Chin. Phys. Lett.

Volume 24 Issue 4

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Electrodynamic Analysis of Dissipative Electromagnetic Materials Based on Fractional Derivative

TAN Kang-Bo, LIANG Chang -Hong, DANG Xiao-Jie

Chin. Phys. Lett. 2007, 24 (4): 847-850 .

Abstract

PDF(pc) (210KB) ( 638 )

The generalized Lagrangian is defined in a dissipative electromagnetic medium on the basis of the combination of dynamical analysis and fractional derivative. Lorentz medium models are obtained by formulating relevant Euler--Lagrange equations. The invariance is obtained subsequently by investigating the invariance of time variation in the system, and then the relation between the related Hamiltonian and electromagnetic energy density is investigated. Canonical equations are obtained eventually. The electrodynamic interpretation on dissipative electromagnetic systems is revealed.

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Coherence-Like States of Two Coulomb-Correlated Ions Confined in a Paul Trap

LI Hui, HAI Wen-Hua, CHEN Wen-Qin, XU Jun

Chin. Phys. Lett. 2007, 24 (4): 851-854 .

Abstract

PDF(pc) (214KB) ( 773 )

We report the n×n coherence-like state solutions in the cases of n,n'=1,2,... for the system including two Coulomb-correlated ions confined in a one-dimensional Paul trap with a time-dependent harmonic potential. One of the n' exact solutions of the centre-of-mass motion describes a generalized coherent state. For a small driving strength the n approximate solutions of relative motion are constructed, which describe the coherent oscillations of the two ions around the classical equilibrium position.

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Entanglement Transfer and Periodic Sudden Death Phenomenon in Two Parallel 1D Spin Chains of Quantum Spin Network

WANG Zhao-Ming, SHAO Bin, ZOU Jian

Chin. Phys. Lett. 2007, 24 (4): 855-858 .

Abstract

PDF(pc) (288KB) ( 657 )

We investigate the entanglement transfer in two parallel 1D spin chains of a quantum spin network, and show that the perfect entanglement transfer can be realized at some special times. In addition, the so-called `sudden death' phenomenon of entanglement is found in the spin network system.

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Fluctuation of Quantum Information Density in Curved Time--Space

BI Qiao,

Chin. Phys. Lett. 2007, 24 (4): 859-862 .

Abstract

PDF(pc) (226KB) ( 502 )

A dynamical equation for quantum information density (QID) in curved spacetime is presented. The related fluctuation of QID with quantum Einstein equation is also discussed, which reveals the measuring of the dynamical mutual information condition using a Gaussian quantum channel.

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Multiparty Quantum Secret Sharing of Quantum States with Quantum Registers

GUO Ying, ZENG Gui-Hua, CHEN Zhi-Gang

Chin. Phys. Lett. 2007, 24 (4): 863-866 .

Abstract

PDF(pc) (320KB) ( 602 )

A quantum secret sharing scheme is proposed by making use of quantum registers. In the proposed scheme, secret message state is encoded into multipartite entangled states. Several identical multi-particle entanglement states are generated and each particle of the entanglement state is filled in different quantum registers which act as shares of the secret message. Two modes, i.e. the detecting mode and the message mode, are employed so that the eavesdropping can be detected easily and the secret message may be
recovered. The security analysis shows that the proposed scheme is secure against eavesdropping of eavesdropper and cheating of participants.

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Photoassociation of Atomic BEC within Mean-Field Approximation: Exact Solutions

CAI Wei, JING Hui, ZHAN Ming-Sheng, XU Jing-Jun

Chin. Phys. Lett. 2007, 24 (4): 867-870 .

Abstract

PDF(pc) (239KB) ( 609 )

We propose an exactly solvable method to study the coherent two-colour photoassociation of an atomic Bose--Einstein condensate, by linearizing the bilinear atom--molecule coupling, which allows us to conveniently probe the quantum dynamics and statistics of the system. By preparing different initial states of the atomic condensate, we can observe very different quantum statistical properties of the system by exactly calculating the quadrature-squeezed and mode-correlated functions.

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Switching and Self-trapping Dynamics of Dark Solitons in a Two-Component Bose--Einstein Condensate

LI Hong, WANG D. N.

Chin. Phys. Lett. 2007, 24 (4): 871-873 .

Abstract

PDF(pc) (199KB) ( 507 )

Two coupled dark solitons are considered in a two-component Bose--Einstein
condensate, and their dynamics are investigated by the variational approach based the renormalized integrals of motion. The stationary states as physical solutions to the describing equations are obtained, and the dynamic mechanism is demonstrated by performing a coordinate of a classical particle moving in an effective potential field. The switching and self-trapping dynamics of the coupled dark vector solitons are discussed by the evolution of the atom population transferring ratio.

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Moller Energy Complexes of Monopoles and Textures in General Relativity and Teleparallel Gravity

Melis Ayg, Ihsan Yilmaz,

Chin. Phys. Lett. 2007, 24 (4): 874-877 .

Abstract

PDF(pc) (218KB) ( 537 )

The energy problem of monopole and texture spacetimes is investigated in
the context of two different approaches of gravity such as general relativity and teleparallel gravity. In this connection, firstly the energies for monopoles and textures are evaluated by using the Moller energy--momentum prescription in different approximations. It is obtained that energy distributions of Moller definition give the same results for these topological defects (monopole and texture) in general relativity (GR) and teleparallel gravity (TG). The results strengthen the importance of the Moller energy--momentum definitions in given spacetimes and the viewpoint of Lessner that Moller energy--momentum complex is a powerful concept for energy and momentum.

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Radiative Energy Shifts of an Accelerated Multilevel Atom Coupled to the Derivative of a Scalar Field

ZHU Yun-Feng, YU Hong-Wei

Chin. Phys. Lett. 2007, 24 (4): 878-881 .

Abstract

PDF(pc) (217KB) ( 381 )

We study the energy level shifts of an accelerated multilevel atom in dipole coupling to the derivative of a quantum massless scalar field and separately calculate the contributions of vacuum fluctuations and radiation reaction to the shifts. It is found that, in contrast to the case of a monopole-like interaction, both the vacuum fluctuations and radiation reaction contributions are changed by acceleration, and they all contain non-thermal correction terms. Our results suggest that the effect of acceleration on the energy shifts is dependent on the type of the interaction between the atom and the quantum field.

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From Autonomous Coherence Resonance to Periodically Driven Stochastic Resonance

CAO Zhou-Jian, LI Peng-Fei, HU Gang,

Chin. Phys. Lett. 2007, 24 (4): 882-885 .

Abstract

PDF(pc) (301KB) ( 1290 )

In periodically driven nonlinear stochastic systems, noise may play a role of enhancing the output periodic signal (termed as stochastic resonance or SR). While in autonomous excitable systems, noise may play a role of increasing coherent motion (termed as coherence resonance or CR). So far the topics of SR and CR have been investigated separately as two major fields of studying the active roles of noise in nonlinear systems. We find that these two topics are closely related to each other. Specifically, SR occurs in such periodically driven systems that the corresponding autonomous systems show CR. The SR with sensitive frequency dependence can be observed when the corresponding autonomous system shows CR with finite characteristic frequency. Moreover, `resona

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Non-Smooth Bifurcation and Chaos in a DC-DC Buck Converter

QIN Zhi-Ying, LU Qi-Shao

Chin. Phys. Lett. 2007, 24 (4): 886-889 .

Abstract

PDF(pc) (307KB) ( 984 )

A direct-current--direct-current (DC-DC) buck converter with integrated load current feedback is studied with three kinds of Poincare maps. The external corner-collision bifurcation occurs when the crossing number per period varies, and the internal corner-collision bifurcations occur along with period-doubling and period-tripling bifurcations in this model. The multi-band chaos roots in external corner-collision bifurcation and often grows into 1-band chaos. A new kind of chaotic sliding orbits, which is more complex for non-smooth systems, is also found in this model.

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Synchronization Scheme for Uncertain Chaotic Systems via RBF Neural Network

CHEN Mou, JIANG Chang-Sheng, WU Qing-Xian, CHEN Wen-Hua

Chin. Phys. Lett. 2007, 24 (4): 890-893 .

Abstract

PDF(pc) (231KB) ( 590 )

A sliding mode adaptive synchronization controller is presented with a neural network of radial basis function (RBF) for two chaotic systems. The uncertainty of the synchronization error system is approximated by the RBF neural network. The synchronization controller is given based on the output of the RBF neural network. The proposed controller can make the synchronization error convergent to zero in 5s and can overcome disruption of the uncertainty of the system and the exterior disturbance. Finally, an example is given to illustrate the effectiveness of the proposed synchronization control method.

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Marchenko Equation for the Derivative Nonlinear Schrodinger Equation

HUANG Nian-Ning

Chin. Phys. Lett. 2007, 24 (4): 894-897 .

Abstract

PDF(pc) (212KB) ( 1239 )

A simple derivation of the Marchenko equation is given for the derivative nonlinear Schrodinger equation. The kernel of the Marchenko equation is demanded to satisfy the conditions given by the compatibility equations. The soliton solutions to the Marchenko equation are verified. The derivation is not concerned with the revisions of Kaup and Newell.

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Anomalous Heat Conduction in One-Dimensional Dimerized Lattices

LI Xin-Xia, TANG Yi

Chin. Phys. Lett. 2007, 24 (4): 898-901 .

Abstract

PDF(pc) (244KB) ( 501 )

The process of heat conduction in one-dimensional dimerized systems is studied by means of numerical simulation. Taking into account the difference between the strong bond and the weak one of the systems, our calculation indicates that heat conduction in the lattice is anomalous. For the typical parameter related to a real physical system, the divergent exponent is shown to be in agreement with that predicted by the mode-coupling theory. Moreover, our study shows that the homogeneous chain is the best thermal conductor.

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Influence of Photon Mass on Vacuum Birefringence Experiment

CHEN Min, SHAO Cheng-Gang

Chin. Phys. Lett. 2007, 24 (4): 902-904 .

Abstract

PDF(pc) (190KB) ( 549 )

Influence of photon mass on vacuum birefringence experiment is analysed according to the nonlinearities of vacuum quantum electrodynamics for the light propagation through an intense electromagnetic field. It is shown that although the photon mass will cause a change of the refractive indices n_⊥ and n_|| of vacuum birefringence, the difference n_||-n_⊥ is unchanged, which means that the effect of photon mass cannot be observed in vacuum birefringence experiment.

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Modified Woods--Saxon Potential for Heavy-Ion Fusion Reaction

TIAN Jun-Long, WANG Ning, LI Zhu-Xia,

Chin. Phys. Lett. 2007, 24 (4): 905-908 .

Abstract

PDF(pc) (308KB) ( 1003 )

A modified Woods--Saxon (MWS) potential is proposed for describing nucleus-nucleus interaction based on the Skyrme energy-density functional approach. Fusion barriers for a large number of fusion reactions from light to heavy systems can be described well with this potential. The suitable incident energies for fusion reactions leading to superheavy nuclei are also explored. It seems to us that the MWS potential is useful for selecting the suitable incident energies for fusion reactions for producing super-heavy nuclei.

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Importance of Relativistic Effects for Intermediate-Z Elements: Photoionization Process of Excited Na

HAN Xiao-Ying, WANG Xiao-Lu, VOKY Lan, FEAUTRIER Nicole, LI Jia-Ming,

Chin. Phys. Lett. 2007, 24 (4): 909-912 .

Abstract

PDF(pc) (310KB) ( 517 )

Using a modified R-matrix code, the fine-structure-resolved partial photoionization cross sections of excited Na (Z=11) are calculated within the Breit--Pauli approximation. Our calculated energy levels of Na⁺ and Na are in good agreement with the experimental values within 1% and the branching ratios of the J-resolved partial cross sections are consistent with the recent measurements within the experimental uncertainties. The agreements are impossible to be obtained without adequately taking into account the relativistic effects and the electron correlations together. Therefore, even for the intermediate-Z elements (e.g. Na with Z=11), the relativistic effects (mainly the spin-orbit interactions) should not be neglected.

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Solvent Suppression in Intermolecular Multiple-Quantum Coherence Nuclear Magnetic Resonance Spectra with Only z-axis Gradients

FENG Hai, ZHANG Sheng-Chun, CAI Shu-Hui, CHEN Zhong, FENG Ji

Chin. Phys. Lett. 2007, 24 (4): 913-916 .

Abstract

PDF(pc) (310KB) ( 751 )

The solvent peak in the intermolecular multiple-quantum coherence spectra can be suppressed by either applying pulse field gradients or spinning sample along the magic angle direction (ψ=54.7). However, these two methods also suppress the signals of the solute. We design　two pulse sequences with only z-axis gradients to suppress the　solvent peak without reducing the intensity of solute signals. Compared　to the former pulse sequence, the latter pulse sequence is insensitive　to the imperfection of pulse flip angles. When the flip angles of the　second pulse sequence are purposely deviated 1/10 from the optimal　values, the solvent peak is still weak. Theoretical expressions,　experimental observations and computer simulations demonstrate that the　two methods can be used to effectively suppress solvent peak in　intermolecular multiple-quantum coherence spectra.

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Experimental Study on Electrostatic Guiding of Supersonic D₂O Molecular Beam with Two Charged Wires

YIN Ya-Ling, XIA Yong, Chen Hai-Bo, YIN Jian-Ping

Chin. Phys. Lett. 2007, 24 (4): 917-920 .

Abstract

PDF(pc) (401KB) ( 453 )

We demonstrate the guiding of a supersonic heavy-water (D₂O) molecular beam using a hollow electrostatic field generated by the combination of two parallel charged-wires and two grounded metal-plates, and report some new and preliminary experimental results. In the experiment, we detect the guiding signals by using the method of time-of-flight mass spectrum and study the dependence of the relative transmission of the beam guide on the guiding voltage. Our study shows that the relative transmission of the beam guide is increased linearly with increasing guiding voltage V_guid, and the number of the guided D₂O molecules is at least increased by 89.4% when the guiding voltage is +20.0kV. Finally, some potential applications of our guiding scheme in the molecule optics are briefly discussed.

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Multi-Electron Processes in 4.15--11.08keV/u¹³C⁶⁺on Argon Collisions

RUAN Fang-Fang, CAI Xiao-Hong, YU De-Yang, LU Rong-Chun, SHAO Cao-Jie, LI Ming-Sheng, ZHANG Hong-Qiang, CUI Ying, SHAO Jian-Xiong, DING Bao-Wei, XUE Ying-Li, QI De-Jun, YANG Zhi-Hu, CHEN Xi-Meng

Chin. Phys. Lett. 2007, 24 (4): 921-924 .

Abstract

PDF(pc) (286KB) ( 501 )

The relative partial cross sections for ¹³C⁶⁺--Ar collisions at 4.15--11.08keV/u incident energy are measured. The cross-section ratios σ^2E/σ^SC,σ^3E/σ^SC, σ^4E
σ^SC and σ^5Eσ^SC are approximately the constants of 0.51±0.05, 0.20±0.03, 0.06±0.03 and 0.02±0.01 in this region. The significance of the multi-electron
process in highly charged ions (HCIs) with argon collisions is demonstrated (σ^ME/σ^SC as high as 0.79±0.06). In multi-electron processes, it is shown that transfer ionization is dominant while pure electron capture is weak and negligible. For all reaction channels, the cross-sections are independent of the incident energy in the present energy region, which is in agreement with the static characteristic of classic models, i.e. the molecular Coulomb over-the-barrier model (MCBM), the extended classical over-the-barrier model (ECBM) and the semiempirical scaling laws (SL). The result is compared with these
classical models and with our previous work of ¹³C⁶⁺-Ne collisions [Chin. Phys. Lett. 23(2006)95].

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Resonance Excitation Rate Coefficient of Ni-Like Tantalum

SHEN Tian-Ming, CHEN Chong-Yang, WANG Yan-Sen, GU Ming-Feng

Chin. Phys. Lett. 2007, 24 (4): 925-928 .

Abstract

PDF(pc) (254KB) ( 634 )

The ab initio calculations of electron-impact resonant excitation rate coefficients from the ground level to 54 fine-structure levels of 3d⁹4l(l=s,p,d,f) configurations of Ni-like tantalum ion are performed by using a fully relativistic distorted-wave approximation. The configuration-interaction effects are taken into account. The decays to autoionizing levels possibly followed by autoionization cascades are also included in the calculation. The contributions from doubly-excited intermediate states of Cu-like 3l¹⁷n'l'n''l''(n'=4,5; n''=5-15) are calculated explicitly, and the contributions from high Rydberg states (n''>15) are taken into account by using n^-3 scaling law. The present results should be more accurate than the existent calculations.

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Enhancing Coherent Combining Efficiency via Choosing Appropriate Lasing Wavelength in a Michelson Compound Cavity Based on Two 3dB Fibre Loop Mirrors and One Fibre Bragg Grating

LIU Feng-Nian, JIA Xiu-Jie, LIU Yan-Ge, YUAN Shu-Zhong, DONG Xiao-Yi

Chin. Phys. Lett. 2007, 24 (4): 929-932 .

Abstract

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Enhancing coherent combining efficiency via choosing appropriate lasing wavelength in a Michelson compound cavity based on two 3dB fibre loop mirrors and one fibre Bragg grating (FBG) has been experimentally demonstrated. The FBG with 4.5% reflectivity is replaced at the cleaved facet with 4% Fresnel reflection. A high coherent combining efficiency of 93.5% is obtained when the FBG with central wavelength at 1559.845nm is introduced into the cavity, while it is only 90.1% combining efficiency with the FBG at central wavelength 1557.830nm. In comparison with other reports, the proposed compound-cavity laser has the advantage of needless tuning FBG to obtain the coherent condition, and it is facile to ascertain the seemly
wavelength lasing for a Michelson compound cavity.

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Sub-Half-Wavelength Atom Localization via Coherent Control of Autler--Townes Spontaneous Spectrum

XU Jun, HU Xiang-Ming

Chin. Phys. Lett. 2007, 24 (4): 933-936 .

Abstract

PDF(pc) (344KB) ( 644 )

We show that it is possible to localize an atom in a half-wavelength region
by relaxing the strict condition that the atom is prepared in a specific excited state as in the recently proposed scheme [Phys. Rev. A 65(2002)043819]. In particular, we consider a four-level atom, for which a weak exciting field transfers population from the ground state to the excited state and three control fields (one standing-wave field while two travelling-wave fields) couple the excited state and two auxiliary states. By tuning the exciting field and by varying the collective phase of the control fields, the atom is localized in one of the two half-wavelength regions with 50% detecting probability. The main advantage of the scheme is the experimental accessibility and controllability.

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Absorption Spectra of a Three-Level Atom Embedded in a PBG Reservoir

ZHANG Han, ZHANG Ke, ZHANG Han-Zhuang

Chin. Phys. Lett. 2007, 24 (4): 937-940 .

Abstract

PDF(pc) (238KB) ( 938 )

We introduce the `decay rate' terms into the density matrix equations of an atom embedded in a photonic band gap (PBG) reservoir successfully. By utilizing the master equations, the probe absorption spectra and the refractivity properties of a three-level atom in the PBG reservoir are obtained. The interaction between the atom and the PBG reservoir as well as the effects of the quantum interference on the absorption of the atom has also been taken into account. It is interesting that two different types of the anomalous dispersion relations of refractivity are exhibited in one dispersion line. The methodology used here can be applied to theoretical investigation of quantum interference effects of other atomic models embedded in a PBG reservoir.

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Multiwavelength All-Optical Clock Recovery of Non-Return-to-Zero Data

ZHANG Feng, CHEN Ming, QIN Xi, LV Bo, LU Dan, CHEN Yong, CAO Ji-Hong, JIAN Shui-Sheng

Chin. Phys. Lett. 2007, 24 (4): 941-943 .

Abstract

PDF(pc) (677KB) ( 720 )

A novel scheme of all-optical clock recovery from mutiwavelength non-return-to-zero (NRZ) data stream is proposed and demonstrated. The chirp induced by a chirped fibre Bragg grating and a semiconductor optical amplifier is used to enhance the clock. The clock is recovered after injecting the enhanced signal into the scheme based on the stimulated Brillouin scattering. The experiment is carried out and the dual-wavelength clock is recovered. This novel scheme can realize clock recovery of multiwavelength NRZ signal in the total wavelength range of 3.3nm. This clock recovery technology is transparent to the data bit rate and modulation format, also without pattern dependence.

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Harmonic Mode-Locked Ytterbium-Doped Fibre Ring Laser

YANG Ling-Zhen, WANG Yun-Cai, CHEN Guo-Fu, WANG Yi-Shan, ZHAOWei

Chin. Phys. Lett. 2007, 24 (4): 944-946 .

Abstract

PDF(pc) (216KB) ( 1236 )

We demonstrate a harmonic mode-locked ytterbium-doped fibre ring laser,
which consists of a polarization-sensitive isolator, two polarization controllers, two 976nm laser diodes as the pump source and a two-segment ytterbium-doped fibre. Utilizing an additive pulse mode-locked technique based on nonlinear polarization evolution, the ytterbium-doped fibre laser can operate in mode-locked state by adjusting the position of polarization controllers. The cavity fundamental repetition rate is 23.78MHz. We also observe the second-
and third-harmonic mode locking in the normal dispersion region, and their repetition rates are 47.66MHz and 71.56MHz, respectively. Over-driving of the saturable absorber in the harmonic mode-locking pulse is analysed and discussed in detail.

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A Compact Diode-Pumped Injection Seeded Nd:YAG Laser with Resonance-Detection Technique

ZHOU Jun, ZANG Hua-Guo, YU Ting, BI Jin-Zi, ZHU Xiao-Lei, CHEN Wei-Biao

Chin. Phys. Lett. 2007, 24 (4): 947-949 .

Abstract

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A diode pumped injection seeded single-longitudinal-mode (SLM) Nd:YAG laser is achieved by using the resonance-detection technique in Q-switching operation. The pulsed oscillator laser uses a folded cavity to achieve compact construction. This system operates at 100Hz and provides over 20mJ/pulse of single-frequency 1064nm output. The M² values of horizontal and vertical axes are 1.58 and 1.41, respectively. The probability of putting out single-longitudinal-mode pulses is 100%. The 355nm laser output produced by frequency tripling has a linewidth less than 200MHz. The laser can run over eight hours continually without mode hopping.

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Nonlinear Optical Properties of Novel C₆₀ Derivatives under Picosecond Laser Excitation

MAO Yan-Li, CHENG Yong-Guang, LIU Jun-Hui, LIN Bing-Chen, HUO Yan-Ping, ZENG He-Ping

Chin. Phys. Lett. 2007, 24 (4): 950-953 .

Abstract

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We investigate the third-order nonlinear optical properties of six novel ullerene derivatives under picosecond laser excitation by Z-scan technique. The experimental results reveal that all the derivatives have very large nonlinear absorption coefficient under 532nm pulses excitation and great third-order nonlinear refraction index under 1064nm pulses excitation. The molecular second hyperpolarizabilities are obtained from the experimental results.

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Effect of Ag Nanoparticles on Optical Properties of R6G Doped PMMA Films

DENG Yan, SUN You-Yi, WANG Pei, ZHANG Dou-Guo, JIAO Xiao-Jin, MIN Hai, ZHANG Qi-Jing, JIAO Yang, SUN Xiao-Quan

Chin. Phys. Lett. 2007, 24 (4): 954-956 .

Abstract

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The composite PMMA films containing Ag nanoparticles and rhodamine 6G are prepared. We investigate the fluorescence properties and nonlinear optical properties of R6G/PMMA films influenced by Ag nanoparticles. The fluorescence enhancement factor is about 3.3. The corresponding nonlinear refractive index is measured to be -2.423×10^-8esu using the Z-scan technique, which is much enhanced compared with the R6G/PMMA film. The results indicate that these enhancements are attributed to surface plasmon resonance of Ag nanoparticles.

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Induced Diffraction in Phase-Mismatched Second-Harmonic Generation

SU Wen-Hua, QIAN Lie-Jia, FU Xi-Quan, YANG Hua, ZHU He-Yuan

Chin. Phys. Lett. 2007, 24 (4): 957-960 .

Abstract

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We show analytically that in phase-mismatched second-harmonic generation, an effective diffraction is induced at the second-harmonic (SH) frequency. Numerical simulation results agree with the analytical predictions. Compared to the case of linear propagation, the effect of the overall diffraction at the SH frequency becomes doubled due to the induced diffraction, which causes an interesting result that the SH beam width will be larger than that of the fundamental field.

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Optical Pulse Generation with Self-Cascaded Electroabsorption Modulator

WU Jian, QIU Ji-Fang, ZHOU Guang-Tao, XU Kun, LIN Jin-Tong

Chin. Phys. Lett. 2007, 24 (4): 961-964 .

Abstract

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A novel scheme for pulse generation with a self-cascaded electroabsorption modulator is presented and experimentally demonstrated at 10GHz. In the case of optimal tuning of time delay in the fibre loop, the improvement of 50% on pulsewidth with improved extinction ratio is obtained and the narrowest pulse generated with this method is about 11 ps.

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An Isotropic Electric-Field Sensing System Using Optical Probe

YANG Yong-Jun, CHEN Fu-Shen, SUN Bao

Chin. Phys. Lett. 2007, 24 (4): 965-967 .

Abstract

PDF(pc) (482KB) ( 2587 )

We design an isotropic electric-field sensing system using an optical probe. The optical probe consists of three electric-field sensors based on a Mach--Zehnder interferometer with the structure of segmented electrodes, which are perpendicular to each other. The measured results show that the ±5dB baseband can reach 3GHz, the linear dynamics range is 70dB, and the minimum detectable electric field is lower than 90dBμV/m (the spectrum analyser resolution is 100Hz). The directional characteristics are almost isotropic within deviations of ±1.5dB. Therefore this sensing system can be used in the electromagnetic compatibility measurements.

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Broadband Infrared Luminescence of Ni ²⁺ in Petalite-Type Transparent Glass Ceramics

FENG Gao-Feng, ZHOU Shi-Feng, ZHANG Song-Min, YANG Hu-Cheng, QIU Jian-Rong

Chin. Phys. Lett. 2007, 24 (4): 968-970 .

Abstract

PDF(pc) (230KB) ( 775 )

Transparent Ni ²⁺ -doped magnesium aluminosilicate glass ceramics are
prepared. The formation of petalite-type crystallites in the glass
ceramics is confirmed by x-ray diffraction. Broadband infrared
luminescence centred at around 1235nm with full width at half maximum
(FWHM) of about 300nm is observed from the Ni ²⁺ -doped glass
ceramics. The observed infrared emission could be attributed to the
³T ₂(F) →³ A ₂(F) transition of octahedral Ni ²⁺ions in petalite-type crystallites. The product of the fluorescence lifetime and the stimulated emission cross sections is 1.2×10 ^-24 cm ²s.

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Red Laser-Induced Domain Inversion in MgO-Doped Lithium Niobate Crystals

LI Da-Shan, LIU De-An, ZHI Ya-Nan, QU Wei-Juan, LIU Li-Ren, ZHANG Juan

Chin. Phys. Lett. 2007, 24 (4): 971-974 .

Abstract

PDF(pc) (316KB) ( 727 )

A laser beam at wavelength 647nm is focused on a sample of 5mol% MgO-doped lithium niobate crystal for domain inversion by a conventional external electric field. In this case, a reduction of 36% in the electric field required for domain nucleation (nucleation field) is observed. To the best of our knowledge, it is the longest wavelength reported for laser-induced domain inversion. This extends the spectrum of laser inducing, and the experimental results are helpful to understand the nucleation dynamics under laser illumination. The dependence of nucleation fields on intensities of laser beams is analysed in experiments.

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Linewidth Narrowing in Microstrip Resonator Using Effective Highly Dispersive Medium

LI Yun-Hui, JIANG Hai-Tao, HE Li, LI Hong-Qiang, ZHANG Ye-Wen, CHEN Hong, ZHU Shi-Yao

Chin. Phys. Lett. 2007, 24 (4): 975-978 .

Abstract

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An effective highly dispersive medium is proposed by utilizing strong dispersion of localized defect mode in a microstrip photonic crystal. Linewidth narrowing in a composite microstrip resonator using this photonic-crystal-based effective medium is investigated and its dependence on the structure parameters is presented. Both numerical simulations and experimental results demonstrate that compared to the traditional resonator, the Q-factor increases much more quickly and the peak transmission decreases more slowly at the same time for the composite resonator.

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Surface Light Extraction Mapping from Two-Dimensional Array of 12-Fold Photonic Quasicrystal on Current Injected GaN-Based LEDs

DAI Tao, ZHANG Bei, ZHANG Zhen-Sheng, LIU Dan, WANG Xiao, BAO Kui, KANGXiang-Ning, XU Jun, YU Da-Peng, ZHU Xing

Chin. Phys. Lett. 2007, 24 (4): 979-982 .

Abstract

PDF(pc) (559KB) ( 606 )

A two-dimensional array of dodecagonal photonic quasicrystal (12PQC) is fabricated on the surface of current injected GaN-based LEDs to out-couple guided modes. The spatially-resolved surface light extraction mapping of 12PQC is observed and compared with that of triangular lattice photonic crystal (3PC) by microscopic electrical luminescence and scanning near-field microscopy. The higher enhancement factor of 12PQC is obtained to be larger than that of 3PC. It is shown that 12PQC is more favourable and efficient for light extraction of guided lights.

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Fabrication of Two-Dimensional Photonic Crystals with Triangular Rods by Single-Exposure Holographic Lithography

PU Yi-Ying, LIANG Guan-Quan, MAO Wei-Dong, DONG Jian-Wen, WANG He-Zhou

Chin. Phys. Lett. 2007, 24 (4): 983-985 .

Abstract

PDF(pc) (504KB) ( 669 )

We demonstrate a single-exposure holographic fabrication of two-dimensional photonic crystal with round-cornered triangular `atoms' arranged in a triangular lattice. Simulation results show that double absolute photonic band gaps exist in this structure. Our experimental results show that holographic lithography can be used to fabricate photonic crystals not only with various lattice structures but also with various kinds of structures of the atoms, to obtain absolute band gaps or a particular band gap structure. Furthermore, the single-exposure holographic method not only makes the fabrication process simple and convenient but also makes the structures of the atoms more perfect.

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Feasibility of Non-Collinear TeO₂ Acoustic-Optic Tunable Filters Used in the Optical Communication

LIU Wei, SUN Yu-Nan, CUI Fang, BAN Long

Chin. Phys. Lett. 2007, 24 (4): 986-989 .

Abstract

PDF(pc) (267KB) ( 546 )

The characteristics and the structure of TeO₂ acoustic-optic tunable filter used in communication are discussed briefly based on the acoustic-optic theory and it is shown that a large optical incident angle and a long interaction length are suitable for the optical add/drop multiplexer based on the TeO₂ acoustic-optic tunable filter. The distribution of acoustic energy flow in the device supports
the large optical incident angle. The long interaction length depends on the change of the device structure to some degree. The measured results of the samples show that the diffraction efficiency reaches at 96% in the tuning range larger than 100nm and the bandwidth is about 2nm. It can be found that there is a good consistency with the basic theoretical mode. The optimized design result shows that the diffraction efficiency can arrive at 100%, and the bandwidth can be less than 0.4nm. Thus, the non-collinear TeO₂acoustic-optic tunable filter can play an important role in the coming general optical network.

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Theoretical Study of SOA-Based Wavelength Conversion with NRZ and RZ Format at 40Gb/s

DONG Jian-Ji, ZHANG Xin-Liang, FU Song-Nian, SHUM Ping, HUANG De-Xiu

Chin. Phys. Lett. 2007, 24 (4): 990-993 .

Abstract

PDF(pc) (423KB) ( 739 )

We theoretically discuss 40Gb/s semiconductor optical amplifier (SOA)-based wavelength conversion (WC) using a detuning optical bandpass filter based on ultrafast dynamic characteristics of SOA. Both the inverted and non-inverted WCs are obtained by shifting the filter central wavelength with respect to the probe wavelength when input data signal is in return-to-zero (RZ) format. However, we can obtain format conversion from nonreturn-to-zero (NRZ) to pseudo-return-to-zero (PRZ) and inverted WC when the input signal is in NRZ format.

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Super-Resolution Recording by an Organic Photochromic Mask Layer

SHI Ming, ZHAO Sheng-Min, YI Jia-Xiang, ZHAO Fu-Qun, NIU Li-Hong, LI Zhong-Yu, ZHANG Fu-Shi

Chin. Phys. Lett. 2007, 24 (4): 994-997 .

Abstract

PDF(pc) (722KB) ( 531 )

By using the super-resolution near-field structure (super-RENS) method, the super-resolution recording marks are obtained practically by an organic photochromic diarylethene mask layer, under much lower recording laser power of 0.45mW. The size of recording marks is decreased by 60% (from 1.6μm to 0.7μm) for a diarylethene (photo-mode) recording layer by the optical detection method (limited by optical diffraction), or decreased by 97% (from 1600nm to 50nm) for a heptaoxyl copper phthalocyanine (thermo-optical) recording layer, the latter is much smaller than the limitation of optical diffraction. In order to obtain a desirable result, a proper extent of photochemistry reaction in the mask layer is needed. Thus, the super-resolution recording marks can be obtained by adjusting the concentration of
diarylethene in the mask layer, the recording laser power, and the moving speed of the sample disc.

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Amplification Characteristics of Optical Fibres Doped with Nano Materials of InP

ZHANG Ru, GUAN Li-Ming, LEE Ly-Guat, LIU Gang, LU Peng-Fei

Chin. Phys. Lett. 2007, 24 (4): 998-999 .

Abstract

PDF(pc) (229KB) ( 734 )

We take an enhanced structure of existing optical fibres to investigate the amplification characteristics. Nano and optical fibre technologies both are employed in our structure, i.e. the so-called nano-film amplification fibre where nano-film is inserted between the core and the inner cladding of the optical fibre. In the developed model, InP is chosen as a doped semiconductor to examine its amplification performance and 69.7nm is chosen as the thickness of the film. From our experimental results, the optical fibre structure shows its significant amplification characteristics for wavelength between 1080nm and 1491nm. Amplification characteristics are also found in wavelengths 906--1044nm and 1524--1596nm.

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Electrostatic Instabilities at High Frequency in a Plasma Shock Front

LV Jian-Hong, HE Yong, HU Xi-Wei

Chin. Phys. Lett. 2007, 24 (4): 1000-1003 .

Abstract

PDF(pc) (0KB) ( 391 )

New electrostatic instabilities in the plasma shock front are reported. These instabilities are driven by the electrostatic field which is caused by charge separation and the parameter gradients in a plasma shock front. The linear analysis to the high frequency branch of electrostatic instabilities has been carried out and the dispersion relations are obtained numerically. There are unstable disturbing waves in both the parallel and perpendicular directions of shock propagation. The real frequencies of both unstable waves are similar to the electron electrostatic wave, and the unstable growth rate in the parallel
direction is much greater than the one in the perpendicular direction. The dependence of growth rates on the electric field and parameter gradients is also presented.

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Growth and Characterization of InN Thin Films on Sapphire by MOCVD

XIE Zi-Li, ZHANG Rong, XIU Xiang-Qian, LIU Bin, LI Liang, HAN Ping, GU Shu-Lin, SHI Yi, ZHENG You-Dou

Chin. Phys. Lett. 2007, 24 (4): 1004-1006 .

Abstract

PDF(pc) (333KB) ( 698 )

Indium nitride thin films are grown on sapphire substrates by metal-organic chemical vapour deposition (MOCVD). By employing three-step layer buffers, the mirror-like layers on two-inch sapphire wafers have been obtained. The structural, optical and electrical characteristics of InN are investigated by x-ray diffraction, scanning electron microscopy, atomic force microscopy, hotoluminescence and infrared optical absorption. The photoluminescence and the absorption studies of the materials reveal a marked energy bandgap structure around 0.70eV at room temperature. The room-temperature Hall mobility and carrier concentration of the film are typically 939cm²/Vs,
and 3.9×10¹⁸cm^-3, respectively.

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Refit Silver Nanostructures Using a Convergent Electron Beam

ZHANG Jian-Hong

Chin. Phys. Lett. 2007, 24 (4): 1007-1009 .

Abstract

PDF(pc) (678KB) ( 677 )

Using a superionic conductor AgI thin film and a direct current electric field, we synthesize silver nanowires in diameter of about 100nm. In order to refit the prepared nanowires, the samples are irradiated by a convergent electron beam (200kV) inside a transmission electron microscope to prepare new small silver nanostructures. The new nanostructures are investigated in situ by high-resolution transmission electron microscope. This electron-induced crystal growth method is useful for technical applications in fabrication of nanodevices.

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Resistivity Measurement of Molten Olivine in a Laser-Heated Diamond

LI Ming, GAO Chun-Xiao, MA Yan-Zhang, HE Chun-Yuan, HAO Ai-Min, ZHANG Dong-Mei, LI Yan-Chun, LIU Jing, WANG Duo-Jun

Chin. Phys. Lett. 2007, 24 (4): 1010-1012 .

Abstract

PDF(pc) (349KB) ( 641 )

The electrical conductivity of molten olivine is studied up to 3720K and 13.2GPa. The results indicate that the electrical conductivity of molten olivine exhibits the perfect Arrhenius behaviour. The activation energy as well as temperature effect is much smaller than that of the solid olivine. It is expected that the high conductivity zone in the mantle is almost independent of the melting based on our experimental data.

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Phase Transition Kinetics in Bi₃NbO₇ Evaluated by in situ Isothermal Conductivity Measurements

WANG Xian-Ping, CHENG Zhi-Jun, FANG Qian-Feng

Chin. Phys. Lett. 2007, 24 (4): 1013-1016 .

Abstract

PDF(pc) (252KB) ( 851 )

Kinetics of phase transformation from pseudocubic to tetragonal phase
in Bi₃NbO₇ solid solution is studied by using the ac impedance method under isothermal conditions. Conductivity of the investigated compound is used to characterize the kinetic process of the transition. The Avrami exponent and the activation energy of phase transition are around 1.5 and 3.5eV, respectively. These kinetic parameters reveal that the pseudocubic-tetragonal transition in Bi₃NbO₇ belongs to a three-dimensional diffusion-controlled
growth with zero nucleation rate.

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Phonon Transmission and Thermal Conductance in Fibonacci Wire at Low Temperature

ZHANG Yong-Mei, XU Chen-Hua, XIONG Shi-Jie

Chin. Phys. Lett. 2007, 24 (4): 1017-1020 .

Abstract

PDF(pc) (273KB) ( 761 )

We investigate the phonon transmission and thermal conductance in a general Fibonacci quasicrystal by the model of lattice dynamics and the technique of transfer matrix. It is found that quasiperiodic distribution of masses may greatly destroy the phonon transport at both low and high frequencies and thus may affect the thermal conductance. The thermal conductance increases with temperature at low temperatures and displays saturation with further increase of the temperature. Such saturation behaviour is preserved even when the mass ratio of atoms in the Fibonacci chain is changed.

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Large Slip Length over a Nanopatterned Surface

LI Ding, DI Qin-Feng, LI Jing-Yuan, QIAN Yue-Hong, FANG Hai-Ping

Chin. Phys. Lett. 2007, 24 (4): 1021-1024 .

Abstract

PDF(pc) (258KB) ( 930 )

A thermodynamic method is employed to analyse the slip length of hydrophobic nanopatterned surface. The maximal slip lengths with respect to the hydrophobicity of the nanopatterned surface are computed. It is found that the slip length reaches more than 50mum if the nanopatterned surfaces have a contact angle larger than 160°. Such results are expected to find extensive applications in micro-channels and helpful to understand recent
experimental observations of the slippage of nanopatterned surfaces.

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Extremely Low Density InAs Quantum Dots with No Wetting Layer

HUANG She-Song, NIU Zhi-Chuan, NI Hai-Qiao, ZHAN Feng, ZHAO Huan, SUN Zheng, XIA Jian-Bai

Chin. Phys. Lett. 2007, 24 (4): 1025-1028 .

Abstract

PDF(pc) (447KB) ( 827 )

Extremely low density InAs quantum dots (QDs) are grown by molecular
beam droplet epitaxy. The gallium deposition amount is optimized to
saturate exactly the excess arsenic atoms present on the GaAs substrate
surface during growth, and low density InAs/GaAs QDs (4×10⁶cm ^-2) are formed by depositing 0.65 monolayers (MLs) of indium. This is much less than the critical deposition thickness (1.7ML), which is necessary to form InAs/GaAs QDs with the conventional Stranski--Krastanov growth mode. The narrow
photoluminescence linewidth of about 24meV is insensitive to cryostat
temperatures from 10K to 250K. All measurements indicate that there is
no wetting layer connecting the QDs.

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Graded Index 532HR/1064HT Filter by Glancing Angle Deposition

SHEN Zi-Cai, LIU Shi-Jie, HUANG Jian-Bing, SHAO Jian-Da, FAN Zheng-Xiu

Chin. Phys. Lett. 2007, 24 (4): 1029-1031 .

Abstract

PDF(pc) (384KB) ( 887 )

Glancing angle deposition is a novel method to prepare graded index
coatings. By using this method and physical vapour deposition, ZrO ₂
is used to engineer graded index filter on BK7 glass substrate. Controlling the deposition rate and the periodic oscillation of oblique angle of deposited material, a 10-period graded index ZrO₂ filter with high reflection near 532nm and high transmittance at wavelength 1064nm is fabricated. The causes of
difference between the theoretical and experimental results are discussed in detail. The material properties and electron gun nonlinearity are possibly the main origins of the difference, which result in the variations in both thickness control and deposition rate of the film material.

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Ab Initio Comparative Study of Zincblende and Wurtzite ZnO

ZHANG Xin-Yu, CHEN Zhou-Wen, QI Yan-Peng, FENG Yan, ZHAO Liang, QI Li, MA Ming-Zhen, LIU Ri-Ping, WANG Wen-Kui

Chin. Phys. Lett. 2007, 24 (4): 1032-1034 .

Abstract

PDF(pc) (233KB) ( 3420 )

By employing the first-principles pseudopotential plane-wave method, the physical properties of zincblende ZnO are investigated in comparison with those of the common wurtzite structure. Zincblende ZnO is predicted to be a direct gap semiconductor. Compared to the wurtzite structure, the zincblende ZnO is characterized by smaller bandgap and pressure coefficient, larger electron effective mass, increasing static dielectric constants and more covalent bonding. Furthermore, the optical properties including dielectric function and energy loss function of zincblende ZnO were obtained and analysed with some features. These aspects reveal promising applications of zincblende ZnO in optoelectronic devices.

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Scaling Properties of Energy Gap in Dimerized Spinless Fermion Chains with Quasiperiodic Modulation

LI Peng-Fei, CHEN Yu-Guang, CHEN Hong

Chin. Phys. Lett. 2007, 24 (4): 1035-1038 .

Abstract

PDF(pc) (263KB) ( 688 )

By employing the exact diagonalization method, we investigate the low-energy behaviour of the dimerized spinless fermion chains with quasiperiodic modulation. It is found that for off-diagonal modulation, the energy gap with length N scales as exp(-cN^ω) with nonuniversal exponent ω if the dimerization is nonzero. However, for diagonal modulation, there may exist a critical dimerization δ_c beyond which the system exhibits a metal--insulator transition.

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Analytical Study of Nonclassical Behaviour for a Disturbed Non-Degenerated Parameter Amplifier

PANG Qian-Jun

Chin. Phys. Lett. 2007, 24 (4): 1039-1041 .

Abstract

PDF(pc) (198KB) ( 395 )

We analytically discuss the nonclassical behaviour for a disturbed non-degenerated parameter amplifier. The thermal Glauber--Sudarshan diagonal presentation (GSP) function for the system is derived. The detailed analysis on the threshold temperatures of both the individual photon subsystem and the complete photon--photon complex is presented. The effect of the photon--photon interaction on the threshold temperature is observed.

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Electronic Transport in Molecular Junction Based on C₂₀Cages

OUYANG Fang-Ping, XU Hui

Chin. Phys. Lett. 2007, 24 (4): 1042-1045 .

Abstract

PDF(pc) (660KB) ( 716 )

Choosing closed-ended armchair (5, 5) single-wall carbon nanotubes (CCNTs) as electrodes, we investigate the electron transport properties across an all-carbon molecular junction consisting of C₂₀molecules suspended between two semi-infinite carbon nanotubes. It is shown that the conductances are quite sensitive to the number of C₂₀ molecules between electrodes for both configuration CF1 and double-bonded models: the conductances of C₂₀ dimers are markedly smaller than those of monomers. The physics is that incident electrons easily pass the C₂₀ molecules and are predominantly
scattered at the C₂₀--C₂₀ junctions. Moreover, we study the doping effect of such molecular junction by doping nitrogen atoms substitutionally. The bonding property of the molecular junction with configuration CF1 has been analysed by calculating the Mulliken atomic charges. Our results have revealed that the C atoms in N-doped junctions are more ionic than those in pure-carbon ones, leading to the fact that N-doped junctions have relatively large conductance.

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Fano Interference versus Kondo Effect in Strongly Correlated T-Shaped Quantum Dots Embedded in an Aharonov--Bohm Ring

CHEN Bao-Ju, CHEN Xiong-Wen, SHI Zhen-Gang, ZHU Xi-Xiang, SONG Ke-Hui, WU Shao-Quan

Chin. Phys. Lett. 2007, 24 (4): 1046-1049 .

Abstract

PDF(pc) (319KB) ( 805 )

We theoretically investigate the properties of the ground state of the
strongly correlated T-shaped double quantum dots embedded in an
Aharonov--Bohm ring in the Kondo regime by means of the one-impurity
Anderson Hamiltonian. It is found that in this system, the persistent
current depends sensitively on the parity and size of the ring. With the
increase of interdot coupling, the persistent current is suppressed due
to the enhancing Fano interference weakening the Kondo effect. Moreover,
when the spin of quantum dot embedded in the Aharonov--Bohm ring is
screened, the persistent current peak is not affected by interdot
coupling. Thus this model may be a new candidate for detecting Kondo
screening cloud.

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Strongly Correlated Effect in TiS₂

QIAO Yan-Bin, ZHONG Guo-Hua, LI Di, WANG Jiang-Long, QIN Xiao-Ying, ZENG Zhi

Chin. Phys. Lett. 2007, 24 (4): 1050-1053 .

Abstract

PDF(pc) (236KB) ( 928 )

The thermoelectric compound TiS₂ is studied by using the full-potential linearized augmented plane-wave method on the density functional theory with the generalized gradient approximation (GGA) as well as the on-site Coulomb interaction correction (+U). The Seebeck coefficient of TiS₂ is calculated based on the electronic structure obtained within the GGA under the consideration of the on-site Coulomb interaction. The calculated Seebeck coefficient at 300K shows that Coulomb interaction U in the range of 4.97--5.42eV is important to reproduce the experimental data. The obtained energy gap E_g around 0.05eV indicates that TiS₂ is an indirect narrow-gap semiconductor.

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Fano versus Kondo Resonances in a Closed Aharonov--Bohm Interferometer Coupled to Ferromagnetic Electrodes

WU Shao-Quan, SUN Wei-Li

Chin. Phys. Lett. 2007, 24 (4): 1054-1057 .

Abstract

PDF(pc) (296KB) ( 508 )

Using the Keldysh nonequilibrium Green function and equation-of-motion technique, we investigate Fano versus Kondo resonances in a closed Aharonov--Bohm interferometer coupled to ferromagnetic leads and study
their effects on the conductance of this system. The conductance with both parallel and antiparallel lead-polarization alignments is analysed for various values of the magnetic flux. Our results show that this system can provide an excellent spin filtering property, and a large tunnelling magnetoresistance can arise by adjusting the system parameters, which indicates that this system is a possible candidate for spin valve transistors and has important applications in spintronics.

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Effect of Hydrostatic Pressure on Interband Transitions in Coupled Quantum Wires

E. Kasapoglu, M. Gunes, I. Sokmen

Chin. Phys. Lett. 2007, 24 (4): 1058-1061 .

Abstract

PDF(pc) (241KB) ( 655 )

We calculate the exciton binding energy and interband optical absorption in a rectangular coupled quantum wire under the hydrostatic pressure in the effective-mass approximation, using the variational approach. It is found that the interband optical absorption strongly depend on the hydrostatic pressure and the coupling parameter, and that the magnitude of the absorption coefficient for the HH1--E1 transition in the coupled quantum wire is larger than that of the single quantum wire.

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Effects of Yb ³⁺ in Er ^3+/Yb ³⁺ Codoped Fluorophosphate Glasses

LIAO Mei-Song, FANG Yong-Zheng, Hu Li-li, ZHANG Li-Yan, XU Shi-Qing

Chin. Phys. Lett. 2007, 24 (4): 1062-1065 .

Abstract

PDF(pc) (274KB) ( 451 )

For the Er³⁺/Yb³⁺ codoped fluorophosphate glasses, Judd--Ofelt theory is used to analyse the influence of YbF₃ as not a sensitizer but an average component on the spectroscopic properties around 1530\,nm emission. The double roles of Yb³⁺, as a sensitizer and as an average component, are discussed. It is found that Yb³⁺ as an average component contributes to the increase of fluorescence lifetime, and Yb³⁺ as a sensitizer has the best sensitization when its concentration is 2.4mol%.

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Fano Resonance in Landau Fermi and Luttinger Liquids

HAN Yue-Wu, LIU Yu-Liang, CAI Shao-Hong,

Chin. Phys. Lett. 2007, 24 (4): 1066-1069 .

Abstract

PDF(pc) (237KB) ( 710 )

With a two-channel model, we study the influence of temperature, external
voltage and magnetic flux on the line shape of the Fano resonance, and show
that in the Luttinger liquid case, the background transmittance and the
asymmetric parameter depend strongly on the temperature and external
voltage, while for the Landau Fermi liquid case they are nearly independent
of these parameters in the low energy region. Moreover, we demonstrate that the asymmetric parameter changes periodically with an external magnetic flux, which is consistent with the recent experimental data.

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Electron Transport Property of CdTe under High Pressure and Moderate Temperature by In-Situ Resistivity Measurement in Diamond Anvil Cell

HE Chun-Yuan, GAO Chun-Xiao, LI Ming, HAO Ai-Min, HUANG Xiao-Wei, ZHANG Dong-Mei, YU Cui-Ling, WANG Yue

Chin. Phys. Lett. 2007, 24 (4): 1070-1072 .

Abstract

PDF(pc) (283KB) ( 568 )

In situ resistivity measurement has been performed to investigate the electron transport property of powered CdTe under high pressure and moderate temperature in a designed diamond anvil cell. Several abnormal
resistivity changes can be found at room temperature when the pressure
increases from ambient to 33GPa. The abnormal resistivity changes at about 3.8GPa and 10GPa are caused by the structural phase transitions to the rock-salt phase and to the Cmcm phase, respectively. The other abnormal resistivity changes at about 6.5GPa, 15.5GPa, 22.2GPa and about 30GPa never observed before are due to the electronic phase transitions of CdTe. The origin of the abnormal change occurred at about 6.5GPa is discussed. The temperature dependence of the resistivity of CdTe shows its semiconducting behaviour at least before 11.3GPa.

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Room-Temperature Ferromagnetism in Zn _1-x Mn_xO Thin Films Deposited by Pulsed Laser Deposition

TENG Xiao-Yun, YU Wei, YANG Li-Hua, HAO Qiu-Yan, ZHANG Li, XU He-Ju, LIU Cai-Chi, FU Guang-Sheng

Chin. Phys. Lett. 2007, 24 (4): 1073-1075 .

Abstract

PDF(pc) (234KB) ( 702 )

Zn_1-x Mn_xO (x=0.01--0.1) thin films with a Curie temperature above 300K are deposited on Al₂O₃ (0001) substrates by pulsed laser deposition. X-ray diffraction (XRD), ultraviolet (UV)-visible transmission and Raman spectroscopy are employed to characterize the microstructural properties of these films.
Room temperature ferromagnetism is observed by superconducting quantum
interference device (SQUID). The results indicate that Mn doping introduces the incorporation of Mn²⁺ ions into the ZnO host matrix and the insertion of Mn²⁺ ions increases the lattice defects, which is correlated with the ferromagnetism of the obtained films. The doping concentration is also proven to be a crucial factor for obtaining highly ferromagnetic Zn_1-x Mn_xO films.

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A Polydisperse Sphere Model Describing the Propagation of Light in Biological Tissue

WANG Qing-Hua, LI Zhen-Hua, LAI Jian-Cheng, HE An-Zhi

Chin. Phys. Lett. 2007, 24 (4): 1076-1079 .

Abstract

PDF(pc) (219KB) ( 649 )

A polydisperse sphere model with the complex refractive index is employed to describe the propagation of light in biological tissue. The scattering coefficient, absorption coefficient and scattering phase function are calculated. At the same time, the inverse problem on retrieving the particles size distribution, imaginary part of the refractive index and number density of scatterers is investigated. The result shows that the retrieval scheme together with the Chahine algorithm is effective in dealing with such an inverse problem. It is also clarified that a group of parameters including the scattering coefficient, absorption coefficient and phase function are associated with another group including the refractive index, particle size distribution and number density of scatterers, which is a problem described in two different ways and the anisotropy factor is not an independent variable, but is determined by the phase function.

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Spectral Hole-Burning of Eu³⁺ :Y₂SiO₅ Crystal at 16K

XUE Shao-Lin, YU Mu-Huo, CHEN Ling-Bing, ZHAO You-Yuan, LI Fu-Ming, ZHANG Shou-Du, WANG Hao-Bing

Chin. Phys. Lett. 2007, 24 (4): 1080-1083 .

Abstract

PDF(pc) (284KB) ( 705 )

By using an Ar⁺ ion laser, a tunable Rh 6G dye laser (linewidth 0.5cm^-1) pumped by the second harmonic of a YAG:Nd laser and a Coherent 899-21 dye laser as light sources and using a monochromator, a phase-locking amplifier and a computer as the data detecting system, we detect the optical properties of Eu³⁺-doped Y₂SiO ₅crystal. Persistent spectral hole burning (PSHB) are observed in the Eu ³⁺ ions spectral lines (⁵D₀- ⁷F₀ transition)
in the crystal at the temperature of 16K. For 15mW dye laser burning the crystal for 0.1s spectral holes with hole width about 80MHz both at 579.62nm and at 579.82nm are detected and the holes can remain for a long time, more than 10h.

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Resonance Absorption of Metallic Plate with Subwavelength Hole Array

CHEN Yue-Gang, WANG Yan-Hua, ZHANG Yan, LIU Shu-Tian

Chin. Phys. Lett. 2007, 24 (4): 1084-1087 .

Abstract

PDF(pc) (465KB) ( 504 )

The optical reflectance by a metallic plate arranged with array consisting of subwavelength periodic square hole is investigated by using the three-dimensional finite-difference time-domain method (3D-FDTD). There are dips in the reflectivity spectra, which indicate the absorption peaks. The absorption peaks behave differently according to the ratio of hole width and the period of the hole array. Combined with the near fields of the absorption peaks, it is found that the surface plasmon (SP) resonance on the surface of plate and localized SP in the hole play a major role for the two absorptions.

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Chemical Synthesis and Characterization of Flaky h-BCN at High Pressure and High Temperature

YANG Da-Peng, LI Ying-Ai, YANG Xu-Xin, DU Yong-Hui, JI Xiao-Rui, GONG Xi-Liang, SU Zuo-Peng, ZHANG Tie-Chen

Chin. Phys. Lett. 2007, 24 (4): 1088-1091 .

Abstract

PDF(pc) (469KB) ( 1229 )

Hexagonal boron carbonitrogen (h-BCN) compound is synthesized from a
mixture of boron powder and CNH compound prepared by pyrolysis of
melamine (C₃H₆N₆) under high temperature (1400--1500°C) and high pressure (5.0--5.5GPa). X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and Raman spectroscopy are used to determine the chemical composition and bonds of the product. The results show that the product has composition of B_0.18C_0.64N_0.16 (near BC₄N) and atomic-level hybrid. X-ray diffraction analysis indicates that the powder has a hexagonal network structure. Scanning and transmission electron microscopy results suggest that h-BCN compound morphology is mainly flaky in width about 1μm and thickness 200nm.

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Chemical Synthesis of C₃N and BC₂N Compounds

SUN Guang, LIU Zhong-Yuan, HE Ju-Long, YU Dong-Li, TIAN Yong-Jun

Chin. Phys. Lett. 2007, 24 (4): 1092-1094 .

Abstract

PDF(pc) (360KB) ( 758 )

A chemical reaction for the preparation of B--C--N compounds by using carbon tetrachloride (CCl₄), boron tribromide (BBr₃), lithium nitride (Li₃N) and sodium as reactants has been carried out at the temperature of 400°C. Measurements of FTIR, XRD, TEM and EELS show that two kinds of compounds have been formed in the prepared sample. One is hollow sphere-like C--N with an amorphous structure; the other is piece-like polycrystalline B--C--N with the hexagonal structure. Their determined compositions are close to C₃N and BC₂N, respectively.

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Mode-Locking Behaviour in Driven Colloids with Random Pinning

CHEN Jiang-Xing, JIAO Zheng-Kuan

Chin. Phys. Lett. 2007, 24 (4): 1095-1098 .

Abstract

PDF(pc) (327KB) ( 447 )

We find mode-locking steps in simulated force-velocity characteristics of external alternating-force (AF) driven colloids on a disordered substrate. Studies of mode-locking patterns in systems show that mode-locking steps are accompanied with the emergence of a dynamics phase: transverse solid phase. We also study the influence of temperature on the width of mode-locking steps. The mode-locked state is destroyed by thermal fluctuation and the width of mode-locking steps decreases rapidly with increasing temperature. In high velocity and low temperature regimes, due to the appearance of transverse solid phase and microscopically periodic velocity modulation, the step width changes little as temperature is varied.

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Structural Evolution of Compressing Amorphous Ice

WANG Yan, DONG Shun-Le

Chin. Phys. Lett. 2007, 24 (4): 1099-1102 .

Abstract

PDF(pc) (282KB) ( 428 )

Molecular dynamics simulation is employed to study structural evolution
during compressing low density amorphous ice from one atmosphere to
2.5GPa. The calculated results show that high density amorphous ice is
formed under intermediate pressure of about 1.0GPa and O--O--O angle
ranges from about 83° to 113° and O--H...O is bent from 112° to 160°. The very high density amorphous ice is also formed under the pressure larger than 1.4GPa and interstitial molecules are found in 0.3--0.4Å just beyond the nearest O--O distance. Low angle O--H...O disappears and it is believed that
these hydrogen bonds are broken or re-bonded under high pressures.

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Remarkable Resistance Change in Plasma Oxidized TiO_x/TiN_x Film for Memory Application

WU Liang-Cai, SONG Zhi-Tang, LIU Bo, RAO Feng, XU Cheng, ZHANG Ting, YIN Wei-Jun, FENG Song-Lin

Chin. Phys. Lett. 2007, 24 (4): 1103-1105 .

Abstract

PDF(pc) (362KB) ( 809 )

We report the experimental phenomenon of large resistance change in
plasma oxidized TiO_x/TiN_x film fabricated on W bottom-electrode-contact (W-BEC) array. The W-BEC in diameter 260nm is fabricated by a 0.18μm CMOS technology, and the TiO_x/TiN_x cell array is formed by rf magnetron sputtering
and reactive ion etching. In current--voltage (I--V) measurement for current-sweeping mode, large snap-back of voltage is observed, which indicates that the sample changes from high-resistance state (HRS) to low-resistance state (LRS). In the I--V measurement for voltage-sweeping mode, large current collapse is observed, which indicates that the sample changes from LRS to HRS. The current difference between HRS and LRS is about two orders. The threshold current and voltage for the resistance change is about 5.0×10 ^-5 A and 2.5V, respectively. The pulse voltage can also change the resistance and the pulse time is as shorter as 30ns for the resistance change. These properties of TiO_x/TiN_x film are comparable to that of conventional phase-change material, which makes it possible for RRAM application.

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Slow Wave Characteristics of Helix Structure with Elliptical Cross Section

XIE Jian-Xiang, WEI Yan-Yu, GONG Yu-Bin, FU Cheng-Fang, YUE Ling-Na, WANGWen-Xiang

Chin. Phys. Lett. 2007, 24 (4): 1106-1109 .

Abstract

PDF(pc) (270KB) ( 451 )

We present a novel helix slow wave structure with an elliptical cross section shielded by an elliptical waveguide. The rf characteristics including dispersion properties, interaction impedance of zero mode in this structure have been studied in detail. The theoretical results reveal that weaker dispersion even abnormal dispersion characteristics is obtained with the increasing eccentricity of the elliptical waveguide, while the interaction impedance is enhanced by enlarging the eccentricity of elliptical helix.

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A Flip-Chip AlGaInP LED with GaN/Sapphire Transparent Substrate Fabricated by Direct Wafer Bonding

LIANG Ting, GUO Xia, GUAN Bao-Lu, GUO Jing, GU Xiao-Ling, LIN Qiao-Ming, SHEN Guang-Di

Chin. Phys. Lett. 2007, 24 (4): 1110-1113 .

Abstract

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A red-light AlGaInP light emitting diode (LED) is fabricated by using direct wafer bonding technology. Taking N-GaN wafer as the transparent substrate, the red-light LED is flip-chiped onto a structured silicon submount. Electronic luminance (EL) test reveals that the luminance flux is 130% higher than that of the conventional LED made from the same LED wafer. Current--voltage (I--V) measurement indicates that the bonding processes do not impact the electrical property of AlGaInP LED in the small voltage region (V<1.5V). In the large voltage region (V>1.5V), the I--V characteristic exhibits space-charge-limited currents characteristic due to the p-GaAs/n-GaN bonding interface.

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Modular Epidemic Spreading in Small-World Networks

ZHAO Hui, GAO Zi-You

Chin. Phys. Lett. 2007, 24 (4): 1114-1117 .

Abstract

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We study the epidemic spreading of the susceptible-infected-susceptible model on small-world networks with modular structure. It is found that the epidemic threshold increases linearly with the modular strength. Furthermore, the modular structure may influence the infected density in the steady state and the spreading velocity at the beginning of propagation. Practically, the propagation can be hindered by strengthening the modular structure in the view of network topology. In addition, to reduce the probability of econnection between modules may also help to control the propagation.

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Epidemic Diffusion on Complex Networks

WU Xiao-Yan, LIU Zong-Hua

Chin. Phys. Lett. 2007, 24 (4): 1118-1121 .

Abstract

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Both diffusion and epidemic are well studied in the stochastic systems and complex networks, respectively. Here we combine these two fields and study epidemic diffusion in complex networks. Instead of studying the threshold of infection, which was focused on in previous works, we focus on the diffusion behaviour. We find that the epidemic diffusion in a complex network is an anomalous superdiffusion with varying diffusion exponent γ and that γ is influenced seriously by the network structure, such as the clustering coefficient and the degree distribution. Numerical simulations have confirmed the theoretical predictions.

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Alfven Waves in a Plasma Sheet Boundary Layer Associated with Near-Tail Magnetic Reconnection

YUAN Zhi-Gang, DENG Xiao-Hua, PANG Ye, LI Shi-You, WANG Jing-Fang

Chin. Phys. Lett. 2007, 24 (4): 1122-1124 .

Abstract

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We report observations from Geotail satellite showing that large Poynting fluxes associated with Alfven waves in the plasma sheet boundary layer (PSBL) occur in the vicinity of the near-tail reconnection region on 10 December 1996. During the period of large Poynting fluxes, Geotail also observed strong tailward plasma flows. These observations demonstrate the importance of near-tail reconnection process as the energy source of Alfven waves in the PSBL. Strong tailward (Earthward) plasma flows ought to be an important candidate in generating Alfven waves. Furthermore, the strong perturbations not only of the magnetic field but also of the electric field observed in the PSBL indicate that the PSBL plays an important role in the generation and propagation of the energy flux associated with Alfven waves.

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Probability of Field-Aligned Currents Observed by the Satellite Cluster in the Magnetotail

CHENG Zheng-Wei, SHI Jian-Kui, ZHANG Tie-Long, LIU Zhen-Xing

Chin. Phys. Lett. 2007, 24 (4): 1125-1127 .

Abstract

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Field-aligned current (FAC) density distribution at the plasma sheet boundary layers is statistically studied. The FAC is calculated by the so-called curlometer technique with the data from FGM onboard the four Cluster spacecraft in 2001. By calculation we obtain a large number of FAC samples. In the samples, most of calculated FAC densities were very small and around zero caused by some errors or noise. In order to get the real FAC density distribution in the magnetotail, we use a three-Gaussian distribution to fit the errors, then subtract the estimated error contribution from the full distribution and obtain the FAC density distribution. The result shows that the FAC occurrence versus its density has a distribution consisting of a Gaussian
distribution with an additional decreasing exponential distribution. The most probable value of the FAC density is 3.45pT/km.

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Editorial Announcement: Withdrawal of Chinese Physics Letters 23 (2006) 1603, `Diffuse Backscattering Mueller Matrices Patterns from Turbid Media' by Zhang Lian-Shun et al.

Chin. Phys. Lett. 2007, 24 (4): 1128-1128 .

Abstract

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