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Volume 18 Issue 9
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Original Articles
Cooperation in the Mixed Population Minority Game with Imitation
QUAN Hong-Jun, WANG Bing-Hong, HUI Pak-Ming, LUO Xiao-Shu
Chin. Phys. Lett. 2001, 18 (9): 1156-1158 .  
Abstract   PDF(pc) (321KB) ( 382 )
After studying the effects of imitation on the mixed population of adaptive agents with different memories competing in a minority game, we have found that when pure population lies in a crowded regime, the introduction of imitation can considerably improve cooperation among agents in a money market.
Telebroadcasting of a Cat-Like State via Local Operations
WEN Hai-Dan, LI Chuan-Feng, GUO Guang-Can
Chin. Phys. Lett. 2001, 18 (9): 1159-1162 .  
Abstract   PDF(pc) (339KB) ( 419 )
The quantum telebroadcasting of a cat-like state in combination with the quantum teleportation and the local copying of entanglement is presented. This gives a general way of distributing entanglement among distant parties. All of the operations of our scenario is local and within the reach of current technology.
Casimir Energies on a Twisted Two-Torus
CHENG Hong-Bo, LI Xin-Zhou
Chin. Phys. Lett. 2001, 18 (9): 1163-1166 .  
Abstract   PDF(pc) (277KB) ( 407 )
We consider a twisted massless multiplet on a two-torus, one side with the normal boundary and the other with twisted boundary. The Casimir energy is calculated and regularized by means of the Epstein-Hurwitz type zeta function introduced by Elizalde. The resulted dimensions of spacetime for the twisted case may be integers. The results are compared with those of untwisted case. Since twisted Casimir energy is lower than untwisted energy, the untwisted cases may change into the twisted state in the spacetime.
Fermions Entropy of Vaidya-Bonner Black Hole
GAO Chang-Jun, SHEN You-Gen,
Chin. Phys. Lett. 2001, 18 (9): 1167-1169 .  
Abstract   PDF(pc) (183KB) ( 665 )
Using the membrane model which is based on brick-wall model, the authors calculated the free energy and entropy of the Vaidya-Bonner black hole due to fermions fields. The result shows that the entropy of the Vaidya-Bonner black hole is exactly proportional to the area of its event horizon. The relationship between entropy and event horizon in such non-static case is just the same as that in the static or stationary case.
Dynamical Temperature of a One-Dimensional Many-Body System in the Lennard-Jones Model
LIU Jue-Ping, YUAN Bao-Lun
Chin. Phys. Lett. 2001, 18 (9): 1170-1172 .  
Abstract   PDF(pc) (221KB) ( 580 )
A new way to derive the formula of the dynamical temperature by
using the invariance of the Liouville measure and the ergodicity
hypothesis is presented, based on the invariance of the functional under the transformation of the measure. The obtained dynamical temperature is intrinsic to the underlying dynamics of the system. A molecular dynamical simulation of a one-dimensional many-body system in the Lennard-Jones model has been performed. The temperature calculated from the Hamiltonian for the stationary state of the system coincides with that determined with the thermodynamical method.
Multi-soliton Solutions of the Konopelchenko-Dubrovsky Equation
LIN Ji, , LOU Sen-Yue, WANG Ke-Lin
Chin. Phys. Lett. 2001, 18 (9): 1173-1175 .  
Abstract   PDF(pc) (338KB) ( 477 )
By using the standard truncated Painlevé analysis, a Bäcklund transformation is used to obtain some new types of multi-soliton solutions of (2+1)-dimensional integrable Konopelchenko-Dubrovsky equation from the trivial vacuum solution.
Time-Averaged Behaviour at the Critical Parameter Point of Transition to Spatiotemporal Chaos
HE Kai-Fen
Chin. Phys. Lett. 2001, 18 (9): 1176-1178 .  
Abstract   PDF(pc) (509KB) ( 344 )
A time-averaged behaviour is found to be important for investigating the critical behaviour in parameter space for the transition from temporal chaos to spatiotemporal chaos by using an energy representation. Considering any wave solution as a superposition of the steady wave with its perturbation wave, we find that when approaching to the critical parameter point, their averaged positive interaction energy for the k = 1 mode becomes competitive with the negative one, with the summation displaying a scaling behaviour of power law.

Erraticity in Random-Cascading α Model
ZHOU Yi-Fei, LIU Qin, TANG Ying, CHENG Chun
Chin. Phys. Lett. 2001, 18 (9): 1179-1182 .  
Abstract   PDF(pc) (414KB) ( 318 )
The erraticity in the random-cascading α model is investigated. It is found that, contrary to the previous expectation, even in the pure single-α random-cascading model without putting in any particle, erraticity behaviour exists and the corresponding entropy indices do not vanish. This means that the dynamical fluctuations in a pure single-α model have already occured event-by-event. The models with multiple-αstrengthen this fluctuation. Taking double-α model as example, the variation of the event space fluctuation strength with the mixing ratio of the two αs is studied in some detail. The influence of particle number on the results when the particles are put into the system is also investigated.

Excitation Halo States of 12B
LIN Cheng-Jian, LIU Zu-Hua, ZHANG Huan-Qiao, WU Yue-Wei, YANG Feng, RUAN Ming
Chin. Phys. Lett. 2001, 18 (9): 1183-1185 .  
Abstract   PDF(pc) (319KB) ( 391 )
Angular distributions for the 11B(d,p 12B transfer reactions have been measured at Elab = 11.8 MeV. The asymptotic normalization coefficients (ANC) of the ground state, the second and third excitation states for 12B(11B+n) are extracted from the differential cross sections at three forward angles. With these ANCs, the root-mean-square radii are calculated for these three states. The results show that the second and third excitation states of 12B are neutron halo states.
Garvey-Kelson Mass Relations and n-p Interaction
GAO Zao-Chun, CHEN Yong-Shou, MENG Jie,
Chin. Phys. Lett. 2001, 18 (9): 1186-1188 .  
Abstract   PDF(pc) (287KB) ( 370 )
Two Garvey-Kelson mass relations are found to be directly related to the n-p interaction. In the case of the same nuclear core, the neutron-proton interaction energy between two neutrons and one proton ε2n-1p is experimentally found to be close to that between one neutron and two protons ε1n-2p, which is equivalent to the first Garvey-Kelson mass relation. The sum of ε2n-1p and ε1n-2p is close to the n-p interaction energy between two neutrons and two protons ε2n-2p, which leads to the second Garvey-Kelson mass relation. An explanation about these two n-p interaction relations is presented. It is shown that both of these mass relations hold more accurately when the core is an even-even one.
Total Reaction Cross Section Measurements at Intermediate Energy for Proton-Halo Candidate 23Al and Its Neighbours
CAI Xiang-Zhou, SHEN Wen-Qing, , FENG Jun, FANG De-Qing, ZHU Zhi-Yuan, JIANG Wei-Zhou, MA Yu-Gang, ZHANG Hu-Yong, ZHONG Chen, YU Li-Ping, ZHAN Wen-Long, GUO Zhong-Yan, XIAO Guo-Qing, WANG Jian-Song, ZHU Yong-Tai, WANG Jin-Chuan, LI Jia-Xing, WANG Meng, WANG Jian-Feng, NING Zhen-Jiang, WANG Quan-Jin, CHEN Zhi-Qiang
Chin. Phys. Lett. 2001, 18 (9): 1189-1191 .  
Abstract   PDF(pc) (280KB) ( 544 )
Total reaction cross sections σR for some proton-rich isotones (N = 10) near 23Al on a carbon target have been measured at intermediate energies in the experiment performed at the Radioactive Ion Beam Line of the Heavy Ion Research Facility in Lanzhou. The Z-dependence of σR shows a remarkable enhancement for 23Al relative to its neighbours. The difference factor d has been deduced from the measured σR by using the Glauber or Boltzmann-Uehling-Uhlenbeck models. From the above analysis, a possible one-proton halo structure is suggested for 23Al.
Perturbed 6snd1,3D2 Rydberg Series of Neutral Barium
LÜ, Jun, DAI Chang-Jian, XU Yun-Fei, LI Shi-Ben
Chin. Phys. Lett. 2001, 18 (9): 1192-1195 .  
Abstract   PDF(pc) (374KB) ( 359 )
The Ba even-parity J = 2 spectrum has been studied by using an
autoionization approach. Energy levels of the Ba 6snd1,3D2 Rydberg states have been measured and interpreted by the multichannel quantum defect theory. The results are in good agreement with the previous studies.
Quantum Electrodynamics Basis of Classical-Field High-Harmonic Generation Theory
WANG Bing-Bing, LI Xiao-Feng, GAO Liang-Hui, FU Pan-Ming, GUO Dong-Sheng, R. R.Freeman
Chin. Phys. Lett. 2001, 18 (9): 1196-1198 .  
Abstract   PDF(pc) (265KB) ( 475 )
From the nonperturbative quantum electrodynamics theory, We derive the Landau-Dykhne formula which represents the quantum-mechanical formulation of the three-step model. These studies provide a basis for the classical-field approaches to high-order harmonic generation and justify some assumptions used in the classical-field modeling.
Connection Between High-Harmonic Generation and Above-Threshold Ionization
WANG Bing-Bing, LI Xiao-Feng, GAO Liang-Hui, FU Pan-Ming, GUO Dong-Sheng, R. R.Freeman
Chin. Phys. Lett. 2001, 18 (9): 1199-1201 .  
Abstract   PDF(pc) (447KB) ( 441 )
Based on the nonperturbative quantum electrodynamics theory of high-order harmonic generation (HHG), we establish a direct connection between above-threshold ionization (ATI) and HHG. HHG can be described simply as an ATI followed by laser assisted recombination (LAR). The plateau reflects mainly the characteristic of LAR.
Observation of Rydberg Series in Sodium Vapor by Two-Photon Resonant Nondegenerate Four-Wave Mixing
WANG Yan-Bang, JIANG Qian, LI Long, MI Xin, YU Zu-He, FU Pan-Ming
Chin. Phys. Lett. 2001, 18 (9): 1202-1204 .  
Abstract   PDF(pc) (346KB) ( 395 )
We apply two-photon resonant nondegenerate four-wave mixing
with a resonant intermediate state for the observation of Rydberg states in sodium vapor. The broadening and shift of the sodium 3S -11D transition perturbed by argon are investigated. This technique can achieve Doppler-free resolution of narrow spectral structures of Rydberg levels if lasers with narrow bandwidths are employed.
Enhancement of Er3+ Luminescence in LiNbO3:Mg Crystals
ZHAO Li-Juan, YANG Jian, XU Jing-Jun, HUANG Hui, ZHANG Guang-Yin,
Chin. Phys. Lett. 2001, 18 (9): 1205-1207 .  
Abstract   PDF(pc) (346KB) ( 361 )
The luminescent properties of Er3+ ions in LiNbO3:Er and LiNbO3:Mg,Er crystals at room temperature were investigated by the emission spectra and the selective excitation spectra. The energy transition processes of Er3+ luminescence were analysed. It is found that the luminescent intensity of Er3+ ions in the LiNbO3:Mg,Er crystal is increased up to 7.8 times compared with that in the LiNbO3:Er crystal. Decrease of the defect center (NbLi) concentration due to doping with Mg2+ ions plays a key role in this phenomenon.
Propagation of Optical Pulses and Pulsed Beams in the Frequency Domain
LIN Qiang, WANG Li-Gang
Chin. Phys. Lett. 2001, 18 (9): 1208-1210 .  
Abstract   PDF(pc) (218KB) ( 515 )
The diffraction integral formulae in the temporal frequency domain and spatial-temporal frequency domain are derived by using a Fourier transform and tensor analysis method. Based on these formulae, the abcd law in the temporal frequency domain and the tensor ABCD law in the four-dimensional spatial-temporal frequency domain are derived. An application example of the derived formulae is provided.
Enhanced Pulse Compression Induced by Third-Order Dispersion in Birefringent Fiber
XU Wen-Cheng, CHEN Wei-Cheng, LUO Ai-Ping, GUO Qi, LIU Song-Hao
Chin. Phys. Lett. 2001, 18 (9): 1211-1213 .  
Abstract   PDF(pc) (319KB) ( 462 )
We report the enhanced pulse compression due to the interaction
of positive third-order dispersion and cross-phase-modulation effects in birefringent fibers. Polarization soliton compression along the slow axis can be enhanced in birefringent fibers with positive third-order dispersion, and the polarization soliton compression along the fast axis can be enhanced in fibers with negative third-order dispersion. Moreover, the third-order dispersion parameter can be optimized to obtain the optimal pulse compression.
Nearly-Noncritical Phase Matching in MgO:LiNbO3 Optical Parametric Oscillator
YAO Jian-Quan, YU Yi-Zhong, WANG Peng, WANG Tao, ZHANG Bai-Gang, DING Xin, CHEN Ji, H. J. Peng, H. S. Kwok
Chin. Phys. Lett. 2001, 18 (9): 1214-1217 .  
Abstract   PDF(pc) (515KB) ( 677 )
We have proposed and demonstrated a nearly-noncritical
phase-matched (NCPM) optical parametric oscillation (OPO) in an MgO: LiNbO3 crystal with 5-mol% MgO by temperature tuning. By giving up perfect NCPM, the practical tuning range for the OPO is increased by two times. For the crystal, the operated temperature decreases with the phase-matching angle at degeneracy. With a cutting angle of 82°instead of the noncritical case of 90°, the tuning range was increased. In order to obtain sufficiently high output pulse energy for both signal and idler throughout the entire tuning range, five sets of mirrors were used for the resonator. The tuning range of the OPO was 800-1700 nm with temperatures tuning from 83°C to 224.2°C. The output energy was about 6.45 mJ with a conversion efficiency of nearly 13%. The bandwidth of the output was 1.0-1.1 nm.
Defect Mode Computation in Two-Dimensional Photonic Crystals Consisting of Nearly-Free-Electron Metals
XIAO San-Shui, HE Sai-Ling, LIN Qing-Chun, SHEN Lin-Fang
Chin. Phys. Lett. 2001, 18 (9): 1218-1221 .  
Abstract   PDF(pc) (1059KB) ( 384 )
Defect modes in two-dimensional photonic crystals consisting of nearly-free-electron metals are considered. To avoid any time-consuming time convolution, modified time stepping formulas are used in a finite-difference time-domain (FDTD) method. Compared to the FDTD transmission spectra method, the present method significantly reduces the computation domain. With the present method one can also find defect modes that are not excited by the incident plane wave in the FDTD transmission spectra method.
Suppression and Compensation of the Third-Order Dispersion Effect on Polarization Modes in Birefringent Fibers
XU Wen-Cheng, CHEN Wei-Cheng, LUO Ai-Ping, CUI Hu, CHEN Yong-Zhu, LIU Song-Hao
Chin. Phys. Lett. 2001, 18 (9): 1222-1224 .  
Abstract   PDF(pc) (481KB) ( 490 )
The influence of the third-order dispersion (TOD) on polarization mode dispersion (PMD) is investigated. It is found that the TOD effect destroys orthogonal polarization modes in optical birefringent fibers. A new method is proposed to compensate for the PMD by means of cascading the fibers with the positive and negative TOD. This has been proved to be practicable in long transmission.
Electromagnetic Wave Attenuation in Atmospheric Pressure Plasmas
LIU Ming-Hai, HU Xi-Wei, JIANG Zhong-He, LU Xin-Pei, GU Cheng-Lin, PAN Yuan
Chin. Phys. Lett. 2001, 18 (9): 1225-1226 .  
Abstract   PDF(pc) (308KB) ( 693 )
The properties of electromagnetic waves in atmospheric pressure plasmas are investigated with the Lorentz model. The effects of the electromagnetic wave frequency, plasma density, and the electron-neutral collision frequency on the attenuation of electromagnetic wave were discussed. The numerical results indicate that the wave attenuation is stronger at the region of the longer wavelength and at the higher plasma density.
Fishbone Instability Excited by Electrons in a Tokamak
YAN Long-Wen, DONG Jia-Qi, DING Xuan-Tong, LIU Yi, GUO Gan-Cheng, WANG En-Yao, HL-M team
Chin. Phys. Lett. 2001, 18 (9): 1227-1229 .  
Abstract   PDF(pc) (339KB) ( 392 )
Fishbone instability excited by electrons in tokamak plasma is investigated theoretically and experimentally. The analysis of mode precession resonance indicates that the instability can be excited by barely trapped suprathermal electrons. The fishbone instability of electrons is more easily excited in the region of
negative magnetic shear than that of positive magetic shear and it is first observed by using electron cyclotron resonance heating in an HL-1M tokamak.
Nonlinear Evolutions of Stimulated Raman and Brillouin Scattering Processes in Partially Stripped-Ion Plasmas
HU Ye-Min, HU Xi-Wei
Chin. Phys. Lett. 2001, 18 (9): 1230-1233 .  
Abstract   PDF(pc) (636KB) ( 441 )
Numerical analyses for the nonlinear evolutions of stimulated Raman scattering (SRS) and stimulated Brillouin scattering (SBS) processes are given. Various effects of the second- and third-order nonlinear susceptibilities on the SRS and SBS processes are studied. The nonlinear evolutions of SRS and SBS processes are affected more efficiently than their linear growth rates by the nonlinear susceptibility.
Theoretical Scanning Tunneling Microscopy Images of Metal (Fe, Co, Ni, and Cu) Phthalocyanines
LI Qun-Xiang, YANG Jin-Long, YUAN Lan-Feng, HOU Jian-Guo, ZHU Qing-Shi
Chin. Phys. Lett. 2001, 18 (9): 1234-1236 .  
Abstract   PDF(pc) (848KB) ( 708 )
The scanning tunneling microscopy (STM) images of isolated iron
phthalocyanine (FePc), cobalt phthalocyanine (CoPc), nickel
phthalocyanine (NiPc) and copper phthalocyanine (CuPc) are simulated theoretically. All the simulated STM images show submolecular structures and reproduce well the features of the experimental images. The results show that there is a strong dependence of the STM images on the ion valence configuration of the metal ion. At the small tip bias voltages of less than 0.5 V, the central metal ions in NiPc and CuPc appear as holes in the molecular images, while they are the highlighted bumps in FePc and CoPc. The simulated images are interpreted by the fact that both FePc and CoPc systems have significant dz2 character near the Fermi level while the NiPc and CuPc systems do not. Moreover, we predict that the central nickel ion for NiPc appears a highlighted point when the tip bias voltage is larger than 0.7 V.
Elastic Constants of Na and K from Non-parameter Perturbation Calculation
CHEN Jun, JING Fu-Qian, CHEN Dong-Quan, ZHANG Jing-Lin, DUAN Su-Qing
Chin. Phys. Lett. 2001, 18 (9): 1237-1239 .  
Abstract   PDF(pc) (318KB) ( 424 )
Combined a linear muffin-tin orbital method, which can be used to calculate the total energy and pressure of solids in self-consistent manner, with a generalized elastic energy equation, a non-parameter perturbation method was proposed to compute the elastic constant for cubic metals. The pressure dependence of the shear modulus and bulk modulus for Na and K was calculated. It was found that the computed results agree well with experiments.
Pressure Induced Phase Transition in TiB
LI Feng-Ying, CHEN Liang-Chen, WANG Li-Jun, GU Hui-Cheng, WANG Ru-Ju, CHE Rong-Zheng, SHEN Zhong-Yi
Chin. Phys. Lett. 2001, 18 (9): 1240-1241 .  
Abstract   PDF(pc) (252KB) ( 363 )
In situ high pressure x-ray diffraction and electrical resistance experiments on TiB have been carried out by using a diamond anvil cell device. The results revealed that the sample undergoes a first-order phase transition at pressures of 3.5-5.0 GPa and 4.0-5.5 GPa for the x-ray diffraction and electrical resistance experiments, respectively. The parameters of the state equation are calculated before and after the phase transition and compared with the values calculated by Mohn et al. [J. Phys. C 21(1988)2829] using the augmented spherical wave method.
Influence of Grain Boundary on Melting
WANG Tun, ZHOU Fu-Xin, LIU Yue-Wu
Chin. Phys. Lett. 2001, 18 (9): 1242-1244 .  
Abstract   PDF(pc) (656KB) ( 426 )
The temperature behaviour of an Al bicrystal with surfaces consisting of the (110) and (111) crystals is simulated using molecular dynamics. The result shows that the (110) crystal losses its crystalline order at 820 K, whereas the disorder does not propagate through the (111) crystal at this temperature. Instead, some disordered atoms are recrystallized into the (111) crystal and the initial grain boundary changes into stable order-disorder interface. Thus, it was discovered that at temperature near its melting point, the (111) crystal grew and obstructed the propagation of disorder. Such an obstruction is helpful for understanding the melting.
Interlayer Segregation of Cu Atoms in Metal Multilayers
YU Guang-Hua, LI Ming-Hua, ZHU Feng-Wu, JIANG Hong-Wei, LAI Wu-Yan, CHAI Chun-Lin
Chin. Phys. Lett. 2001, 18 (9): 1245-1248 .  
Abstract   PDF(pc) (462KB) ( 455 )
The experimental results show that the exchange coupling field Hex of NiFe/FeMn for Ta/NiFe/FeMn/Ta multilayers is higher than that for the spin valve multilayers Ta/NiFe/Cu/NiFe/FeMn/Ta. The composition and chemical states at the surface of Ta(12 nm)/NiFe(7 nm), Ta(12 nm)/NiFe(7 nm)/Cu(4 nm) and Ta(12 nm)/NiFe(7 nm)/ Cu(3 nm)/NiFe(5 nm) were studied by using the x-ray photoelectron spectroscopy. The results show that no element from the underlayers floats out or segregate to the surface for Ta(12 nm)/NiFe(7 nm), Ta(12 nm)/NiFe(7 nm)/ Cu(4 nm). However, Cu atoms segregate to the surface of Ta(12 nm)/NiFe(7 nm)/Cu(3 nm)/NiFe(5 nm) multilayers, i.e. to the NiFe/FeMn interface for Ta/NiFe/Cu/NiFe/FeMn/Ta multilayers. The authors believe that the presence of Cu atoms at the interface of NiFe/FeMn is one of the important factors which will cause the exchange coupling field Hex of Ta/NiFe/FeMn/Ta multilayers to be higher than that of Ta/NiFe/Cu/NiFe/FeMn/Ta multilayers.
GaInNAs/GaAs Multiple-Quantum Well Resonant-Cavity-Enhanced Photodetectors at 1.3 μm
PAN Zhong, LI Lian-He, XU Ying-Qiang, ZHANG Wei, LIN Yao-Wang, ZHANG Rui-Kang, ZHONG Yuan, REN Xiao-Min
Chin. Phys. Lett. 2001, 18 (9): 1249-1251 .  
Abstract   PDF(pc) (364KB) ( 466 )
A GaInNAs/GaAs multiple quantum well (MQW) resonant-cavity enhanced photodetector (RCE-PD) operated at wavelength of 1.3 μm with the full-width at half-maximum of 4 nm was demonstrated. The GaInNAs RCE-PD was grown by molecular-beam epitaxy using a home-made ion-removed dc-plasma cell as nitrogen source. GaInNAs/GaAs MQW shows a strong exciton peak at room temperature, which is very beneficial for applications in long-wavelength absorption devices. For a 100 μm diameter RCE-PD, the dark current is 20 and 32 pA at biases of 0 and 6 V, respectively, and the breakdown voltage is -18 V. The measured 3dB bandwidth is 308 MHz, which is limited by the resistance of p-type distributed Bragg reflector mirror. The tunable wavelength in a range of 18 nm with the angle of incident light was observed.

Native Point Defect States in ZnO
XU Peng-Shou, SUN Yu-Ming, SHI Chao-Shu, XU Fa-Qiang, PAN Hai-Bin
Chin. Phys. Lett. 2001, 18 (9): 1252-1253 .  
Abstract   PDF(pc) (269KB) ( 958 )
The native point defect states in ZnO have been calculated by using a full-potential linear Muffin-tin orbital method. The results show that Zn vacancy and O interstitial produce the shallow acceptor levels above the valence band. The O vacancy produces a deep donor level, while Zn interstitial produces a shallow donor level, both below the conduction band. The Zn interstitial is the main factor to induce the native n-type conductivity in ZnO.
Josephson Effect in MgB2: Large IcRN Product and Superconducting Energy Gap
XUAN Yi, LI Zhuang-Zhi, TAO Hong-Jie, REN Zhi-An, CHE Guang-Can, ZHAO Bai-Ru, ZHAO Zhong-Xian
Chin. Phys. Lett. 2001, 18 (9): 1254-1255 .  
Abstract   PDF(pc) (252KB) ( 373 )
We report the observation of the Josephson effect on the newly
discovered superconductor MgB2 with break-junction technique. Similar to the conventional superconductors, the I - V curve can be fitted with the resistively shunted junction model including the noise effect, and a large characteristic voltage Vc = IcRN = 9.6 meV was obtained. The energy gap determined by the Ambegaokar-Baratoff relation with the fitted Vc is consistent with the Bardeen-Cooper-Schrieffer weak-coupling value well. Our result implies that the superconductor MgB2 is a promising material for the Josephson device applications.
Theoretical Calculation for the Dip Feature in Tunnelling Experiment on Bi2212
XIE Gang, HAN Ru-Shan
Chin. Phys. Lett. 2001, 18 (9): 1256-1257 .  
Abstract   PDF(pc) (262KB) ( 308 )
We generalize a model, which was presented by Norman [Phys. Rev. Lett. 79 (1997) 3506], to calculate the Bi2Sr2CaCu2O8+δ (Bi2212) single-electron tunnelling conductance. In our calculation result, the dip feature appears which has been widely observed in tunnelling experiments. It is found that this dip feature in tunnelling experiment and the dip/hump feature in angle-resolved photoemission experiment have a common physics. Moreover, it is shown from our numerical calculation method that if the spectral function A(K,ω) is known, the tunnelling conductance can be obtained.
Anomalous Suppression of the Vortex Hall Current in Underdoped YBa2Cu3Ox
XU Zhu-An, HUANG You-Xing, ZHAO Yan-Li, ZHANG Xuan-Jia, JIAO Zheng-Kuan
Chin. Phys. Lett. 2001, 18 (9): 1258-1260 .  
Abstract   PDF(pc) (440KB) ( 454 )
The transport properties of underdoped YBa2Cu3Ox (YBCO) crystals with x = 6.95, 6.80, 6.66 were measured and the effect of pseudogap on the Hall conductivity was studied. In the normal state, the Hall angle remains unperturbed at the crossover temperature of resistivity for the underdoped samples. An anomalous suppression of the vortex Hall current was observed near Tc and the contribution of the vortices to the Hall current is absent above 4K in 6K YBCO (x = 6.66).
Specific Heat of the Spin-1/2 Antiferromagnetic Heisenberg Chain
YUN Guo-Hong, LIANG Xi-Xia
Chin. Phys. Lett. 2001, 18 (9): 1261-1263 .  
Abstract   PDF(pc) (272KB) ( 461 )
A simple analytic theory of thermodynamics at finite temperature for the spin-1/2 antiferromagnetic Heisenberg chain is proposed based on the picture of the particle-hole pair excitations. The dispersion relation of the particle-hole pairs is derived in the formulation of thermodynamic Bethe ansatz providing that the particles and holes have the same energy and they are excited as normal modes. It is shown that the behaviour of the specific heat is in excellent agreement with the numerical and experimental results.
Magnetic Long-Range Order and Colossal Magnetoresistance Effect in Double Exchange Ladders
MA Dong-Mei, ZOU Liang-Jian,
Chin. Phys. Lett. 2001, 18 (9): 1264-1267 .  
Abstract   PDF(pc) (456KB) ( 373 )
By applying Bogoliubov's inequality to double-exchange (DE)
ladders, we show that the ferromagnetic (FM) order is absent in the new DE systems at finite temperature. The incorporations of Jahn-Teller electron-phonon coupling, orbital degeneracy and on-site Coulomb interaction with the DE interaction do not preserve these orders. The long-wavelength thermal fluctuations of the spins overcome the DEFM correlation and destroy the FM orders. The implication of the absence of FM order on the transport of the DE ladders is discussed.
Nonlinear Magnetoimpedance Effect in FeCoNi Ferromagnetic Tubes
G. V. Kurlyandskaya, H. Yakabchuk, E. Kisker, N. G. Bebenin, H. García-Miquel, M. Vázquez, V. O. Vas’kovskiy
Chin. Phys. Lett. 2001, 18 (9): 1268-1270 .  
Abstract   PDF(pc) (429KB) ( 430 )
The very high (up to 820% of the magnetoimpedance ratio) and sensitive nonlinear giant magnetoimpedance effect has been studied in the FeCoNi magnetic tubes electroplated onto Cu(3%)Be nonmagnetic wire for frequencies from 1 to 10MHz. Special annealing was done in order to induce the magnetic anisotropy. The high harmonic generation was observed and the harmonics show larger variations with the external magnetic field than the fundamental frequency. The super high sensitivity of the harmonics is promising in regards for the increase of the sensitivity of magnetoimpedance sensors.
Dielectric Characteristics and Layer Periodic Effects of Ferroelectric Superlattice BaTiO3/SrTiO3
ZHANG Jiang, YIN Zhen, ZHANG Ming-Sheng, CHEN Wan-Chun
Chin. Phys. Lett. 2001, 18 (9): 1271-1274 .  
Abstract   PDF(pc) (369KB) ( 397 )
A pseudospin-phonon coupled model in double-time Green's function theory has been developed to investigate dielectric susceptibility of the ferroelectric-dielectric superlattice BaTiO3/SrTiO3(BTO/STO). As the pseudospin-pseudospin interaction and the pseudospin-phonon interactions increase, the dielectric susceptibility changes from narrow shape into the strong-broad shape with the peak shift to higher temperature region. With increasing pseudospin-phonon interaction in the BTO layer and at small pseudospin-pseudospin interaction in BTO layer, the dielectric susceptibility was sensitively adjusted around the transition temperature of strontium titanate, and at large pseudospin-pseudospin interaction in the BTO layer, the dielectric susceptibility was increased in high temperature region covering the tetragonal-cubic transition temperature of barium titanate. A critical period of 10/10 in the BTO/STO superlattice has been obtained, which is in good agreement with experimental data of 40Å, for ten unit cells.
Core-Shell Structure and Photoluminescence of CdS Quantum Dots
ZOU Bing-Suo, WU Zhen-Yu, CAO Li, DAI Jian-Hua, ZHANG Ze-Bo, NIE Yu-Xin, XIE Si-Shen
Chin. Phys. Lett. 2001, 18 (9): 1275-1277 .  
Abstract   PDF(pc) (353KB) ( 476 )
A double-potential-well model is proposed to describe the core-shell thickness-dependent photoluminescence peaks and energy relaxations in semiconductor quantum dots(QDs). The surface effect plays an important role in the formation of new states-polaronic states around the surface of QDs. The polaronic states formed emit light due to the strong interaction between the core state (confined state) and the surface state with an enhanced participation of the size effect.
A New Mechanism Responsible for the Enhancement of Local Electric Field on the Surface of Emitting Carbon Nanotubes
XU Ning-Sheng, CHEN Yue, DENG Shao-Zhi, CHEN Jun, MA Xu-Cun, WANG En-Ge
Chin. Phys. Lett. 2001, 18 (9): 1278-1281 .  
Abstract   PDF(pc) (564KB) ( 359 )
Aligned carbon nanotube (CNT) films exhibit excellent electron emission properties at very low fields. This has been attributed to the high aspect ratio of CNTs, i.e., their emitting surface can have high local field due to geometrical enhancement. It is found that a new mechanism can be responsible for enhancement of the local field on the emitting surface of CNTs. This results from the space charge in the vacuum gap, which is readily generated due to the high emission current density of CNTs. Details are given of both experimental and theoretical study on this effect. The mechanism also accounts for the distinct non-linearity in Fowler-Nordheim plots often observed with CNTs. The implication in technical application of our findings is also included.
Preparation of AlN Films by Ion-Beam-Enhanced Deposition
MEN Chuan-Ling, XU Zheng, ZHENG Zhi-Hong, DUO Xin-Zhong, ZHANG Miao, LIN Cheng-Lu
Chin. Phys. Lett. 2001, 18 (9): 1282-1284 .  
Abstract   PDF(pc) (303KB) ( 465 )
Aluminum nitride (AlN) films have been synthesized on Si(100)
substrates by ion-beam-enhanced deposition. Spreading resistance profile results suggest that the spreading resistance decreases with increasing rates of Al evaporation. If the evaporation rate of Al is higher than 2.5Å/s, the quality of AlN film will greatly deteriorate. The spreading resistance of the best quality film deposited at 0.5Å/s rate of Al was larger than 108Ω. X-ray photoelectron spectroscopy measurements indicate the formation of AlN films at 0.5 and 1.0Å/s evaporation rate of Al. With the increasing evaporation rate of Al, the ratio of N to Al is decreased. When deposited at 0.5 and 1.0Å/s evaporation rates of Al, the ratio of N to Al was 0.402:1 and 0.250:1, respectively. Atomic force microscopy observation also exhibits that the surface of the AlN film formed at 0.5Å/s rate is smoother and more uniform than that formed at 1.0Å/s.

Converters for the TE11 Mode Generation from TM01 Vircator at 4GHz
LING Gen-Shen, ZHOU Jin-Juan
Chin. Phys. Lett. 2001, 18 (9): 1285-1287 .  
Abstract   PDF(pc) (334KB) ( 1499 )
The measurements and calculations (coupled mode equations) on the conversion of transverse magnetic TM01 vircator (virtual cathode oscillator)mode at 4GHz to the linearly polarized TE11 mode are presented by means of mode converter systems using circular waveguide with curvature. The mode converter is composed of the 38.78°bend with 39.07cm curvature and of the 50.78°inverse bend with 25.24cm curvature in the circular waveguide of 9cm internal diameter. The efficiency of conversion from TM01 to TE11 at 4GHz exceeds 90%, and the overall efficiency from TM01 to TE11 exceeds 90% in the calculated range from 3.72 to 4.8GHz.

Mechanism of a Variable Optical Attenuator Based on Guided Wave Resonance
JIANG Yi, CAO Zhuang-Qi, DOU Xiao-Ming
Chin. Phys. Lett. 2001, 18 (9): 1288-1290 .  
Abstract   PDF(pc) (336KB) ( 468 )
The mechanism of an electrically controlled variable optical attenuator is investigated based on the varying energy coupling efficiency of a light beam into a guided wave resonance. Compared to the conventional attenuated total internal reflection devices based on the surface plasmon resonance, the driving voltage for this attenuator is greatly reduced because of the newly chosen working interior angle. This paper explains the principle of attenuator operation and presents experimental results obtained on a realization of the device.
Selective Acceleration in Impulsive Solar Flares
WANG De-Yu
Chin. Phys. Lett. 2001, 18 (9): 1291-1293 .  
Abstract   PDF(pc) (264KB) ( 286 )
A plasma acceleration mechanism is proposed to explain the dramatic enhancement in the ratio of 3He/4He, (enhancement factor 102-103) observed in solar 3He-rich flares. Consideration that coronal plasma is mainly composed of hydrogen and helium ions, the hydrogen ion-helium ion hybrid waves and quasi-perpendicular waves can be excited by energetic electron beam during the impulsive solar flares. The frequencies of these waves are close to the 3He++ ion gyrofrequencies, but it is far from the 4He++ ion gyrofrequency. Most of these waves are selectively absorbed by 3He ions. These preheated 3He ions can be successively stochastic accelerated by Alfvén turbulence, when their velocities are larger than the local Alfvén velocity. It makes the ratio of 3He/4He dramatic enhanced and the acceleration energy spectrum of 3He ions forms a power-law distribution during the impulsive solar flares.
State Transitions of Black Hole Accretion Flows
LU Ju-Fu, PAN Liu-Bin
Chin. Phys. Lett. 2001, 18 (9): 1294-1296 .  
Abstract   PDF(pc) (250KB) ( 295 )
We show that the thermal instability-triggered transition from the state of Shakura-Sunyaev disc to the state of advection-dominated accretion flow is possible for black hole accretion flows composed of two-temperature plasma with bremsstrahlung and synchrotron radiation and Comptonization.
45 articles