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Volume 34 Issue 6
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GENERAL
From Nothing to Something II: Nonlinear Systems via Consistent Correlated Bang
Sen-Yue Lou
Chin. Phys. Lett.. 2017, 34 (6): 060201 .   DOI: 10.1088/0256-307X/34/6/060201
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The Chinese ancient sage Laozi said that everything comes from 'nothing'. In the work [Chin. Phys. Lett. 30 (2013) 080202], infinitely many discrete integrable systems have been obtained from nothing via simple principles (Dao). In this study, a new idea, the consistent correlated bang, is introduced to obtain nonlinear dynamic systems including some integrable ones such as the continuous nonlinear Schrödinger equation, the (potential) Korteweg de Vries equation, the (potential) Kadomtsev–Petviashvili equation and the sine-Gordon equation. These nonlinear systems are derived from nothing via suitable 'Dao', the shifted parity, the charge conjugate, the delayed time reversal, the shifted exchange, the shifted-parity-rotation and so on.
A High-Order Conservative Numerical Method for Gross–Pitaevskii Equation with Time-Varying Coefficients in Modeling BEC
Xiang Li, Xu Qian, Ling-Yan Tang, Song-He Song
Chin. Phys. Lett.. 2017, 34 (6): 060202 .   DOI: 10.1088/0256-307X/34/6/060202
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We propose a high-order conservative method for the nonlinear Schrödinger/Gross–Pitaevskii equation with time-varying coefficients in modeling Bose–Einstein condensation (BEC). This scheme combined with the sixth-order compact finite difference method and the fourth-order average vector field method, finely describes the condensate wave function and physical characteristics in some small potential wells. Numerical experiments are presented to demonstrate that our numerical scheme is efficient by the comparison with the Fourier pseudo-spectral method. Moreover, it preserves several conservation laws well and even exactly under some specific conditions.
Stability of Dirac Equation in Four-Dimensional Gravity
F. Safari, H. Jafari, J. Sadeghi, S. J. Johnston, D. Baleanu
Chin. Phys. Lett.. 2017, 34 (6): 060301 .   DOI: 10.1088/0256-307X/34/6/060301
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We introduce the Dirac equation in four-dimensional gravity which is a generally covariant form. We choose the suitable variable and solve the corresponding equation. To solve such equation and to obtain the corresponding bispinor, we employ the factorization method which introduces the associated Laguerre polynomial. The associated Laguerre polynomials help us to write the Dirac equation of four-dimensional gravity in the form of the shape invariance equation. Thus we write the shape invariance condition with respect to the secondary quantum number. Finally, we obtain the spinor wave function and achieve the corresponding stability of condition for the four-dimensional gravity system.
Observation of Topological Links Associated with Hopf Insulators in a Solid-State Quantum Simulator
X.-X. Yuan, L. He, S.-T. Wang, D.-L. Deng, F. Wang, W.-Q. Lian, X. Wang, C.-H. Zhang, H.-L. Zhang, X.-Y. Chang, L.-M. Duan
Chin. Phys. Lett.. 2017, 34 (6): 060302 .   DOI: 10.1088/0256-307X/34/6/060302
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Hopf insulators are intriguing three-dimensional topological insulators characterized by an integer topological invariant. They originate from the mathematical theory of Hopf fibration and epitomize the deep connection between knot theory and topological phases of matter, which distinguishes them from other classes of topological insulators. Here, we implement a model Hamiltonian for Hopf insulators in a solid-state quantum simulator and report the first experimental observation of their topological properties, including nontrivial topological links associated with the Hopf fibration and the integer-valued topological invariant obtained from a direct tomographic measurement. Our observation of topological links and Hopf fibration in a quantum simulator opens the door to probe rich topological properties of Hopf insulators in experiments. The quantum simulation and probing methods are also applicable to the study of other intricate three-dimensional topological model Hamiltonians.
Spherically Symmetric Wormhole Gravitational Lens Deflection Angle Signifying Braneworld Cosmology
Anuar Alias, Wan Ahmad Tajuddin Wan Abdullah
Chin. Phys. Lett.. 2017, 34 (6): 060401 .   DOI: 10.1088/0256-307X/34/6/060401
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Previously, the gravitational lens of a wormhole was introduced by various researchers. Their treatment was focused basically on the lens signature that describes wormhole geometrical character such as the differences from a black hole or between any various types of wormhole models. The braneworld scenario provides the idea of spacetime with underlying extra-dimensions. The inclusion of extra-dimensional terms in the lens object spacetime line element will result in some variation in the expression for its gravitational lens deflection angle. Thus in this paper we investigate such variation by deriving this deflection angle expression. As such, this paper not only shows the existence of such variation but also suggests the potential utilization of gravitational lensing to prove the existence of extra dimensions by studying the deflection angle characteristic in accordance with the spacetime expansion rate of the universe.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
Localization of Vector Field on Pure Geometrical Thick Brane
Tao-Tao Sui, Li Zhao
Chin. Phys. Lett.. 2017, 34 (6): 061101 .   DOI: 10.1088/0256-307X/34/6/061101
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We investigate the localization of a five-dimensional vector field on a pure geometrical thick brane. By introducing two types of interactions between the vector field and the background scalar field, we obtain a typical volcano potential for the first type of coupling and a Pöschl–Teller potential for the second one. These two types of couplings guarantee that the vector zero mode can be localized on the pure geometrical thick brane under certain conditions.
The $B-L+xY$ Model and the Higgs-strahlung Processes at a Collider
Wen-Qi Cao, Chong-Xing Yue
Chin. Phys. Lett.. 2017, 34 (6): 061401 .   DOI: 10.1088/0256-307X/34/6/061401
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The gauge extension of the standard model with the $U(1)_{B-L+xY}$ symmetry predicts the existence of a light gauge boson $Z'$ with small couplings to ordinary fermions. We discuss its contributions to the muon anomalous magnetic moment $a_{\mu}$. Taking account of the constraints on the relevant free parameters, we further calculate the contributions of the light gauge boson $Z'$ to the Higgs-strahlung processes $e^{+}e^{-}\rightarrow ZH$ and $e^{+}e^{-}\rightarrow Z'H$.
NUCLEAR PHYSICS
Elliptic Flow Splitting between Particles and their Antiparticles in Au+Au Collisions from a Multiphase Transport Model
Zhen-Yu Xu, Jian-Li Liu, Pan-Pan Zhang, Jing-Bo Zhang, Lei Huo
Chin. Phys. Lett.. 2017, 34 (6): 062501 .   DOI: 10.1088/0256-307X/34/6/062501
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The elliptic flow $v_2$, for $\pi^\pm$, $K^\pm$, $p$ and $\bar {p}$ in Au+Au collisions at center-of-mass energies $\sqrt {s_{_{\rm NN}}}=7.7$, 11.5, 14.5 and 19.6 GeV, is analyzed using a multiphase transport model. A significant difference in the $v_2$ values for $p$ and $\bar {p}$ is observed, and the values of $v_2$ splitting are larger compared with $\pi^+$ and $\pi^-$, $K^+$ and $K^-$. The difference increases with decreasing the center-of-mass energy. The effect of the quark coalescence mechanism in a multi-phase transport model to the value of elliptic difference $\Delta v_2$ between $p$ and $\bar {p}$ has been discussed. The simulation of Au+Au collisions at 14.5 GeV shows that the effect of hadron cascade to $\Delta v_2$ is not obvious, and a larger parton-scattering cross section can lead to a larger $\Delta v_2$.
ATOMIC AND MOLECULAR PHYSICS
Angle-Resolved Electron Spectra of F$^{-}$ Ions by Few-Cycle Laser Pulses
Jian-Hong Chen, Song-Feng Zhao, Guo-Li Wang, Xiao-Ping Zheng, Zheng-Rong Zhang
Chin. Phys. Lett.. 2017, 34 (6): 063201 .   DOI: 10.1088/0256-307X/34/6/063201
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The above-threshold detachment of F$^{-}$ ions induced by a linearly polarized few-cycle laser pulse is investigated theoretically using the strong-field approximation model without considering the rescattering mechanism. We first derive an analytical form of transition amplitude for describing the strong-field photodetachment of F$^{-}$ ions. The integration over time in transition amplitude can be performed using the numerical integration method or the saddle-point (SP) method of Shearer et al. [Phys. Rev. A 88 (2013) 033415]. The validity of the SP method is carefully examined by comparing the energy spectra and photoelectron angular distributions (PADs) with those obtained from the numerical integration method. By considering the volume effect of a focused laser beam, both the energy spectra and the low-energy PADs calculated by the numerical integration method agree very well with the experimental results.
Measurement of Heating Rates in a Microscopic Surface-Electrode Ion Trap
Jiu-Zhou He, Lei-Lei Yan, Liang Chen, Ji Li, Mang Feng
Chin. Phys. Lett.. 2017, 34 (6): 063701 .   DOI: 10.1088/0256-307X/34/6/063701
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We report measurement of heating rates of $^{40}$Ca$^{+}$ ions confined in our home-made microscopic surface-electrode trap by a Doppler recooling method. The ions are trapped with approximately 800 μm above the surface, and are subjected to heating due to various noises in the trap. There are 3–5 ions involved to measure the heating rates precisely and efficiently. We show the heating rates in variance with the number and the position of the ions as well as the radio-frequency power, which are helpful for understanding the trap imperfection.
Dick Effect in the Integrating Sphere Cold Atom Clock
Xiu-Mei Wang, Yan-Ling Meng, Ya-Ning Wang, Jin-Yin Wan, Ming-Yuan Yu, Xin Wang, Ling Xiao, Tang Li, Hua-Dong Cheng, Liang Liu
Chin. Phys. Lett.. 2017, 34 (6): 063702 .   DOI: 10.1088/0256-307X/34/6/063702
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The Dick effect is an important factor limiting the frequency stability of sequentially-operating atomic frequency standards. Here we study the impact of the Dick effect in the integrating sphere cold atom clock (ISCAC). To reduce the impact of the Dick effect, a 5 MHz local oscillator with ultra-low phase noise is selected and a new microwave synthesizer is built in-house. Consequently, the phase noise of microwave signal is optimized. The contribution of the Dick effect is reduced to $2.5\times 10^{-13}\tau ^{-1/2}$ ($\tau $ is the integrating time). The frequency stability of $4.6\times 10^{-13}\tau ^{-1/2}$ is achieved. The development of this optimization can promote the space applications of the compact ISCAC.
FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)
Compact Optical Add-Drop De-Multiplexers with Cascaded Micro-Ring Resonators on SOI
Huan Guan, Zhi-Yong Li, Hai-Hua Shen, Yu-De Yu
Chin. Phys. Lett.. 2017, 34 (6): 064201 .   DOI: 10.1088/0256-307X/34/6/064201
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A four-channel integrated optical wavelength de-multiplexer is experimentally illustrated on a silicon-on-insulator (SOI) substrate. With the aid of cascaded micro-ring resonators, the whole performance of the wavelength de-multiplexer is improved, such as 3 dB bandwidth and channel crosstalk. Based on the transform matrix theory, a four-channel wavelength de-multiplexer with average channel spacing 4.5$\pm$0.5 nm (3 dB bandwidth $\sim 2\pm 0.5$ nm) is demonstrated at telecommunication bands. For each channel, the extinction at the adjacent channel is below $-$39 dB and the out-of-band rejection ratio is up to 40 dB. The channel dropping loss is below 5 dB in the five FSR spectral response periods (near 100 nm).
The 5.2kW Nd:YAG Slab Amplifier Chain Seeded by Nd:YVO$_{4}$ Innoslab Laser
Lei Liu, Shou-Huan Zhou, Yang Liu, Zhe Wang, Gang Wang, Hong Zhao
Chin. Phys. Lett.. 2017, 34 (6): 064202 .   DOI: 10.1088/0256-307X/34/6/064202
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A high power Nd:YAG end-pumped slab amplifier chain with a Nd:YVO$_{4}$ innoslab laser as the master oscillator is demonstrated. A chain output power of 5210 W with beam quality of 4 times the diffraction limit is achieved by double-passing the first amplifier stage and single-passing the second stage with an optical efficiency of 29% while working at a frequency of 1 kHz and pulse width of 200 μs.
High-Stability High-Energy Picosecond Optical Parametric Chirped Pulse Amplifier as a Preamplifier in Nd:Glass Petawatt System for Contrast Enhancement
Ting-Rui Huang, Xue Pan, Peng Zhang, Jiang-Feng Wang, Xiao-Ping Ouyang, Xue-Chun Li
Chin. Phys. Lett.. 2017, 34 (6): 064203 .   DOI: 10.1088/0256-307X/34/6/064203
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We demonstrate a novel picosecond optical parametric preamplification to generate high-stability, high-energy and high-contrast seed pulses. The 5 ps seed pulse is amplified from 60 pJ to 300 $\mu$J with an 8.6 ps/ 3 mJ pump laser in a signal stage of short pulse non-collinear optical parametric chirped pulse amplification. The total gain is more than 10$^{6}$ and the rms energy stability is under 1.35%. The contrast ratio is higher than 10$^{8}$ within a scale of 20 ps before the main pulse. Consequently, the improvement factor of the signal contrast is approximately equal to the gain 10$^{6}$ outside the pump window.
Temperature and Pressure inside Sonoluminescencing Bubbles Based on Asymmetric Overlapping Sodium Doublet
Tai-Yang Zhao, Wei-Zhong Chen, Sheng-De Liang, Xun Wang, Qi Wang
Chin. Phys. Lett.. 2017, 34 (6): 064301 .   DOI: 10.1088/0256-307X/34/6/064301
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We experimentally measure the sodium $D$-lines from the multibubble sonoluminescence in sodium hydroxide aqueous solution. The asymmetric overlapping $D$-lines are successfully decomposed based on the Fourier transform analysis. The line broadening of the decomposed sodium $D$-lines shows the effective temperature of 3600–4500 K and the pressure of 560–1000 atm during sonoluminescence.
Influence of Change in Inner Layer Thickness of Composite Circular Tube on Second-Harmonic Generation by Primary Circumferential Ultrasonic Guided Wave Propagation
Ming-Liang Li, Ming-Xi Deng, Guang-Jian Gao, Han Chen, Yan-Xun Xiang
Chin. Phys. Lett.. 2017, 34 (6): 064302 .   DOI: 10.1088/0256-307X/34/6/064302
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The influence of change in inner layer thickness of a composite circular tube is investigated on second-harmonic generation (SHG) by primary circumferential ultrasonic guided wave (CUGW) propagation. Within a second-order perturbation approximation, the nonlinear effect of primary CUGW propagation is treated as a second-order perturbation to its linear response. It is found that change in inner layer thickness of the composite circular tube will influence the efficiency of SHG by primary CUGW propagation in several aspects. In particular, with change in inner layer thickness, the phase velocity matching condition that is originally satisfied for the primary and double-frequency CUGW mode pair selected may no longer be satisfied. This will remarkably influence the efficiency of SHG by primary CUGW propagation. Theoretical analyses and numerical results show that the effect of SHG by primary CUGW propagation is very sensitive to change in inner layer thickness, and it can be used to accurately monitor a minor change in inner layer thickness of the composite circular tube.
Valid Regions of Formulas of Sound Speed in Bubbly Liquids
Yu-Ning Zhang, Zhong-Yu Guo, Yu-Hang Gao, Xiao-Ze Du
Chin. Phys. Lett.. 2017, 34 (6): 064701 .   DOI: 10.1088/0256-307X/34/6/064701
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There are numerous formulae relating to the predictions of sound wave in the cavitating and bubbly flows. However, the valid regions of those formulae are rather unclear from the view point of physics. In this work, the validity of the existing formulae is discussed in terms of three regions by employing the analysis of three typical lengths involved (viscous length, thermal diffusion length and bubble radius). In our discussions, viscosity and thermal diffusion are both considered together with the effects of relative motion between bubbles and liquids. The importance of relative motion and thermal diffusion are quantitatively discussed in a wide range of parameter zones (including bubble radius and acoustic frequency). The results show that for large bubbles, the effects of relative motion will be prominent in a wide region.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
Nonlinear Propagation of Positron-Acoustic Periodic Travelling Waves in a Magnetoplasma with Superthermal Electrons and Positrons
E. F. EL-Shamy
Chin. Phys. Lett.. 2017, 34 (6): 065201 .   DOI: 10.1088/0256-307X/34/6/065201
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The nonlinear propagation of positron acoustic periodic (PAP) travelling waves in a magnetoplasma composed of dynamic cold positrons, superthermal kappa distributed hot positrons and electrons, and stationary positive ions is examined. The reductive perturbation technique is employed to derive a nonlinear Zakharov–Kuznetsov equation that governs the essential features of nonlinear PAP travelling waves. Moreover, the bifurcation theory is used to investigate the propagation of nonlinear PAP periodic travelling wave solutions. It is found that kappa distributed hot positrons and electrons provide only the possibility of existence of nonlinear compressive PAP travelling waves. It is observed that the superthermality of hot positrons, the concentrations of superthermal electrons and positrons, the positron cyclotron frequency, the direction cosines of wave vector $k$ along the $z$-axis, and the concentration of ions play pivotal roles in the nonlinear propagation of PAP travelling waves. The present investigation may be used to understand the formation of PAP structures in the space and laboratory plasmas with superthermal hot positrons and electrons.
CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES
Compressive Behavior of TATB Grains inside TATB-Based PBX Revealed by In-Situ Neutron Diffraction
Yi Tian, Hong Wang, Chang-Sheng Zhang, Qiang Tian, Wei-Bin Zhang, Hong-Jia Li, Jian Li, Ben-De Liu, Guang-Ai Sun, Tai-Ping Peng, Yao Xu, Jian Gong
Chin. Phys. Lett.. 2017, 34 (6): 066101 .   DOI: 10.1088/0256-307X/34/6/066101
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We investigate the (002) lattice strain evolution of triaminotrinitrobenzene (TATB) grains inside one TATB-based plastic bonded explosive (PBX) through the in-situ neutron diffraction. By comparing the untreated specimen with the thermal-treated one, it is found that the volume-average response of measured TATB grains remains nearly elastic during quasi-static uniaxial compression. The observed changes in TATB (002) lattice strains correlate tightly with the evolution of damage. A damage parameter defined by the macroscopically determined residual strain is further used to describe the damage degree of PBX, which suggests that the compressive behavior of TATB-based PBX is significantly influenced by the damage evolution.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
Local Heating in a Normal-Metal–Quantum-Dot–Superconductor System without Electric Voltage Bias
Li-Ling Zhou, Xue-Yun Zhou, Rong Cheng, Cui-Ling Hou, Hong Shen
Chin. Phys. Lett.. 2017, 34 (6): 067101 .   DOI: 10.1088/0256-307X/34/6/067101
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We investigate the heat generation $Q$ in a quantum dot (QD), coupled to a normal metal and a superconductor, without electric bias voltage. It is found that $Q$ is quite sensitive to the lead temperatures $T_{\rm L,R}$ and the superconductor gap magnitude ${\it \Delta}$. At $T_{\rm L,R}\ll \omega_0$ ($\omega_0$ is the phonon frequency), the superconductor affects $Q$ only at ${\it \Delta} < \omega_0$, and the maximum magnitude of negative $Q$ appears at some ${\it \Delta}$ slightly smaller than $\omega_0$. At elevated lead temperature, contribution to $Q$ from the superconductor arises at ${\it \Delta}$, ranging from less than to much larger than $\omega_0$. However, the peak value of $Q$ is several times smaller than that in the case of $T_{\rm L,R}\ll \omega_0$. Interchanging lead temperatures $T_{\rm L}$ and $T_{\rm R}$ leads to quite different $Q$ behaviors, while this makes no difference for a normal-metal–quantum-dot–normal-metal system, and the QD can be cooled much more efficiently when the superconductor is colder.
The Nonlinear Electronic Transport in Multilayer Graphene on Silicon-on-Insulator Substrates
Yu-Bing Wang, Wei-Hong Yin, Qin Han, Xiao-Hong Yang, Han Ye, Shuai Wang, Qian-Qian Lv, Dong-Dong Yin
Chin. Phys. Lett.. 2017, 34 (6): 067201 .   DOI: 10.1088/0256-307X/34/6/067201
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We conduct a study on the superlinear transport of multilayer graphene channels that partially or completely locate on silicon which is pre-etched by inductively coupled plasma (ICP). By fabricating a multilayer-graphene field-effect transistor on a Si/SiO$_{2}$ substrate, we obtain that the superlinearity results from the interaction between the multilayer graphene sheet and the ICP-etched silicon. In addition, the observed superlinear transport of the device is found to be consistent with the prediction of Schwinger's mechanism. In the high bias regime, the values of $\alpha$ increase dramatically from 1.02 to 1.40. The strength of the electric field corresponding to the on-start of electron–hole pair production is calculated to be $5\times10^{4}$ V/m. Our work provides an experimental observation of the nonlinear transport of the multilayer graphene.
Mechanisms of Spin-Dependent Heat Generation in Spin Valves
Xiao-Xue Zhang, Yao-Hui Zhu, Pei-Song He, Bao-He Li
Chin. Phys. Lett.. 2017, 34 (6): 067202 .   DOI: 10.1088/0256-307X/34/6/067202
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The extra heat generation in spin transport is usually interpreted in terms of the spin relaxation. Reformulating the heat generation rate, we find alternative current-force pairs without cross effects, which enable us to interpret the product of each pair as a distinct mechanism of heat generation. The results show that the spin-dependent part of the heat generation includes two terms. One is proportional to the square of the spin accumulation and arises from the spin relaxation. However, the other is proportional to the square of the spin-accumulation gradient and should be attributed to another mechanism, the spin diffusion. We illustrate the characteristics of the two mechanisms in a typical spin valve with a finite nonmagnetic spacer layer.
Coulomb-Dominated Oscillations in Fabry–Perot Quantum Hall Interferometers
Yu-Ying Zhu, Meng-Meng Bai, Shu-Yu Zheng, Jie Fan, Xiu-Nian Jing, Zhong-Qing Ji, Chang-Li Yang, Guang-Tong Liu, Li Lu
Chin. Phys. Lett.. 2017, 34 (6): 067301 .   DOI: 10.1088/0256-307X/34/6/067301
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Periodic resistance oscillations in Fabry–Perot quantum Hall interferometers are observed at integer filling factors of the constrictions, $f_{\rm c}=1$, 2, 3, 4, 5 and 6. Rather than the Aharonov–Bohm interference, these oscillations are attributed to the Coulomb interactions between interfering edge states and localized states in the central island of an interferometer, as confirmed by the observation of a positive slope for the lines of constant oscillation phase in the image plot of resistance in the $B$–$V_{\rm S}$ plane. Similar resistance oscillations are also observed when the area $A$ of the center regime and the backscattering probability of interfering edge states are varied, by changing the side-gate voltages and the configuration of the quantum point contacts, respectively. The oscillation amplitudes decay exponentially with temperature in the range of 40 mK$ < T\leq 130$ mK, with a characteristic temperature $T_{\rm 0}\sim 25$ mK, consistent with recent theoretical and experimental works.
Controlling Fusion of Majorana Fermions in One-Dimensional Systems by Zeeman Field
Lu-Bing Shao, Zi-Dan Wang, Rui Shen, Li Sheng, Bo-Gen Wang, Ding-Yu Xing
Chin. Phys. Lett.. 2017, 34 (6): 067401 .   DOI: 10.1088/0256-307X/34/6/067401
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We propose the realization of Majorana fermions (MFs) on the edges of a two-dimensional topological insulator in the proximity with s-wave superconductors and in the presence of transverse exchange field $h$. It is shown that there appear a pair of MFs localized at two junctions and that a reverse in the direction of $h$ can lead to permutation of two MFs. With decreasing $h$, the MF states can either be fused or form one Dirac fermion on the $\pi$-junctions, exhibiting a topological phase transition. This characteristic can be used to detect physical states of MFs when they are transformed into Dirac fermions localized on the $\pi$-junction. A condition of decoupling two MFs is also given.
Synchrotron X-Ray Diffraction Studies on the New Generation Ferromagnetic Semiconductor Li(Zn,Mn)As under High Pressure
Fei Sun, Cong Xu, Shuang Yu, Bi-Juan Chen, Guo-Qiang Zhao, Zheng Deng, Wen-Ge Yang, Chang-Qing Jin
Chin. Phys. Lett.. 2017, 34 (6): 067501 .   DOI: 10.1088/0256-307X/34/6/067501
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The pressure effect on the crystalline structure of the I–II–V semiconductor Li(Zn,Mn)As ferromagnet is studied using in situ high-pressure x-ray diffraction and diamond anvil cell techniques. A phase transition starting at $\sim$11.6 GPa is found. The space group of the high-pressure new phase is proposed as $Pmca$. Fitting with the Birch–Murnaghan equation of state, the bulk modulus $B_{0}$ and its pressure derivative $B'_0$ of the ambient pressure structure with space group of $F\bar{4}3m$ are $B_{0}=75.4$ GPa and $B'_0=4.3$, respectively.
Fast Measurement of Dielectric Conductivity for Space Application by Surface Potential Decay Method
Rong-Hui Quan, Kai Zhou, Mei-Hua Fang, Wei-Ying Chi, Zhen-Long Zhang
Chin. Phys. Lett.. 2017, 34 (6): 067901 .   DOI: 10.1088/0256-307X/34/6/067901
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Surface potential decay of polymers for electrical insulation can help to determine the dark conductivity for spacecraft charging analysis. Due to the existence of radiation-induced conductivity, it decays fast in the first few hours after irradiation and exponentially slowly for the remaining time. The measurement of dark conductivity with this method usually takes the slow part and needs a couple of days. Integrating the Fowler formula into the deep dielectric charging equations, we obtain a new expression for the fast decay part. The experimental data of different materials, dose rates and temperatures are fitted by the new expression. Both the dark conductivity and the radiation-induced conductivity are derived and compared with other methods. The result shows a good estimation of dark conductivity and radiation-induced conductivity in high-resistivity polymers, which enables a fast measurement of dielectric conductivity within about 600 min after irradiation.
CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
Radio-Frequency Characteristics of Partial Dielectric Removal HR-SOI and TR-SOI Substrates
Shi Cheng, Yong-Wei Chang, Nan Gao, Ye-Min Dong, Lu Fei, Xing Wei, Xi Wang
Chin. Phys. Lett.. 2017, 34 (6): 068101 .   DOI: 10.1088/0256-307X/34/6/068101
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High-resistivity silicon-on-insulator (HR-SOI) and trap-rich high-resistivity silicon-on-insulator (TR-SOI) substrates have been widely adopted for high-performance rf integrated circuits. Radio-frequency loss and non-linearity characteristics are measured from coplanar waveguide (CPW) transmission lines fabricated on HR-SOI and TR-SOI substrates. The patterned insulator structure is introduced to reduce loss and non-linearity characteristics. A metal-oxide-semiconductor (MOS) CPW circuit model is established to expound the mechanism of reducing the parasitic surface conductance (PSC) effect by combining the semiconductor characteristic analysis (pseudo-MOS and $C$–$V$ test). The rf performance of the CPW transmission lines under dc bias supply is also compared. The TR-SOI substrate with the patterned oxide structure sample has the minimum rf loss ($ < $0.2 dB/mm up to 10 GHz), the best non-linearity performance, and reductions of 4 dB and 10 dB are compared with the state-of-the-art TR-SOI sample's, HD2 and HD3, respectively. It shows the potential application for integrating the two schemes to further suppress the PSC effect.
Efficient Visible Photoluminescence from Self-Assembled Ge QDs Embedded in Silica Matrix
Alireza Samavati, Zahra Samavati, A. F. Ismail, M. H. D. Othman, M. A. Rahman, A. K. Zulhairun
Chin. Phys. Lett.. 2017, 34 (6): 068102 .   DOI: 10.1088/0256-307X/34/6/068102
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Measuring the growth parameters of Ge quantum dots (QDs) embedded in SiO$_{2}$/Si hetero-structure is pre-requisite for developing the optoelectronic devices such as photovoltaics and sensors. Their optical properties can be tuned by tailoring the growth morphology and structures, where the growth parameters' optimizations still need to be explored. We determine the effect of annealing temperature on surface morphology, structures and optical properties of Ge/SiO$_{2}$/Si hetero-structure. Samples are grown via rf magnetron sputtering and subsequent characterizations are made using imaging and spectroscopic techniques.
A Simple Deposition Method for Self-Assembling Single Crystalline Hybrid Perovskite Nanostructures
Wen-Rong Xie, Bin Liu, Tao Tao, Guo-Gang Zhang, Bao-Hua Zhang, Zi-Li Xie, Peng Chen, Dun-Jun Chen, Rong Zhang
Chin. Phys. Lett.. 2017, 34 (6): 068103 .   DOI: 10.1088/0256-307X/34/6/068103
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A sequential deposition method is developed, where the hybrid organic–inorganic halide perovskite (CH$_{3}$NH$_{3}$Pb (I$_{1-x}$Br$_{x}$)$_{3}$) is synthesized using precursor solutions containing CH$_{3}$NH$_{3}$I and PbBr$_{2}$ with different mole ratios and reaction times. The perovskite achieved here is quite stable in the atmosphere for a relatively long time without noticeable degradation, and the perovskite nanowires are proved to be single crystalline structure, based on transmission electron microscopy. Furthermore, strong red photoluminescence from perovskite is observed in the wavelength range from 746 nm to 770 nm with the increase of the reaction time, on account of the exchanges between I$^{-}$ ions and Br$^{-}$ ions in the perovskite crystal. Lastly, the influences of concentration and reaction time of the precursor solutions are discussed, which are important for evolution of hybrid perovskite from nanocuboid to nanowire and nanosheet.
Allosteric Mechanism of Calmodulin Revealed by Targeted Molecular Dynamics Simulation
Qian-Yun Liang, Chun-Li Pang, Jun-Wei Li, Su-Hua Zhang, Hui Liu, Yong Zhan, Hai-Long An
Chin. Phys. Lett.. 2017, 34 (6): 068701 .   DOI: 10.1088/0256-307X/34/6/068701
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Calmodulin (CaM) is involved in the regulation of a variety of cellular signaling pathways. To accomplish its physiological functions, CaM binds with Ca$^{2+}$ at its EF-hand Ca$^{2+}$ binding sites which induce the conformational switching of CaM. However, the molecular mechanism by which Ca$^{2+}$ binds with CaM and induces conformational switching is still obscure. Here we combine molecular dynamics with targeted molecular dynamics simulation and achieve the state-transition pathway of CaM. Our data show that Ca$^{2+}$ binding speeds up the conformational transition of CaM by weakening the interactions which stabilize the closed state. It spends about 6.5 ns and 5.25 ns for transition from closed state to open state for apo and holo CaM, respectively. Regarding the contribution of two EF-hands, our data indicate that the first EF-hand triggers the conformational transition and is followed by the second one. We determine that there are two interaction networks which contribute to stabilize the closed and open states, respectively.
Enhanced Efficiency of Metamorphic Triple Junction Solar Cells for Space Applications
Du-Xiang Wang, Ming-Hui Song, Jing-Feng Bi, Wen-Jun Chen, Sen-Lin Li, Guan-Zhou Liu, Ming-Yang Li, Chao-Yu Wu
Chin. Phys. Lett.. 2017, 34 (6): 068801 .   DOI: 10.1088/0256-307X/34/6/068801
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Metamorphic In$_{0.55}$Ga$_{0.45}$P/In$_{0.06}$Ga$_{0.94}$As/Ge triple-junction (3J-MM) solar cells are grown on Ge (100) substrates via metal organic chemical vapor deposition. Epi-structural analyses such as high resolution x-ray diffraction, photoluminence, cathodoluminescence and HRTEM are employed and the results show that the high crystal quality of 3J-MM solar cells is obtained with low threading dislocation density of graded buffer (an average value of 6.8$\times$10$^{4}$/cm$^{2})$. Benefitting from the optimized bandgap combination, under one sun, AM0 spectrum, 25$^{\circ}\!$C conditions, the conversion efficiency is achieved about 32%, 5% higher compared with the lattice-matched In$_{0.49}$Ga$_{0.51}$P/In$_{0.01}$Ga$_{0.99}$As/Ge triple junction (3J-LM) solar cell. Under 1-MeV electron irradiation test, the degradation of the EQE and $I$–$V$ characteristics of 3J-MM solar cells is at the same level as the 3J-LM solar cell. The end-of-life efficiency is $\sim$27.1%. Therefore, the metamorphic triple-junction solar cell may be a promising candidate for next-generation space multi-junction solar cells.
Modeling Information Popularity Dynamics via Branching Process on Micro-Blog Network
Jin-Jie Li, Lian-Ren Wu, Jia-Yin Qi, Qi-Ming Sun
Chin. Phys. Lett.. 2017, 34 (6): 068901 .   DOI: 10.1088/0256-307X/34/6/068901
Abstract   PDF(pc) (863KB) ( 259 ) PDF(mobile)(862KB) ( 1 ) HTML  
Predicting and modeling of items popularity on web 2.0 have attracted great attention of many scholars. From the perspective of information competition, we propose a probabilistic model using the branching process to characterize the process in which micro-blogging gains its popularity. The model is analytically tractable and can reproduce several characteristics of empirical micro-blogging data on Sina micro-blog, the most popular micro-blogging system in China. We find that the information competition on micro-blog network leads to the decay of information popularity obeying power law distribution with exponent about 1.5, and the value is similar to the exponent of degree distribution of micro-blog network. Furthermore, the mean popularity is decided by the probability of innovating a new message. Our work presents evidence supporting the idea that two distinct factors affect information popularity: information competition and social network structure.
User Heterogeneity and Individualized Recommender
Qing-Xian Wang, Jun-Jie Zhang, Xiao-Yu Shi, Ming-Sheng Shang
Chin. Phys. Lett.. 2017, 34 (6): 068902 .   DOI: 10.1088/0256-307X/34/6/068902
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Previous works on personalized recommendation mostly emphasize modeling peoples' diversity in potential favorites into a uniform recommender. However, these recommenders always ignore the heterogeneity of users at an individual level. In this study, we propose an individualized recommender that can satisfy every user with a customized parameter. Experimental results on four benchmark datasets demonstrate that the individualized recommender can significantly improve the accuracy of recommendation. The work highlights the importance of the user heterogeneity in recommender design.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
Viscous Modified Chaplygin Gas in Classical and Loop Quantum Cosmology
D. Aberkane, N. Mebarki, S. Benchikh
Chin. Phys. Lett.. 2017, 34 (6): 069801 .   DOI: 10.1088/0256-307X/34/6/069801
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We investigate the cosmological model of viscous modified Chaplygin gas (VMCG) in classical and loop quantum cosmology (LQC). Firstly, we constrain its equation of state parameters in the framework of standard cosmology from Union 2.1 SNe Ia data. Then, we probe the dynamical stability of this model in a universe filled with VMCG and baryonic fluid in LQC background. It is found that the model is very suitable with $(\chi^{2/d.o.f}=0.974)$ and gives a good prediction of the current values of the deceleration parameter $q_{0}=\in(-0.60,-0.57)$ and the effective state parameter $\omega_{\rm eff}\in(-0.76,-0.74)$ that is consistent with the recent observational data. The model can also predict the time crossing when $(\rho_{\rm DE}\approx\rho_{\rm matter})$ at $z=0.75$ and can solve the coincidence problem. In LQC background, the Big Bang singularity found in classical cosmology ceases to exist and is replaced by a bounce when the Hubble parameter vanishes at $\rho_{\rm tot}\approx \rho_{\rm c}$.
34 articles