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Volume 18 Issue 12
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Original Articles
Probabilistic Teleportation of an Arbitrary Two-particle State
GU Yong-Jian, ZHENG Yi-Zhuang, GUO Guang-Can
Chin. Phys. Lett. 2001, 18 (12): 1543-1545 .  
Abstract   PDF(pc) (195KB) ( 713 )
A scheme for the teleportation of an arbitrary two-particle state via two non-maximally entangled particle pairs is proposed. We show that teleportation can be successfully realized with a certain probability if the receiver adopts an appropriate unitary-reduction strategy. A specific strategy is provided in detail. The probability of successful teleportation is determined by the smaller coefficients of the two entangled pairs.
Electrogravitational Resonance of a Gaussian Beam to a High-Frequency Relic Gravitational Wave
LI Fang-Yu, TANG Meng-Xi
Chin. Phys. Lett. 2001, 18 (12): 1546-1549 .  
Abstract   PDF(pc) (227KB) ( 307 )
We consider the resonant response of a Gaussian beam passing through a static magnetic field to a high-frequency relic gravitational wave (GW). It is found that under the synchroresonance condition, the first-order perturbative electromagnetic energy fluxes will contain a “left circularly wave” and a “right circularly wave”around the symmetrical axis of the Gaussian beam, but the perturbative effects produced by the + and x polarization of the GW have different physical behaviour. For the high-frequency relic GW with vg = 1010Hz, h = 10-30, recently expected by the quintessential inflationary models, the corresponding perturbative photon flux passing through the region 10-2m2 would be expected to be 104s-1, This is the largest perturbative photon flux we recently analysed and estimated using the typical laboratory parameters.
Universal Behaviour on the Break-up of the Spiral Mean Torus
ZHOU Ji-Lin, Bambi HU, SUN Yi-Sui
Chin. Phys. Lett. 2001, 18 (12): 1550-1553 .  
Abstract   PDF(pc) (534KB) ( 415 )
We study numerically the critical behaviour during the break-up of the spiral mean torus in a four-dimensional symplectic map. At each point of the paramter space, the stability indices of a serial of periodic orbits are calculated with their winding numbers approaching the spiral mean torus. The critical values of the parameters when the torus breaks are determined by the criterion that the variance of the distribution on the indices reaches a minimum. Some evidence are revealed on the possible existence of a univsersal distribution on the stability indices of the periodic orbits at the critical. This confirms the picture given by the approximate renormalization theory of the Hamiltonian systems with three degrees of freedom.
Controlling Beam Halo-Chaos
FANG Jin-Qing, LUO Xiao-Shu, CHEN Guan-Rong, WENG Jia-Qiang
Chin. Phys. Lett. 2001, 18 (12): 1554-1557 .  
Abstract   PDF(pc) (339KB) ( 515 )
Beam halo-chaos is essentially a complex spatiotemporal chaotic motion in a periodic-focusing channel of a high-power linear proton accelerator. The controllability condition for beam halo-chaos is analysed qualitatively. A special nonlinear control method, i.e., the wavelet-based function feedback, is proposed for controlling beam halo-chaos. Particles-in-cell simulations are used to explore the nature of halo-chaos formation, which has shown that the beam halo-chaos is suppressed effectively after using nonlinear control for the proton beam with an initial full Gaussian distribution. The halo intensity factor Hav is reduced from 14% to zero, and the other statistical physical quantities of beam halo-chaos are more than doubly reduced. The potential applications of such nonlinear control in experiments are briefly pointed out.
Heavy Quarkonium Spectra in a Quark Potential Model
CHEN Hong, ZHANG Jing, DONG Yu-Bing, SHEN Peng-Nian
Chin. Phys. Lett. 2001, 18 (12): 1558-1560 .  
Abstract   PDF(pc) (198KB) ( 601 )
By solving the eigenvalue equation for the quark-antiquark
potential which emerges from an effective dilaton-gluon coupling
inspired by superstring theory, we obtain the spin-averaged energy levels of charmonium (cc) and bottonium (bb) and show that the masses of the cc and bb states are well in agreement with the available experimental data.
One Neutron Halo in a 12B Excited State
CHEN Bao-Qiu, MA Zhong-Yu
Chin. Phys. Lett. 2001, 18 (12): 1561-1563 .  
Abstract   PDF(pc) (257KB) ( 447 )
The nonlinear relativistic mean field (RMF) theory with a new effective interaction NL3 has been used to investigate the bulk properties of the 12B nucleus. The results obtained in the RMF predict one neutron halo in a 12B excited state. 12B does not show the neutron halo structure if it is in its ground state.
Reflection Asymmetric Shell Model on the Projected Woods-Saxon+BCS Basis
GAO Zao-Chun, CHEN Yong-Shou, MENG Jie,
Chin. Phys. Lett. 2001, 18 (12): 1564-1567 .  
Abstract   PDF(pc) (534KB) ( 416 )
The projected Woods-Saxon(WS) quasi-particle states have been used as the bases in the calculation of the reflection asymmetric shell model (RASM). The WS potential has been modified but constrainted to give the similar single-particle levels of the standard WS potential. Correspondingly, the multipole interactions in the total RASM Hamiltonian are constructed according to the modified WS potential. The calculated octupole band of 228Th from this approach is in good agreement with experimental data.


HBT Parameters and Space-Momentum Correlations in Relativistic Heavy-Ion Collisions
ZHANG Jing-Bo, HUO Lei, ZHANG Wei-Ning, LI Xin-Hua, XU Nu, LIU Yi-Ming
Chin. Phys. Lett. 2001, 18 (12): 1568-1570 .  
Abstract   PDF(pc) (357KB) ( 597 )
Using the relativistic quantum molecular dynamics approach,
with a correlation after-burner, the physics of transverse momentum dependence of the Hanbury-Brown and Twiss parameters is studied for Au + Au, Si + Si and p + p collisions at the center-of-mass energy √s = 200AGeV. The results indicate that the space-momentum correlations would affect such dependence in both heavy-ion and elementary collisions. The size parameters as a function of the transverse mass mt are sensitive to the degree of space-momentum correlations.
How and When Will a Neutron Star Become a Hyperon Star?
JIA Huan-Yu, SUN Bao-Xi, MENG Jie, , ZHAO En-Guang
Chin. Phys. Lett. 2001, 18 (12): 1571-1574 .  
Abstract   PDF(pc) (428KB) ( 347 )
In the framework of the extended relativistic mean-field theory with hyperons, the properties of neutron star matter have been investigated. It is found that at a density of four to five times of nuclear matter saturation density ρ0, a neutron star will become a hyperon star. This transition is strongly influenced by the coupling constants of hyperons to the mesons and different parameter set. For a given parameter set, a minimum transition baryon density exists when the hyperon coupling ratios satisfy x = x = x = 0.65 or x = x = 0.62, x = 0.7.
Optimum Metallic-Bond Scheme: A Quantitative Analysis of Mass Spectra of Sodium Clusters
SU Chang-Rong, LI Jia-Ming,
Chin. Phys. Lett. 2001, 18 (12): 1575-1577 .  
Abstract   PDF(pc) (315KB) ( 485 )
Based on the results of the optimum metallic-bond scheme for
sodium clusters, we present a quantitative analysis of the detailed features of the mass spectra of sodium clusters. We find that, in the generation of sodium clusters with various abundances, the quasi-steady processes through adding or losing a sodium atom dominate, and the quasi-steady processes through adding or losing a sodium dimer are also important to understand the detailed features of mass spectra for small clusters.
Anomalous Photofragmentation of Fullerene Doped in Silica Aerogel─Enhanced Formation of Odd-Numbered “Fullerene” Fragments
KONG Qing-Yu, ZHAO Li, ZHUANG Jun, QIAN Shi-Xiong, LI Yu-Fen, WANG Jue
Chin. Phys. Lett. 2001, 18 (12): 1578-1581 .  
Abstract   PDF(pc) (793KB) ( 618 )
Photofragmentation of fullerene-doped silica aerogels has been investigated by the excimer laser ablation reflectron time-of-flight mass spectrometric technique. Great enhancement in the formation of odd-numbered ‘fullerene’fragments has been observed in the negative ion channel for the chemically doped aerogel sample. Generally, odd-numbered species C57, C55, C53, C51 appeared in the mass spectra. Under optimal experimental conditions C55 can be even more intense than the neighboring even-numbered carbon clusters. In contrast, for the physically doped sample, just like pristine C60, only weak odd-numbered fragments were observed. In the positive-ion channel, the behaviour of all these samples is similar, no odd-numbered species was ever detected. A mechanism related to the interaction between the fullerene dopant and the silica aerogel host is suggested for the anomalous enhancement of the odd-numbered cluster formation. A preliminary discussion on the structures of the odd-numbered ‘fullerene’fragments is given.

More Magic Numbers in Titanium-Carbon Anion Clusters: Can This Be Explained by Any Structural Growth Pattern?
ZHAI Hua-Jin, LIU Bing-Chen, ZHOU Zheng-Wen, ZHOU Ru-Fang, NI Guo-Quan, XU Zhi-Zhan
Chin. Phys. Lett. 2001, 18 (12): 1582-1585 .  
Abstract   PDF(pc) (409KB) ( 359 )
Titanium-carbon anion clusters with a mass range up to 1800 amu have been generated in a Smalley-type cluster source involving a target rod composed of titanium and graphite powders, and have been analysed by time-of-flight mass spectrometry. In the lower mass range (up to 1200 amu), our mass spectrum reproduces all the magic numbers, which have been reported previously, i.e., Ti3C-8, Ti6C-13, Ti7C-13, Ti9C-15, Ti13C-22, and Ti14C-24, in spite of many differences in experimental conditions. In the higher mass range (1200-1800 amu), we observe new magic numbers at Ti15C-26, Ti20C-33/Ti20C-34 and Ti25C-42, which cannot be accounted for by the previously proposed structural growth patterns. All the magic and local maximum TixC-y peaks have a metal-to-carbon ratio of approximately 1:1.7. The present results suggest a further complexity to the structural growth patterns of the transition metal-carbon mixed cluster systems.


Experimental Demonstration of Electromagnetic Induced Transparency and Dispersion Effects in Cs Atoms Vapor
ZHANG Jun-Xiang, DONG Rui-Fang, CHANG Hong, XIE Chang-De, PENG Kun-Chi, XIAO Min
Chin. Phys. Lett. 2001, 18 (12): 1586-1588 .  
Abstract   PDF(pc) (357KB) ( 603 )
The effects of the electromagnetically induced transparency and dispersion of a Λ-type three-level atomic system are experimentally measured with a vapor cell of Cs atoms. The steep dispersion at low absorption is observed. Thus a small group velocity for the probe beam is inferred from the measured dispersion curve.
Single Pass Third-Harmonic Generation of 310mW of 355nm with an All-Solid-State Laser
JIA Yu-Lei, HE Jing-Liang, WANG Hui-Tian, ZHU Shi-Ning, ZHU Yong-Yuan
Chin. Phys. Lett. 2001, 18 (12): 1589-1591 .  
Abstract   PDF(pc) (335KB) ( 877 )
A maximum of 310mW average output power at 355nm has been obtained by extracavity frequency tripling with a BBO crystal in a Q-switched Nd:YVO4 laser with 11.2W of laser diode pump power. The single pass frequency conversion efficiency (infrared-to-ultraviolet) is 14.3%. The power stability of the ultraviolet laser is better than 1% in 30min.

Yb3+-Doped Double-Clad Fiber Laser Pumped by Rectangular Inner Cladding
NING Ding, LI Yi-Gang, HUANG Bang-Cai, SUN Jian-Jun, LÜ, Ke-Cheng, YUAN Shu-Zhong, DONG Xiao-Yi
Chin. Phys. Lett. 2001, 18 (12): 1592-1594 .  
Abstract   PDF(pc) (333KB) ( 456 )
A novel Yb3+-doped double-clad silica fiber with rectangular inner cladding was designed and developed by using the modified chemical vapour deposition process, solution-doping and optical machining altogether. The dimension of inner cladding is 100 x 70μm, and Yb3+-doped concentration in the core is about 0.24wt.%. The operation of the fiber laser pumped by inner cladding is reported. The threshold of the laser is 34mW. When the pump power launched is 141mW, the laser output is 84mW at the wavelength 1075.6nm, and the slope efficiency is 77%.
Light-Induced Absorption in Nominally Pure Bismuth Silicon Oxide
LI Fei-Fei, XU Jing-Jun, KONG Yong-Fa, HUANG Hui, ZHANG Guang-Yin, YANG Chun-Hui, XU Yu-Heng
Chin. Phys. Lett. 2001, 18 (12): 1595-1597 .  
Abstract   PDF(pc) (349KB) ( 370 )
Light-induced absorption in the nominally pure bismuth silicon oxide is investigated experimentally and the result shows that it consists of a transient and persistent part. The experiment evidence is analysed based on the model of three groups of trap (donor) centers.
Large Third-Order Nonlinear Optical Susceptibility of Rh-Doped BaTiO3 Thin Films Prepared by Pulsed Laser Deposition
YANG Guang, WANG Huan-Hua, TAN Guo-Tai, JIANG An-Quan, ZHOU Yue-Liang, YANG Guo-Zhen, CHEN Zheng-Hao
Chin. Phys. Lett. 2001, 18 (12): 1598-1600 .  
Abstract   PDF(pc) (305KB) ( 515 )
Rh-doped barium titanate (BaTiO3) epitaxial thin films have been fabricated on SrTiO3 (100) substrates by pulsed laser deposition. The nonlinear optical properties of the films were determined using z-scan method at a wavelength of 532nm with a laser duration of 10ns. The real and imaginary parts of the third-order nonlinear susceptibility x(3) were 5.71 x 10-7 esu and 9.59 x 10-8 esu, respectively. The real part value of x(3) of the Rh:BaTiO3 films is about one order larger than that of Ce-doped BaTiO3 thin films. The results show that Rh:BaTiO3 thin films have great potential applications for nonlinear optical devices.

Forward Phase Conjugation wave due to Multi-wave Coupling and Grating Share in Lithium Niobate Crystal
QIAO Hai-Jun, XU Jing-Jun, ZHANG Xin-Zheng, LI Fei-Fei, SUN Qian, WU Qiang, ZHANG Guang-Yin
Chin. Phys. Lett. 2001, 18 (12): 1601-1603 .  
Abstract   PDF(pc) (297KB) ( 397 )
The steady intensity of a forward phase conjugate wave (FPCW) is successfully observed along the c-axis in the highly magnesium-doped lithium niobate crystal. We put forward a physical picture for our experiment phenomena. The FPCW is generated from the phase-mismatch in a three-wave coupling process, and tends to be stable accompanied with the building of photorefractive gratings and four-wave coupling processes. Our experiment result is also discussed and analysed by means of the wave coupling theory, and the theoretical expression is provided for the experiment.

Zero-Phonon Transition and Spectral Hole Burning of Colour Centers in Doped Lithium Fluoride Crystals Bombarded by Electrons
GU Hong-En, WANG Ke-Qi, LIU Hong-Hai
Chin. Phys. Lett. 2001, 18 (12): 1604-1606 .  
Abstract   PDF(pc) (299KB) ( 474 )
Two zero-phonon lines with wide linewidth on R-1 and unknown colour centers have been observed in the magnesium-doped lithium fluoride crystals coloured by electron beam bombardment at 200K in the measured temperature range of 10 - 77K. The R-1 zero-phonon line can be nearly completely bleached using the normal spectrophotometer light at 10 K. An obvious spectral burning hole in the absorption profile of the R-1 zero-phonon line of colour centers in the coloured lithium fluoride crystals has been obtained by using the spectrophotometer light adjusted to narrower bandwidth at 10K. The optical bleaching of the zero-phonon line can be partially recovered by annealing the crystals to room temperature for a short time period or irradiating the crystals with ultraviolet light at above 40K, and nearly complete restoration can be obtained after the ultraviolet light irradiation and storage in the dark for a long time at room temperature.

Incoherently Coupled Bright-Dark Soliton Pairs in Biased Centrosymmetric Photorefractive Media
HOU Chun-Feng, DU Chun-Guang, Abdurusul, LI Shi-Qun
Chin. Phys. Lett. 2001, 18 (12): 1607-1609 .  
Abstract   PDF(pc) (237KB) ( 569 )
It is shown theoretically that incoherently coupled bright-dark soliton pairs can exist in biased centrosymmetric photorefractive media under steady-state conditions. These soliton pairs can be established provided that the two optical beams have the same polarization, wavelength, and are mutually incoherent.
A Novel Titania Membrane with Uniform Macropores
NI Pei-Gen, CHENG Bing-Ying, DONG Peng, ZHANG Dao-Zhong
Chin. Phys. Lett. 2001, 18 (12): 1610-1612 .  
Abstract   PDF(pc) (1043KB) ( 530 )
A procedure for fabricating novel TiO2 membrane material with sub-micron pores and large specific surface area from the template has been demonstrated. The morphology and structure of the membrane have been characterized by scanning electron microscopy. The results have indicated that the macroporous membrane consists of uniform hollow spheres which are interconnected to each other by ‘small windows’. Potential unique applications of this macroporous material in the fields of catalysis, optics, sensors, etc. were suggested.


Theoretical Analysis of a Vertical Channel Dropping Tunneling Process in a Photonic Crystal for Wavelength Division Demultiplexing
FU Jian, HE Sai-Ling, XIAO San-Shui, QIU Min, HE Jian-Jun
Chin. Phys. Lett. 2001, 18 (12): 1613-1616 .  
Abstract   PDF(pc) (686KB) ( 305 )
A theoretical analysis is presented for a channel drop tunneling structure composed of a horizonal input channel, a vertical output channel and a multi-mode cavity in a photonic crystal. Criteria for a complete transfer are derived for applications of wavelength devision demultiplexing. The analytical results are verified with a numerical simulation using a finite difference time domain method. The vertical
channel dropping tunneling system makes the demultiplexing device much more compact, as compared to the conventional parallel channel dropping system.

Simultaneous Static Strain, Temperature and Vibration Measurement Using an Integrated FBG/EFPI Sensor
ZENG Xiang-Kai, RAO Yun-Jiang
Chin. Phys. Lett. 2001, 18 (12): 1617-1619 .  
Abstract   PDF(pc) (398KB) ( 789 )
A novel technique for simultaneous measurement of static strain, temperature and vibration in health monitoring of structures is demonstrated using an integrated in-fiber Bragg grating(FBG)/extrinsic Fabry-Pérot interferometer (EFPI) sensor. The EFPI sensor provides static strain and vibration information simultaneously by using the channel-spectrum method and the low-coherence interferometric technique, respectively. The FBG sensor is used for temperature measurement. The experimental results show that a static strain accuracy of ±20με, a temperature accuracy of ±1°C and a vibration resolution of 1 nm have been achieved with a good repeatability.

A New Inverse Method of Elastic Constants for a Fiber-Reinforced Composite Plate from Laser-Based Ultrasonic Lamb Waves
YANG Jing, CHENG Jian-Chun
Chin. Phys. Lett. 2001, 18 (12): 1620-1623 .  
Abstract   PDF(pc) (432KB) ( 582 )
A new inverse method based on the wavelet transform and the artificial neural networks (ANN) is presented to recover elastic constants of a fiber-reinforced composite plate from the laser-based ultrasonic Lamb waves. The transient waveforms obtained by numerical simulations under different elastic constants are taken as input of the ANN for training and learning. The wavelet transform is employed for extracting the eigen-vectors from the raw Lamb wave signals so as to simplify the structure of the ANN, then these eigen-vectors are inputed to a multi-layer internally recurrent neural network with back-propagation algorithm. Finally, the experimental waveforms are used as the input in the whole system to inverse elastic constants of the experimental material.
Magnetoacoustic Waves in the Solar Stratified Atmosphere
ZHENG Hui-Nan, WANG Shui, S. T. Wu, LI Bo
Chin. Phys. Lett. 2001, 18 (12): 1624-1627 .  
Abstract   PDF(pc) (734KB) ( 447 )
The propagation of magnetoacoustic waves in the solar atmosphere consisting of the photosphere, chromosphere and corona has been studied numerically by time-dependent multi-dimensional magnetohydrodynamic (MHD) simulation. Pressure disturbances are introduced at the bottom of the chromosphere and at the bottom of the corona, respectively. The computational results show that incurred fast and slow MHD waves propagate away from the source of the disturbances. The fast MHD wave propagates as an expansive wave in the radial direction, while the slow one steepens and it may evolve into a slow shock. We suggest that the extreme ultraviolet imaging telescope wave observed by the SOHO and Moreton wave are a fast MHD wave propagating in the corona and in the chromosphere,
respectively.
Particle Simulation Research on the Detail Process of Bubble Generatio
MA Yan-Yun, CHANG Wen-Wei, YIN Yan, CAO Li-Hua, YUE Zong-Wu
Chin. Phys. Lett. 2001, 18 (12): 1628-1631 .  
Abstract   PDF(pc) (1384KB) ( 421 )
The detail process of bubble generation in laser-plasma interaction has been studied by particle simulation. During the interaction between laser and plasma, a strong electrostatic field caused by charge separation is observed, whose structure looks like a potential well. Electrons are accelerated to 10MeV within some tens of femtoseconds when the laser intensity is 5 x 1018W/cm2. After manya electrons escape from the potential-well-like structure, electron cavitons are generated. Because of laser filamentation, the intensity of the laser becomes very asymmetric, the caviton structure is squeezed and deformed, and then electron bubbles are generated, which result in ion bubble formation at last. It is the electron caviton and laser beam filamentation that cause bubble generation. The 10MeV superthermal electron generation accompanied with the electron caviton is attributed to E▽.E heating, which is a locally oscillating electron heating mechanism.
Sound Velocities in Porous Iron Shocked to 177GPa and the Implications for Shock Melting
LI Xi-Jun, ZHOU Xian-Ming, WANG Fan-Hou, LIU Fu-Sheng, GONG Zi-Zheng, JING Fu-Qian,
Chin. Phys. Lett. 2001, 18 (12): 1632-1634 .  
Abstract   PDF(pc) (397KB) ( 491 )
Sound velocities in shock-loaded solids are not only important to determine bulk moduli of solids at high pressures, but also crucial to inform the shock melting of solids upon loading. In this letter, we first report on shock melting of porous solids at high pressures by measuring sound velocities in the porous iron of average density 6.90g/cm3 in the pressure range of 110-180GPa. The measured sound velocity softens at pressures from 122 to 156Gpa, which may be attributed to shock melting of the porous iron.
Entire Period Halving of Persistent Current in a Mesoscopic Double-Ring System
WANG Hai-Jun, YI Xue-Xi, BA Xin-Wu
Chin. Phys. Lett. 2001, 18 (12): 1635-1637 .  
Abstract   PDF(pc) (220KB) ( 336 )
For the non-interacting electrons confined by a mesoscopic double-ring with a magnetic flux threading its center, we consider the problem of persistent current at zero and finite temperature. Furthermore, the tight-binding model is applied to give the expression of persistent current in this system. It is shown that in this double-ring system, the phenomena of entire period halving will occur.
Transient Process of Transport Through a Quantum Dot in a Stepped Bias: a Numerical Approach
XIONG Yong-Jian, XIONG Shi-Jie
Chin. Phys. Lett. 2001, 18 (12): 1638-1640 .  
Abstract   PDF(pc) (272KB) ( 315 )
The time evolution of current though a quantum dot responding to a stepped bias voltage is studied by a numerical approach in the mixed-valence regime and the Kondo regime. Our numerical results show the quasi-periodic oscillations of the current with a short damping time. When the deviation of the Fermi energy from the resonant dot level is increased by changing the gate voltage, the frequency of the oscillations is increased, but the average current decreases. The results also show a relatively slow oscillation in the Kondo regime.
Origin of the Novel Magnetoresistance Oscillation of the Two-Dimensional Electron Gas in AlxGa1-xN/GaN Heterostructures
ZHENG Ze-Wei, SHEN Bo, JIANG Chun-Ping, ZHANG Rong, SHI Yi, HENG You-Dou, ZHENG Guo-Zhen, GUO Shao-Ling, CHU Jun-Hao
Chin. Phys. Lett. 2001, 18 (12): 1641-1643 .  
Abstract   PDF(pc) (328KB) ( 509 )
In the magnetotransport measurements of the two-dimensional electron gas (2DEG) in modulation-doped Al0.22Ga0.78N/GaN heterostructures, a new magnetoresistance oscillation of the 2DEG is observed at low magnetic fields when the Al0.22Ga0.78N layer on GaN is under partially relaxed. It is thought that the misfit dislocations induced by the partialy relaxed Al0.22Ga0.78N layer modulate the distribution of the piezoelectric polarization-induced charges at the Al0.22Ga0.78N/GaN heterointerface, and thus produce a strong modulation-potential at the heterointerface. The strong modulation-potential results in the novel magnetoresistance oscillation of the 2DEG at low magnetic fields.
Electronic States in Quasi-one-Dimensional Copolymeric Sandwich Structures
LIU De-Sheng, WANG Lu-Xia, WEI Jian-Hua, ZHENG Bin, XIE Shi-Jie, HAN Sheng-Hao, MEI Liang-Mo
Chin. Phys. Lett. 2001, 18 (12): 1644-1647 .  
Abstract   PDF(pc) (405KB) ( 364 )
The electronic properties of xPA/nPPP/yPA sandwiched copolymers with a well-barrier-well structure have been studied by using a tight-binding calculation. It was found that the electronic properties of the neutral states of these sandwiched copolymers are sensitive to the constitutions of PPP and PA monomers and the interface coupling between PA and PPP. It is verified that the quantum tunneling effect will occur at the lowest conductive state of xPA/nPPP/xPA copolymers.
Possible Superconductivity at 37K in Graphite-Sulfur Composite
YANG Hai-Peng, WEN Hai-Hu, ZHAO Zhi-Wen, LI Shi-Liang, ZHAO Zhong-Xian
Chin. Phys. Lett. 2001, 18 (12): 1648-1650 .  
Abstract   PDF(pc) (194KB) ( 436 )
Sulfur intercalated graphite composites with diamagnetic transitions at 6.7 and 37K are prepared. The magnetization hysteresis loops (MHL), x-ray diffraction (XRD) patterns, and resistance were measured. From the MHL, a slight superconducting-like penetration process is observed at 15K in low field region. The XRD shows no large difference from the mixture of graphite and sulfur indicating that the volume of the superconducting phase (if any) is very small. The temperature dependence of resistance shows a typical semi-conducting behaviour with a saturation in low temperature region. This saturation is either induced by the de-localization of conducting electrons or by possible superconductivity in this system.
New Features of the Coercivity in Exchange-Coupled Ni81Fe19/CoO Bilayers
CAI Jian-Wang, LAI Wu-Yan
Chin. Phys. Lett. 2001, 18 (12): 1651-1654 .  
Abstract   PDF(pc) (343KB) ( 426 )
The coercivity behaviour of the Ni81Fe19 film exchange-coupled with an antiferromagnetic CoO underlayer has been investigated systematically. It has been found that the coercivity is greatly enhanced not only at the easy axis but also at the hard axis direction when the temperature is below the Néel temperature of CoO, Also, the thickness dependence of coercivity at low temperature follows the scaling relation as 1/tαNiFe with α = 2.5 at the hard axis, which is quite in contrast with the case of the easy axis, i.e., α =1.5, predicted theoretically and verified experimentally previously. The increase of the temperature leads to the decrease of the coercivity at both the easy and hard axes, but the scaling relations are held except the narrow region just below the Néeel temperature of CoO, at which the coercivity varies as 1/tαNiFe with α = 1.0 for both the easy and hard axes. Based upon Hoffmann's ripple theory and Malozemoff's random field model, a simple interpretation on the experiment findings is presented.
Optical Absorption in SiGe/Si Quantum Well Structures Created by Subband Transitions
YANG Yu, MAO Xu, YANG Hong-Wei, ZHOU Wei, ZHOU Zhen-Lai, LIU Huan-Lin, WANG Xun
Chin. Phys. Lett. 2001, 18 (12): 1655-1657 .  
Abstract   PDF(pc) (283KB) ( 429 )
The absorption in Si1-xGex/Si multiple quantum-well structures is measured. Several separated well absorption peaks corresponding to both intersubband and intervalance band transitions in the samples are observed. In the normal incidence, two broadband peaks are attributed to intervalence band transitions HH0-SO0(2.5μm), HH0-LH0(~ 3μm), respectively. Using 45°incidence of unpolarized light, both the intervalance band transitions and intersubband transitions are observed. The intervalance band transitions (HH0-LH0) are Ge composition dependent, but the intersubband transitions, HH0-HH1(5.9μm) and HH0-HH2(4.3μm), are not sensitive to the Ge composition.
An Organic Quantum-Well Electroluminescent Device with Enhanced Performance
YANG Kai-Xia, GAO Wen-Bao, LIU Hong-Yu, LI Chuan-Nan, ZHAO Yi, LIU Shi-Yong, HUANG Jing-Song
Chin. Phys. Lett. 2001, 18 (12): 1658-1659 .  
Abstract   PDF(pc) (242KB) ( 674 )
An organic electroluminescent (EL) device has been constructed with double quantum-well structure consisting of N,N'-bis-(1-naphthl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (NPB) doped with 5,6,11,12-tetraphenylnaphtha- cene (rubrene) as a potential well and emitter, undoped NPB as a barrier potential. The maximum EL efficiency and brightness reach to 5.6cd/A and 40000cd/m2, respectively. Most meaningfully, with the increase of the drive voltage, the EL efficiency (cd/A) declines very slowly after reaching its maximum, almost independent of the drive voltage in a wide range from 5 to 13V. The characteristic may be useful in improvement of the lifetime of the device.
Photocurrent Properties of AlGaN/GaN/AlGaN Multilayer Structure on Si
JIANG Ruo-Lian, ZHAO Zuo-Ming, CHEN Pen, XI Dong-Juan, SHEN Bo, ZHANG Rong, ZHENG You-Dou
Chin. Phys. Lett. 2001, 18 (12): 1660-1662 .  
Abstract   PDF(pc) (245KB) ( 501 )
Al0.2Ga0.8N/GaN/Al0.2Ga0.8N multilayer structures and GaN monolayer structures with AlN as the buffer layers were grown on Si substrates by metal-organic chemical vapor deposition. The photocurrent responses of these structures were measured and analysed. The multilayer structures showed a high response in a narrow range of wavelength. The peak wavelength is located at 365 nm at which the responsivity is as high as 24A/W under 5.5 V bias; this is much higher than the GaN monolayer structure. This high responsivity results mainly from the high polarization electric-field in the GaN layer of the Al0.2Ga0.8N/GaN/Al0.2Ga0.8N heterostructure.
High-Velocity H2O Masers Associated Massive Star Formation Regions
XU Ye, JIANG Dong-Rong, ZHENG Xing-Wu, GU Min-Feng, YU Zhi-Yao, PEI Chun-Chuan
Chin. Phys. Lett. 2001, 18 (12): 1663-1665 .  
Abstract   PDF(pc) (216KB) ( 436 )
We report on the results of 12CO (1-0) emission associated with H2O masers and massive star formation regions to identify high-velocity H2O masers. Several masers have a large blue-shift, even up to 120km.s-1, with respect to the CO peak, but no large redshifted maser appears. This result suggests that high-velocity H2O masers can most probably occur in high mass star-forming regions and quite a number of masers stem from the amplifications of a background source, which may enable those undetectable weak masers to become to an observable level.
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