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Block Entanglement in the Single-Hole Hubbard Model
YAO Kai-Lun, SUN Xiao-Zhong, LIU Zu-Li, LI Yan-Chao, YU Li, GAO Guo-Ying
Chin. Phys. Lett. 2006, 23 (9):
2352-2355
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We investigate the distribution of the entanglement of the one-dimensional single-hole Hubbard model (HM) and study the relationship between the entanglement and quantum phase transition in the model. The von Neumann entropy of a block with neighbouring spins L for a single-hole HM is calculated using the density-matrix renormalization group. The distributions of the entanglement entropy in the ground state, as a function of block length, show a dramatic effect, i.e. effectively decoupling with the centres, no matter how the Coulomb interaction u>0 or u<0. Contrarily, for the Coulomb interaction u=0 or close to zero, the entanglement entropy in the single-hole model reaches a saturation value for a certain block size. For a fixed size L=40, the ground state entanglement entropy measure, as a function of u, shows a peak corresponding to the critical quantum phase transition.
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Radiative Decays of Charmonium into Light Mesons
GAO Ying-Jia, ZHANG Yu-Jie, CHAO Kuang-Ta
Chin. Phys. Lett. 2006, 23 (9):
2376-2378
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We apply perturbative QCD to the radiative decays of charmonia J/ψ and XcJ into light mesons. We perform a complete numerical calculation for the quark--gluon loop diagrams involved in these processes. The calculated J/ψ decay branching ratios into p-wave mesons f2(1270) and f1(1285) fit the data well, while that of f0(980) (if treated as an ss meson) is predicted to be 1.6×10-4, which implies that f0(1710) can not be the ss or (uu+dd)√2 meson. Decays of p-wave charmonia XcJ → ρ (ω,Ф) γ (J=0,1,2) are also studied, and the branching ratio of Xcl → ρ γ is predicted to be 1.4×10-5, which may be tested by CLEO-c ollaboration and BESIII collaboration with future experiments.
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Finite-Width Correction to Form Factors of γγ→ π0 Transition
HANG Sheng-Xi, ZHANG Zhen-Yu, LIU Jue-Ping
Chin. Phys. Lett. 2006, 23 (9):
2387-2390
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Instead of the usual zero-width approximation for one resonance, we use the finite-width approximation for the two low resonances, i.e. the ρ-ω mesons, to investigate the light-cone local QCD sum rules for the form factor of the transition γγ→ π0. According to the method of the analytic continuation by duality, the weight function, the polynomial of a low order N, is added to the dispersion integral to annihilate the integrand in the region where both resonance saturation and the QCD asymptotic expression are least reliable. The resultant form factor in the cases for the zero- and finite-widths are almost the same, both agree well with the experimental measurements. A comparison with the result from the Laplacian transformed light-cone sum rules and a brief discussion are given.
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Superluminal Behaviour of Modified Bessel Waves
WANG Zhi-Yong, XIONG Cai-Dong
Chin. Phys. Lett. 2006, 23 (9):
2422-2425
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Much experimental evidence of superluminal phenomena has been available by electromagnetic wave propagation experiments, with the results showing that the phase time describes the barrier traversal time. Based on the extrapolated phase time approach and numerical methods, we show that, in contrast to the ordinary Bessel waves of real argument, the group velocities of modified Bessel waves are superluminal. We obtain the following results. The group velocities increase with the increase of propagation distance, which is similar to the evanescent plane-wave cases. For large wave numbers, the group velocities fall off as the wave numbers increase, which is similar to the evanescent plane-wave cases. For small wave numbers, the group velocities increase with the increase of wave numbers, this is different from the evanescent plane-wave cases.
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Nonclassical Properties of Superposition of Two Coherent States Shifted in Phase by 3π/2
AHMAD Muhammad Ashfaq, ZENG Ran, LIU Shu-Tian
Chin. Phys. Lett. 2006, 23 (9):
2438-2441
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We consider the quantum superposition of two coherent states shifted in phase by 3π/2, |α> and |-iα>, as well as special states that are characterized solely with respect to amplitude α. According to analysis of nonclassical properties such as oscillatory and sub-Poissonian distribution of photon numbers, photon antibunching, quadrature squeezing, and negativity of Wigner function, it is concluded that the considered superposition state is a nonclassical state. Also, the special state is found to exhibit even stronger onclassical features when relative phase Ф of the superposition is equal to the average photon number |α|2.
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Modulation Frequency Multiplexed Tunable Diode Laser Spectroscopy System for Simultaneous CO, CO2 Measurements
CHEN Dong, LIU Wen-Qing, ZHANG Yu-Jun, LIU Jian-Guo, WEI Qing-Nong, KAN Rui-Feng, WANG Min, CUI Yi-Ben, CHEN Jiu-Ying
Chin. Phys. Lett. 2006, 23 (9):
2446-2449
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A modulation frequency multiplexed dual diode-laser system is developed for simultaneous detection of the two most common fire gas products CO and CO2. Simultaneous detection is achieved by modulating each laser at different frequencies, demodulating the signal by a pair of lock-in amplifiers for each gas. Laser beams are combined and detected by one detector after passing through an identical optical path. The experimental results show little performance degradation associated with modulation frequency multiplexing, and no cross-talk between the two multiplexed detection channels is measured.
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A Simple Model to Describe the Requirement of Realizing All-Optical Poling
GUO Bin, GUO Fu-Quan, CHEN Yong, ZHU Li-Jun, LIU Fu-Sheng, ZHANG Qi-Jin, WANG Gong-Ming
Chin. Phys. Lett. 2006, 23 (9):
2458-2460
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All-optical poling (AOP) of a crosslinkable polymer based on hexamethoxymethyl melamine (HMMM) and Disperse red 1 (DR-1) is investigated. It is found that the saturation second harmonic generation (SHG) intensity decreases significantly with the increase of the sample temperature from 33°C to 63°C. From the perspective of energy equilibrium, the main factors of AOP are analysed, and by introducing the classical ideal gas model, a simple inequation is first deduced to describe the requirement of realizing AOP.
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Pellet Enhanced Performance on the HL-2A Tokamak
DING Xuan-Tong, YANG Qing-Wei, YAN Long-Wen, ZHU Gen-Liang, XIAO Zheng-Gui, LIU De-Quan, CAO Zeng, GAO Qing-Di, LONG Yong-Xing, LIU Yi, ZHOU Yan, PAN Yu-Dong, CUI Zheng-Ying, HUANG Yuan, LIU Ze-Tian), SHI Zhong-Bing,
JI Xiao-Quan, XIAO Wei-Wen, LIU Yong
Chin. Phys. Lett. 2006, 23 (9):
2502-2505
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Enhanced confinement has been achieved by the centre fuelling of pellet injection on the HL-2A tokamak. The energy confinement time increases from 50ms to 140ms after the pellet injection. Experimental results show that the improvement of the confinement is related to the decrease of the electron heat transport. everal phenomena which may lead to the improved confinement have been observed in the experiments. After the pellet injection the hollow electron temperature profile and the peaked electron density profile can be sustained for about 200ms, but the improved confinement remains at about 500ms. Sawtooth features and MHD modes have been observed by soft x-ray array and the Mirnov probes. The weak (or reversed) magnetic shear is thought to be an important cause of the low electron heat transport.
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Discontinuous Structural Phase Transition Behaviour in Multiple Component Alloy Melts
WANG Yu-Qing, WU Yu-Qin, LIU Jian-Tong, BIAN Xiu-Fang
Chin. Phys. Lett. 2006, 23 (9):
2513-2515
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Discontinuous structural phase transition behaviour in seven kinds of liquid multiple component alloys are found by using a torsional oscillation viscometer. There are different phases existing in the system and the number of phases is discussed using the equilibrium thermodynamics phase rule. The phase parameters (η0,ε) and order parameter df in different phase regions are calculated based on the researched results. It is found that the parameters (η0,ε, df) change at the structural transition point. The diameter of the fluid clusters, df, is stable in each phase region, which indicates that the structure is uniform.
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A Kilowatt Diode-Pumped Solid-State Heat-Capacity Double-Slab Laser
GUO Ming-Xiu, LI Jin-Dong, FU Wen-Qiang, SHI Xiang-Chun, HU Qi-Quan, CHEN Wei-Biao
Chin. Phys. Lett. 2006, 23 (9):
2530-2533
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A kilowatt diode-pumped solid state heat capacity laser is fabricated with a double-slab Nd:YAG. Using the theoretical model of heat capacity laser output laser characteristics, the relationships between the output power, temperature and time are obtained. The slab is 59×40×4.5mm3 in size. The average pump power is 11.2kW, the repetition rate is 1kHz, and the duty cycle is 20%. During the running time of 1s, the output energy of the laser has a fluctuation with the maximal output energy at 2.06J, and the maximal output average power is 2.06kW. At the end of the second, the output energy declines to about 50% compared to the beginning. The thermal effects can be improved with one slab cooled by water. The experimental results are consistent with the calculation data.
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High Spectral Resolution Mo/Si Multilayers Working at High Order Reflection
WU Wen-Juan, ZHU Jing-Tao, WANG Zhan-Shan, ZHANG Zhong, WANG Feng-Li, WANG Hong-Chang, ZHANG Shu-Min, XU Yao, CHENG Xin-Bin, WANG Bei, LI Cun-Xia, WU Yong-Rong, QIN Shu-Ji, CHEN Ling-Yan, ZHOU Hong-Jun, HUO Tong-Lin
Chin. Phys. Lett. 2006, 23 (9):
2534-2537
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The high reflectance orders are used to improve the spectral resolution of Mo/Si multilayers. The multilayers for the first-, second- and third-order reflectance are designed and optimized, respectively. These multilayers are fabricated by using a directed current magnetron sputtering system, and the reflectivity is measured in an extreme ultraviolet range by synchrotron radiation. The experimental results show that the spectral resolution λ/Δλ (λ=14nm) increases from 24.6 for the first order to 66.6 for the third order.
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Effects of High Pressure on BC3
ZHOU Jin-Ling, CUI Tian, MA Yan-Ming, LIU Zhi-Ming, LIU Bing-Bing, ZOU Guang-Tian
Chin. Phys. Lett. 2006, 23 (9):
2538-2541
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High-pressure phases of BC3 are studied within the local density approximation under the density functional theory framework. When the pressure reaches 20GPa, the layered BC3 that is a semiconductor at ambient pressure, becomes metallic. As the pressure increases, the material changes into a network structure at about 35GPa. To understand the mechanism of phase transitions, band structure and density of states are discussed. With the increase of pressure, the width of bands broadens and the dispersion of bands enlarges. Additionally, the density of states of the network bears great resemblance to that of diamond. Formation of the sp3 bonding in the network is the main reason for the structural transformation at 35GPa.
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Improved Fluorescence from Tm3+/Er3+/Ce3+ Triply Doped Bismuth-Silicate Glasses for S+C-bands Amplifiers
WANG Xun-Si, NIE Qiu-Hua, LIU Li-Ren, XU Tie-Feng, SHEN Xiang, DAI Shi-Xun, ZHANG Xiang-Hua
Chin. Phys. Lett. 2006, 23 (9):
2553-2556
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Fluorescence of Tm3+/Er3+ codoped bismuth-silica (BS) glasses and the sensitization of Ce3+ are investigated. It shows that Ce3+ codoping with Tm3+/Er3+ in BS glasses results in a quenching of Tm3+ ion emission from 3+F4 to the 3+H4 level. Consequently, the 1.47μm emission occurs after the population inversion between the 3+H4 and 3+F4 levels. Furthermore, the codoped glasses show the broad emission spectra over the whole S and C bands with full-width at half-maximum (FWHM) up to about 119nm, as it combines 1.55μm emission band of Er3+ with 1.47μm emission band of Tm3+ under 800nm excitation.
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Influence of GaAsP Insertion Layers on Performance of InGaAsP/InGaP/AlGaAs Quantum-Well Laser
CAO Yu-Lian, LIAN Peng, MA Wen-Quan, WANG Qing, WU Xu-Ming, HE Guo- Rong, LI Hui, WANG Xiao-Dong, SONG Guo-Feng, CHEN Liang-Hui
Chin. Phys. Lett. 2006, 23 (9):
2586-2586
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We report on the use of very thin GaAsP insertion layers to improve the performance of an GaAsP/InGaP/AlGaAs single quantum-well laser structure grown by metal organic chemical vapour deposition. Compared to the non-insertion structure, the full width at half maximum of photoluminescence spectrum of the insertion structure measured at room temperature is decreased from 47 to 38nm indicating sharper interfaces. X-ray diffraction shows that the GaAsP insertion layers between AlGaAs and InGaP compensates for the compressive strain to improve the total interface. The laser performance of the insertion structure is significantly improved as compared with the counterpart without the insertion layers. The threshold current is decreased from 560 to 450mA while the slope efficiency is increased from 0.61 to 0.7W/A and the output power is increased from 370 to 940mW. The slope efficiency improved is very high for the devices without coated facets. The improved laser performance is attributed to the suppression of indium carry-over due to the use of the GaAsP insertion layers.
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Reduction of Dislocations in GaN Epilayer Grown on Si (111) Substrates using a GaN Intermedial Layer
WANG Jian-Feng, ZHANG Bao-Shun, ZHANG Ji-Cai, ZHU Jian-Jun, WANG Yu-Tian, CHEN Jun, LIU Wei, JIANG De-Sheng, YAO Duan-Zheng, YANG Hui
Chin. Phys. Lett. 2006, 23 (9):
2591-2594
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GaN intermedial layers grown under different pressures are inserted between GaN epilayers and AlN/Si(111) substrates. In situ optical reflectivity measurements show that a transition from the three-dimensional (3D) mode to the 2D one occurs during the GaN epilayer growth when a higher growth pressure is used during the preceding GaN intermedial layer growth, and an improvement of the crystalline quality of GaN epilayer will be made. Combining the in situ reflectivity and transmission electron microscopy (TEM) measurements, it is suggested that the lateral growth at the transition of growth mode is favourable for bending of dislocation lines, thus reducing the density of threading dislocations in the epilayer.
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Influence of Positive Bias on Electrical Properties of Undoped Nanocrystalline Diamond Films
WU Nan-Chun, XIA Yi-Ben, TAN Shou-Hong, WANG Lin-Jun, LIU Jian-Min, SU Qing-Feng
Chin. Phys. Lett. 2006, 23 (9):
2595-2597
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By means of electron assisted hot filament chemical vapour deposition technology, nanocrystalline diamond films are deposited on polished n-(100)Si wafer surface at 1kPa gas pressure. The deposited films are characterized with a Raman spectrometer, atomic force microscope, semiconductor characterization system and Hall effect measurement system. The results show that, when bias current is larger than 2A, sheet hole concentration can increase to a value greater than 1013cm-2 and undoped nanocrystalline diamond films with a p-type semiconducting characteristic form. Heterojunction between n-Si substrate and the nanocrystalline diamond films deposited with 2A and 6A bias current has an evident junction effect. Hole formation mechanisms in the films are discussed.
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Recombination Reduction in Dye-Sensitized Solar Cells by Screen-Printed TiO2 Underlayers
LIU Xi-Zhe, HUANG Zhen, LI Ke-Xin, LI Hong, LI Dong-Mei, CHEN Li-Quan, MENG Qing-Bo
Chin. Phys. Lett. 2006, 23 (9):
2606-2608
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In dye-sensitized solar cells (DSSCs), the TiO2 underlayer can block the electron recombination at the FTO (fluorine doped SnO2) glass/electrolyte interface. This underlayer was traditionally prepared by spray-pyrolysis or spin coating. In this study, we develop an alternative method based on screen-printing. The quality of the screen-printed underlayers is characterized by SEM, XPS and the hotoelectrochemistry measurements. The prepared underlayers are smooth and effective. The screen-printing technique is cheap and easy to handle and can produce films with different patterns. These advantages will facilitate applications of the screen-printed underlayer.
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Effects of Relative Orientation of Molecules on Electron Transport in Molecular Devices
ZHOU Yan-Hong, ZHENG Xiao-Hong, XU Ying, ZENG Zhao-Yang, ZENG Zhi
Chin. Phys. Lett. 2006, 23 (9):
2609-2612
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Effects of relative orientation of the molecules on electron transport in molecular devices are studied by the non-equilibrium Green function method based on density functional theory. In particular, two molecular devices with planar Au7 and Ag3 clusters sandwiched between the Al(100) electrodes are studied. In each device, two typical configurations with the clusters parallel and vertical to the electrodes are considered. It is found that the relative orientation affects the transport properties of these two devices completely differently. In the Al(100)--Au7--Al(100) device, the conductance and the current of the parallel configuration are much larger than those in the vertical configuration, while in the Al(100)--Ag3--Al(100) device, an opposite conclusion is obtained.
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Effects of Spatial Variation of Thermal Electrons on Whistler-Mode Waves in Magnetosphere
CHEN Lun-Jin, ZHENG Hui-Nan, XIAO Fu-Liang, WANG Shui
Chin. Phys. Lett. 2006, 23 (9):
2613-2616
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A ray-tracing method is developed to evaluate the wave growth/damping and specifically propagation trajectories of the magnetospherically reflected Whistler-mode waves. The methodology is valid for weak wave growth/damping when plasma is comprised of a cold electron population and a hot electron population, together with background neutralizing ions, e.g. protons. The effect of anisotropic thermal electrons on the propagation of Whistler-mode waves is studied in detail. Numerical results are obtained for a realistic spatial variation model of plasma population, including the cold electron density distribution, and the thermal electron density and temperature distribution. It is found that, analogous to the case of the typical cold plasma approximation, the overall ray path of Whistler-mode waves is insensitive to the thermal electron density and temperature anisotropy, and the ray path reflects where wave frequency is below or comparable to the local lower hybrid resonance frequency flhr. However, the wave growth is expected to be influenced by the thermal electron population. The results present a first detailed verification for the validity of the typical cold plasma approximation for the propagation of Whistler-mode waves and may account for the observation that the Whistler-mode waves tend to propagate on a particular magnetic shell L where the wave frequency is comparable to flhr.
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75 articles
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