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Chin. Phys. Lett.  
  Chin. Phys. Lett.--2015, 32 (5)   Published: 21 April 2015
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High-Capacity Quantum Secure Communication with Authentication Using Einstein–Podolsky–Rosen Pairs

XIAO Min, XU Hong-Wei
Chin. Phys. Lett. 2015, 32 (5): 050301 doi: 10.1088/0256-307X/32/5/050301
Full Text: [PDF 418 KB] (225)
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A new protocol for quantum secure communication with authentication is proposed. The proposed protocol has a higher capacity as each EPR pair can carry four classical bits by the XOR operation and an auxiliary photon. The security and efficiency are analyzed in detail and the major advantage of this protocol is that it is more efficient without losing security.

Thermal Entanglement in the Pure Dzyaloshinskii–Moriya Model with Magnetic Field

LI Da-Chuang, LI Xiao-Man, LI Hu, TAO Rui, YANG Ming, CAO Zhuo-Liang
Chin. Phys. Lett. 2015, 32 (5): 050302 doi: 10.1088/0256-307X/32/5/050302
Full Text: [PDF 3356 KB] (101)
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We investigate the effects of the directions of Dzyaloshinskii–Moriya (DM) interaction and magnetic field on the thermal entanglement in the pure DM model. It is found that when the Hamiltonian is H1= D(σ1σ2)+Bσ1, the entanglement can reach its maximum if the directions of the magnetic field and the DM vector are parallel. In addition, when the Hamiltonian is H2=D⋅(σ1σ2)+B⋅(σ1+σ2), if the directions of the magnetic field and the DM vector are perpendicular in a high magnetic field, or their directions are parallel in a weak magnetic field, the entanglement can also reach its maximum. Thus the entanglement can be enhanced by adjusting the direction of the external magnetic field, and this is feasible within the current experimental technology.

An Ideal Experiment to Determine the 'Past of a Particle' in the Nested Mach–Zehnder Interferometer

LI Fu, Hashmi F. A., ZHANG Jun-Xiang, ZHU Shi-Yao
Chin. Phys. Lett. 2015, 32 (5): 050303 doi: 10.1088/0256-307X/32/5/050303
Full Text: [PDF 427 KB] (69)
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An ideal experiment is designed to determine the past of a particle in the nested Mach–Zehnder interferometer (MZI) by using standard quantum mechanics with quantum non-demolition measurements. We find that when the photon reaches the detector, it only follows one arm of the outer interferometer and leaves no trace in the inner MZI. When it goes through the inner MZI, it cannot reach the detector. Our result obtained from the standard quantum mechanics contradicts the statement based on two-state vector formulism, 'the photon did not enter the (inner) interferometer, the photon never left the interferometer, but it was there'. Therefore, the statement and also the overlapping claim are incorrect.

Scattering of Scalar Wave by Extended Black Hole in f(R) Gravity

LIAO Ping, ZHANG Ruan-Jing, CHEN Ju-Hua, WANG Yong-Jiu
Chin. Phys. Lett. 2015, 32 (5): 050401 doi: 10.1088/0256-307X/32/5/050401
Full Text: [PDF 611 KB] (39)
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We analyze the Schrödinger-type scalar wave equation of an extended black hole in f(R) gravity, and numerically investigate its absorption/scattering cross sections using the partial wave method. It is found that the dimension of length α makes the peak value of the effective scattering potential fall down, and the absorption cross section oscillates around the geometric optical value in the high frequency regime. We can also see that the scattering flux becomes stronger and its angle width becomes narrower in the forward direction, the glory peak becomes lower and the glory width becomes narrower along the backward direction when the coupling parameter α increases.

Bifurcation Scenarios of a Modified Mathematical Model for Intracellular Ca2+ Oscillations

JI Quan-Bao, ZHOU Yi, YANG Zhuo-Qin, MENG Xiang-Ying
Chin. Phys. Lett. 2015, 32 (5): 050501 doi: 10.1088/0256-307X/32/5/050501
Full Text: [PDF 709 KB] (26)
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The contribution of this work is the modification of a mathematical model for bursting Ca2+ oscillations by introducing the proportion of receptors not inactivated by Ca2+ as a new variable. Generation mechanisms of different oscillatory patterns in this modified model are investigated and classified, based on fast/slow dynamical analysis. It is shown that periodic oscillations appear around the original chaotic regions. Moreover, two new types of oscillatory phenomena are observed at the sustaining region. The results may be instructive for understanding the difference between direct observation of dynamical behavior in real cells and theoretical explanations under a variety of stimulus conditions.

Dilemma Produced by Infinity of a Random Walk

LI Jing-Hui
Chin. Phys. Lett. 2015, 32 (5): 050502 doi: 10.1088/0256-307X/32/5/050502
Full Text: [PDF 360 KB] (36)
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We report a dilemma produced by the infinity of a random walk moving along a two-dimensional space sidestep. For this random walk, our investigation shows that using a different model can lead to a different diffusion coefficient of the random walk, which is produced by the infinity of the random walk. The result obtained by us in the present work can serve as a warning to us when we build the models to investigate the corresponding scientific problems.

Spectrum of the Open Asymmetric Simple Exclusion Process with Arbitrary Boundary Parameters

WEN Fa-Kai, YANG Zhan-Ying, CUI Shuai, CAO Jun-Peng, YANG Wen-Li
Chin. Phys. Lett. 2015, 32 (5): 050503 doi: 10.1088/0256-307X/32/5/050503
Full Text: [PDF 467 KB] (37)
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We study the one-dimensional asymmetric simple exclusion process (ASEP) with generic open boundaries (including current-counting deformation), and obtain the exact solutions of this ASEP via the off-diagonal Bethe ansatz method. In particular, numerical results for the small size asymmetric simple exclusion process indicate that the spectrum obtained by the Bethe ansatz equations is complete. Moreover, we present the eigenvalue of the totally asymmetric exclusion process and the corresponding Bethe ansatz equations.

A New Research about Pion Parton Distribution Function

LOU Li-Yang, RUAN Jian-Hong
Chin. Phys. Lett. 2015, 32 (5): 051201 doi: 10.1088/0256-307X/32/5/051201
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A new fit of the pion parton distribution functions is provided. Only valence quark distributions are used at a low evolution scale and are evolved with the modified Dokshitzer–Gribov–Lipatov–Altarelli–Parisi equation which is briefly introduced in this work, and the sea quark and gluon distributions are only generated by the quantum chromodynamics processes. We find that the parton distributions can explain the pion-nucleon experiments data well, and it can also be compared with the data from the leading neutron data of experiments at HERA. The momentum distributions among the partons are discussed and our results are consistent with some models.

Effective Field Theory Techniques Applied to the Properties of the Axion

LING Rui, PING Jia-Lun
Chin. Phys. Lett. 2015, 32 (5): 051401 doi: 10.1088/0256-307X/32/5/051401
Full Text: [PDF 428 KB] (21)
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We utilize the effective field theory approach to study the properties of the axion. In particular, with s as well as u and d quarks regarded to be relatively light we derive a formula for the mass of the axion; a rough estimate of the rate for its dominant decay mode at low energy is also carried out.

The Recent Development of the EAST Neutral Beam Injector

HU Chun-Dong, XU Yong-Jian, XIE Yuan-Lai, LIU Sheng, LIU Zhi-Min, SHENG Peng, XIE Ya-Hong, LIANG Li-Zhen, NBI Team
Chin. Phys. Lett. 2015, 32 (5): 052901 doi: 10.1088/0256-307X/32/5/052901
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Neutral beam injection has been recognized as one of the most effective means for plasma heating. According to the research plan of the EAST physics experiment, two sets of neutral beam injectors (4–8 MW, 10–100 s) were built and operated in 2014. We present the development of the EAST neutral beam injector (NBI) and the latest experiment results obtained on the test-stand about operation of ion source, beam extraction, and measurement of key parameters. Those results show that all targets reach or almost reach the design targets. All these lay a solid foundation for the achievement of plasma heating and current drive for EAST in 2014.

Empirical Scaling Laws of Neutral Beam Injection Power in HL-2A Tokamak

CAO Jian-Yong, WEI Hui-Ling, LIU He, YANG Xian-Fu, ZOU Gui-Qing, YU Li-Ming, LI Qing, LUO Cui-Wen, PAN Yu-Dong, JIANG Shao-Feng, LEI Guang-Jiu, LI Bo, RAO Jun, DUAN Xu-Ru
Chin. Phys. Lett. 2015, 32 (5): 052902 doi: 10.1088/0256-307X/32/5/052902
Full Text: [PDF 726 KB] (23)
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We present an experimental method to obtain neutral beam injection (NBI) power scaling laws with operating parameters of the NBI system on HL-2A, including the beam divergence angle, the beam power transmission efficiency, the neutralization efficiency and so on. With the empirical scaling laws, the estimating power can be obtained in every shot of experiment on time, therefore the important parameters such as the energy confinement time can be obtained precisely. The simulation results by the tokamak simulation code (TSC) show that the evolution of the plasma parameters is in good agreement with the experimental results by using the NBI power from the empirical scaling law.

All-Optical Production of Quantum Degeneracy and Molecular Bose–Einstein Condensation of 6Li

DENG Shu-Jin, DIAO Peng-Peng, YU Qian-Li, WU Hai-Bin
Chin. Phys. Lett. 2015, 32 (5): 053401 doi: 10.1088/0256-307X/32/5/053401
Full Text: [PDF 630 KB] (34)
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We achieve a highly degenerate and strongly interacting Fermi gas in a mixture of the two lowest hyperfine states of 6Li by direct evaporative cooling in a high power crossed optical dipole trap. The trap is loaded from a large atom number magneto-optical trap realized by a laser system of 2.5-W intracavity-frequency-doubled light output at 671 nm. With this system, we also demonstrate the production of a molecular Bose–Einstein condensate (mBEC) of 6Li2, and observe the anisotropic expansion of Fermi gases in the so-called BEC–Bardeen–Cooper–Schrieffer crossover regime.

Design of a Solid-Core Large-Mode-Area Bragg Fiber

LI Lu, PANG Li-Hui, ZHOU Zhi-Guang, ZHANG Ai-Dong, HE Jian-Li, SI Jin-Hai, LIN Ao-Xiang
Chin. Phys. Lett. 2015, 32 (5): 054201 doi: 10.1088/0256-307X/32/5/054201
Full Text: [PDF 729 KB] (27)
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We report the design and simulation results of a solid-core Bragg fiber with 3-bilayer periodic cladding. The simulation results present single mode bandgap guidance, a large effective area of ∼400 μm2 around 1.08 μm, a very low bend loss of 0.038 dB/m at 1.08 μm even under tight bend radius (R=4 cm), and excellent beam quality. The results indicate that the proposed fiber could be a competitive solution for high-power fiber laser applications.

Design and Fabrication of a 400 GHz InP-Based Arrayed Waveguide Grating with Flattened Spectral Response

ZHANG Xi-Lin, LIU Song-Tao, LU Dan, ZHANG Rui-Kang, JI Chen
Chin. Phys. Lett. 2015, 32 (5): 054202 doi: 10.1088/0256-307X/32/5/054202
Full Text: [PDF 946 KB] (24)
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A four-channel 400 GHz channel spacing InP-based arrayed waveguide grating with a flattened wavelength response by employing a multimode interference coupler at the input waveguide of the filter is prepared. The fabricated devices show a flattened spectral response with a broadened 3-dB bandwidth up to 3.5 nm, interchannel non-uniformity of <0.7 dB and excellent match to the simulation results.

High-Efficiency Mid-Infrared Picosecond MgO:PPLN Single Resonant Optical Parametric Oscillator

HAN Ke-Zhen, NING Jian, HE Jing-Liang, HOU Jia, ZHANG Bai-Tao, WANG Zhao-Wei
Chin. Phys. Lett. 2015, 32 (5): 054203 doi: 10.1088/0256-307X/32/5/054203
Full Text: [PDF 514 KB] (24)
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We demonstrate a high-efficiency mid-infrared picosecond optical parametric oscillator (OPO) based on MgO doped periodically poled lithium niobate (MgO:PPLN) with a laser diode array (LDA) pumped Innoslab amplifier as the pumping source. Under a 16 W synchronously pumping power, 4.5 W of idler light at 2896 nm is obtained. A tuning range of idler light from 2688 nm to 3016 nm is achieved, within which the highest optical-optical conversion efficiency from pump power to OPO output is 35.1%. Moreover, a signal light of ∼500 mW from 1644 to 1700 nm with a repetition rate of 233.8 MHz is generated.

Design of Photonic Crystal Triplexer with Core-Shell Rod Defects

Labbani Amel, Benghalia Abdelmadjid
Chin. Phys. Lett. 2015, 32 (5): 054204 doi: 10.1088/0256-307X/32/5/054204
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We investigate an optical compact triplexer based on two photonic crystal waveguides and resonant cavities. For performing wavelength selection, we use three core−shell rods as the resonant cavities. The core rods are created by introducing air holes in the center of the silicon rods. By varying the radii of the air holes, three specific wavelengths 1.31, 1.49 and 1.55 μm can be obtained. This structure is designed and its performance is verified by the finite-difference time-domain method, which is highly suitable for photonic integrated circuits (PICs). The average output transmission efficiency and quality factor are more than 98.85% and 560, respectively. The mean value of the crosstalk between output channels is about -36.49 dB. The present device is extremely compact with total size 96.24 μm2, which is suitable for PICs and can be utilized in the fiber-to-the-home system.

Fabrication of 32 Gb/s Electroabsorption Modulated Distributed Feedback Lasers by Selective Area Growth Technology

ZHOU Dai-Bing, WANG Hui-Tao, ZHANG Rui-Kang, WANG Bao-Jun, BIAN Jing, AN Xin, LU Dan, ZHAO Ling-Juan, ZHU Hong-Liang, JI Chen, WANG Wei
Chin. Phys. Lett. 2015, 32 (5): 054205 doi: 10.1088/0256-307X/32/5/054205
Full Text: [PDF 665 KB] (21)
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A 32 Gb/s monolithically integrated electroabsorption modulated laser is fabricated by selective area growth technology. The threshold current of the device is below 13 mA. The output power exceeds 10 mW at 0 V bias when the injection current of the distributed feedback laser is 100 mA at 25°C. The side mode suppression ratio is over 50 dB. A 32Gb/s eye diagram is measured with a 3.5Vpp nonreturn-to-zero pseudorandom modulation signal at -2.3 V bias. A clearly opening eyediagram with a dynamic extinction ratio of 8.01 dB is obtained.

Improvement of Laser Frequency Stabilization for the Optical Pumping Cesium Beam Standard

WANG Qing, DUAN Jun, QI Xiang-Hui, ZHANG Yin, CHEN Xu-Zong
Chin. Phys. Lett. 2015, 32 (5): 054206 doi: 10.1088/0256-307X/32/5/054206
Full Text: [PDF 493 KB] (26)
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A method is presented to improve the laser frequency stabilization for the optical pumping cesium clock. By comparing the laser frequency stabilization of different schemes, we verify that the light angle is an important factor that limits the long-term frequency stability. We minimize the drift of the light angle by using a fiber-coupled output, and lock the frequency of a distributed-feedback diode laser to the fluorescence spectrum of the atomic beam. The measured frequency stability is about 3.5 ×10−11 at 1 s and reaches 1.5 ×10−12 at 2000 s. The Allan variance keeps going down for up to thousands of seconds, indicating that the medium- and long-term stability of the laser frequency is significantly improved and perfectly fulfills the requirement for the optical pumping cesium clock.

Generation of Continuous-Wave 194 nm Laser for Mercury Ion Optical Frequency Standard

ZOU Hong-Xin, WU Yue, CHEN Guo-Zhu, SHEN Yong, LIU Qu
Chin. Phys. Lett. 2015, 32 (5): 054207 doi: 10.1088/0256-307X/32/5/054207
Full Text: [PDF 2135 KB] (16)
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A 194-nm cw laser is an essential part in the mercury ion optical frequency standard. We report the generation of over 2 mW continuous-wave radiation at 194 nm in a beta barium borate crystal using a simple sum frequency mixing (SFM) system. One source beams at 718 nm is resonantly enhanced with a cavity and the other at 266 nm makes a single pass. Considering the walk-off effect in SFM, the source beam waists are designed to be elliptical, thus the conversion efficiency can be promoted. The 266-nm beam produced by frequency doubling of 532-nm laser is shaped close to the diffraction limit to achieve better mode matching.

The Mode Matching of Hybrid Trap by Frequency Calibration

WANG Zhong-Kai, HU Dong, NIU Lin-Xiao, ZHANG Jia-Hua, CHEN Xu-Zong, ZHOU Xiao-Ji
Chin. Phys. Lett. 2015, 32 (5): 054208 doi: 10.1088/0256-307X/32/5/054208
Full Text: [PDF 738 KB] (23)
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We demonstrate a method to precisely calibrate the relative position between an optical dipole trap and a magnetic quadrupole potential in making a Bose–Einstein condensate via the hybrid trap. We measure the displacement by the dipole oscillation in the gravity direction, where the oscillation frequency can be adjusted through an additional bias magnetic field. One frequency corresponds to the case of the mode matching while two frequencies are not, and the great consistency between theoretical simulation and experimental results indicates its usefulness.

The Line Shape of Double-Sided Tooth-Disk Waveguide Filters Based on Plasmon-Induced Transparency

ZHANG Xin-Yuan, WANG Lu-Lu, CHEN Zhao, CUI Lu-Na, SHANG Ce, ZHAO Yu-Fang, DUAN Gao-Yan, LIU Jian-Bin, YU Li
Chin. Phys. Lett. 2015, 32 (5): 054209 doi: 10.1088/0256-307X/32/5/054209
Full Text: [PDF 1367 KB] (49)
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We numerically investigate a coupled-resonator structure consisting of a stub resonator and a nanodisk resonator using a two-dimensional finite element method. Simulation results show that plasmon-induced transparency (PIT) occurs in the transmission spectra, and the sharp asymmetric Fano lines increase the sensitivity to 1.4×103 nm/RIU. We also analyze the properties of the structure with different radii of the nanodisk and the length of the tooth cavity. Moreover, we find that the PIT only happens when the staggered system is around a fixed location with different separate distances, which is not similar to the previous researches. Our model may be important to photonic-integrated circuits and the sensitivity in sensors.

Temperature-Dependent Fluorescence Properties and Diode-Pumped Deep Red Laser Performance of Pr:LiGdF4 Crystal

ZHANG Yu-Xia, WANG Shu-Xian, Alberto Di Lieto, YU Guo-Lei, YU Hao-Hai, ZHANG Huai-Jin, Mauro Tonelli, XU Xian-Gang, WANG Ji-Yang
Chin. Phys. Lett. 2015, 32 (5): 054210 doi: 10.1088/0256-307X/32/5/054210
Full Text: [PDF 640 KB] (31)
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We demonstrate the temperature-dependent fluorescence properties of Pr:LiGdF4 crystal for the first time, to the best of our knowledge, and its blue diode pumped cw red laser at 720 nm at room temperature. The fluorescence lifetime and polarized emission cross sections in the visible range are measured and calculated in a temperature range from 77 K to 300 K, and the variations of the fluorescence lifetime and spectra are discovered. The reasons for these changes are explained accordingly. The output wavelength of the 720 nm laser is first reported on the laser performance by using a fiber-coupled laser diode at the wavelength of 442 nm as the pump source, and the maximum cw output power is about 303 mW.

Generation of Broadband Spectrum from a Simple Nonlinear-Polarization-Evolution Mode-Locked Yb-Doped Fiber Oscillator

XIE Yang, HAN Hai-Nian, LIU Wen-Jun, WEI Zhi-Yi
Chin. Phys. Lett. 2015, 32 (5): 054211 doi: 10.1088/0256-307X/32/5/054211
Full Text: [PDF 501 KB] (51)
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We demonstrate a nonlinear polarization evolution mode-locked Yb-doped fiber oscillator with the broadband spectrum output operating in a dispersion-managed regime. Pumped by a 976 nm single-mode laser diode, stable mode-locked ultrashort pulses are emitted with an average power of 198 mW at a repetition rate of 124 MHz, corresponding to a pulse energy of 1.6 nJ. The output spectrum spans from 950 nm to 1150 nm so that the transform-limited pulse duration is as short as 23 fs. Due to the imperfect dispersion compensation, we compress the pulses to 32 fs in this experiment.

Configurations of the Penrose Tiling beyond Nearest Neighbors

PENG Ben-Yi, FU Xiu-Jun
Chin. Phys. Lett. 2015, 32 (5): 056101 doi: 10.1088/0256-307X/32/5/056101
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Starting from the eight vertex types in the Penrose tiling, we investigate the configurations beyond the nearest neighbors. The detailed structure of configurations and their concentrations in the whole pattern are obtained. It is found that the number of configuration types increases greatly when the observed clusters are becoming larger, which indicates that it is difficult to generate a perfect Penrose tiling according to the local matching rules.

Room-Temperature Annealing of 1 MeV Electron Irradiated Lattice Matched In0.53Ga0.47As/InP Multiple Quantum Wells

WANG Hai-Jiao, LI Yu-Dong, GUO Qi, MA Li-Ya, WEN Lin, WANG Bo
Chin. Phys. Lett. 2015, 32 (5): 056102 doi: 10.1088/0256-307X/32/5/056102
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Long-term room-temperature annealing effects of InGaAs/InP quantum wells with different wells (namely triple wells and five wells embedded) and bulk InGaAs are investigated after high energy electron irradiation. It is observed that the photoluminescence (PL) intensity of bulk InGaAs materials is enhanced after low dose electron irradiation and the PL intensity for all the three samples is degraded dramatically when the electron dose is relatively high. With respect to the room-temperature annealing, we find that the PL intensity for both samples recovers relatively fast at the initial stage. The PL performance of multiple quantum-well samples shows better recovery after irradiation compared with the results of bulk InGaAs materials. Meanwhile, the recovery speed factors of multiple quantum-well samples are relatively faster than those of the bulk InGaAs materials as well. We infer that the recovery difference between the quantum-well materials and bulk materials originates from the fact that the radiation induced defects are confined in the quantum wells as a consequence of the free energy barrier between the In0.53Ga0.47As wells and InP barrier layers.

Effect of Crystallinity of Fullerene Derivatives on Doping Density in the Organic Bulk Heterojunction Layer in Polymer Solar Cells

LIU Qian, HE Zhi-Qun, LIANG Chun-Jun, ZHAO Yong, XIAO Wei-Kang, LI Dan
Chin. Phys. Lett. 2015, 32 (5): 056801 doi: 10.1088/0256-307X/32/5/056801
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Polymer solar cells (PSCs) based on poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) are fabricated by using 1,8-diiodooctane (DIO) as a solvent additive to control the doping density of the PSCs. It is shown that the processing of DIO does not change the doping density of the P3HT phase, while it causes a dramatic reduction of the doping density of the PCBM phase, which decreases the doping density of the whole blend layer from 3.7×1016 cm−3 to 1.2×1016 cm−3. The reduction of the doping density in the PCBM phase originates from the increasing crystallinity of PCBM with DIO addition, and it leads to a decreasing doping density in the blend film and improves the short circuit current of the PSCs.

Electrical Conduction in Deuterated Ammonium Dihydrogen Phosphate Crystals with Different Degrees of Deuteration

ZHU Li-Li, GAN Xiao-Yu, ZHANG Qing-Hua, LIU Bao-An, XU Ming-Xia, ZHANG Li-Song, XU Xin-Guang, GU Qing-Tian, SUN Xun
Chin. Phys. Lett. 2015, 32 (5): 057201 doi: 10.1088/0256-307X/32/5/057201
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Conductivity measurements of deuterated ammonium dihydrogen phosphate (DADP) crystals with different deuterated degrees are described. The conductivities increase with the deuterium content, and the value of the a-direction is larger than that of the c-direction. Compared with DKDP crystals, DADP crystals have larger conductivities, which is partly due to the existence of A defects. The ac conductivity over the temperature range 25–170°C has shown a knee in the curve of ln(σT) versus T−1. The conductivity activation energy calculated by the slope of the high temperature region decreases with the deuterium content. The previously reported phase transition is not seen.

GaNAs/InGaAs Superlattice Solar Cells with High N Content in the Barrier Grown by All Solid-State Molecular Beam Epitaxy

LU Jian-Ya, ZHENG Xin-He, WANG Nai-Ming, CHEN Xi, LI Bao-Ji, LU Shu-Long, YANG Hui
Chin. Phys. Lett. 2015, 32 (5): 057301 doi: 10.1088/0256-307X/32/5/057301
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We demonstrate nearly 1 eV GaN0.03As0.97/In0.09Ga0.91As strain-compensated short-period superlattice solar cells by all solid-state molecular beam epitaxy. The optimal period thickness for the superlattice growth is achieved to realize high structural quality. Meanwhile, the annealing conditions are optimized to realize a photoluminescence (PL) at a low temperature. However, no PL signal is detected at room temperature, which could be reflected by a lower open-circuit voltage of the fabricated devices. The GaN0.03As0.97/In0.09Ga0.91As superlattice solar cells show a reasonably-high short-circuit current density (Jsc) of over 10 mA/cm2. Furthermore, a concentration behavior is measured, which shows a linear relationship between Jsc and concentration ratios. The extrapolated ideality factor and saturated current density by the concentration action are in good agreement with that extracted by the dark case of the p-i-n diodes.

The First Principles Study of Hydrogen Adsorption on Ni-Decorated LiB (001) Surface

ZHANG Fu-Chun, LIU Yang, ZHANG Wei-Bin
Chin. Phys. Lett. 2015, 32 (5): 057302 doi: 10.1088/0256-307X/32/5/057302
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The hydrogen adsorption on the one and three Ni−decorated LiB (001) 2×2 surface is investigated by the first principles study. It is demonstrated that Ni atoms are preferentially adsorbed on the top B atom, and form a covalent bond of NiB and an ionic bond of NiLi on the surface. Four H2 molecules can adsorb on the one−Ni-decorated LiB (001) surface, and the average adsorption energy is in a range from -0.35 to -0.58 eV/H2. The charge population analysis shows that the dipole moments on the Ni decorated surface is responsible for the polarization and adsorption of H2. Then, we show that three Ni atoms can be decorated on the LiB (001) 2×2 surface, and form a Ni3B nano cluster on the surface, which agrees with experimental results. Three Ni-decorated LiB (001) can adsorb up to six H2 molecules, indicating that the Ni-decorated LiB (001) system might be a promising hydrogen storage material.

Magnetism in Quasi-One-Dimensional A2Cr3As3 (A=K,Rb) Superconductors Hot!

WU Xian-Xin, LE Cong-Cong, YUAN Jing, FAN Heng, HU Jiang-Ping
Chin. Phys. Lett. 2015, 32 (5): 057401 doi: 10.1088/0256-307X/32/5/057401
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We predict that the recently discovered quasi-one-dimensional superconductors, A2Cr3As3 (A=K,Rb), possess strong frustrated magnetic fluctuations and are nearby a novel in-out co-planar magnetic ground state. The frustrated magnetism is very sensitive to the c-axis lattice constant and can thus be suppressed by increasing pressure. Our results qualitatively explain strong non-Fermi liquid behaviors observed in the normal state of the superconductors as the intertwining between the magnetism and superconductivity can create a large quantum critical region in quasi-one-dimensional systems and also suggest that the materials share similar phase diagrams and superconducting mechanism with other unconventional superconductors, such as cuprates and iron-based superconductors.

Tuning the Electronic Structure of Sr2IrO4 Thin Films by Bulk Electronic Doping Using Molecular Beam Epitaxy

LI Ming-Ying, LIU Zheng-Tai, YANG Hai-Feng, ZHAO Jia-Lin, YAO Qi, FAN Cong-Cong, LIU Ji-Shan, GAO Bo, SHEN Da-Wei, XIE Xiao-Ming
Chin. Phys. Lett. 2015, 32 (5): 057402 doi: 10.1088/0256-307X/32/5/057402
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By means of oxide molecular beam epitaxy with shutter-growth mode, we fabricate a series of electron-doped (Sr1−xLax)2IrO4 (001) (x=0, 0.05, 0.1 and 0.15) single crystalline thin films and then investigate the doping dependence of the electronic structure utilizing in-situ angle-resolved photoemission spectroscopy. It is found that with the increasing doping content, the Fermi levels of samples progressively shift upward. Prominently, an extra electron pocket crossing the Fermi level around the M point is evidently observed in the 15% nominal doping sample. Moreover, bulk-sensitive transport measurements confirm that the doping effectively suppresses the insulating state with respect to the as-grown Sr2IrO4, though the doped samples still remain insulating at low temperatures due to the localization effect possibly stemming from disorders including oxygen deficiencies. Our work provides another feasible doping method to tune electronic structure of Sr2IrO4.

Chiral Current in the Lattice Model of Weyl Semimetal

SUN Liang, WAN Shao-Long
Chin. Phys. Lett. 2015, 32 (5): 057501 doi: 10.1088/0256-307X/32/5/057501
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We demonstrate the existence of the chiral magnetic effect in a simple lattice model of Weyl semimetal, which is a hallmark of chiral anomaly in the Weyl semimetal, by calculating the anomalous charge current directly. We identify that the uniform external magnetic field can induce a non-dissipative charge current along its direction in Weyl semimetal, even in the absence of an external electric field if the right and left handed Weyl points are separated in energy, and that the anomalous current is proportional to the strength of the magnetic field and the energy separation with a universal coefficient e2/h2, which coincide with the ones predicted on the basis of the field theory treatment. Our results give the possibility to detect these nontrivial electrodynamic phenomena in real materials of Weyl semimetal.

Structural and Magnetic Properties of Co2MnSi Thin Film with a Low Damping Constant

QIAO Shi-Zhu, ZHANG Jie, QIN Yu-Feng, HAO Run-Run, ZHONG Hai, ZHU Da-Peng, KANG Yun, KANG Shi-Shou, YU Shu-Yun, HAN Guang-Bing, YAN Shi-Shen, MEI Liang-Mo
Chin. Phys. Lett. 2015, 32 (5): 057601 doi: 10.1088/0256-307X/32/5/057601
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Co2MnSi thin films are made by magnetron sputtering onto MgO (001) substrates. The crystalline quality is improved by increasing depositing temperature and/or annealing temperature. The sample deposited at 550°C and subsequently annealed at 550°C (sample I) exhibits a pseudo-epitaxial growth with partially ordered L21 phase. Sample I shows a four-fold magnetic anisotropy, in addition to a relatively weak uniaxial anisotropy. The Gilbert damping factor of sample I is smaller than 0.001, much smaller than reported ones. The possible reasons responsible for the small Gilbert damping factor are discussed, including weak spin-orbit coupling, small density of states at Fermi level, and so on.

Dynamic Investigations of Pressure-Induced Abnormal Phase Transitions in PbTiO3

WU Hong-Bo, DUAN Yi-Feng, LIU Kun, LV Dong, QIN Li-Xia, SHI Li-Wei, TANG Gang
Chin. Phys. Lett. 2015, 32 (5): 057701 doi: 10.1088/0256-307X/32/5/057701
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The effects of pressure on phonon modes of ferroelectric tetragonal P4mm and paraelectric cubic Pm3m PbTiO3 are systematically investigated by using first-principles simulations. The pressure-induced tetragonal-to-cubic and subsequent cubic-to-tetragonal phase transitions are the second-order transitions, which are different from the phase transitions induced by temperature [Phys. Rev. Lett. 25 (1970) 167]. As pressure increases, the lowest A1 and E modes of the tetragonal phase become softer and converge to the F1u mode of the cubic phase. As pressure further increases, the lowest F1u mode first hardens and then softens again, and finally diverges into A1 and E modes. The behaviors of optical phonon modes confirm the ferroelectric-to-paraelectric-to-ferroelectric phase transitions.

Temperature-Dependent Photoluminescence from GaN/Si Nanoporous Pillar Array

WANG Xiao-Bo, LI Yong, YAN Ling-Ling, LI Xin-Jian
Chin. Phys. Lett. 2015, 32 (5): 057801 doi: 10.1088/0256-307X/32/5/057801
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A GaN/Si nanoheterostructure is prepared by growing wurtzite GaN on a silicon nanoporous pillar array (Si-NPA) with a chemical vapor deposition method. The temperature evolution of the photoluminescence (PL) of GaN/Si-NPA is measured and the PL mechanism is analyzed. It is found that the PL spectrum is basically composed of two narrow ultraviolet peaks and a broad blue peak, corresponding to the near band edge emission of GaN and its phonon replicas, and the emission from Si-NPA. No GaN defect-related PL is observed in the as-prepared GaN/Si-NPA. Our experiments prove that Si-NPA might be an ideal substrate for preparing high-quality Si-based GaN nanomaterials or nanodevices.

Raman Study of Polydimethylsiloxane Substrate Effect on Hydrogenation of Graphene

GAO Chuan-Wei, WANG Ying-Ying, JIANG Jie, NAN Hai-Yan, NI Zhen-Hua
Chin. Phys. Lett. 2015, 32 (5): 058101 doi: 10.1088/0256-307X/32/5/058101
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Raman spectroscopy is used to monitor hydrogenation of graphene on polydimethylsiloxane (PDMS) as well as on SiO2/Si substrates. It is found that hydrogenation of graphene on SiO2/Si is much more feasible than that on PDMS. For graphene on PDMS substrates, hydrogenation of graphene is favored on very flexible substrates. The substrate (SiO2/Si and PDMS) and flexibility (PDMS with different flexibility) dependent hydrogenation behavior can be understood by different interactions between graphene and substrate. The interaction between graphene and SiO2/Si is relative weak (van der Waals force) and the interaction between graphene and PDMS is relative strong, where substrate induced prestrain in the graphene layer is observed. For graphene embedded on the PDMS substrate, the more flexible the substrate is, the weaker the interaction between PDMS and graphene. The understanding of the effect of PDMS's flexibility on hydrogenation of graphene will be helpful for graphene based flexible electronics.

Factors Affecting the Top Stripping of GaAs Microwire Array Fabricated by Inductively Coupled Plasma Etching

CHENG Ying, ZOU Ji-Jun, WAN Ming, WANG Wei-Lu, PENG Xin-Cun, FENG Lin, DENG Wen-Juan, ZHU Zhi-Fu
Chin. Phys. Lett. 2015, 32 (5): 058102 doi: 10.1088/0256-307X/32/5/058102
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The effects of different masks and patterns on the top stripping of GaAs microwire arrays fabricated by inductively coupled plasma etching for 20 min and 40 min are investigated. The results show that the mask layer is the main affect of the top stripping of the GaAs microwires in 40 min. Increasing the mask layers and reducing the photoresist layers can prevent top stripping and result in a suitable GaAs microwire array.

Structure and Strain Properties of GaN Films Grown on Si (111) Substrates with AlxGa1−xN/AlyGa1−yN Superlattices

PAN Lei, NI Jin-Yu, YU Xin-Xin, DONG Xun, PENG Da-Qing, LI Chuan-Hao, LI Zhong-Hui, CHEN Tang-Sheng
Chin. Phys. Lett. 2015, 32 (5): 058103 doi: 10.1088/0256-307X/32/5/058103
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GaN films with an AlxGa1−xN/AlyGa1−yN superlattice (SL) buffer layer are grown on Si(111) substrates by metal-organic chemical vapor deposition (MOCVD). The structure and strain properties of the samples are studied by optical microscopy, Raman spectroscopy, x-ray diffractometry and atomic force microscopy. The results show that the strain status and crystalline quality of the GaN layers are strongly dependent on the difference of the Al composition between AlxGa1−xN barriers and AlyGa1−yN wells in the SLs. With a large Al composition difference, the GaN film tends to generate cracks on the surface due to the severe relaxation of the SLs. Otherwise, when using a small Al composition difference, the crystalline quality of the GaN layer degrades due to the poor function of the SLs in filtering dislocations. Under an optimized condition that the Al composition difference equals 0.1, the crack-free and compressive strained GaN film with an improved crystalline quality is achieved. Therefore, the AlxGa1−xN/AlyGa1−yN SL buffer layer is a promising buffer structure for growing thick GaN films on Si substrates without crack generation.

Left-Handedness with Three Zero-Absorption Windows Tuned by the Incoherent Pumping Field and Inter-Dot Tunnelings in a GaAs/AlGaAs Triple Quantum Dots System

ZHAO Shun-Cai, ZHANG Shuang-Ying, WU Qi-Xuan, JIA Jing
Chin. Phys. Lett. 2015, 32 (5): 058104 doi: 10.1088/0256-307X/32/5/058104
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Left-handedness with three zero-absorption windows is achieved in a triple-quantum-dot system. With the typical parameters of a GaAs/AlGaAs heterostructure, the simultaneous negative relative electric permittivity and magnetic permeability are obtained by the adjustable incoherent pumping field and two inter-dot tunnelings. Furthermore, three zero-absorption windows in the left-handedness frequency bands are observed. The left-handedness with zero-absorption in the solid state heterostructure may solve the challenges not only in the left-handed materials achieved by the photonic resonant scheme but also in the application of negative refractive materials with a large amount of absorption.

Effects of Thermal Annealing on the Solvent Additive P3HT PC61BM Bulk Heterojunction Solar Cells

FAN Xing, ZHAO Su-Ling, CHEN Yu, ZHANG Jie, YANG Qian-Qian, GONG Wei, XU Zheng, XU Xu-Rong
Chin. Phys. Lett. 2015, 32 (5): 058401 doi: 10.1088/0256-307X/32/5/058401
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Effects of thermal annealing on the optical, electrical and structural properties of 3 vol% 1,8-diiodoctane added P3HT:PC61BM active layers are investigated, concerning the performance of the bulk heterojunction polymer solar cells by changing the heat temperature. The structure information of the active layer is analyzed by using the grazing incidence wide angle scattering diffraction combined with the optical microscope, light absorption, photoluminescence and the external quantum efficiency spectra. The relationship between the detail of morphology and the optical, electrical properties is investigated.

A Novel Multi-Finger Gate Structure of AlGaN/GaN High Electron Mobility Transistor

CUI Lei, WANG Quan, WANG Xiao-Liang, XIAO Hong-Ling, WANG Cui-Mei, JIANG Li-Juan, FENG Chun, YIN Hai-Bo, GONG Jia-Min, LI Bai-Quan, WANG Zhan-Guo
Chin. Phys. Lett. 2015, 32 (5): 058501 doi: 10.1088/0256-307X/32/5/058501
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A novel multi-finger gate high electron mobility transistor (HEMT) is designed to reduce the peak electric field value at the drain-side gate edge when the device is at off-state. The effective gate length (Leff) of the multi-finger gate device is smaller than that of the field plate gate device. In this work, field plate gate, five-finger gate and ten-finger gate devices are simulated. The results of the simulation indicate that the multi-finger gate device has a lower peak value than the device with the gate field plate. Moreover, this value would be further reduced when the number of gate fingers is increased. In addition, it has the potential to make the HEMT work in a higher frequency since it has a lower effective length of gate.

Cooperation and Phase Separation Driven by a Coevolving Snowdrift Game

DU Peng, XU Chen, ZHANG Wen
Chin. Phys. Lett. 2015, 32 (5): 058901 doi: 10.1088/0256-307X/32/5/058901
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We investigate the cooperative behavior and the phase separation in a coevolving system. Agents in the system constructed by a regular random network initially play the snowdrift game with their neighbors. They try to obtain a better competing environment by imitating a neighbor's more successful strategy or cutting the connection to a defective neighbor and randomly rewiring to another agent so as to seek a better neighborhood. The dynamic process of strategy imitation and relationship among agents due to rewiring neighbors may drive the system into different states. The simulation results show that there are three different phases in the qr plane, where q is the rewiring probability and r is the cost-to-benefit ratio. One is a static phase of a pure cooperative cluster with a few isolated defectors. The other two belong to active phases with one of a main mixed-strategy cluster and the other of a pure defective state. We find that a simple mean field theory can predict correctly the static phase and the active phase of the main mixed-strategy cluster. The theoretical boundary line between the two phases is in good agreement with the simulation result.

Constraining the Generalized and Superfluid Chaplygin Gas Models with the Sandage–Loeb Test

ZHU Wen-Tao, WU Pu-Xun, YU Hong-Wei
Chin. Phys. Lett. 2015, 32 (5): 059501 doi: 10.1088/0256-307X/32/5/059501
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The Sandage–Loeb (SL) test is a direct measurement of the cosmic expansion by probing the redshift drifts of quasi-stellar objects in the 'redshift desert' of 2<z<5. In this work, we investigate its constraints on the unified dark energy and dark matter models including the generalized Chaplygin gas and the superfluid Chaplygin gas. In addition, type Ia supernovae (SNIa) data and the distance ratios derived from the cosmic microwave background radiation and baryon acoustic oscillation observations (CMB/BAO) are also used. We find that the mock SL data gives the tightest constraints on the model parameters and it can help to reduce the parameter regions allowed by the present SNIa+CMB/BAO by about 75% when all datasets considered are combined. Thus the SL test is a worthy and long awaited measurement to probe effectively the cosmic expanding history and the properties of dark energy.

Effects of Gravitational Correction on Neutrino Emission from Neutron Stars

DING Wen-Bo, E Shan-Shan, YU Zi, ZHANG Qi, QI Zhan-Qiang
Chin. Phys. Lett. 2015, 32 (5): 059701 doi: 10.1088/0256-307X/32/5/059701
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Considering the gravitational correction through introduction of weakly interacting light vector U bosons, not only the equation of state (EoS) of the neutron star matter, but also the cooling properties of neutron stars may be changed. In this work, effects of gravitational correction on neutrino emission and cooling of neutron stars in the matter with neutrons, protons, electrons, muons, Δ and Δ0 are studied by the relativistic mean field theory and the related cooling theory. The results show that the effects are sensitive to the ratio of coupling strength to mass squared of U bosons, defined as gU. With increasing gU, the radial region where direct Urca process of nucleons can be allowed in a neutron star with the fixed mass becomes narrower, while the neutrino emissivity is somewhat higher. Moreover, the gravitational correction suppresses the effects of Δ on neutrino emission. The gravitational correction leads the star to cool faster, and the higher the gU is, the faster the star cools.

Constraining Equation of State of Dark Matter: Including Weak Gravitational Lensing

YANG Lei, YANG Wei-Qiang, XU Li-Xin
Chin. Phys. Lett. 2015, 32 (5): 059801 doi: 10.1088/0256-307X/32/5/059801
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Usually the equation of state (EoS) of dark matter is zero when it is cold, however there exists the possibility of a (effective) nonzero EoS of dark matter due to its decay and interaction with dark energy. In this work, we try to constrain the EoS of dark matter wdm using the currently available cosmic observations which include the geometrical and dynamical measurements. For the geometrical measurements, the luminosity distance of type Ia supernovae, the angular diameter distance and comoving sound horizon from baryon acoustic oscillations and the cosmic microwave background radiation will be employed. The data points from the redshift-space distortion and weak gravitational lensing will be taken as dynamical measurements. Using the Markov chain Monte Carlo method, we obtain a very tight constraint on the EoS of dark matter: wdm=0.0000532−0.000686−0.00136−0.00177+0.000692+0.00136+0.00183.
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