakly ionized plasmas is analysed. Under the strong-coupling condition such as in the Sun's photosphere, it allows us to express the current sheet analytically. In this case the current sheet scales as η1/2. Then this model is used to understand magnetic flux cancellation which is observed in the Sun's magnetograms. To account for a canceling flux of 1 x 1018Max in a time interval of 77 min, the width of the current sheet is about ten kilometers.
Pressure Driven Magnetohydrodynamics Instabilities in Peaked Pressure Profile Reversed Magnetic Shear Plasmas
GAO Qing-Di, ZHANG Jin-Hua, QU Hong-Peng
Chin. Phys. Lett. 2001, 18 (6): 790-792 .  
Abstract   PDF(pc) (381KB) ( 350 )
For a reversed magnetic shear plasma formed by early neutral beam injection into the HL-2A tokamak, magnetohydrodynamics instability analysis against ideal low-n modes and resistive interchange modes is carried out. Low-n modes located in the low shear region around the shear reversal point are driven unstably by large pressure gradient, and they are of the characteristics of infernal modes. High pressure in the central negative shear region drives resistive interchange modes with the unstable window extending to r/a ≈ 0.2, but not covering the low shear region around the shear reversal point.
Self-Organized Criticality Properties of the Turbulence-Induced Particle Flux at the Plasma Edge of the HT-6M Tokamak
WANG Wen-Hao, YU Chang-Xuan, WEN Yi-Zhi, XU Yu-Hong, LING Bi-Li, GONG Xian-Zu, LIU Bao-Hua, WAN Bao-Nian
Chin. Phys. Lett. 2001, 18 (6): 793-795 .  
Abstract   PDF(pc) (429KB) ( 447 )
Power spectrum and the probability distribution function (PDF) of the turbulence-induced particle flux Γ in the velocity shear layer of the HT-6M edge region have been measured and analysed. Three regions of frequency dependence (f0, f-1, f-4) have been observed in the spectrum of the flux. The PDF of the flux displays a Γ-1 scaling over one decade in Γ. Using the rescaled-range statistical technique, we find that the degree of the self-similarity (Hurst exponent) of the particle flux in the measured region ranges from 0.64 to 0.83. All of these results may mean that the plasma transport is in a state characterized by the self-organized criticality.
Ion Acceleration by an Electrostatic Field in the Interaction Between Femtosecond Laser Pulses and Solid Targets
DONG Quan-Li, ZHANG Jie, LIANG Tian-Jiao, ZHANG Ping, CHEN Li-Ming, TANG Xiao-Wei
Chin. Phys. Lett. 2001, 18 (6): 796-798 .  
Abstract   PDF(pc) (621KB) ( 399 )
We have studied the ion emission in the interaction between femtosecond laser pulses and solid targets by experiments and particle-in-cell (PIC) simulations. We found experimentally that almost all of the fast ions are confined within a cone symmetrically around the normal direction of targets. The PIC simulation results demonstrate that the fast ion beam can be accelerated by the laser-induced electrostatic field in front of solid targets.
Particle Simulation of the Fast Ignition Mechanism for Laser Fusion
ZHANG Jia-Tai, He Bin, N. E. Andreev
Chin. Phys. Lett. 2001, 18 (6): 799-801 .  
Abstract   PDF(pc) (282KB) ( 437 )
We have developed the two and half-dimension electromagnetic relativistic electron and mobile ion cloud-in-cell (CIC)code. Mechanisms of the fast ignition and interaction of ultra-intense and ultra-short pulse laser with plasma are analysed theoretically and simulated numerically using CIC code.Strong flows of relativistic electron and form of the channel are observed. The results show that the temperature of superhot electron is about MeV to tens of MeV, and the boring velocity is 0.05c-0.1c with c being the light speed. Some preliminary scale laws are obtained. This simulation quantitatively reproduces the experimental results at early and long times.

Effects of Magnetic Shear on Current Penetration in a Tokamak
ZHANG Peng-Yun, WANG Long
Chin. Phys. Lett. 2001, 18 (6): 802-804 .  
Abstract   PDF(pc) (351KB) ( 356 )
The penetrations of the parallel and perpendicular components of plasma currents are interrelated to each other due to the existence of magnetic shear in a tokamak configuration. Effects of the shear on the penetration of Fourier components of toroidal plasma current are analysed in a cylindrical column model. The current penetration is obviously strengthened by the shear for a bell-like conductivity profile and low safety factor and low aspect ratio.
Mie Potential and Equation of State of Zr48Nb8Cu14Ni12Be18 Bulk Metallic Glass
ZHANG Yong, PAN Ming-Xiang, WANG Wei-Hua,
Chin. Phys. Lett. 2001, 18 (6): 805-807 .  
Abstract   PDF(pc) (299KB) ( 813 )
The linear expansion of Zr48Nb8Cu14Ni12Be18 bulk metallic glass (BMG) with excellent glass forming ability and high thermal stability is investigated by a dilatometry method. The average expansion coefficient is αTG= 1.04 x 10-5 K-1 (300-656 K) for the BMG and αTG= 1.11 x 10-5 K-1 (356~890 K) for the crystallized alloy. The Mie potential as well as the equation of state of the BMG and its corresponding crystallized state are determined from the thermal expansion and ultrasonic data, and the differences among them are phenomenologically explained.
Void Evolution in α-Al2O3 Irradiated by En ≥1 MeV Neutrons of 3 x 1020cm-2
XU Yong-Jun, FAN Zhi-Guo, LUO Qi, WANG Rong, ZHU Jia-Zheng, T. Iwata, T. Minamisono, K. Matsuta, M. Fukuda, M. Mihara, ZHU Sheng-Yun
Chin. Phys. Lett. 2001, 18 (6): 808-809 .  
Abstract   PDF(pc) (289KB) ( 501 )
The void evolution in α-Al2O3 irradiated by En ≥1 MeV neutrons of 3 x 1020cm-2 and post-annealed from 100°C to 1050°C has been studied by a positron annihilation lifetime technique. The void nucleation starts at 500°C. In the annealing temperature region from 550°C to 750°C, the radius of created voids keeps constant at a value of about 0.29 nm and the number of voids increases with increasing temperature. Afterwards,the radius of voids increases rapidly with the increasing annealing temperature and reaches 1.21nm at 1050°C.
X-Ray Diffraction Analysis on Gallium-Indium Interdiffusion in Quantum Dot Superlattices
WANG Hui, XU Shi-Jie, LI Qing, FENG Song-Lin
Chin. Phys. Lett. 2001, 18 (6): 810-812 .  
Abstract   PDF(pc) (404KB) ( 679 )
Thermal induced interdiffusion in InAs/GaAs quantum dot superlattices is studied by high-resolution x-ray diffraction rocking curve and photoluminescence techniques. With increasing annealing temperature, up to 300 meV a blueshift of the emission peak position and down to 16.6 meV a narrowing of the line width are found in photoluminescence spectra, and respective intensity of the higher-order satellite peaks to lower-order ones in the x-ray rocking curves decreases. Dynamical theory is employed to simulate the measured x-ray diffraction data. Excellent agreement between the experimental curves and the simulations is achieved when the composition, thickness and stress variations caused by interdiffusion are taken into account. It is found that the significant In-Ga intermixing occurs even in the as-grown InAs/GaAs quantum dots. The estimated diffusion coefficient is 1.8 x 10-17cm2.s-1 at 650°C, 3.2 x 10-17cm2.s-1 at 750°C, and 1.2 x 10-14cm2.s-1 at 850°C.
Crystal Tilts in Epitaxially Laterally Overgrown GaN Films Determined by Four-Circle X-Ray Diffraction
WANG Feng, ZHANG Rong, CHEN Zhi-Zhong, WU Xiao-Shan, GU Shu-Lin, SHEN Bo, ZHENG You-Dou, JIANG Shu-Sheng
Chin. Phys. Lett. 2001, 18 (6): 813-815 .  
Abstract   PDF(pc) (537KB) ( 621 )
Crystal tilts in epitaxially laterally overgrown (ELO) GaN films via hydride vapor phase epitaxy (HVPE) on sapphire substrates have been investigated by using four-circle x-ray diffraction method. Three diffraction peaks corresponding to the (0002) reflection of vertically epitaxial and tilted GaN domains are observable in the x-ray rocking curve. The angle separations Δω between the main peak and two lobes change with the azimuth angle Ф. The dependence of Δω on Ф and the crystal tilt angle θ has been calculated based on the standard kinetic x-ray diffraction model. The crystal tilt angle of a typical HVPE ELO GaN sample has been determined to be 2.379°C.

Strong Quantum Fluctuation of Vortices in Bulk Samples of the New Superconductor MgB2
WEN Hai-Hu, LI Shi-Liang, ZHAO Zhi-Wen, NI Yong-Ming, REN Zhi-An, CHE Guang-Can, YANG Hai-Peng, LIU Zhi-Yong, ZHAO Zhong-Xian
Chin. Phys. Lett. 2001, 18 (6): 816-819 .  
Abstract   PDF(pc) (501KB) ( 617 )
By using transport and magnetic measurement, the upper critical field Hc2(T) and the irreversibility line Hirr(T) has been determined. A big separation between Hc2(0) and Hirr(0) has been found showing the existence of a quantum vortex liquid state induced by quantum fluctuation of vortices in the new superconductor MgB2. Further investigation on the magnetic relaxation shows that both the quantum tunneling and the thermally activated flux creep depends weakly on temperature. However, when the melting field Hirr is approached, a drastic rise of the relaxation rate is observed. This may indicate that the melting of the vortex matter at a finite temperature is also induced by the quantum fluctuation of vortices.
Low Temperature Specific Heat of Superconducting MgB2
LUO Jian-Lin, ZHANG Jie, CHEN Zhao-Jia, BAI Hai-Yang, WANG Yu-Peng, MENG Ji-Bao, JIN Duo, REN Zhi-An, CHE Guang-Can, ZHAO Zhong-Xian
Chin. Phys. Lett. 2001, 18 (6): 820-822 .  
Abstract   PDF(pc) (304KB) ( 448 )
The specific heat of the recently discovered superconductor MgB2 has been measured at temperatures ranging from 4.5 to 80 K. Superconducting anomaly ΔC at Tc is clearly observed. The total specific heat in normal state can be well fitted by electronic and phonon contributions. The Debye temperature θD is obtained to be 737 K, much larger than other intermetallic superconductors. Normal state electronic specific heat coefficient γ is found to be 2.48 ± 0.5 mJ/mol.K2 and ΔC/γTc is between 1.41 and 2.15.
Upper Critical Field and Irreversibility Line Determined by Transport Measurement of the New Superconductor MgB2
JIN Hao, WEN Hai-Hu, LI Shi-Liang, ZHAO Zhi-Wen, NI Yong-Ming, REN Zhi-An, CHE Guang-Can, YANG Hai-Peng, LIU Zhi-Yong, ZHENG Dong-Ning, ZHAO Zhong-Xian
Chin. Phys. Lett. 2001, 18 (6): 823-825 .  
Abstract   PDF(pc) (343KB) ( 637 )
Resistive transitions of the new superconductor MgB2 are carried out under magnetic fields from 0 to 8 T. It is found that the irreversibility field Hirr(T) and the upper critical field Hc2(T) obtained are very close to those determined in the magnetic measurement. By using the Arrhenius activation law ρ = ρ0exp(-U/kBT), the activation barrier U has been determined by the low dissipation part of R(T) curves. It is found that U kBT manifests a very weak thermal activation and thermal fluctuation effect. This may further indicate that the flux dynamics near Hirr(T) is induced by strong quantum fluctuation and tunneling of vortices.
An Electronic Structure of Ferroelectric PbZr0.5Ti0.5O3
WANG Yuan-Xu, ZHONG Wei-Lie, WANG Chun-Lei, ZHANG Pei-Lin
Chin. Phys. Lett. 2001, 18 (6): 826-828 .  
Abstract   PDF(pc) (466KB) ( 871 )
An electronic structure of ferroelectric PbZr1/2Ti1/2O3 is presented. The full potential linearized augmented plane wave method is used and the exchange correlation effects are treated by the generalized gradient approximation. In order to understand the ferroelectricity of PbZr1/2Ti1/2O3, the density of states, charge density distribution and band structure are calculated. The results show that the atoms Pb and Ti act similarly as in pure PbTiO3. Like other perovskite ABO3 ferroelectrics, there is a hybridization between the Ti d and O p states, which is responsible for the tendency to ferroelectricity.
Energy Transfer in Cubic PbF2:Gd Crystals
ZHANG Guo-Bin, SHI Jun-Yan, ZHANG Zeng-Ming, HAN Zheng-Fu, SHI Chao-Shu, ZHANG Xin-Yi, G. Zimmerer, M. Kirm, SHEN Ding-Zhong
Chin. Phys. Lett. 2001, 18 (6): 829-830 .  
Abstract   PDF(pc) (278KB) ( 429 )
The emission and excitation spectra of cubic PbF2:Gd were measured. Compared with pure crystals, the emissions from Gd3+ were observed upon cation exciton excitation in lattices, while the emission from intrinsic self-trapped exciton was quenched. It indicates the energy transfer from exciton to the 4f state of Gd3+.
Compound Derived from Anthracene and Pyrazol for a Light-Emitting Diode
WANG Ming-Liang, ZHANG Jun-Xiang, LIU Ju-Zheng XU Chun-Xiang
Chin. Phys. Lett. 2001, 18 (6): 831-833 .  
Abstract   PDF(pc) (315KB) ( 440 )
A new compound, 5-(9-anthryl)-1,3-diphenyl-1H-pyrazol (ADPP), with an anthryl moiety as an emissive group and a diphenylpyrazoline moiety as a charge transporting group is designed and synthesized. The absorption, photoluminescence, electroluminescence, and electrochemistry are measured. Absorption of ADPP is similar to that of anthracene in the vibonic structure but shows slight red shifts because anthryl moiety twists strongly with respect to pyrazol moiety although delocalization still exists between the two moieties. Light emitting devices fabricated with ADPP show a bright blue emission at 470 nm. The turn-on voltage is 12 V and the light emission follows the current closely, indicating an efficient charge injection and transport for both electrons and holes.
A Non-invasive Method of Tracing Spiral Tips
WANG Kai, MAO Xiao-Ming, OU-YANG Qi
Chin. Phys. Lett. 2001, 18 (6): 834-836 .  
Abstract   PDF(pc) (864KB) ( 357 )
A new method is developed to trace the tip of spiral waves in an excitable medium. The information of a spiral tip movement is obtained from only six probes. This method can trace the tip of a simple rotating spiral as well as a complex spiral tip movement. More importantly, it can be used to distinguish between a spiral and a target wave. The method is checked with data by experiments and numerical simulations, and found to be successful.
The Fastest Rotating Pulsar: a Strange Star?
XU Ren-Xin, XU Xuan-Bin, WU Xin-Ji
Chin. Phys. Lett. 2001, 18 (6): 837-840 .  
Abstract   PDF(pc) (337KB) ( 401 )
According to the observational limits on the radius and mass, the fastest rotating pulsar (PSR 1937+21) is probably a strange star, or at least some neutron star equations of state should be ruled out, if we suggest that a dipole magnetic field is relevant to its radio emission. We presume that the millisecond pulsar is a trange star with much low mass, small radius and weak magnetic moment.
Infrared Characters of Host Galaxies with H2O Megamaser
YU Zhi-Yao
Chin. Phys. Lett. 2001, 18 (6): 841-843 .  
Abstract   PDF(pc) (246KB) ( 346 )
Infrared characters of all the host galaxies with H2O megamaser have been studied. The most striking feature is anticorrelation of S(60)/S(100) versus S(12)/S(25), and S(25)/S(60) versus S(12)/S(25). The anticorrelation in flux density ratio can been explained by coexistence of large and very small dust particles. The latter, which are heated by absorption of single photon, are believed to be resposible for bulk of 12 μm radiation. If the photon energy of the host galaxy is small, this implies large S(12)/S(25) and small S(60)/S(100). However, when photon energy density becomes larger, the infrared spectrum will peak at wavelengths ≤ 100μm and enhance emission at 25μm. As a consequence small S(12)/S(25) and large S(60)/S(100) are observed.
43 articles