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Volume 29 Issue 3
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GENERAL
New Explicit Multisymplectic Scheme for the Complex Modified Korteweg-de Vries Equation
CAI Jia-Xiang, MIAO Jun
Chin. Phys. Lett. 2012, 29 (3): 030201 .   DOI: 10.1088/0256-307X/29/3/030201
Abstract   PDF(pc) (664KB) ( 662 )
We propose an explicit multisymplectic Fourier pseudospectral scheme for the complex modified Korteweg-de Vries equation. Two test problems, the motion of a single solitary wave and interaction of solitary waves, are simulated. Numerical experiments show that the present scheme not only provides highly accurate numerical solutions, but also displays good performance in preserving the three integral invariants during long-time computation. Especially, the excellent ability to preserve the higher order invariant indicates that the proposed algorithm is robust and reliable.
Application of the Homotopy Perturbation Method to the Burgers Equation with Delay
S. Karimi Vanani, F. Soleymani
Chin. Phys. Lett. 2012, 29 (3): 030202 .   DOI: 10.1088/0256-307X/29/3/030202
Abstract   PDF(pc) (390KB) ( 880 )
The homotopy perturbation method (HPM) is presented to obtain the solution of the time-delayed Burgers equation. The HPM is a an efficient approach to obtain an analytical approximate solution of linear and nonlinear problems. The HPM provides approximate solutions in the form of a convergent series with easily computable components. Some experiments are employed to illustrate the validity and flexibility of the HPM for solving the time-delayed Burgers equation.
Entanglement of the Thermal State of an Anisotropic XYZ Spin Chain in an Inhomogeneous Constant Magnetic Field
A. -S. F. Obada, G. M. Abd Al-Kadar, F. K. Faramawy, A. A. Youssef
Chin. Phys. Lett. 2012, 29 (3): 030301 .   DOI: 10.1088/0256-307X/29/3/030301
Abstract   PDF(pc) (239KB) ( 523 )
A system of a two-qubit Heisenberg anisotropic XYZ spin chain in an inhomogeneous constant magnetic field with the Dzyaloshinskii–Moriya interaction is studied. The energy eigenvalues, the corresponding eigenstates and the thermal states of the system are evaluated. The entanglement is investigated according to Wootter's concurrence. The concurrence is studied against temperature for different values of the parameters involved.
Controlling Single-Photon Transport along an Optical Waveguide by using a Three-Level Atom
TIAN Wei, CHEN Bin, XU Wei-Dong
Chin. Phys. Lett. 2012, 29 (3): 030302 .   DOI: 10.1088/0256-307X/29/3/030302
Abstract   PDF(pc) (260KB) ( 629 )
We theoretically investigate the single-photon transport properties in an optical waveguide embedded with a V-type three-level atom (VTLA) based on symmetric and asymmetric couplings between the photon and the VTLA. Our numerical results show that the transmission spectrum of the incident photon can be well controlled by virtue of both symmetric and asymmetric coupling interactions. A multifrequency photon attenuator is realized by controlling the asymmetric coupling interactions. Furthermore, the influences of dissipation of the VTLA for the realistic physical system on single-photon transport properties are also analyzed.
On Universality of Quantum Fourier Transform
Arpita Maitra, Santanu Sarkar
Chin. Phys. Lett. 2012, 29 (3): 030303 .   DOI: 10.1088/0256-307X/29/3/030303
Abstract   PDF(pc) (366KB) ( 398 )
A methodology is presented to obtain the basis of qudits which are admissible to quantum Fourier transform (QFT) in the sense that the set of such kets are related by the QFT in the same way as the kets of the computational basis. We first study this method for qubits to characterize the ensemble that works for the Hadamard transformation (QFT for two dimension). In this regard we identify certain incompleteness in the result of Maitra and Parashar (Int. J. Quantum Inform. 4 (2006) 653). Next we characterize the ensemble of qutrits for which QFT is possible. Further, some theoretical results related to higher dimensions are also discussed. Considering the unitary matrix Un related to QFT, the issue boils down to the problem of characterizing matrices that commute with Un.
Transport Properties of the Universal Quantum Equation
A. I. Arbab
Chin. Phys. Lett. 2012, 29 (3): 030304 .   DOI: 10.1088/0256-307X/29/3/030304
Abstract   PDF(pc) (431KB) ( 465 )
The universal quantum equation (UQE) is found to describe the transport properties of the quantum particles. This equation describes a wave equation interacting with constant scalar and vector potentials propagating in spacetime. A new transformation that sends the Schrödinger equation with a potential energy V=−1/2mc2 to Dirac's equation is proposed. The Cattaneo telegraph equation as well as a one-dimensional UQE are compatible with our recently proposed generalized continuity equations. Furthermore, a new wave equation resulted from the invariance of the UQE under the post-Galilean transformations is derived. This equation is found to govern a Klein–Gordon's particle interacting with a photon-like vector field (ether) whose magnitude is proportional to the particle's mass.
Effect of Spin-Orbit Interaction and Input State on Quantum Discord and Teleportation of Two-Qubit Heisenberg Systems
QIN Meng, ZHAI Xiao-Yue, CHEN Xuan, LI Yan-Biao, WANG Xiao, BAI Zhong
Chin. Phys. Lett. 2012, 29 (3): 030305 .   DOI: 10.1088/0256-307X/29/3/030305
Abstract   PDF(pc) (745KB) ( 408 )
We study the quantum discord and teleportation of a two-qubit Heisenberg XXX chain with spin-orbit interaction. The analytical expressions of quantum discord, output state quantum discord and fidelity are obtained for this model. The classical correlation, quantum correlation and entanglement of this system depending on coupling interaction, spin-orbit interaction and temperature are investigated in detail. It is found that the quantum discord exists for the ferromagnetic case, but entanglement is zero under the same condition. We can obtain fidelity better than any classical communication protocol for the antiferromagnetic case. The robustness of quantum discord against the temperature is helpful for the realization of quantum computation.
Pulse Designed Coherent Dynamics of a Quantum Dot Charge Qubit
CAO Gang, WANG Li, TU Tao, LI Hai-Ou, XIAO Ming, GUO Guo-Ping
Chin. Phys. Lett. 2012, 29 (3): 030306 .   DOI: 10.1088/0256-307X/29/3/030306
Abstract   PDF(pc) (1111KB) ( 389 )
We propose an effective method to design the working parameters of a pulse-driven charge qubit implemented with double quantum dot. It is shown that intrinsic qubit population leakage to undesired states in the control and measurement process can be determined by the simulation of coherent dynamics of the qubit and minimized by choosing proper working parameters such as pulse shape. The result demonstrated here bodes well for future quantum gate operations and quantum computing applications.
Spin Dynamics in the XY Model
GE Rong-Chun, LI Chuan-Feng, GUO Guang-Can
Chin. Phys. Lett. 2012, 29 (3): 030307 .   DOI: 10.1088/0256-307X/29/3/030307
Abstract   PDF(pc) (1689KB) ( 482 )
We investigate the dynamics of entanglement, quantum correlation and classical correlation for the one-dimensional XY model in a transverse magnetic field. With the initial state polarized along the z axis, we find that the first maximum of the classical correlation between the nearest neighbor sites peaks around the critical point for large anisotropy parameter. It may indicate the quantum phase transition. For all kinds of correlation, we find that their behaviors between the nearest neighbor sites are significantly different from those of the next-nearest neighbor sites.
Quantum State Tomography and Quantum Games
Ahmad Nawaz
Chin. Phys. Lett. 2012, 29 (3): 030308 .   DOI: 10.1088/0256-307X/29/3/030308
Abstract   PDF(pc) (446KB) ( 407 )
A technique is developed for single qubit quantum state tomography using the mathematical setup of generalized quantization scheme for games. In this technique, Alice sends an unknown pure quantum state to Bob who appends it with |0><0| and then applies the unitary operators on the appended quantum state and finds the payoffs for Alice and himself. It is shown that for a particular set of unitary operators, these payoffs are equal to Stokes parameters for an unknown quantum state. In this way an unknown quantum state can be measured and reconstructed. Strictly speaking, this technique is not a game as no strategic competitions are involved.
Anisotropic Bianchi Type-I Model with a Varying Λ Term
R. K. Tiwari, Divya Singh
Chin. Phys. Lett. 2012, 29 (3): 030401 .   DOI: 10.1088/0256-307X/29/3/030401
Abstract   PDF(pc) (391KB) ( 411 )
Einstein field equations with variable gravitational and cosmological constants are considered in the presence of a perfect fluid for a Bianchi type-I universe by assuming that the cosmological term is proportional to the Hubble parameter. The variation law for vacuum density was recently proposed by Schützhold on the basis of quantum field estimation in a curved expanding background. The cosmological term tends asymptotically to a genuine cosmological constant and the model tends to a de Sitter universe. We obtain that the present universe is accelerating with a large fraction of cosmological density in the form of a cosmological term.
Noise-Induced Voltage Collapse in Power Systems
WEI Du-Qu, LUO Xiao-Shu, ZHANG Bo
Chin. Phys. Lett. 2012, 29 (3): 030501 .   DOI: 10.1088/0256-307X/29/3/030501
Abstract   PDF(pc) (861KB) ( 468 )
We investigate numerically the influences of Gaussian white noise on the dynamical behaviors of power systems. The studied model is a three-bus system at some specific parameters, and it demonstrates a stable regime that is far from collapse. It is found that with the increasing noise intensity σ, power systems become unstable and fall into oscillations; as σ is further increased, noise-induced voltage collapse in power systems takes place. Our results confirm that the presence of noise has a detrimental effect on power system operation. Furthermore, the possible mechanism behind the action of noise is addressed based on a dynamical approach where the bifurcation of the system is analyzed. Our results may provide useful information for avoiding instability problems in power systems.
Quantifying Information Flow between Two Chaotic Semiconductor Lasers Using Symbolic Transfer Entropy
LI Nian-Qiang, PAN Wei, YAN Lian-Shan, LUO Bin, XU Ming-Feng, TANG Yi-Long
Chin. Phys. Lett. 2012, 29 (3): 030502 .   DOI: 10.1088/0256-307X/29/3/030502
Abstract   PDF(pc) (560KB) ( 538 )
Symbolic transfer entropy (STE) is employed to quantify the dominant direction of information flow between two chaotic-semiconductor-laser time series. The information flow in unidirectionally and bidirectionally coupled systems was analyzed systematically. Numerical results show that the dependence relationship can be revealed if there exists any coupling between two chaotic semiconductor lasers. More importantly, in both unsynchronized and good synchronization regimes, the STE can be used to quantify the direction of information flow between the lasers, although the former case leads to a better identification. The results thus establish STE as an effective tool for quantifying the direction of information flow between chaotic-laser-based systems.
Temperature Uniformity of Wafer on a Large-Sized Susceptor for a Nitride Vertical MOCVD Reactor
LI Zhi-Ming, JIANG Hai-Ying, HAN Yan-Bin, LI Jin-Ping, YIN Jian-Qin, ZHANG Jin-Cheng
Chin. Phys. Lett. 2012, 29 (3): 030701 .   DOI: 10.1088/0256-307X/29/3/030701
Abstract   PDF(pc) (687KB) ( 492 )
The effect of coil location on wafer temperature is analyzed in a vertical MOCVD reactor by induction heating. It is observed that the temperature distribution in the wafer with the coils under the graphite susceptor is more uniform than that with the coils around the outside wall of the reactor. For the case of coils under the susceptor, we find that the thickness of the susceptor, the distance from the coils to the susceptor bottom and the coil turns significantly affect the temperature uniformity of the wafer. An optimization process is executed for a 3-inch susceptor with this kind of structure, resulting in a large improvement in the temperature uniformity. A further optimization demonstrates that the new susceptor structure is also suitable for either multiple wafers or large-sized wafers approaching 6 and 8 inches.
A Single-Transistor Active Pixel CMOS Image Sensor Architecture
ZHANG Guo-An, ZHANG Dong-Wei, HE Jin, SU Yan-Mei, WANG Cheng, CHEN Qin, LIANG Hai-Lang, YE Yun
Chin. Phys. Lett. 2012, 29 (3): 030702 .   DOI: 10.1088/0256-307X/29/3/030702
Abstract   PDF(pc) (538KB) ( 1989 )
A single-transistor CMOS active pixel image sensor (1 T CMOS APS) architecture is proposed. By switching the photosensing pinned diode, resetting and selecting can be achieved by diode pull-up and capacitive coupling pull-down of the source follower. Thus, the reset and selected transistors can be removed. In addition, the reset and selected signal lines can be shared to reduce the metal signal line, leading to a very high fill factor. The pixel design and operation principles are discussed in detail. The functionality of the proposed 1 T CMOS APS architecture has been experimentally verified using a fabricated chip in a standard 0.35 µm CMOS AMIS technology.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
Dissociation Temperature of Strictly Confined Charmonium States
QU Zhen, LIU Yun-Peng, ZHUANG Peng-Fei
Chin. Phys. Lett. 2012, 29 (3): 031201 .   DOI: 10.1088/0256-307X/29/3/031201
Abstract   PDF(pc) (497KB) ( 334 )
We study the dissociation of strictly confined charmonium states at finite temperature. The strict confinement constraint to the Cornell potential leads to a 10% higher J/ψ dissociation temperature and in turn a weaker J/ψ suppression in relativistic heavy ion collisions.
Direct Graviton Production via Photon-Photon Fusion at the CERN-LHC
S. C. İ, nan
Chin. Phys. Lett. 2012, 29 (3): 031301 .   DOI: 10.1088/0256-307X/29/3/031301
Abstract   PDF(pc) (467KB) ( 423 )
The potential of pp →p γγp →pGp process in scenarios of the Arkani-Hamed, Dimopoulos, Dvali (ADD) and Randall-Sundrum (RS) model at the LHC is examined, and 95% C.L. bounds on the model parameters are obtained. It is found that the sensitivity of the model parameters can be improved in the present colliders by using this reaction.
Effects of Anomalous Tensor Couplings in Bs0Bs0 Mixing
CHANG Qin, HAN Lin, YANG Ya-Dong
Chin. Phys. Lett. 2012, 29 (3): 031302 .   DOI: 10.1088/0256-307X/29/3/031302
Abstract   PDF(pc) (763KB) ( 292 )
Motivated by the recently observed anomalous large dimuon charge asymmetry in neutral B decays, we study the effects of the anomalous tensor couplings to pursue a possible solution. With the constraints from the observables φsJ/ψ(φ,f0), asls and ΔMs, the new physics parameter spaces are severely restricted. We find that the contributions induced by the color−singlet or the color-octet tensor operators are helpful to moderate the anomaly in Bs0-Bs0 mixing. Numerically, the observable asls could be enhanced by about two orders of magnitude by the contributions of color−singlet or color-octet tensor operators with their respective nontrivial new weak phase φT1=41°±35° or φT8=−47°±33° and relevant strength parameters |gT1|=(2.89±1.40)×10−2 or |gT8|=(0.79±0.34)×10−2. However, due to the fact that the NP contributions are severely suppressed by the recent LHCb measurement for φsJ/ψ(φ,f0), our theoretical result of asls is still much smaller than the central value of the experimental data.
ATOMIC AND MOLECULAR PHYSICS
An Effective Eigenchannel R-Matrix Method for Calculating Electron-Ion Scattering Processes with Spectroscopic Precision
GAO Xiang, LI Jia-Ming
Chin. Phys. Lett. 2012, 29 (3): 033101 .   DOI: 10.1088/0256-307X/29/3/033101
Abstract   PDF(pc) (584KB) ( 429 )
The electron-ion scattering processes are very important in various scientific research fields such as astrophysical studies and inertial confinement fusion research. We report our recent development of an efficient method for providing such atomic data with spectroscopic precision. Based on the Breit–Pauli and the Dirac R-matrix theory, we develop two eigenchannel R-matrix codes, referred to as R-eigen (non-relelativistic eigenchannel R-matrix) and R-R-eigen (relativistic eigenchannel R-matrix), to directly calculate the physical quantities in multichannel quantum defect theory in the whole energy regions. From such physical quantities, we can obtain all energy levels and the related scattering cross sections with accuracies comparable with spectroscopic precision. The e+Kr+ system is used as an illustration example, the degrees of accuracies of scattering matrices are calculated within about 2%, which should be much more accurate than state-of-the-art scattering experiments.
Microscopic Surface-Electrode Ion Trap for Scalable Quantum Information Processing
CHEN Liang, WAN Wei, XIE Yi, ZHOU Fei, FENG Mang
Chin. Phys. Lett. 2012, 29 (3): 033701 .   DOI: 10.1088/0256-307X/29/3/033701
Abstract   PDF(pc) (1543KB) ( 372 )
In this paper we try to develop a scalable surface-electrode architecture for ion trap quantum information processing. The confinement of the ions by the rf pseudopotential and the movement of the ions by changing the rf pseudopotential are investigated by numerical simulation. Particular concern is paid to the +-shaped junction, which is the connection of different components of the architecture, and also on the place which yields heat and escaping ions. We show the feasibility of fabricating and operating on the architecture for quantum information processing with currently available technology.
FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)
Grating-Coupled Waveguide Cloaking
WANG Jia-Fu, QU Shao-Bo, XU Zhuo, MA Hua, WANG Cong-Min, XIA Song, WANG Xin-Hua, ZHOU Hang
Chin. Phys. Lett. 2012, 29 (3): 034101 .   DOI: 10.1088/0256-307X/29/3/034101
Abstract   PDF(pc) (1406KB) ( 420 )
Based on the concept of a grating-coupled waveguide (GCW), a new strategy for realizing EM cloaking is presented. Using metallic grating, incident waves are firstly coupled into the effective waveguide and then decoupled into free space behind, enabling EM waves to pass around the obstacle. Phase compensation in the waveguide keeps the wave-front shape behind the obstacle unchanged. Circular, rectangular and triangular cloaks are presented to verify the robustness of the GCW cloaking. Electric field animations and radar cross section (RCS) comparisons convincingly demonstrate the cloaking effect.
Characteristics of Plane Wave Propagation in Biaxially Anisotropic Gyrotropic Media
PAN Wei-Tao, LIU Song-Hua, QIU Zhi-Liang
Chin. Phys. Lett. 2012, 29 (3): 034102 .   DOI: 10.1088/0256-307X/29/3/034102
Abstract   PDF(pc) (611KB) ( 479 )
Propagation characteristics of electromagnetic waves at the interface between an isotropic regular medium and a biaxially anisotropic gyrotropic medium are investigated. The results indicate that the reflection and refraction properties of electromagnetic waves are closely dependent on the dispersion relation of the gyrotropic media, and that anomalous total reflection and negative refraction may occur. The existence conditions of total transmission are also considered. It is found that total transmission arises when the TE-polarized incident waves are normal to the interface and the physical parameters of the two media are chosen properly, which are quite different from the existence conditions of total transmission at the anisotropic left-handed material interface. Numerical results are given to validate our theoretical analysis.
Calculation of the Spin-Dependent Optical Lattice in Rubidium Bose–Einstein Condensation
CAO Ming-Tao, HAN Liang, QI Yue-Rong, ZHANG Shou-Gang, GAO Hong, LI Fu-Li
Chin. Phys. Lett. 2012, 29 (3): 034201 .   DOI: 10.1088/0256-307X/29/3/034201
Abstract   PDF(pc) (529KB) ( 428 )
We provide a theoretical study to calculate the spin-dependent optical lattice with rubidium Bose–Einstein condensation (BEC) in a steady magnetic field. The optical dipole potential variation at different Zeeman levels are obtained. We also show that atoms can be transported in three dimensions by changing the polarization of the trapping field. An explanation of this transportation process in an atomic coordinate is presented.
Angular Tolerance Enhancement in Guided-Mode Resonance Filters with a Photonic Crystal Slab
LI Cheng-Guo, GAO Yong-Hao, XU Xing-Sheng
Chin. Phys. Lett. 2012, 29 (3): 034202 .   DOI: 10.1088/0256-307X/29/3/034202
Abstract   PDF(pc) (1589KB) ( 490 )
Two different triple-layer guided-mode resonance (GMR) filters with photonic crystal (PC) slab structures are designed, and their main optical properties are investigated. It is shown that under normal incidence, the PC slab GMR filters exhibit narrower bandwidth, a more symmetric line shape, and larger angular tolerance, compared with the planar grating GMR filters. The rod-slab type GMR filter works better than the hole-slab one. The resonance wavelength location and the angular tolerance can be tuned by varying the periods. The angular tolerance with narrow bandwidth can be improved by increasing the ratio of the periods in the two crossed directions.
Polarization Beam Splitter Based on an Annular Photonic Crystal of Negative Refraction
WU Hong, JIANG Li-Yong, JIA Wei, LI Xiang-Yin
Chin. Phys. Lett. 2012, 29 (3): 034203 .   DOI: 10.1088/0256-307X/29/3/034203
Abstract   PDF(pc) (808KB) ( 482 )
An annular photonic crystal is used to design a novel kind of polarization beam splitter based on the negative refraction effect. Since TE and TM polarization waves can be excited at the first and second bands, respectively, they will result in different refractive angles and make separation possible. To improve the splitting efficiency, the cut-off treatment along the ΓM direction and the antireflection coating are introduced to enlarge the separation angle and to decrease the reflection loss. Simulation results show that the proposed polarization beam splitter has a tunable working incident angle that is in the range of 18°–26°. In particular, when the incident angle is 20°, over 90% transmissions can be achieved for both TE and TM polarizations in a wide working frequency range from 0.279(2πc/a) to 0.287(2πc/a).
A 46-W Laser Diode Stack End-Pumped Slab Amplifier with a Pulse Duration of Picoseconds
YAN Ying, FAN Zhong-Wei, NIU Gang, YU Jin, ZHANG Heng-Li
Chin. Phys. Lett. 2012, 29 (3): 034204 .   DOI: 10.1088/0256-307X/29/3/034204
Abstract   PDF(pc) (709KB) ( 381 )
A 46-W laser diode end-pumped amplifier is demonstrated by using a SESAM passively mode-locked oscillator and a compact LD stack end-pumped slab amplifier. For the oscillator, a 5-W picosecond mode-locked laser with a repetition frequency of 79 MHz is obtained with beam quality factors of M2<1.3. A beam shaping system made up of cylindrical lens is designed according to different sizes of the active medium in both directions, and a plane−plane cavity is used in the amplifier for high efficiency. At the absorbed pumping power of 174 W, the highest output power of 46 W is obtained with the slope efficiency of 29.5%. The beam quality factors M2 in both directions are measured to be 1.43 and 1.76, respectively.
Remarkable Franz-Keldysh Effect in Ge-on-Si p-i-n Diodes
LI Ya-Ming, HU Wei-Xuan, CHENG Bu-Wen, LIU Zhi, WANG Qi-Ming
Chin. Phys. Lett. 2012, 29 (3): 034205 .   DOI: 10.1088/0256-307X/29/3/034205
Abstract   PDF(pc) (510KB) ( 534 )
Ge-on-Si p-i-n diodes are fabricated by using two-step Ge film epitaxial technology on Si substrates. A remarkable Franz–Keldysh effect is observed in the wavelength range of 1620–1640 nm with a largest Δα/α of 2.8 at 1640 nm by optical responsivity measurement. The remarkable change of absorption coefficient in the considerable large wavelength range makes Ge−on-silicon a promising candidate for Si-based electro-absorption modulators. The initial design predicts a modulator of bandwidth ∼50 GHz, and the extinction ratio >7 dB by the measured parameter.
Temperature and Input Energy Dependence of the 946-nm Stimulated Emission Cross Section of Nd3+:YAG Pumped by a Flashlamp
Seyed Ebrahim Pourmand, Noriah Bidin, Hazri Bakhtiar
Chin. Phys. Lett. 2012, 29 (3): 034206 .   DOI: 10.1088/0256-307X/29/3/034206
Abstract   PDF(pc) (432KB) ( 587 )
The thermal effect on the laser transition at 946 nm is investigated. The temperature of the cooling system is verified in the range 2-60°C. A Nd:YAG laser crystal is utilized as a gain medium and is pumped by a newly developed flashlamp. The variable pumping energy is accomplished within the 5-40 J range. The stimulated emission cross section of the 946-nm line is estimated based on the fluorescence spectrum of the Nd:YAG laser. The stimulated emission cross section of the 946-nm line is found to be inversely proportional to the temperature and to the input energy due to the increase of the thermal population at the ground level.
Multiple Dissipative Solitons in a Long-Cavity Normal-Dispersion Mode-Locked Yb-Doped Fiber Laser
ZHAO Guang-Zhen, XIAO Xiao-Sheng, MEI Jia-Wei, YANG Chang-Xi
Chin. Phys. Lett. 2012, 29 (3): 034207 .   DOI: 10.1088/0256-307X/29/3/034207
Abstract   PDF(pc) (540KB) ( 582 )
Transitional operations of multiple dissipative solitons in a long-cavity normal-dispersion Yb-doped fiber laser are experimentally investigated. Multiple dissipative solitons, including a stable soliton pair and a soliton triplet are observed by increasing the pump power or adjusting the polarization controllers. Two main boundaries of the stable asymmetric soliton and oscillating soliton are found between steady mode-locking. Moreover, multiple dissipative solitons with greater quantities of solitons are observed with pump power increasing. The experimental results agree well with a previous numerical study of multiple dissipative solitons.
Actively Q−Switched Laser Performance of Holmium-Doped Lu2SiO5 Crystal
YAO Bao-Quan, DUAN Xiao-Ming, YU Zheng-Ping, WANG Yue-Zhu
Chin. Phys. Lett. 2012, 29 (3): 034208 .   DOI: 10.1088/0256-307X/29/3/034208
Abstract   PDF(pc) (475KB) ( 469 )
We present the actively Q−switched performance of Ho3+ in LSO crystal for operation at cryogenic and room temperature. For a cryogenic−temperature Q−switched Tm,Ho:LSO laser, a total incident diode power of 12.1 W is used to generate a maximum pulse energy of 1.15 mJ at a pulse repetition frequency (PRF) of 2 kHz (15.8 kW peak power). For a room-temperature Q−switched Ho:LSO laser pumped directly by a 1.91-µm Tm:YLF laser, the maximum average output power of 1.75 W and the shortest pulse width of 39 ns are achieved at a PRF of 5 kHz when the absorbed pump power is 12.2 W.
Performance of a c− and a-Cut Ho:YAP Laser at Room Temperature
SHEN Ying-Jie, YAO Bao-Quan, DAI Tong-Yu, LI-Gang, DUAN Xiao-Ming, JU You-Lun, WANG Yue-Zhu
Chin. Phys. Lett. 2012, 29 (3): 034209 .   DOI: 10.1088/0256-307X/29/3/034209
Abstract   PDF(pc) (619KB) ( 428 )
Continuous-wave operation of room-temperature c− and a−cut Ho:YAP lasers resonantly end-pumped by a diode-pumped Tm:YLF laser at 1.91 µm are comparatively investigated. The maximum output powers of 7.8 W at 2103 nm and 6.09 W at 2130 nm for c−cut Ho:YAP crystal are obtained. The maximum output power of 8.78 W at 2119 nm for a−cut Ho:YAlO3 crystal is achieved. The maximum slope efficiency in terms of absorbed pump power approximately reaches 57.8% for c−oriented crystal and about 52.7% for a-oriented crystal.
FIB Moiré Gratings and Their Application in the Measurement of Optical Fibers' Mechanical Properties
JIANG Ming, TANG Min-Jin, WU Hao, LI Yan-Jie, XIE Hui-Min
Chin. Phys. Lett. 2012, 29 (3): 034210 .   DOI: 10.1088/0256-307X/29/3/034210
Abstract   PDF(pc) (854KB) ( 487 )
Focused ion beam (FIB) milling technique is used to fabricate specimen grating with frequency of 1000 lines/mm on the surface of optical fiber, and in-situ tensile tests are carried out by using a scanning electron microscope (SEM). The SEM scanning Moiré is formed by the superposition of the specimen grating and SEM scanning lines. The displacement field and strain field are obtained by taking advantage of the SEM Moiré method combining with random phase-shifting technique. The tensile properties of the optical fibers are measured according to the stress-strain curve. The experimental results of the SEM Moiré method based on FIB grating demonstrate a good agreement with the parameters obtained from commercial tensile testing machine.
Band Gap Properties of Magnetoelectroelastic Grid Structures with Initial Stress
WANG Yi-Ze, LI Feng-Ming
Chin. Phys. Lett. 2012, 29 (3): 034301 .   DOI: 10.1088/0256-307X/29/3/034301
Abstract   PDF(pc) (417KB) ( 411 )
The propagation of elastic waves in magnetoelectroelastic grid structures is studied. Band gap properties are presented and the effects of the magnetoelectroelastic coupling and initial stress are considered. Numerical calculations are performed using the plane-wave expansion method. The results show that the band gap width can be tuned by the initial stress. It is hoped that our results will be helpful for designing acoustic filters with magnetoelectroelastic materials and grid structures.
Calculation and Analysis of Near-Field Head-Related Transfer Functions from a Simplified Head-Neck-Torso Model
CHEN Ze-Wei, YU Guang-Zheng, XIE Bo-Sun, GUAN Shan-Qun
Chin. Phys. Lett. 2012, 29 (3): 034302 .   DOI: 10.1088/0256-307X/29/3/034302
Abstract   PDF(pc) (3168KB) ( 583 )
To evaluate the overall effect of the neck and torso on the head-related transfer function (HRTF), a simplified head-neck-torso (HNT) model, which consists of a spherical head, spherical torso and cylindrical neck, is proposed and the corresponding HRTFs are calculated using the boundary element method (BEM). The results indicate that the HRTF magnitudes for the HNT model are different from those of the existing spherical head-and-torso model (HAT) above 0.5 kHz, especially in the near-field and contralateral region. The discrepancy in the HRTF magnitudes leads to a discrepancy in the interaural level differences (ILDs) for the HNT and HAT models, which reaches a level of ±10 dB at source distance of 0.2 m. As the source distance increases, the discrepancy in the results of the HNT and HAT models reduces. Measurement on practical HNT and HAT models validates the analysis. Therefore, the neck influences near-field HRTFs and should be included in the near-field HRTF calculation.
Irregular Oscillation of Bi-disperse Granular Gas in Cyclic Three Compartments
Sajjad Hussain Shah, LI Yin-Chang, CUI Fei-Fei, ZHANG Qi, Pierre Evesque, HOU Mei-Ying
Chin. Phys. Lett. 2012, 29 (3): 034501 .   DOI: 10.1088/0256-307X/29/3/034501
Abstract   PDF(pc) (920KB) ( 455 )
A 3-D molecular dynamics simulation of a bi-disperse vibro-fluidized granular gas in a cyclic three-compartment cell is performed. A cluster of particles is randomly found in one of the compartments. Lohse's flux model is modified to incorporate inelastic particle-boundary collisions. This model predicts that periodically there is clustering in each compartment. It is then found that if the model is further modified to incorporate Gaussian white noise, it correctly predicts the non-sequential clustering behavior confirming that there is no chaotic behavior.
Poincaré-MacMillan Equations of Motion for a Nonlinear Nonholonomic Dynamical System
Amjad Hussain, Syed Tauseef Mohyud-Din, Ahmet Yildirim
Chin. Phys. Lett. 2012, 29 (3): 034502 .   DOI: 10.1088/0256-307X/29/3/034502
Abstract   PDF(pc) (360KB) ( 372 )
MacMillan's equations are extended to Poincaré's formalism, and MacMillan's equations for nonlinear nonholonomic systems are obtained in terms of Poincaré parameters. The equivalence of the results obtained here with other forms of equations of motion is demonstrated. An illustrative example of the theory is provided as well.
Unsteady Squeezing Flow of Jeffery Fluid between Two Parallel Disks
A. Qayyum, M. Awais, A. Alsaedi, T. Hayat
Chin. Phys. Lett. 2012, 29 (3): 034701 .   DOI: 10.1088/0256-307X/29/3/034701
Abstract   PDF(pc) (487KB) ( 908 )
We investigate an unsteady axisymmetric flow of a Jeffrey fluid between two parallel disks. The relevant partial differential equations are modeled and simplified by using appropriate transformations. The resulting ordinary differential system is solved and a series solution is obtained. Effects of various parameters of interest on the flow quantities are seen. It is found that the velocity profile increases when porosity and squeezing parameters are increased.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
Preliminary Experimental Study of Ion Beam Extraction of EAST Neutral Beam Injector
XU Yong-Jian, HU Chun-Dong, LIU Sheng, XIE Ya-Hong, LIANG Li-Zhen, JIANG Cai-Chao
Chin. Phys. Lett. 2012, 29 (3): 035201 .   DOI: 10.1088/0256-307X/29/3/035201
Abstract   PDF(pc) (461KB) ( 470 )
Neutral beam injection is recognized as one of the most effective means for plasma heating. The preliminary data of ion beam extraction is obtained on the EAST neutral beam injector test-stand. Beam extraction from the ion source of EAST-NBI is verified by measuring the beam current with a Faraday cup and by analyzing the results obtained by means of water calorimetric measurement on the temperature rises of water cooling the accelerator electrodes.
Quasi-monoenergetic Tens-of-MeV Proton Beams by a Laser-Illuminated Funnel-Like Target
BAN Hong-Ye, GU Yan-Jun, KONG Qing, LI Ying-Ying, ZHU Zhen, S. Kawata
Chin. Phys. Lett. 2012, 29 (3): 035202 .   DOI: 10.1088/0256-307X/29/3/035202
Abstract   PDF(pc) (2704KB) ( 368 )
From numerical simulations, we study the generation of quasi-monoenergetic MeV proton beams from a laser-illuminated funnel-like target. We show that, when passing through such a target, the laser beam can be focused and constricted within a cylindrical bore at the funnel apex from which proton beams are produced. Accompanied by a much-enhanced laser intensity, the proton beams experience more acceleration time than with normal funnel targets. Constriction from the cylinder bore, combined with an enhancement of a separated charge field from Al electrons, protons can attain higher energies up to several tens of MeV. At the same time, strong suppression of the transverse divergence of the laser and proton beams yields a localized, collimated, mono-energetic proton beam.
Competition between Buneman and Langmuir Instabilities
GUO Jun, YU Bin
Chin. Phys. Lett. 2012, 29 (3): 035203 .   DOI: 10.1088/0256-307X/29/3/035203
Abstract   PDF(pc) (965KB) ( 431 )
The electron-ion beam instabilities are studied by one-dimensional electrostatic particle-in-cell simulation. The simulation results show that both the low-frequency Buneman mode and high-frequency Langmuir wave (LW) are excited in the nonlinear phase. The power of Buneman instability is stronger than that of the LW. The Buneman instability is firstly excited. Then the backward LW appears, which is probably excited by the particles trapped in the wave potential and moving opposite to the original beam direction. After some time, the forward LW can be found, which has a larger maximum frequency than that of the backward LW. With the decrease of the electron drift velocity, the instabilities become weaker; the LW appears to have almost equal intensities and becomes symmetric for forward and backward propagation directions. The LW can also heat the electron, so the relative drift speed cannot far exceed the electron thermal speed, which is not helpful to the development of Buneman instability.
CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES
Crystallization Characteristics of SiNx-Doped SbTe Films for Phase Change Memory
WAN Qi-Jian, FENG Jie, GUO Gang
Chin. Phys. Lett. 2012, 29 (3): 036101 .   DOI: 10.1088/0256-307X/29/3/036101
Abstract   PDF(pc) (1588KB) ( 568 )
SbTe films doped with different SiNx concentrations (2, 5, 17, 25at.%) are prepared by co-sputtering with Si3N4 and SbTe alloy targets. In order to study the crystallization process and amorphous state stability and to compare with Ge2Sb2Te5 (GST) and pure SbTe films, x-ray diffraction (XRD), transmission electron microscopy (TEM) and in situ film resistance measurements are carried out. SiNx doping enhances the amorphous state stability of the SbTe films. The temperature for 10−year retention of amorphous state of pure SbTe films is −11°C and that of 17at.% SiNx-doped SbTe films increases to 75°C. SiNx addition increases the crystallization temperature and the electrical resistivity of SbTe films. The microstructures of SiNx-doped SbTe films are analyzed through XRD and TEM. After annealing at 350°C, SiNx-doped SbTe films crystallized into a kind of nanocomposite films with rhombohedra Sb2Te3 nanoparticles embedded into an amorphous SiNx matrix. The nanocomposite structure and higher crystalline resistivity of the SiNx-doped SbTe films is helpful to reduce the RESET current of phase change memory.
High-Quality Single Crystalline Ge(111) Growth on Si(111) Substrates by Solid Phase Epitaxy
SUN Bing, CHANG Hu-Dong, LU Li, LIU Hong-Gang, WU De-Xin
Chin. Phys. Lett. 2012, 29 (3): 036102 .   DOI: 10.1088/0256-307X/29/3/036102
Abstract   PDF(pc) (645KB) ( 419 )
Heterogeneous integration of crystalline Ge layers on cleaned and H-terminated Si(111) substrates are demonstrated by employing a combination of e-beam evaporation and solid phase epitaxy techniques. High-quality single crystalline Ge(111) layers on Si(111) substrates with a smooth Ge surface and an abrupt interface between Ge and Si are obtained. An XRD rocking curve scan of the Ge(111) diffraction peak shows a FWHM of only 260 arcsec for a 50-nm-thick Ge layer annealed at 600°C with a ramp−up rate of 20°C/s and a holding time of 1 min. The AFM images exhibit that the rms surface roughness of all the crystalline Ge layers are less than 2.1 nm.
Generation of Nitrogen-Vacancy Centers in Diamond with Ion Implantation
CUI Jin-Ming, CHEN Xiang-Dong, FAN Le-Le, GONG Zhao-Jun, ZOU Chong-Wen, SUN Fang-Wen, HAN Zheng-Fu, GUO Guang-Can
Chin. Phys. Lett. 2012, 29 (3): 036103 .   DOI: 10.1088/0256-307X/29/3/036103
Abstract   PDF(pc) (1118KB) ( 612 )
Nitrogen-vacancy defect color centers are created in a high purity single crystal diamond by nitrogen-ion implantation. Both optical spectrum and optically detected magnetic resonance are measured for these artificial quantum emitters. Moreover, with a suitable mask, a lattice composed of nitrogen-vacancy centers is fabricated. Rabi oscillation driven by micro-waves is carried out to show the quality of the ion implantation and potential in quantum manipulation. Along with compatible standard lithography, such an implantation technique shows high potential in future to make structures with nitrogen-vacancy centers for diamond photonics and integrated photonic quantum chip.
B–C–N Compounds with Mixed Hybridization of sp2-Like and sp3-Like Bonds
LUO Xiao-Guang, HE Ju-Long
Chin. Phys. Lett. 2012, 29 (3): 036104 .   DOI: 10.1088/0256-307X/29/3/036104
Abstract   PDF(pc) (731KB) ( 452 )
We perform first-principles calculations of the structural and electronic properties of hypothetical bc6-BC4N and N-substituted bc6-BC4N, which are derived from a body−center-cubic carbon structure. Our calculations show that the former is a semiconductor with an indirect band gap of 0.91 eV and the latter is metallic. The calculated bond length, bond population, and charge density of N-substituted bc6-BC4N indicate that one C−N bond has been broken after N-substitution, which means that the structure contains a mixed hybridization of sp2-like and sp3-like bonds. At the pressure above 100 GPa, the structure changes to a pure sp3-like hybridization.
Fabrication of GaAs Nanowires by Colloidal Lithography and Dry Etching
CHEN Ke, HE Jian-Jun, LI Ming-Yu, LaPierre R
Chin. Phys. Lett. 2012, 29 (3): 036105 .   DOI: 10.1088/0256-307X/29/3/036105
Abstract   PDF(pc) (1346KB) ( 805 )
A method for the fabrication of well-ordered periodic GaAs nanowires (NWs) is developed based on a combination of colloidal lithography and an inductively coupled plasma (ICP) etching technique using CHF3/Ar and Cl2/N2/BCl3 chemistry. The effects of etching parameters such as flow rate, and etching duration on NW fabrication are investigated. The reflectance spectra of the GaAs NW samples are measured and compared with NWs fabricated by molecular beam epitaxy.
Adsorption, Diffusion, and Dissociation of H2O on Kaolinite (001): a Density Functional Study
HE Man-Chao, ZHAO Jian
Chin. Phys. Lett. 2012, 29 (3): 036801 .   DOI: 10.1088/0256-307X/29/3/036801
Abstract   PDF(pc) (701KB) ( 692 )
Density functional theory is used to investigate the adsorption, diffusion, and dissociation of H2O on kaolinite(001) surface. It is found that the preferred adsorption sites on the kaolinite(001) surface for H2O are the threefold hollow sites with the adsorption energies ranging from 1.06 to 1.15 eV. H2O does not adsorb on the six−fold hollow site of the aluminium(001) face of the third layer of kaolinite, implying that it is difficult for water molecules to penetrate the ideal kaolinite(001) surface. In addition, we calculate the energetic barriers for the diffusion of H2O between the most stable and next most stable adsorption sites, which range from 0.073 to 0.129 eV. The results also show that H2O molecules are easy to diffuse on kaolinite(001) surface. Finally, our study indicates that no dissociation state exists for the H2O on kaolinite(001) surface.
Influence of Heating Rate on Morphologies and Magnetic Properties of α-Fe2O3
LI Zi-Yue, ZHANG Hui-Min, LIU Li-Hu, SUN Hui-Yuan
Chin. Phys. Lett. 2012, 29 (3): 036802 .   DOI: 10.1088/0256-307X/29/3/036802
Abstract   PDF(pc) (980KB) ( 508 )
A variety of hematite microstructures are synthesized through oxalic acid-assisted thermal treatment of iron films sputtered onto glass substrates. Petal-like α-Fe2O3 nanoslices and honeycomb-like α-Fe2O3 particles of micrometer sizes are obtained after annealing at 500°C but with different rates of heating to the final annealing temperature. Structures and morphologies of the samples are studied by means of x-ray diffraction, scanning electron microscopy and atomic force microscopy. These structures are believed to be formed during the period of increasing temperature to the final annealing temperature. Superconducting-quantum-interference-device magnetometer measurements show room-temperature ferromagnetism in these samples.
Effect of Multiple Depositions and Annealing Treatments on the Erbium Silicide Nanoislands Self-Assembled on Si(001) Substrates
DING Tao, SONG Jun-Qiang, CAI Qun
Chin. Phys. Lett. 2012, 29 (3): 036803 .   DOI: 10.1088/0256-307X/29/3/036803
Abstract   PDF(pc) (856KB) ( 447 )
Erbium silicide nanoislands on Si(001) surface are fabricated by novel multiple depositions and annealing treatments method. The morphological investigations determine that the islands could grow with stable square shapes rather than the shape transformation exhibited in the traditional single time evaporation growth. Size distributions analyses further elucidate the effect of multiple depositions and annealing treatments on the nanoisland growth. It is suggested that strain relaxation and static coalescence play important roles in the cyclic growth. Specifically, after 15 times of the cycles, the larger islands are found to undergo the Ostwald ripening, which make the shape of nanoislands irregular. This gives us the direction to adjust the growth parameters to control the island morphology. Furthermore, the crystalline structure of the Er silicide nanoislands is efficiently characterized by grazing incidence synchrotron x-ray diffraction.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
First-Principles Study on Electronic Structures and Optical Properties of Doped Ag Crystal
CAO Can, CHEN Ling-Na, JIA Shu-Ting, ZHANG Dan, XU Hui
Chin. Phys. Lett. 2012, 29 (3): 037101 .   DOI: 10.1088/0256-307X/29/3/037101
Abstract   PDF(pc) (752KB) ( 373 )

By using the first-principles calculation based on density functional theory, we investigate the electronic structures and optical properties of Cl-doped Ag crystal. The results show that the electronic structure of Cl-doped Ag crystal depends on the doped concentration and the site of impurity defect. Interestingly, the calculated adsorption spectra of Cl-doped Ag crystal show isotropy or anisotropy coincide with the symmetry of Ag crystal. These features are discussed to provide guidance to experimental efforts for Ag-based nanoeletronic devices.

Fabrication and Electrical Characteristics of Individual ZnO Submicron-Wire Field-Effect Transistor
JIANG Wei, GAO Hong, XU Ling-Ling
Chin. Phys. Lett. 2012, 29 (3): 037102 .   DOI: 10.1088/0256-307X/29/3/037102
Abstract   PDF(pc) (872KB) ( 315 )

Fabrication and electrical characteristics of individual ZnO submicro-wire field-effect transistors (FETs) are investigated by a simple micro-grid template method. The fabricated back-gate ZnO submicro-wire FET is characterized at room temperature in air. The gate voltage Vgs curves reveal gating effect characteristic of n−type conductivity. The field effect mobility of the ZnO submicro-wire is determined to be 7.9 cm2/V·s at Vds=2 V, the capacitance and transconductance are estimated to be about 3.9 fF and 15.5 nS, respectively. UV sensitive property is measured using a 325-nm laser as the excitation source. Compared to the result carried in darkness, the ZnO submicro-wire FET is sensitive to UV irradiation, which indicates its potential application on UV detectors. Experimental results show that the approach introduced here allows the possibility of fabricating low-cost, reliable and flexible microelectronic devices.

Preparation and Photocatalytic Activity of ZnO/Fe2O3 Nanorod Arrays and ZnO/NiO Nanotube Arrays
CUI Yin-Fang, WANG Cong, WU Su-Juan, LIU Yu, WANG Tian-Min
Chin. Phys. Lett. 2012, 29 (3): 037201 .   DOI: 10.1088/0256-307X/29/3/037201
Abstract   PDF(pc) (819KB) ( 1298 )

ZnO/Fe2O3 nanorod arrays (NRs) and ZnO/NiO nanotube arrays (NTs) are synthesized on Si substrates by using a facile two-step growth method. The absorption spectrum of the ZnO/Fe2O3 NRs shows significant absorption in the visible light region. Their photocatalytic properties are evaluated by the degradation of methylene blue (MB). It is found that the ZnO/Fe2O3 NRs display higher photocatalytic activity than the ZnO/NiO nanotube arrays under UV-vis light irradiation. This is most likely attributed to an effective separation of photoelectrons and holes.

Effect of Rapid Thermal Annealing Ambient on Photoluminescence of ZnO Films
XU Xiao-Yan, MA Xiang-Yang, JIN Lu, YANG De-Ren
Chin. Phys. Lett. 2012, 29 (3): 037301 .   DOI: 10.1088/0256-307X/29/3/037301
Abstract   PDF(pc) (1052KB) ( 459 )

The effects of rapid thermal annealing (RTA) ambient on photoluminescence (PL) of sputtered ZnO films are investigated. The RTA at 800°C under either oxygen (O2) or argon (Ar) ambient can remarkably enhance the PL of the ZnO films due to the improved crystallinities of the ZnO films. It is somewhat unexpected that the ZnO film which received the RTA under O2 ambient exhibits weaker near−band-edge (NBE) PL than that which received the RTA under Ar ambient. It is supposed that a certain amount of negatively charged oxygen species exist on the surface of the ZnO film that received the RTA under O2 ambient, leading to a build-in electric field. This in turn reduces the recombination probability of photo-generated electrons and holes, resulting in the suppressed NBE PL.

Structural and Optical Properties of GaAs0.5Sb0.5 and In0.5Ga0.5As0.5Sb0.5: ab initio Calculations for Pure and Doped Materials
Mazin SH. Othman, Khudheir A. Mishjil, Nadir F. Habubi
Chin. Phys. Lett. 2012, 29 (3): 037302 .   DOI: 10.1088/0256-307X/29/3/037302
Abstract   PDF(pc) (662KB) ( 467 )

We perform a first-principles study to evaluate the structural, electronic and optical properties of GaAsxSb1−x ternary and InyGa1−yAsxSb1−x quaternary semiconductor alloys up to x=0.5, y=0.5. We employ the Perdew–Burke–Ernzerhof form of the generalized gradient approximation (GGA) within the framework of density functional theory (DFT) by using a simulation program. Calculations are carried out in different configurations. For these alloys, lattice parameters and optical band gap energy are calculated. The optical band gaps vary with increasing and decreasing As and In concentrations, respectively. The optical conductivity, absorption and the real part of the dielectric function ε1(ω) are discussed. Our results agree well with the theoretical and experimental data available in the literature.

Effect of Electronic Correlations on Magnetotransport through a Parallel Double Quantum Dot
FANG Dong-Kai, WU Shao-Quan, ZOU Cheng-Yi, ZHAO Guo-Ping
Chin. Phys. Lett. 2012, 29 (3): 037303 .   DOI: 10.1088/0256-307X/29/3/037303
Abstract   PDF(pc) (698KB) ( 358 )

We theoretically investigate the effect of electronic correlations (including spin and Coulomb correlations) on magnetotransport through a parallel double quantum dot coupled to ferromagnetic leads. Within the framework of the generalized master equation, we analyze the current, differential conductance and tunnel magnetoresistance versus bias for different electron correlations. Our results reveal that spin correlations can induce a giant tunnel magnetoresistance, while Coulomb correlations can lead to the occurrence of negative tunnel magetoresistance and negative differential conductance, and the relevant underlying physics of this problem is discussed.

Zero-Bias Conductance versus Potential Strength of Interface in Ferromagnetic Superconductors
Hamidreza Emamipour, Jafar Emamipour
Chin. Phys. Lett. 2012, 29 (3): 037401 .   DOI: 10.1088/0256-307X/29/3/037401
Abstract   PDF(pc) (433KB) ( 363 )

We study zero-bias conductance (ZBC) spectra of a normal-metal/insulator/singlet (and triplet) ferromagnetic superconductor as a function of potential strength of interface in the Blonder–Tinkham–Klapwijk (BTK) theory framework. We consider possible pairing states including spin singlet s-wave pairing (SWP), spin triplet opposite spin pairing (OSP) and spin triplet equal spin pairing (ESP). It is found that ZBC as a function of potential strength of interface shows a clear difference between SWP, OSP and ESP states. These results may serve as a useful tool for discriminating pairing states in ferromagnetic superconductors.

Interface-Induced High-Temperature Superconductivity in Single Unit-Cell FeSe Films on SrTiO3
WANG Qing-Yan, LI Zhi, ZHANG Wen-Hao, ZHANG Zuo-Cheng, ZHANG Jin-Song, LI Wei, DING Hao, OU Yun-Bo, DENG Peng, CHANG Kai, WEN Jing, SONG Can-Li, HE Ke, JIA Jin-Feng, JI Shuai-Hua, WANG Ya-Yu, WANG Li-Li, CHEN Xi, MA Xu-Cun, XUE Qi-Kun
Chin. Phys. Lett. 2012, 29 (3): 037402 .   DOI: 10.1088/0256-307X/29/3/037402
Abstract   PDF(pc) (869KB) ( 1879 )

We report high transition temperature superconductivity in one unit-cell (UC) thick FeSe films grown on a Se-etched SrTiO3(001) substrate by molecular beam epitaxy (MBE). A superconducting gap as large as 20 meV and the magnetic field induced vortex state revealed by in situ scanning tunneling microscopy (STM) suggest that the superconductivity of the 1 UC FeSe films could occur around 77 K. The control transport measurement shows that the onset superconductivity temperature is well above 50 K. Our work not only demonstrates a powerful way for finding new superconductors and for raising TC, but also provides a well-defined platform for systematic studies of the mechanism of unconventional superconductivity by using different superconducting materials and substrates.

Electron Paramagnetic Resonance of Mn2+-Doped Cadmium Formate Dihydrate Single Crystals
Indrajeet Mishra, Ram Kripal, Sanjay Misra
Chin. Phys. Lett. 2012, 29 (3): 037601 .   DOI: 10.1088/0256-307X/29/3/037601
Abstract   PDF(pc) (428KB) ( 979 )
An electron paramagnetic resonance (EPR) study on Mn2+ doped Cadmium formate dihydrate single crystals is carried out. The EPR spectrum at room temperature exhibits only one out of five fine structural transitions which split into six hyperfine lines in all directions. The spectrum is simulated using the EasySpin program and evaluated spin Hamiltonian parameters. The simulated EPR spectrum is in good agreement with the experiment. By comparing direction cosines of spectroscopic splitting factor g and the direction cosines of different bonds determined by the crystal structure data it is found that Mn2+ enters the lattice substitutionally and only one Mn2+ site is identified. The obtained g and the hyperfine interaction constant A achieved are g=2.006±0.002, A=(98±2)×10−4 cm−1 and the second-order axial zero-field splitting parameter D=(60±2)×10−4 cm−1.
Size Effects of the Properties in a Ferroelectric Bilayer Film with Surface Transition Layers
CUI Lian, XU Quan, HAN Zhi-You, XU Xu
Chin. Phys. Lett. 2012, 29 (3): 037701 .   DOI: 10.1088/0256-307X/29/3/037701
Abstract   PDF(pc) (680KB) ( 398 )
Using the transverse Ising model theory, a ferroelectric bilayer film, considering the surface transition layer within each constituent slab and an interfacial coupling between two slabs, is investigated in the framework of the mean-field approximation. We discuss in detail the thickness effects of the spontaneous polarization and dielectric susceptibility of a ferroelectric bilayer film under two conditions of interfacial coupling: ferroelectric and antiferroelectric coupling. The results show some unexpected phenomena for a small thickness of a ferroelectric bilayer film.
Wavelength Dependence of Laser-Induced Bulk Damage Morphology in KDP Crystal: Determination of the Damage Formation Mechanism
HU Guo-Hang, ZHAO Yuan-An, LI Da-Wei, XIAO Qi-Ling
Chin. Phys. Lett. 2012, 29 (3): 037801 .   DOI: 10.1088/0256-307X/29/3/037801
Abstract   PDF(pc) (560KB) ( 729 )
Wet etch process is applied to expose the bulk damage sites in KDP crystals to the surface for the examination by scanning electron microscopy (SEM) and optical microscopy. The damage sites induced by 1064 nm laser consist of three distinct regions: a core, an outer region of modified material, and some oriented cracks. Laser irradiated with 355 nm results in an increase of damage density, a decrease of core diameter and, rarely, occurrence of the crack. Wavelength dependence of the damage feature suggests that a repulsive force exists among the adjacent plasmas, which prevents further expansion of plasma and decreases the size of plasma. The deposited energy absorbed by the smaller plasma may not be able to generate the crack.
Optical Bistability in Graded Core-Shell Granular Composites
WU Ya-Min, CHEN Guo-Qing, MA Chao-Qun, XUE Si-Zhong, ZHU Zhuo-Wei
Chin. Phys. Lett. 2012, 29 (3): 037802 .   DOI: 10.1088/0256-307X/29/3/037802
Abstract   PDF(pc) (493KB) ( 458 )
The intrinsic optical bistability (OB) of graded core-shell granular composites is investigated. The coated particles are made of cores with gradient dielectric function εc(r)=A(r/a)k and nonlinear shells. In view of the exponential distribution of the core dielectric constant, the potential functions of each region are obtained by solving the Maxwell equations, and the mathematical expressions of electric field in the shells and cores are determined. Numerical study reveals that the optical bistable threshold and the threshold width of the composite medium are dependent on the shell thickness, core dielectric exponent, and power function coefficient. The optical bistable width increases with the decreasing shell thickness and the power exponent and with the increasing power function coefficient.
CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
Removing Impurity of cBN Crystal Prepared at High Pressure and High Temperature
JI Xiao-Rui, YANG Xiao-Hong
Chin. Phys. Lett. 2012, 29 (3): 038101 .   DOI: 10.1088/0256-307X/29/3/038101
Abstract   PDF(pc) (646KB) ( 685 )
The black cubic boron nitride (cBN) single crystal is synthesized by using hBN-LiH and hBN-Li3N−B as the raw materials at high temperature and high pressure (HTHP). The colors of the cBN crystal synthesized in an hBN-Li3N−B system vary from transparent yellow, half-transparent and then opaque black with the increasing B content in the raw materials. It is worth noting that a trigonal shadow is presented at the center of the cBN crystal synthesized in the hBN-Li3N-B system but can not be found in the hBN-LiH system. Analyzing the Raman spectrum, we find that the darkening and the trigonal shadow in the cBN crystal may be due to the presence of excess B atoms. The above-mentioned phenomenon can be determined by removing impurity capacity and growth environment of the cBN crystal.
Phase Evolution of Cubic ZnS Annealed in Mild Oxidizing Atmosphere
XUE Shu-Wen, ZHANG Jun, SHAO Le-Xi
Chin. Phys. Lett. 2012, 29 (3): 038102 .   DOI: 10.1088/0256-307X/29/3/038102
Abstract   PDF(pc) (702KB) ( 1401 )
ZnS thin films are prepared by thermal evaporation of high-purity ZnS powder on quartz glass substrates. The samples were annealed in floating argon at temperatures from 300°C to 900°C. The effects of annealing temperature on the structural and optical properties were investigated by x-ray diffraction (XRD), scanning electron microscope (SEM) and optical absorption. The results show that annealing below 500°C is beneficial to improve the quality of ZnS films. When the annealing temperature exceeds 500°C, ZnS is gradually oxidized into ZnSO4, which has evident influences on the structural and optical properties of ZnS films.
Optical and Mechanical Properties of Transparent Conductive Al-Doped ZnO Films Deposited by the Sputtering Method
ZHU Yun, WANG Yue, WAN Peng-Fei, LI Hong-Yu, WANG Shou-Yu
Chin. Phys. Lett. 2012, 29 (3): 038103 .   DOI: 10.1088/0256-307X/29/3/038103
Abstract   PDF(pc) (1040KB) ( 1501 )
Al-doped ZnO transparent conductive oxide thin films (AZO) are prepared by the magnetron sputtering method. The structural, optical and mechanical properties of the AZO films are studied systematically. The average haze of the AZO sample is increased from 0.34% to 23.6% through wet etching treatment between 380 and 1100 nm, and the etched AZO sample has a higher average transmittance of about 82.3% in infrared wavelength range from 760 to 1100 nm due to the reduction of absorption by carriers. The average hardness and elastic modulus of the as-deposited AZO films, as determined using the nanoindentation technique, are approximately 10.2 GPa and 130 GPa, respectively. The critical fracture load related to the adhesion strength is about 91 mN. The optimized optical and electrical properties and referable mechanical data indicate that AZO films have good prospects for commercial applications.
An Integrated Phase Change Memory Cell with Dual Trench Epitaxial Diode Selector
ZHANG Chao, SONG Zhi-Tang, WU Guan-Ping, LIU Bo, WANG Lian-Hong, XU Jia, LIU Yan, WANG Lei, YANG Zuo-Ya, FENG Song-Lin
Chin. Phys. Lett. 2012, 29 (3): 038104 .   DOI: 10.1088/0256-307X/29/3/038104
Abstract   PDF(pc) (613KB) ( 614 )
An integrated phase change memory cell with dual trench epitaxial diode is successfully integrated in the traditional 0.13 µm CMOS technology. By using dual trench isolated structure in the memory cell, it is feasible to employ a Si−diode as a selector for integration in a crossbar structure for high-density phase change memory even at 45 nm technology node and beyond. A cross-point memory selector with a large on/off current ratio is demonstrated, the diode provides nine orders of magnitude isolation between forward and reverse biases in the SET state. A low SET programming current of 0.7 mA is achieved and RESET/SET resistance difference of 10000× is obtained.
Characterization of a ZnO Epilayer Grown on Sapphire by using Rutherford Backscattering/Channeling and X-Ray Diffraction
DING Bin-Feng
Chin. Phys. Lett. 2012, 29 (3): 038201 .   DOI: 10.1088/0256-307X/29/3/038201
Abstract   PDF(pc) (712KB) ( 459 )
A ZnO layer with rather good crystalline quality (χmin=9.4%) is grown on a sapphire substrate by plasma enhanced chemical vapor deposition (PECVD). Rutherford backscattering (RBS)/channeling and high-resolution x-ray diffraction (XRD) are used to characterize the elastic strain in the ZnO epilayer. The tetragonal distortion is positive and depth dependent. It is highest near the interface and decreases towards the sample surface. By combining the results of RBS and XRD, the average elastic strains in the parallel and the perpendicular directions can be calculated to be 0.50% and −0.17%, respectively.
Chemical Mechanical Polishing of Ge2Sb2Te5 Using Abrasive-Free Solutions of Iron Trichloride
YAN Wei-Xia, WANG Liang-Yong, ZHANG Ze-Fang, HE Ao-Dong, ZHONG Min, LIU Wei-Li, WU Liang-Cai, SONG Zhi-Tang
Chin. Phys. Lett. 2012, 29 (3): 038301 .   DOI: 10.1088/0256-307X/29/3/038301
Abstract   PDF(pc) (710KB) ( 680 )
Chemical mechanical polishing (CMP) of amorphous Ge2Sb2Te5 (GST) is studied using aqueous solutions of iron trichloride (FeCl3) as possible abrasive-free slurries. The polishing performance of abrasive-free solutions is compared with abrasive-containing (3wt% colloidal silica) slurry in terms of polishing rate and surface quality. The experimental results indicate that the abrasive-free solutions have a higher polishing rate and better surface quality. In order to further investigate the polishing mechanism, post-CMP GST films using the abrasive-free solutions and abrasive-containing slurry are characterized by x-ray photoelectron spectroscopy. Finally, it is verified that the abrasive-free solutions have no influence on the electrical property of the post-CMP GST films through the resistivity test.
A New Method to Calculate the Degree of Electromagnetic Impedance Matching in One-Layer Microwave Absorbers
MA Zhi, CAO Chen-Tao, LIU Qing-Fang, WANG Jian-Bo
Chin. Phys. Lett. 2012, 29 (3): 038401 .   DOI: 10.1088/0256-307X/29/3/038401
Abstract   PDF(pc) (1099KB) ( 688 )
A delta-function method is proposed to quantitatively evaluate the electromagnetic impedance matching degree. Measured electromagnetic parameters of α−Fe/Fe3B/Y2O3 nanocomposites are applied to calculate the matching degree by the method. Compared with reflection loss and quarter-wave principle theory, the method accurately reveals the intrinsic mechanism of microwave transmission and reflection properties. A possible honeycomb structure with promising high-performance microwave absorption, devised according to the method, is also proposed.
Tunable Metamorphic Resonant Cavity Enhanced InGaAs Photodetectors Grown on GaAs Substrates
LIU Shao-Qing, HAN Qin, ZHU Bin, YANG Xiao-Hong, NI Hai-Qiao, HE Ji-Fang, WANG Win, NIU Zhi-Chuan
Chin. Phys. Lett. 2012, 29 (3): 038501 .   DOI: 10.1088/0256-307X/29/3/038501
Abstract   PDF(pc) (966KB) ( 385 )
Tunable metamorphic InGaAs partially depleted absorber photodiodes with resonant cavity enhanced structure are fabricated on GaAs substrate. Dark-current densities of 7.2×10−7 A/cm2 at 0 V and 3.6×10−4 A/cm2 at −5 V, a high quantum efficiency of 74.4% at 1546 nm, and a 3-dB bandwidth up to 12 GHz are achieved. The full width at half maximum of the detector is about 16 nm. Furthermore, through thermal tuning, the peak wavelength red shifts from 1527 nm to 1544 nm, and a tuning range of 17 nm is realized without fabricating extra tuning electrodes.
A Novel CMOS Device Capable of Measuring Near-Field Thermal Radiation
FENG Chong, TANG Zhen-An, YU Jun
Chin. Phys. Lett. 2012, 29 (3): 038502 .   DOI: 10.1088/0256-307X/29/3/038502
Abstract   PDF(pc) (1076KB) ( 417 )
We report on the design, fabrication, and characterization of a micro plane-plane geometry CMOS device, which has a heat emitter and a heat receiver, capable of studying the near-field radiative heat transfer at a 550 nm gap. Under high vacuum conditions, the heat emitter is heated by supplying driving currents and heated again after removing the heat receiver. The heating power difference between the two kinds of heating experiments indicates the existence of a proximity effect in the heat transfer between the emitter and the receiver. Our experiments pave the way towards overcoming the construction difficulty of plane-plane geometry with a nanometer gap.
Relaxation of Evolutionary Dynamics on the Bethe Lattice
TIAN Liang, LIN Min
Chin. Phys. Lett. 2012, 29 (3): 038701 .   DOI: 10.1088/0256-307X/29/3/038701
Abstract   PDF(pc) (583KB) ( 315 )
Realistic evolutionary systems are generally structured and are in infinite dimensions. We study the relaxation behavior of evolutionary dynamics on a Bethe lattice, which concerns the invasion of mutants into a population of wild-type individuals. Since the boundary effect plays a significant role in a finite system, with proper approximation we propose an effective method to characterize the evolutionary dynamics. The relaxation behavior of the invasion process is analytically investigated, which is confirmed by extensive simulations. This work is the first systematical investigation on evolutionary dynamics in an infinitely dimensional lattice.
Search for Directed Networks by Different Random Walk Strategies
ZHU Zi-Qi, JIN Xiao-Ling, HUANG Zhi-Long
Chin. Phys. Lett. 2012, 29 (3): 038901 .   DOI: 10.1088/0256-307X/29/3/038901
Abstract   PDF(pc) (706KB) ( 624 )
A comparative study is carried out on the efficiency of five different random walk strategies searching on directed networks constructed based on several typical complex networks. Due to the difference in search efficiency of the strategies rooted in network clustering, the clustering coefficient in a random walker's eye on directed networks is defined and computed to be half of the corresponding undirected networks. The search processes are performed on the directed networks based on Erdös–Rényi model, Watts–Strogatz model, Barabási–Albert model and clustered scale-free network model. It is found that self-avoiding random walk strategy is the best search strategy for such directed networks. Compared to unrestricted random walk strategy, path-iteration-avoiding random walks can also make the search process much more efficient. However, no-triangle-loop and no-quadrangle-loop random walks do not improve the search efficiency as expected, which is different from those on undirected networks since the clustering coefficient of directed networks are smaller than that of undirected networks.
Hyperedge Communities and Modularity Reveal Structure for Documents
XIE Zheng, YI Dong-Yun, OUYANG Zhen-Zheng, LI Dong
Chin. Phys. Lett. 2012, 29 (3): 038902 .   DOI: 10.1088/0256-307X/29/3/038902
Abstract   PDF(pc) (428KB) ( 441 )
Words and their association in documents could be represented by hypergraph in a standard way. Communities of words often overlap. Accepting a community should have more internal than external connections, we view every hyperedge as a vertex, establish a network for hyperedges by their similarity, and use the method of modularity to find their communities. The example here shows that email address' communities, generated by pulling back hyperedges communities, naturally incorporate overlap and reveal hierarchical organization.
Formation Mechanism of the Accumulative Magnification Effect in a Financial Time Series
DUAN Wen-Qi
Chin. Phys. Lett. 2012, 29 (3): 038903 .   DOI: 10.1088/0256-307X/29/3/038903
Abstract   PDF(pc) (568KB) ( 345 )
Structural information contained in financial time series can be magnified effectively by constructing the accumulative return. In order to make the magnification effects of different financial time series comparative, we first propose a standard method to characterize the strength of the accumulative magnification effect. Then, we employ decomposed-randomized technology to uncover the formation mechanism of the accumulative magnification effect. Our results show that (1) the standard deviation pattern is determined by volatility dependence, (2) the Hurst exponent pattern is induced by sign dependence, (3) an approximate entropy pattern is caused by the combined effect of sign dependence and volatility dependence.
Mandelbrot Law of Evolving Networks
REN Xue-Zao, YANG Zi-Mo, WANG Bing-Hong, ZHOU Tao
Chin. Phys. Lett. 2012, 29 (3): 038904 .   DOI: 10.1088/0256-307X/29/3/038904
Abstract   PDF(pc) (618KB) ( 415 )
We show that the degree distribution of a growing network with linear preferential attachment approximately follows the Mandelbrot law, and propose an analytical method based on a recursive formula that can be used to obtain a more accurate expression of the shifting coefficient. Simulations demonstrate the advantages of our method. This work provides a possible mechanism leading to the Mandelbrot law of evolving networks, and refines the mainstream analytical methods for the shifting coefficient.
74 articles