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Volume 20 Issue 2
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Original Articles
Integrable Bogoliubov Transform and Integrable Model
Chin. Phys. Lett. 2003, 20 (2): 177-179 .  
Abstract   PDF(pc) (195KB) ( 342 )
By defining Bogoliubov transform as a function of parameters, the integrability of the Bogoliubov transform in parameter space is investigated. It is shown that integrable Bogoliubov transform is closely related to the known integrable model. The relation between the integrable Bogoliubov transform and geometric phase of vacuum induced by the Bogoliubov transform is also discussed.
Simple Analytic Expression with High Precision for the Barker-Henderson Diameter
SUN Jiu-Xun
Chin. Phys. Lett. 2003, 20 (2): 180-182 .  
Abstract   PDF(pc) (305KB) ( 425 )
A fitting procedure is proposed to establish two analytic approximate expressions for the complicated Barker-Henderson (BH) diameter with Lennard-Jones potential in two temperature ranges. Considering that the differentiation is a process enlarging the errors and the integration decreasing the errors and that the derivative of BH diameter is important in the calculation of internal energy, we propose to fit the derivative directly, instead of usually fitting the original function and subsequently deriving its derivative. The simplicity and precision of two expressions developed are superior to the extensively used expressions in literature. The one with following form only has an average fitting 0.0063% in the reduced temperature range (0.4 ≤ kT/ε ≤ 15), and can be extrapolated to a wider temperature range (0.4 ≤ kT/ε ≤ 50) with an average error 0.13%, which is d /σ = 1.1755 + 0.02878lnτ -0.2072τ1/4+ 0.00463τ3/4.

A Controlled Quantum Key Distribution Scheme with Three-Particle Entanglement
HAN Chao, XUE Peng, GUO Guang-Can
Chin. Phys. Lett. 2003, 20 (2): 183-185 .  
Abstract   PDF(pc) (186KB) ( 463 )
We present a controlled quantum key distribution protocol with a certain entangled state to solve a special cryptographic task. Also, we provide a proof of security of this protocol by generalizing the proof of the modified Lo-Chau Einstein-Podolsky-Rosen scheme.
Novel Formalism for Energy Eigenvalue Problem with Hamiltonian Expressible as Function of Angular Momentum
WU Ying, LUO Ya-Jun, YANG Xiao-Xue
Chin. Phys. Lett. 2003, 20 (2): 186-188 .  
Abstract   PDF(pc) (195KB) ( 576 )
We present a novel formalism for energy eigenvalue problems when the corresponding Hamiltonians can be expressed as a function of an angular momentum. The problems are turned into finding operator polynomials by solving a c-number differential equation. Simple and efficient computer-aided analytical and numerical methods may be developed based on the formalism.
Coherent Superposition States of Atoms and Molecules in a Bose-Einstein Condensate with Exactly Balanced Photo-Associations and Photo-Dissociations
YANG Xiao-Xue, WU Ying,
Chin. Phys. Lett. 2003, 20 (2): 189-191 .  
Abstract   PDF(pc) (193KB) ( 353 )
We show that there exist a series of coherent superposition states of atoms and molecules in a dilute Bose-Einstein condensate with exactly balanced photo-associations and photo-dissociations, and their analytical expressions are explicitly given. They also correspond to the coherent superposition states of two kinds of photons in optical second harmonic generation processes, which shows exactly balanced down- and up-conversions.

A New Exactly Solvable Inflation Model and Its Power Spectrum
LI Xin-Zhou, LIU Dao-Jun, HAO Jian-Gang
Chin. Phys. Lett. 2003, 20 (2): 192-194 .  
Abstract   PDF(pc) (197KB) ( 366 )
We present a new exactly solvable inflation model in which inflation can stop automatically, and in the approximately de Sitter limit, we give its power spectrum which can be tested in the future observations of cosmic microwave background anisotropy.
Extending the First-Order Post-Newtonian Scheme in Multiple Systems to the Second-Order Contributions to Light Propagation
XU Chong-Ming, WU Xue-Jun
Chin. Phys. Lett. 2003, 20 (2): 195-198 .  
Abstract   PDF(pc) (219KB) ( 530 )
We extend the first-order post-Newtonian scheme in multiple systems presented by Damour-Soffel-Xu to the second-order contribution to light propagation without changing the virtue of the scheme on the linear partial differential equations of the potential and vector potential. The spatial components of the metric are extended to the second-order level both in a global coordinates (qij/c4) and a local coordinates (Qab/c4). The equations of qij(or Qab) are obtained from the field equations. The relationship between qij and Qab are also presented. In the special case of the solar system (isotropic condition is applied (qij
= δijq)), we obtain the solution of q. Finally, a further extension of the second-order contributions in the parametrized post-Newtonian formalism is discussed.

Impulsive Synchronization of Discrete Chaotic Systems
ZHENG Yong-Ai, NIAN Yi-Bei, LIU Zeng-Rong
Chin. Phys. Lett. 2003, 20 (2): 199-201 .  
Abstract   PDF(pc) (291KB) ( 465 )
Impulsive synchronization of two chaotic maps is reformulated as impulsive control of the synchronization error system. We then present a theorem on the asymptotic synchronization of two chaotic maps by using synchronization impulses with varying impulsive intervals. As an example and application of the theorem, we derives some sufficient conditions for the synchronization of two chaotic Lozi maps via impulsive control. The effectiveness of this approach has been demonstrated with chaotic Lozi map.
Frequency Resonance in Stochastic Systems
QIAN Min, ZHANG Xue-Juan
Chin. Phys. Lett. 2003, 20 (2): 202-205 .  
Abstract   PDF(pc) (431KB) ( 407 )
The phenomenon of frequency resonance, which is usually related to deterministic systems, is investigated in stochastic systems. We show that for those autonomous systems driven only by white noise, if the output power spectrum exhibits a nonzero peak frequency, then applying a periodic signal just on this noise-induced central frequency can also induce a resonance phenomenon, which we call the frequency stochastic resonance. The effect of such a resonance in a coupled stochastic system is shown to be much better than that in a single-oscillator system.

Control of Unstable Flows
LIU Zeng-Rong, MAO Jian-Min
Chin. Phys. Lett. 2003, 20 (2): 206-208 .  
Abstract   PDF(pc) (276KB) ( 370 )
Without introducing a discrete model, unstable continuous flows in a neighbourhood of an unstable stationary point can be stabilized. The linear part of the vector field of disturbing the flow can be managed to become the state variable multiplied by a negative constant. The nonlinear part of the vector field keeps to be unchanged, therefore flows far away from the stationary point are almost unaffected by the disturbance. The control method is easy to be used, even for practical problems for which a priori analytical knowledge of system dynamics is unavailable.
Projection Operator and Propagator for an Arbitrary Half-Integral Spin
HUANG Shi-Zhong, , RUAN Tu-Nan, WU Ning, ZHENG Zhi-Peng,
Chin. Phys. Lett. 2003, 20 (2): 209-212 .  
Abstract   PDF(pc) (217KB) ( 728 )
Based on the solution to Bargmann-Wigner equation for an arbitrary half-integral spin, a direct derivation of the projection operator and propagator for an arbitrary half-integral spin is presented. The projection operator constructed by Behrends and Fronsdal is confirmed and simplified. The commutation rules and a general expression for the Feynman propagator for a free particle with arbitrary half-integral spin are deduced. Explicit expressions for the propagators for spins 3/2, 5/2 and 7/2 are provided.
Chiral Effective Lagrangian Description of Nuclear Matter with In-Medium Pion Effect
ZHANG Xiao-Bing, NING Ping-Zhi
Chin. Phys. Lett. 2003, 20 (2): 213-215 .  
Abstract   PDF(pc) (182KB) ( 346 )
By including the in-medium pion effect, we study the description of nuclear matter based on the non-linear chiral Lagrangian at the leading order. An in-medium effective Lagrangian is constructed without the necessity of introducing the phenomenological scalar-isoscalar field. At the mean-field level, the in-medium Lagrangian description of nuclear matter is shown to be compatible with that obtained from the Brown-Rho scaled model.

Experimental Evidence of the Rapid Increacing Neutron Yields in Proton-Induced Reaction on Heavy Target Across 0.6-1GeV
ZHANG Li, ZHENG Ji-Wen, ZHAO Jin-Hua, HU Qing-Yuan, WANG Ji-Cheng
Chin. Phys. Lett. 2003, 20 (2): 216-219 .  
Abstract   PDF(pc) (319KB) ( 410 )
The independent yield distribution of the Hg isotopes, measured for the reaction of 600 MeV 18O projectile with a nat.Pb target, is converted to 18O+208Pb system and is compared with an Hg-isotope distribution from the spallation reaction of 1 A GeV 208Pb on proton. The comparison shows the differences between the two distributions on the production cross sections, isotope-distribution widths as well as their shapes. A great increase of the neutron-deficient Hg isotope yield with increase of bombarding energies of protons from 600 MeV to 1 GeV is derived. This fact results in an experimental evidence for rapid increasing neutron yields with rising proton bombarding energy from 0.6 GeV to 1 GeV.

In-Line Phase-Contrast Imaging Using Partially Coherent Hard X-Ray
YU Hong, ZHU Pin-Pin, HAN Shen-Sheng, LUO Zhen-Lin, GAO Chen
Chin. Phys. Lett. 2003, 20 (2): 220-222 .  
Abstract   PDF(pc) (199KB) ( 429 )
An experimental study of in-line hard x-ray phase-contrast imaging had been performed, using the polychromatic output of an x-ray tube. The results are in good agreement with partially coherent theory of hard x-ray phase-contrast imaging. The new technique provides the advantage to obtain the radiographs of large samples in an acceptable exposure time, which is very important to clinical applications.

Quantum Nonlocality in Atom-Field Coupling System via Degenerate Raman Processes with Cavity Damping
LI Gao-Xiang, HUANG Guang-Ming, GAO Yan-Jun
Chin. Phys. Lett. 2003, 20 (2): 223-226 .  
Abstract   PDF(pc) (278KB) ( 614 )
The property of quantum nonlocality in the atom-field coupling system via degenerate Raman processes with cavity damping is investigated. It is found that if the cavity dissipation is very weak, the atom-field state can exhibit quantum nonlocality periodically. The rapidity of the loss of the quantum nonlocality depends on the amplitude of the initial coherent state and the cavity damping constant. The stronger the field is and the larger the damping constant could be, the more rapidly the nonlocality decreases.
A Simple Scheme for Directly Measuring the Wigner Functions of Cavity Fields
ZHANG Zhi-Ming
Chin. Phys. Lett. 2003, 20 (2): 227-229 .  
Abstract   PDF(pc) (183KB) ( 562 )
We propose a scheme for directly measuring the Wigner functions of cavity fields. The scheme is based on the Raman interaction between atoms and cavity fields. We find a simple and direct relation between the Wigner function and the atomic population difference. By suitably choosing the interaction time, we find that the Wigner function is just two times of the atomic population difference. Thus, one can obtain the Wigner function by measuring the atomic populations and calculating the population difference.
Tuning Characteristics of Frequency Difference for Zeeman-Birefringence He-Ne Dual Frequency Laser
XIAO Yan, ZHANG Shu-Lian, LI Yan, ZHU Jun
Chin. Phys. Lett. 2003, 20 (2): 230-233 .  
Abstract   PDF(pc) (432KB) ( 570 )
Characteristics of frequency difference tuning of Zeeman-birefringence He-Ne dual frequency lasers (ZBDFLs) are explored. We design an automatic system of tuning cavity and power detection, which can tune the laser cavity and record the tuning curves of light power and frequency difference simultaneously. A synthetical phenomenon by Zeeman effect, mode pulling effect and birefringence effect is verified to exist in ZBDFLs. By analysing the tuning behaviour, this synthetical phenomenon is discovered and qualitatively explained for the first time.
Experimental and Numerical Analysis of a Two-Order Cascaded Raman Fiber Laser
CHI Rong-Hua, LU Ke-Cheng, LI Yi-Gang, SU Hong-Xin, DONG Xiao-Yi
Chin. Phys. Lett. 2003, 20 (2): 234-236 .  
Abstract   PDF(pc) (389KB) ( 470 )
A two-order cascaded Raman fiber laser based on GeO2-SiO2 fiber and fiber Bragg gratings is fabricated. Output power 309 mW of the second Stokes light around 1176.2 nm is obtained with a slope efficiency of 45.3%. The experimental results agree well with the simulation results obtained by using the double-pass model.
Influence of Channel Power and Pumping Configuration on the Gain Profile of Distributed Raman Fiber Amplifier
XIN Xiang-Jun, YU Chong-Xiu, ZHANG Ru, REN Jian-Hua, LI An-Jian, WU Qiang, XIN Yu, WANG Chuan-Lin, ZHENG Wen-Xiao, RUAN Shuang-Chen, DU Ge-Guo, XIN Gang, YANG Xiao-Qiang
Chin. Phys. Lett. 2003, 20 (2): 237-239 .  
Abstract   PDF(pc) (481KB) ( 530 )
The influence of channel power and pumping configuration on the gain profile of a distributed Raman fiber amplifier has been experimentally measured. The experimental results show that the influence is significant and should be considered during the gain flatness optimization of the distributed Raman fiber amplifier.

Photo-Induced Magnetic Anisotropy of Polymer Film Containing Azobenzene Organic Free Radical Group
XU Ze-Da, ZHANG Yong, CHEN Xiao-Fang, FAN Xing-He, WAN Xin-Hua, ZHOU Qi-Feng
Chin. Phys. Lett. 2003, 20 (2): 240-242 .  
Abstract   PDF(pc) (354KB) ( 407 )
The forward degenerate four-wave mixing geometry was employed to induce microstructure in an organic free radical azobenzene polymer film. Before irradiated with Ar+ laser beams (λ =514.5 nm), the azobenzene organic free radical polymer exhibits magnetic isotropic measured by superconducting quantum interference device. After photo-induced microstructure, the polymer film becomes magnetic anisotropy. When the applied magnetic field H = 50 Gauss, the magnetization along the normal direction of the polymer film is Mz = 5.5 x 10-5 emu/g, which is larger than Mx = 4.1 x 10-5 emu/g in the direction parallel to the polymer film.
Determination of Nonlinear Optical Coefficients of KBe2BO3F2 Crystals
WANG Gui-Ling, ZHANG Cheng-Qian, CHEN Chuang-Tian, XU Zu-Yan, WANG Ji-Yang
Chin. Phys. Lett. 2003, 20 (2): 243-245 .  
Abstract   PDF(pc) (298KB) ( 425 )
Considering that KBe2BO3F2 (KBBF) is an outstanding deep ultraviolet crystal which can generate the shortest wavelengths in second harmonic generation and sum-frequency generation, we report the determination of the nonlinear optical coefficients of the KBBF crystal. The d11 coefficient was determined to be 0.49 pm/V by the Maker fringes method at the wavelength 1064 nm, which is in agreement well with the theoretical value.
Dromion Excitations in Self-Defocusing Optical Media
CUI Wei-Na, SUN Chun-Liu, HUANG Guo-Xiang
Chin. Phys. Lett. 2003, 20 (2): 246-249 .  
Abstract   PDF(pc) (439KB) ( 311 )
We investigate the nonlinear dynamics of multi-dimensional optical pulses propagating in an isotropic self-defocusing medium. Using a method of multiple-scales we show that the nonlinear evolution of the pulses is governed by Davey-Stewartson equations. Dromion-like nonlinear localized structures (high-dimensional optial solitons) excited from a continuous wave background and decaying in all spatial directions are predicted through the interaction between a wave-packet superposed by short-wavelength components and a long-wavelength mean field generated by an optical rectification.
Wavelength Selection of Patterns in a Vibrated Granular Layer
SHI Xiao-Dong, JIN Guo-Jun, MA Yu-Qiang
Chin. Phys. Lett. 2003, 20 (2): 250-252 .  
Abstract   PDF(pc) (339KB) ( 470 )
We present a numerical study on the pattern formation in a two-dimensional vibrated granular layer by a molecular dynamics algorithm. Through analysing the granular density distribution, we can explore the inner movement process of particles. It is confirmed that there are a dispersive regime and a saturation regime for frequency dependence, between which a critical frequency exists. It is found that there is another saturation regime for thickness dependence. The wavelength increases with increasing layer thickness, but there is a critical thickness after which the wavelength is unchanged.

Pattern Structure and Properties of Invasion Percolation in Porous Media
TIAN Ju-Ping, YAO Kai-Lun,
Chin. Phys. Lett. 2003, 20 (2): 253-255 .  
Abstract   PDF(pc) (298KB) ( 500 )
The percolation clusters with varying occupy probability are constructed. Invasion percolation (IP) in percolation cluster is investigated by means of IP algorithm without trapping. The pattern constructions of IP in percolation clusters are obviously different from that of viscous fingering (VF) in percolation clusters. The fractal dimension Df of IP increases with the increase of the percolation probability P. The geometry and the topology of the porous media have strong effects on the pattern structure of IP. For large M (the node numbers occupied by the injected fluid), the rescaled value is Rg/M1/Df, which asymptotically approaches a constant value, and Rg is the gyration radius of IP cluster. Moreover, the chemical dimension Dl and the shortest path exponent dmin are obtained.
Rosseland Mean Opacity of a High-Z Mixture Plasma
YANG Jia-Min, XU Yan, DING Yao-Nan, DING Yong-Kun, JIANG Shao-En, ZHENG Zhi-Jian, MIAO Wen-Yong
Chin. Phys. Lett. 2003, 20 (2): 256-258 .  
Abstract   PDF(pc) (346KB) ( 446 )
An eight-beam 0.351-μm laser with pulse duration of about 1.0ns and energy of 260 J per beam was injected into a cylindrical cavity to generate intense x-ray radiation on the Shengguang II high power laser facility. A mixture foil of gold and gadolinium and a gold foil were attached on portion of a diagnostic hole in the mid-plane of the cavity and ablated by the intense x-ray radiation. The propagating time of the radiation heat wave in the mixture and the pure gold foil were measured with soft-x-ray spectrometer and by adopting space- and time-resolved measurement technology, respectively. The results show that the mixture of gold and gadolinium has higher Rosseland mean opacity than the gold sample in our experiment.
Equilibrium Properties of Hard Sphere Fluid in Confined Geometries: A Density Functional Theory Study
LI Wei-Hua, ZHU Wei-Zhao, MA Hong-Ru
Chin. Phys. Lett. 2003, 20 (2): 259-262 .  
Abstract   PDF(pc) (439KB) ( 446 )
One component hard-sphere fluid confined in two planar hard walls is studied by means of density functional theory with Rosenfeld functional and molecular dynamics simulation. The validity of the Rosenfeld functional is examined. Chemical potential, grand potential and free energy as functions of the wall separation are obtained.
Monte Carlo Simulation of Growth of Thin Film Prepared by Pulsed Laser
ZHANG Duan-Ming, GUAN Li, YU Bo-Ming, LI Zhi-Hua,
Chin. Phys. Lett. 2003, 20 (2): 263-266 .  
Abstract   PDF(pc) (349KB) ( 328 )
We use the Monte-Carlo simulation method to perform the early growth stage of thin film prepared by pulsed laser deposition. We focus on the number of point defects on the substrate surface varying with the energy density of laser and substrate temperature. The results show that the laser energy and the substrate temperature strongly affect the morphology and size of the growth islands and the deposition rate of thin film. Our results are in good agreement with the related experimental results.
Some Invariants of the Silk Quasi-lattices
LUAN Chang-Fu
Chin. Phys. Lett. 2003, 20 (2): 267-268 .  
Abstract   PDF(pc) (170KB) ( 509 )
Based on the spectral structure of a class of one-dimensional three-tile quasiperiodic lattice models that are established in 1990 for which the (concurrent) substitution rules are S → M, M → L, and L → LS, with S, M, and L representing the short, medium, and long tiles of atomic spacings, respectively, we suggest that S is E (egg), M is SI (silkworm) and L is M (moth), for easily understanding. By the use of the number theory, we have rigorously proven the existence of the limit θ = limn → ∞ Sn-1/Sn ≈ 0.68232789 ..., where Sn is the number of elements contained in the n-th silk sequence. Some relations among the sequences En, SIn, and Mn are found, where the subscript n means the n-th generation.

Self-Diffusion Mechanisms of Adatom on Al (001), (011) and (111) Surfaces
SUN Yu-Jie, LI Jia-Ming,
Chin. Phys. Lett. 2003, 20 (2): 269-272 .  
Abstract   PDF(pc) (327KB) ( 432 )
Using the first-principle molecular dynamical calculations, we have studied the adatom self-diffusion mechanisms on fcc Al (001), (011) and (111) surfaces. On each surface, there are several mechanisms, among which there is one favour mechanism with the minimum barrier energy. The atomic exchange mechanism along the [100] direction on the (001) surface, the long bridge hopping mechanism along the [ī10] direction on the (011) surface, and the bridge hopping mechanism along the [112] direction on the (111) surface are the favour mechanisms. The activation energy profiles for various self-diffusion mechanisms are studied in details.
Microstructural and Electrical Properties of ZrO2 Thin Films Prepared on Silicon on Insulator with Thin Top Silicon
ZHANG Ning-Lin, SONG Zhi-Tang, SHEN Qin-Wo, LIN Cheng-Lu
Chin. Phys. Lett. 2003, 20 (2): 273-276 .  
Abstract   PDF(pc) (309KB) ( 600 )
Amorphous zirconia thin films were deposited directly on silicon-on-insulator (SOI) substrates with thin top silicon by ultra-high vacuum electron beam evaporation. Spreading resistance profile and scanning transmission-electron microscopy (TEM) were used to detect the interface quality and microstructure, revealing that the interface between the zirconium oxide films and top silicon was abrupt and clear. The films kept to be amorphous up to the rapid thermal temperature of 700°C for 300 s, but arriving at 700°C an unknown interfacial product appeared, which was probably ZrSixOy. High frequency capacitance-voltage (C-V) characteristics at 1 MHz performed on metal-oxide-SOI structure revealed that this interfacial product exhibited good electrical properties of zirconia thin films. When the annealing temperature increased from 600°C to 700°C, flat voltage VFB changed from -2.451 to -1.741 eV, showing the improvement in the quality of the films. The cumulative region capacitance decreased from 3.058 x 10-11F to 3.012 x 10-11F, indicating the increase of equivalent oxide thickness, which is in agreement with the result of high-resolution cross-sectional TEM.

Direct Current Hopping Conductivity in One-Dimensional Nanometer Systems
SONG Yi-Pu, XU Hui, LUO Feng
Chin. Phys. Lett. 2003, 20 (2): 277-280 .  
Abstract   PDF(pc) (330KB) ( 297 )
A one-dimensional random nanocrystalline chain model is established. A dc electron-phonon-field conductance model of electron tunneling transfer is set up, and a new dc conductance formula in one-dimensional nanometer systems is derived. By calculating the dc conductivity, the relationship among the electric field, temperature and conductivity is analysed, and the effect of the crystalline grain size and the distortion of interfacial atoms on the dc conductance is discussed. The result shows that the nanometer system appears the characteristic of negative differential dependence of resistance and temperature at low temperature. The dc conductivity of nanometer systems varies with the change of electric field and trends to rise as the crystalline grain size increases and to decrease as the distorted degree of interfacial atoms increases.
Magnetic Exchange-Coupled Sm(Co,R)/Cr (R = Al, Si, Ti, Nb, Cu) Series Films for Ultrahigh-Density Longitudinal Recording Media
WANG Xiang, LI Zuo-Yi, LI Zhen, CAI Chang-Bo, HUANG Zhi-Xin, LIAO Hong-Wei, WANG Hao-Min, LIN Geng-Qi
Chin. Phys. Lett. 2003, 20 (2): 281-283 .  
Abstract   PDF(pc) (302KB) ( 453 )
SmCoR (R=Al,Si,Ti,Nb,Cu)/Cr series films were fabricated as one kind of promising materials for the ultrahigh density longitudinal magnetic recording media. The Sm(Co,Al,Si)/Cr thin films with coercivity up to 2.36 kOe, squareness ratio S near 0.94 and coercive squareness ratio S* about 0.9 were obtained. The Cr interlayer caused magnetic decoupling in Sm(Co,Al,Si)/Cr/Sm(Co,Al,Si) thin films. High coercivity of 3400--3840\,Oe and extremely fine grain size of 5-8 nm for the magnetic layer were examined. Using different substrate bias among the Sm(Co,Al,Si)(deposited with substrate bias of -150 V)/Sm(Co,Al,Si)(deposited with no substrate bias)/Sm(Co,Al,Si)(deposited with substrate bias of -150 V), the multilayer exhibited high coercivity of 2960 Oe and S* of 0.96. Sm(Co,Al,Si)/Sm(Co,Ti,Cu)/Sm(Co,Nb,Cu) trilayer improved matching between the magnetic layer and the Cr underlayer, and led to increasing in-plane anisotropy, high coercivity of 3280 Oe and S* of 0.92. Lattice matching of SmCoR {1121} and Cr {110}, etc. were found under various conditions. The microstructures of these four kinds of medium were also examined. The results suggest that it is possible to produce Sm (Co,Al,Si,Ti,Nb,Cu) multi-layer media with the combined magnetic properties required for the ultrahigh density magnetic recording.
Incompatibility of d-Wave Pairing and Ferromagnetism in a Uniform System
LIU Su, SHEN Rui, ZHENG Zhi-Ming, XING Ding-Yu
Chin. Phys. Lett. 2003, 20 (2): 284-286 .  
Abstract   PDF(pc) (252KB) ( 392 )
We discuss the possibility of coexistence of d-wave superconductivity and ferromagnetism in a two-dimensional model on the assumption that the same electrons are responsible for both the pairing order and the ferromagnetic order. The calculated results indicate that the coexistence is difficult to be realized in a uniform system.
The Green Function Approach to the Two-Dimensional t-J model
SONG Bo, , WANG Yu-Peng
Chin. Phys. Lett. 2003, 20 (2): 287-289 .  
Abstract   PDF(pc) (216KB) ( 411 )
We investigate the two-dimensional t-J model by the Green function approach with the Hubbard operator. The phase diagram, including the Neel temperature and the superconducting transition temperature simultaneously, is derived. The results are consistent with experiments of cuprate compounds.
Grain-Size Effect on the Dielectric Properties of Bi0.5Na0.5TiO3
ZHAO Ming-Lei, WANG Chun-Lei, ZHONG Wei-Lie, WANG Jin-Feng, LI Zheng-Fa
Chin. Phys. Lett. 2003, 20 (2): 290-292 .  
Abstract   PDF(pc) (370KB) ( 780 )
We prepared bismuth sodium titanate (Bi0.5Na0.5TiO3) ultrafine powders by the sol-gel method. The dielectric properties of the pressed pellets and fired ceramics with different grain sizes as a function of temperature at various frequencies were studied. With the decrease of grain size, the dielectric anomaly around 200°C increases, while the dielectric thermal hysteresis decreases. All the samples with grain sizes larger than 100 nm show dielectric peaks at temperature of about 350°C. The very little change in Tm observed down to the critical size indicates that Bi0.5Na0.5TiO3 is an order-disorder system above 200°C. In addition, the dielectric peak becomes lower with the decrease of grain size and the ferroelectric critical size of Bi0.5Na0.5TiO3 was eventually determined to be about 100 nm according to the disappearance of dielectric peak.
Mechanism of Low Threshold Lasing of Dye Solution Embedding in Nanoparticle Fractal Aggregates
HE Yong-Jun, HUANG Zhen-Li, WANG He-Zhou
Chin. Phys. Lett. 2003, 20 (2): 293-295 .  
Abstract   PDF(pc) (299KB) ( 420 )
We study the single-photon and two-photon induced emission properties of dye solution embedded with nanoparticle fractal aggregates. The spectral and temporal experimental results show that the lasing threshold of single-photon absorption of dye solution embedded with TiO2 nanoparticle fractal aggregates is significantly reduced compared to that of a neat dye solution; while that of two-photon absorption does not. These experimental results imply that this low threshold single-photon absorption lasing mainly results from the mechanism of random walking, instead of Anderson localization, unless something about two-photon induced emission is unknown.
Utraviolet Lasing from ZnO Single Crystal at Room Temperature
XIANG Wang-Hua, ZHANG Gui-Zhong, SUN Yi, WANG Gang, John. B. Ketterson
Chin. Phys. Lett. 2003, 20 (2): 296-297 .  
Abstract   PDF(pc) (301KB) ( 487 )
We experimentally studied ultraviolet photoluminescence (PL) from ZnO (0001) single crystal at room temperature. The PL spectra taken from the sample edge show spectral width narrowing; lifetime shortening (100 ps) and super linear intensity increase with pumping power, while the PL spectra taken from the sample surface only show broad spontaneous emission with a much longer lifetime ( > 5 ns). These findings suggest that stimulated emission and lasing were only achieved at edges of the ZnO single crystal. Scanning-electron-microscopic images show a smooth sample surface morphology and a rougher morphology at the single crystal edge. Electron-hole plasma enhancement of gain may be attributed to the lasing effect observed from the sample edge.
Electroluminescence and Photoluminescence from Scored Si-Rich SiO2 Film/p-Si Structure
RAN Guang-Zhao, SUN Yong-Ke, CHEN Yuan, DAI Lun, CUI Xiao-Ming, ZHANG Bo-Rui, QIAO Yong-Ping, MA Zhen-Chang, ZONG Wan-Hua, QIN Guo-Gang,
Chin. Phys. Lett. 2003, 20 (2): 298-300 .  
Abstract   PDF(pc) (446KB) ( 460 )
Electroluminescence (EL) is observed from the Au/Si-rich SiO2 film/p-Si diodes, in which the Si-rich SiO2 films are scored purposely by a diamond tip. The EL intensity of the scored diode annealed at 800°C is about 6 times of that of the unscored counterpart. The EL spectrum of the unscored diode could be decomposed into two Gaussian luminescence bands with peaks at about 1.83 and 2.23 eV, while for the EL spectrum of the scored diode, an additional Gaussian band at about 3.0 eV appears, and the 1.83-eV peak increases significantly in intensity. The photoluminescence (PL) spectrum of an unscored Si-rich SiO2 film has only one band peaking at about 1.48 eV, whereas the PL spectrum of the scored one has two bands at about 1.48 and 1.97 eV. We consider that the high-density defect regions produced by the scoring provide new luminescence centers and become some types of nonradiative centers in the Si oxide layer, which thus result in changes of the EL and PL spectra.
Vacuum Electron-Beam Evaporation of Fe Nanocrystals on Si3N4 Buffer Layer for Carbon Nanotube Growth
WAN Qing, WANG Tai-Hong, LIN Cheng-Lu
Chin. Phys. Lett. 2003, 20 (2): 301-303 .  
Abstract   PDF(pc) (295KB) ( 620 )
Vacuum electron-beam evaporated iron nanocrystal is used for the growth of carbon nanotubes. Atomic force microscopy and Raman scattering studies reveal the formation of beta-iron silicide islands on bare silicon substrate after annealing at 700°C in N2 ambient. In order to eliminate the influence of iron-silicon interaction, Si3N4 buffer layer with the thickness of 80 nm is used. This technical route prevents effectively the formation of iron silicide and improves the quality of the iron nanocrystals. Using these iron nanocrystals with high density (about 7 x 1010/cm2) as catalyst, high-density multiwall carbon nanotubes are synthesized on Si3N4/Si substrate.
Cluster Evolution in Undercooled Melt and Solidification of Undercooled Ge-based Alloy Melts Induced by Extrinsic Clusters
WANG Xu, JING Qin, WANG Wen-Kui,
Chin. Phys. Lett. 2003, 20 (2): 304-307 .  
Abstract   PDF(pc) (385KB) ( 474 )
The structure or short-range order of clusters in undercooled metallic melts is influenced, to some extent, by the interfacial free energy between the cluster and the melt. Analyses of the effects of interfacial energy on the cluster structure based on the Gibbs equation show a possibility that atoms in the clusters tend to be packed more loosely with the increasing cluster size (or the undercooling). Nucleation may occur, following these analyses, when clusters reach a definite size and atoms in the clusters relax to some extent to form the crystal structure. Indirect support to this viewpoint is provided by the present results of cluster-induced nucleation experiments on undercooled Ge73.7Ni26.3 alloy melts.

Direct, etching of GaAs Crystal Excited by a Vacuum Ultraviolet Lamp
HAN Zheng-Fu, LIAO Yan-Lin, ZHOU Hong-Jun, JIANG Zuo-Hong, ZHANG Guo-Bin, CAO Zhuo-Liang,
Chin. Phys. Lett. 2003, 20 (2): 308-310 .  
Abstract   PDF(pc) (284KB) ( 467 )
A successful direct, etching system excited by a vacuum ultraviolet hollow cathode lamp is reported. The result shows that the facility can transfer a mesh pattern exactly and directly to n-type GaAs wafer, which is the same as that direct etched by synchrotron radiation.

Self-Aligned InP/InGaAs Single Heterojunction Bipolar Transistor with Novel Micro-airbridge Structure and Quasi-coplanar Contacts
LI Xian-Jie, CAI Dao-Min, ZENG Qing-Ming, LIU Shi-Yong, LIANG Chun-Guang
Chin. Phys. Lett. 2003, 20 (2): 311-313 .  
Abstract   PDF(pc) (306KB) ( 483 )
The fabrication and performance of a self-aligned InP/InGaAs single heterojunction bipolar transistor (SHBT) with a novel micro-airbridge structure and co-planar-contacts are described. The reported structure is based on anisotropy wet, etching of InP and selective wet, etching between InP and InGaAs. The device with a 1.5 x 5μm2 emitter demonstrats a current gain of 30 at collector current Ic = 10 mA and extrapolates the current-gain cutoff frequency Ft of 53 GHz and the maximum oscillation frequency Fmax of 72 GHz. Compared to the one using the conventional structure, the maximum oscillation frequency of the device with micro-airbridge is dramatically improved from 45 GHz to 72 GHz. This result reveals that the extrinsic capacitance of small size SHBT can be greatly reduced.

A Note on the Discovery of Absorption Features in 1E 1207.4-5209
XU Ren-Xin, WANG Hong-Guang, QIAO Guo-Jun
Chin. Phys. Lett. 2003, 20 (2): 314-316 .  
Abstract   PDF(pc) (252KB) ( 380 )
Sanwal et al. [Astrophys. J. 574 (2002) L61] supposed that it is very difficult to interpret the absorption features in terms of cyclotron lines. However, we would like to address here that the possibility of the absorption being cyclotron resonance cannot be ruled out. We propose that the isolate neutron star, 1E 1207.4-5209 in the center of supernova remnant PKS 1209-51/52, has a debris disk and is in a propeller phase, with an accretion rate ~ 6 x 10-11M/year. In this scenario, 1E 1207.4-5209 could also be a bare strange star.

43 articles