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Chin. Phys. Lett.  
  Chin. Phys. Lett.--2017, 34 (04)   Published: 21 March 2017
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GENERAL

Round-Robin Differential Phase Shift with Heralded Single-Photon Source

Ying-Ying Zhang, Wan-Su Bao, Chun Zhou, Hong-Wei Li, Yang Wang, Mu-Sheng Jiang
Chin. Phys. Lett. 2017, 34 (04): 040301 doi: 10.1088/0256-307X/34/4/040301
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Round-robin differential phase shift (RRDPS) is a novel quantum key distribution protocol which can bound information leakage without monitoring signal disturbance. In this work, to decrease the effect of the vacuum component in a weak coherent pulses source, we employ a practical decoy-state scheme with heralded single-photon source for the RRDPS protocol and analyze the performance of this method. In this scheme, only two decoy states are needed and the yields of single-photon state and multi-photon states, as well as the bit error rates of each photon states, can be estimated. The final key rate of this scheme is bounded and simulated over transmission distance. The results show that the two-decoy-state method with heralded single-photon source performs better than the two-decoy-state method with weak coherent pulses.

Continuous Variable Quantum Teleportation in Beam-Wandering Modeled Atmosphere Channel

Sheng-Li Zhang, Chen-Hui Jin, Jian-Hong Shi , Jian-Sheng Guo, Xu-Bo Zou, Guang-Can Guo
Chin. Phys. Lett. 2017, 34 (04): 040302 doi: 10.1088/0256-307X/34/4/040302
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We investigate the continuous variable quantum teleportation in atmosphere channels. The beam-wandering model is employed to analyze the teleportation of the unknown single-mode coherent state. Two methods, one is deterministic by increasing the aperture size of the detecting device and one is probabilistic by entanglement distillation, are proposed to improve the teleportation fidelity in the presence of atmosphere noises.

Destroying a Peldan Electrostatic Solution Black Hole

Hao Tang, Yu Song, Rui-Hong Yue, Cheng-Yi Sun
Chin. Phys. Lett. 2017, 34 (04): 040401 doi: 10.1088/0256-307X/34/4/040401
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By throwing a particle with electric charge and angular momentum into the black holes, much evidence shows that the naked singularity of some (3+1)-dimensional black holes might be seen, which is not allowed in the weak cosmic censorship conjecture. In this study, we consider a (2+1)-dimensional Peldan black hole and find that it could be destroyed under certain conditions in both extreme and near-extreme cases.

Wide-Temperature-Range Dielectric Permittivity Measurement under High Pressure

Zhen Yuan, Jin-Long Zhu, Shao-Min Feng, Chang-Chun Wang, Li-Juan Wang, Qing-Qing Liu, Chang-Qing Jin
Chin. Phys. Lett. 2017, 34 (04): 040701 doi: 10.1088/0256-307X/34/4/040701
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Two measurement systems are developed for in-situ dielectric property measurement under high pressure in a wide-temperature range from 77 K to 1273 K. The high-temperature system ranging from room temperature up to 1273 K is equipped with a hexahedron anvils press, while the low-temperature system ranging from liquid nitrogen temperature to normal condition is equipped using the piston cylinder setup with a specially designed sample chamber. Using these configurations, the dielectric property measurement of ferroelectric BaTiO$_{3}$ and multiferroic Tm$_{0.5}$Gd$_{0.5}$MnO$_{3}$ compounds are demonstrated, which proves the validity of the systems through the tuning of the polarization and phase transition boundary by high pressure. These two systems will be equally applicable to a wide variety of electronic and transport property measurements of insulators, semiconductors, as well as battery materials.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

Curvature of Pseudocritical Transition Line for Two-Flavor QCD with Improved Kogut–Susskind Quarks

Liang-Kai Wu, Xiang-Fei Meng, Fa-Ling Zhang
Chin. Phys. Lett. 2017, 34 (04): 041201 doi: 10.1088/0256-307X/34/4/041201
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The results on the curvature of a pseudocritical transition line for two-flavor QCD through lattice simulations are presented. The simulations are carried out with Symanzik-improved gauge action and Asqtad fermion action on a lattice $12^3\times4$ at quark mass $am=0.010$. At the imaginary chemical potentials $a\mu_{_{\rm I}}=0.050$, 0.150, 0.200, 0.225 and 0.250, we investigate the chiral condensate $\bar\psi\psi$, plaquette variable $P$ and imaginary part of Polyakov loop ${\rm Im}(L)$ and their susceptibilities. Analytic continuation from an imaginary chemical potential to a real one is used to obtain the expression for transition temperature as a function of the chemical potential. The curvature is 0.0326(46).
NUCLEAR PHYSICS

Positive $Q$-Value Neutron Transfer Mediated Sub-Barrier Fusion Reactions

Pei-Wei Wen, Zhao-Qing Feng, Fan Zhang, Cheng Li, Cheng-Jian Lin, Feng-Shou Zhang
Chin. Phys. Lett. 2017, 34 (04): 042501 doi: 10.1088/0256-307X/34/4/042501
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Positive $Q$-value neutron transfer mediated sub-barrier fusion reactions are studied with an empirical coupled channels model, which takes into account neutron rearrangement related only to the dynamical matching condition with no free parameters. Fusion cross sections of collision systems $^{32}$S+$^{90,94,96}$Zr are calculated and analyzed. Logarithmic residual enhancement (LRE) is proposed to evaluate the discrepancy between calculated results and experimental data. The experimental data can be described well with this model for the first time as a whole, while the LRE analysis shows that there are still theoretical systematic deviations.
ATOMIC AND MOLECULAR PHYSICS

Two-Photon Excited State Dynamics of Dark Rydberg and Bright Valence States in Furan

Jin-You Long, Chun-Long Hu, Bing Zhang,
Chin. Phys. Lett. 2017, 34 (04): 043101 doi: 10.1088/0256-307X/34/4/043101
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Two-photon absorption in systems with parity permits access to states that cannot be directly prepared by one-photon absorption. Here we investigate ultrafast internal conversion (IC) dynamics of furan by using this strategy in combination with femtosecond time-resolved photoelectron imaging. The dark Rydberg $S_{1}$ and bright valence $S_{2}$ states are simultaneously excited by two photons of 405 nm, and then ionized by two photons of 800 nm. The IC from $S_{2}$ to $S_{1}$ is clearly observed and extracted from the time dependence of the higher photoelectron kinetic energy (PKE) component. More importantly, the internal conversions to hot $S_{0}$ from directly-prepared $S_{1}$ and secondarily-populated $S_{1}$ are unambiguously identified by the time-dependence of the lower PKE component. The average lifetime of the $S_{2}$ and $S_{1}$ states is measured to be 29 fs. The internal conversions of $S_{2}$ to $S_{1}$, $S_{1}$ to hot $S_{0 }$ occur on estimated timescales of 15.4 fs and 38 fs, respectively.

Controlling Three-Dimensional Electron–Electron Correlation via Elliptically Polarized Intense Laser Field

Jian-Xing Hao, Xiao-Lei Hao, Wei-Dong Li, Shi-Lin Hu, Jing Chen
Chin. Phys. Lett. 2017, 34 (04): 043201 doi: 10.1088/0256-307X/34/4/043201
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The three-dimensional electron–electron correlation in an elliptically polarized laser field is investigated based on a semiclassical model. Asymmetry parameter $\alpha$ of the correlated electron momentum distribution is used to quantitatively describe the electron–electron correlation. The dependence of $\alpha$ on ellipticity $\varepsilon$ is totally different in three directions. For the $z$ direction (major polarization direction), $\alpha$ first increases and reaches a maximum at $\varepsilon=0.275$, then it decreases quickly. For the $y$ direction in which the laser field is always absent, the ellipticity has a minor effect, and the asymmetry parameter fluctuates around $\alpha=-0.15$. However, for the $x$ direction (minor polarization direction), $\alpha$ increases monotonously with ellipticity though starts from the same value as in the $y$ direction when $\varepsilon=0$. The behavior of $\alpha$ in the $x$ direction actually indicates a transformation from the Coulomb interaction dominated correlation to the laser field dominated correlation. Therefore, our work provides an efficient way to control the three-dimensional electron–electron correlation via an elliptically polarized intense laser field.
FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)

Radiation Losses in the Microwave X Band in Al-Cr Substituted Y-Type Hexaferrites

D. Basandrai, R. K. Bedi, A. Dhami, J. Sharma, S. B. Narang, K. Pubby, A. K. Srivastava
Chin. Phys. Lett. 2017, 34 (04): 044101 doi: 10.1088/0256-307X/34/4/044101
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We present a study on radiation losses in the microwave X band in Al-Cr substituted Y-type hexaferrites, namely Ba$_2$Mg$_2$Al$_{x/2}$Cr$_{x/2}$Fe$_{12-x}$O$_{22}$ ($x=0$, 0.5 and 1.0). The study is performed by means of a vector network analyzer, Fourier transform infrared spectroscopy, a vibrating sample magnetometer and x-ray powder diffraction. Ba$_2$Mg$_2$Fe$_{12}$O$_{22}$ hexaferrite shows radiation loss of $-$37.25 dB (99.999% loss) at frequency 9.81 GHz, which can be attributed to its high value of saturation magnetization, i.e., 22.08 emu/g. Moreover, we obtain that magnetic properties have strong influence on the radiation losses.

Microfluidic Channel Fabrication Process Utilizing Nd:YVO$_{4}$ Laser-Melting Technique

Ju-Nan Kuo, Jian-Liang Wu
Chin. Phys. Lett. 2017, 34 (04): 044201 doi: 10.1088/0256-307X/34/4/044201
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A simple and repeatable method is proposed for fabricating microfluidic channels on polydimethylsiloxane (PDMS) substrates. In the proposed approach, ridge structures with the required microchannel dimensions are formed on the surface of a borosilicate glass substrate by means of a laser-induced melting process. The patterned substrate is then used as a mold to transfer the microchannel structures to a PDMS layer. Finally, the PDMS layer is aligned with a glass cover plate and is sealed using an oxygen plasma treatment process. The proposed patterning technique is a maskless method, and is thus cheaper and more straightforward than conventional lithography techniques. Moreover, unlike direct laser ablation methods, the proposed method requires significantly less input energy, and therefore minimizes thermal effects such as substrate cracking and distortion. The feasibility of the proposed fabrication method is demonstrated by measuring the capillary filling speed of human blood plasma in microfluidic channels with cross-section sizes of $19.5\times2.5$, $17.0\times1.6$, and $7.6\times1.1$ μm$^{2}$ (width$\times$height), respectively, and temperatures of 4$^\circ\!$C, 25$^\circ\!$C and 37$^\circ\!$C. It is shown that the filling speed reduces with a reducing channel cross-section size, a lower operating temperature, and an increased filling length.

Zinc Oxide-Based Q-Switched Erbium-Doped Fiber Laser

N. A. Aziz, A. A. Latiff, M. Q. Lokman, E. Hanafi, S. W. Harun
Chin. Phys. Lett. 2017, 34 (04): 044202 doi: 10.1088/0256-307X/34/4/044202
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We demonstrate a Q-switched erbium-doped fiber laser (EDFL) using a newly developed zinc oxide- (ZnO) based saturable absorber (SA). The SA is fabricated by embedding a prepared ZnO powder into a poly(vinyl alcohol) film. A small piece of the film is then sandwiched between two fiber ferrules and is incorporated in an EDFL cavity for generating a stable Q-switching pulse train. The EDFL operates at 1560.4 nm with a pump power threshold of 11.8 mW, a pulse repetition rate tunable from 22.79 to 61.43 kHz, and the smallest pulse width of 7.00 μs. The Q-switching pulse shows no spectral modulation with a peak-to-pedestal ratio of 62 dB indicating the high stability of the laser. These results show that the ZnO powder has a great potential to be used for pulsed laser applications.

Passively Q-Switched Yb-Doped Fiber Laser Operating at 1.06μm with Two-Dimensional Silver Nanoplate as Saturable Absorber

Sheng-Gui Fu, Xue-Ying Ouyang, Jin-Jian Li, Xiao-Juan Liu
Chin. Phys. Lett. 2017, 34 (04): 044203 doi: 10.1088/0256-307X/34/4/044203
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A two-dimensional silver nanoplate is prepared with the seed-mediated growth method and is used for achieving pulse fiber laser operation. By controlling the dimension parameters of the silver nanoplate, the surface plasmon resonance absorption peak of the material is successfully adjusted to 1068 nm. Based on the silver nanoplate as a saturable absorber, a passively Q-switched Yb-doped fiber laser operating at 1062 nm is demonstrated. The maximum average output power of 3.49 mW is obtained with a minimum pulse width of 1.84 μs at a pulse repetition rate of 65.7 kHz, and the corresponding pulse energy and peak power are 53.1 nJ and 28.8 mW, respectively.

Spatial-Variant Geometric Phase of Hybrid-Polarized Vector Optical Fields

Yu Si, Ling-Jun Kong, Yu Zhang, Zhi-Cheng Ren, Yue Pan, Chenghou Tu, Yongnan Li, Hui-Tian Wang
Chin. Phys. Lett. 2017, 34 (04): 044204 doi: 10.1088/0256-307X/34/4/044204
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We investigate a novel spatial geometric phase of hybrid-polarized vector fields consisting of linear, elliptical and circular polarizations by Young's two-slit interferometer instead of the widely used Mach–Zehnder interferometer. This spatial geometric phase can be manipulated by engineering the spatial configuration of hybrid polarizations, and is directly related to the topological charge, the local states of polarization and the rotational symmetry of hybrid-polarized vector optical fields. The unique feature of geometric phase has implications in quantum information science as well as other physical systems such as electron vortex beams.

Distance-Coefficient-Based Imaging Accuracy Improving Method Based on the Lamb Wave

Shao-Jie Chen, Shao-Ping Zhou, Yong Li, Yan-Xun Xiang, Min-Xin Qi
Chin. Phys. Lett. 2017, 34 (04): 044301 doi: 10.1088/0256-307X/34/4/044301
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An imaging accuracy improving method is established, within which a distance coefficient including location information between sparse array configuration and the location of defect is proposed to select higher signal-to-noise ratio data from all experimental data and then to use these selected data for elliptical imaging. The relationships among imaging accuracy, distance coefficient and residual direct wave are investigated, and then the residual direct wave is introduced to make the engineering application more convenient. The effectiveness of the proposed method is evaluated experimentally by sparse transducer array of a rectangle, and the results reveal that selecting experimental data of smaller distance coefficient can effectively improve imaging accuracy. Moreover, the direct wave difference increases with the decrease of the distance coefficient, which implies that the imaging accuracy can be effectively improved by using the experimental data of the larger direct wave difference.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Weakly Nonlinear Rayleigh–Taylor Instability in Incompressible Fluids with Surface Tension

Hong-Yu Guo, Li-Feng Wang, Wen-Hua Ye, Jun-Feng Wu, Wei-Yan Zhang
Chin. Phys. Lett. 2017, 34 (04): 045201 doi: 10.1088/0256-307X/34/4/045201
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A weakly nonlinear model is established for incompressible Rayleigh–Taylor instability with surface tension. The temporal evolution of a perturbed interface is explored analytically via the third-order solution. The dependence of the first three harmonics on the surface tension is discussed. The amplitudes of bubble and spike are greatly affected by surface tension. The saturation amplitude of the fundamental mode versus the Atwood number $A$ is investigated with surface tension into consideration. The saturation amplitude decreases with increasing $A$. Surface tension exhibits a stabilizing phenomenon. It is shown that the asymmetrical development of the perturbed interface occurs much later for large surface tension effect.
CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES

A New View of Incipient Plastic Instability during Nanoindentation

Jian-Qiao Hu, Zhan-Li Liu, Yi-Nan Cui, Feng-Xian Liu, Zhuo Zhuang
Chin. Phys. Lett. 2017, 34 (04): 046101 doi: 10.1088/0256-307X/34/4/046101
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Whether the dislocation nucleation or the sudden dislocation multiplication dominates the incipient plastic instability during the nanoindentation of initial defect-free single crystal still remains unclear. In this work, the dislocation mechanism corresponding to the incipient plastic instability is numerically investigated by coupling discrete dislocation dynamics with the finite element method. The coupling model naturally introduces the dislocation nucleation and accurately captures the heterogeneous stress field during nanoindentation. The simulation results show that the first dislocation nucleation induces the initial pop-in event when the indenter is small, while for larger indenters, the incipient plastic instability is ascribed to the cooperation between dislocation nucleation and multiplication. Interestingly, the local dislocation densities for both cases are almost the same when the sudden load drop occurs. Thus it is inferred that the adequate dislocations generated by either nucleation or multiplication, or both, are the requirement for the trigger of incipient plastic instability. A unified dislocation-based mechanism is proposed to interpret the precipitate incipient plastic instability.

Pressure Effects on the Charge Carrier Transportation of BaF$_{2}$ Nanocrystals

Xiao-Yan Cui, Ting-Jing Hu, Jing-Shu Wang, Jun-Kai Zhang, Xue-Fei Li, Jing-Hai Yang, Chun-Xiao Gao
Chin. Phys. Lett. 2017, 34 (04): 046401 doi: 10.1088/0256-307X/34/4/046401
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The charge transport behavior of barium fluoride nanocrystals is investigated by in situ impedance measurement up to 35 GPa. It is found that the parameters change discontinuously at about 6.9 GPa, corresponding to the phase transition of BaF$_{2}$ nanocrystals under high pressure. The charge carriers in BaF$_{2}$ nanocrystals include both F$^{-}$ ions and electrons. Pressure makes the electronic transport more difficult. The defects at grains dominate the electronic transport process. Pressure could make the charge–discharge processes in the $Fm3m$ phase more difficult.

Simulation Study on the Controllable Dielectrophoresis Parameters of Graphene

Jian-Long Ji, Ya-Li Liu, Yang Ge, Sheng-Dong Xie, Xi Zhang, Sheng-Bo Sang, Ao-Qun Jian, Qian-Qian Duan, Qiang Zhang, Wen-Dong Zhang
Chin. Phys. Lett. 2017, 34 (04): 046601 doi: 10.1088/0256-307X/34/4/046601
Full Text: [PDF 668 KB] (Downloads:5)
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The method of using dielectrophoresis (DEP) to assemble graphene between micro-electrodes has been proven to be simple and efficient. We present an optimization method for the kinetic formula of graphene DEP, and discuss the simulation of the graphene assembly process based on the finite element method. The simulated results illustrate that the accelerated motion of graphene is in agreement with the distribution of the electric field squared gradient. We also conduct research on the controllable parameters of the DEP assembly such as the alternating current (AC) frequency, the shape of micro-electrodes, and the ratio of the gap between electrodes to the characteristic/geometric length of graphene ($\lambda$). The simulations based on the Clausius–Mossotti factor reveal that both graphene velocity and direction are influenced by the AC frequency. When graphene is close to the electrodes, the shape of micro-electrodes will exert great influence on the velocity of graphene. Also, $\lambda$ has a great influence on the velocity of graphene. Generally, the velocity of graphene would be greater when $\lambda$ is in the range of 0.4–0.6. The study is of a theoretical guiding significance in improving the precision and efficiency of the graphene DEP assembly.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Highly Sensitive Detection of Deoxyribonucleic Acid Hybridization Using Au-Gated AlInN/GaN High Electron Mobility Transistor-Based Sensors

Xiang-Mi Zhan, Mei-Lan Hao, Quan Wang, Wei Li, Hong-Ling Xiao, Chun Feng, Li-Juan Jiang, Cui-Mei Wang, Xiao-Liang Wang, Zhan-Guo Wang
Chin. Phys. Lett. 2017, 34 (04): 047301 doi: 10.1088/0256-307X/34/4/047301
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Gallium nitride- (GaN) based high electron mobility transistors (HEMTs) provide a good platform for biological detection. In this work, both Au-gated AlInN/GaN HEMT and AlGaN/GaN HEMT biosensors are fabricated for the detection of deoxyribonucleic acid (DNA) hybridization. The Au-gated AlInN/GaN HEMT biosensor exhibits higher sensitivity in comparison with the AlGaN/GaN HEMT biosensor. For the former, the drain-source current ($V_{\rm DS}=0.5$ V) shows a clear decrease of 69 $\mu$A upon the introduction of 1 $\mu$molL$^{-1}$ ($\mu$M) complimentary DNA to the probe DNA at the sensor area, while for the latter it is only 38 $\mu$A. This current reduction is a notable indication of the hybridization. The high sensitivity can be attributed to the thinner barrier of the AlInN/GaN heterostructure, which makes the two-dimensional electron gas channel more susceptible to a slight change of the surface charge.

Magnetic Transport Properties of Fe-Phthalocyanine Dimer with Carbon Nanotube Electrodes

Yu-Zhuo Lv, Peng Zhao, De-Sheng Liu
Chin. Phys. Lett. 2017, 34 (04): 047302 doi: 10.1088/0256-307X/34/4/047302
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Based on the non-equilibrium Green's method and density functional theory, the magnetic transport of Fe-phthalocyanine dimers with two armchair single-walled carbon nanotube electrodes is investigated. The results show that the system can present high-performance spin filtering, magnetoresistance, and low-bias spin negative differential resistance effects by tuning the external magnetic field. These results show that the Fe-phthalocyanine dimer has the potential to design future molecular spintronic devices.

Interfacial and Electrical Properties of GaAs Metal-Oxide-Semiconductor Capacitor with ZrAlON as the Interfacial Passivation Layer

Han-Han Lu, Jing-Ping Xu, Lu Liu
Chin. Phys. Lett. 2017, 34 (04): 047303 doi: 10.1088/0256-307X/34/4/047303
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The ZrTiON gate-dielectric GaAs metal-oxide-semiconductor (MOS) capacitors with or without ZrAlON as the interfacial passivation layer (IPL) are fabricated and their properties are investigated. The experimental results show that the GaAs MOS capacitor with the ZrAlON IPL exhibits better interfacial and electrical properties, including lower interface-state density ($1.14\times10^{12}$ cm$^{-2}$eV$^{-1})$, smaller gate leakage current ($6.82\times10^{-5}$ A/cm$^{2}$ at $V_{\rm fb}$+1 V), smaller capacitance equivalent thickness (1.5 nm), and larger $k$ value (26). The involved mechanisms lie in the fact that the ZrAlON IPL can effectively block the diffusion of Ti and O towards the GaAs surface, thus suppressing the formation of interfacial Ga-/As-oxides and As-As dimers, which leads to improved interfacial and electrical properties for the devices.

Electrically Tunable Energy Bandgap in Dual-Gated Ultra-Thin Black Phosphorus Field Effect Transistors Hot!

Shi-Li Yan, Zhi-Jian Xie, Jian-Hao Chen, Takashi Taniguchi, Kenji Watanabe
Chin. Phys. Lett. 2017, 34 (04): 047304 doi: 10.1088/0256-307X/34/4/047304
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The energy bandgap is an intrinsic character of semiconductors, which largely determines their properties. The ability to continuously and reversibly tune the bandgap of a single device during real time operation is of great importance not only to device physics but also to technological applications. Here we demonstrate a widely tunable bandgap of few-layer black phosphorus (BP) by the application of vertical electric field in dual-gated BP field-effect transistors. A total bandgap reduction of 124 meV is observed when the electrical displacement field is increased from 0.10 V/nm to 0.83 V/nm. Our results suggest appealing potential for few-layer BP as a tunable bandgap material in infrared optoelectronics, thermoelectric power generation and thermal imaging.

Electrical Transport Properties of Type-VIII Sn-Based Single-Crystalline Clathrates (Eu/Ba)$_{8}$Ga$_{16}$Sn$_{30}$ Prepared by Ga Flux Method

Shu-Ping Deng, Feng Cheng, De-Cong Li, Yu Tang, Zhong Chen, Lan-Xian Shen, Hong-Xia Liu, Pei-Zhi Yang, Shu-Kang Deng
Chin. Phys. Lett. 2017, 34 (04): 047401 doi: 10.1088/0256-307X/34/4/047401
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Single-crystalline samples of Eu/Ba-filled Sn-based type-VIII clathrate are prepared by the Ga flux method with different stoichiometric ratios. The electrical transport properties of the samples are optimized by Eu doping. Results indicate that Eu atoms tend to replace Ba atoms. With the increase of the Eu initial content, the carrier density increases and the carrier mobility decreases, which leads to an increase of the Seebeck coefficient. By contrast, the electrical conductivity decreases. Finally, the sample with Eu initial content of $x=0.75$ behaves with excellent electrical properties, which shows a maximal power factor of 1.51 mW$\cdot$m$^{-1}$K$^{-2}$ at 480 K, and the highest $ZT$ achieved is 0.87 near the temperature of 483 K.

Periodic Boundary Conditions for Finite-Differentiation-Method Fast-Fourier-Transform Micromagnetics

Jiang-Nan Li, Dan Wei,
Chin. Phys. Lett. 2017, 34 (04): 047501 doi: 10.1088/0256-307X/34/4/047501
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We describe an accurate periodic boundary condition (PBC) called the symmetric PBC in the calculation of the magnetostatic interaction field in the finite-differentiation-method fast-Fourier-transform (FDM-FFT) micromagnetics. The micromagnetic cells in the regular mesh used by the FDM-FFT method are finite-sized elements, but not geometrical points. Therefore, the key PBC operations for FDM-FFT methods are splitting and relocating the micromagnetic cell surfaces to stay symmetrically inside the box of half-total sizes with respect to the origin. The properties of the demagnetizing matrix of the split micromagnetic cells are discussed, and the sum rules of demagnetizing matrix are fulfilled by the symmetric PBC.

Simulation of $M$–$H$ Loops in FeCo Polycrystalline Thin Films at Finite Temperatures

Long-Ze Wang, Jiang-Nan Li, Jun-Jie Song, Chuan Liu, Dan Wei
Chin. Phys. Lett. 2017, 34 (04): 047502 doi: 10.1088/0256-307X/34/4/047502
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We apply the hybrid Monte Carlo (HMC) micromagnetic method to FeCo soft magnetic polycrystalline films and test the new method by comparing with the result worked out by micromagnetics using Landau–Lifshitz–Gilbert equations, and the magnetic properties of FeCo films are understood better by carefully considering the effects of polycrystalline microstructures. The hysteresis loops of the FeCo film from low temperature up to 1100 K are simulated by the new HMC micromagnetic method.

Photoluminescence Characteristics of ZnCuInS-ZnS Core-Shell Semiconductor Nanocrystals

Qiu-Lin Zhong, Ming-Rui Tan, Qing-Hui Liu, Ning Sui, Ke Bi, Mou-Cui Ni, Ying-Hui Wang, Han-Zhuang Zhang
Chin. Phys. Lett. 2017, 34 (04): 047801 doi: 10.1088/0256-307X/34/4/047801
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The photoluminescence (PL) characteristics of ZnCuInS quantum dots (QDs) with varying ZnS shell thicknesses of 0, 0.5, and 1.5 layers are investigated systemically by time-correlated single-photon counting measurements and temperature-dependent PL measurements. The results show that a ZnS shell thickness of 1.5 layers can effectively improve the PL quantum yield in one order of magnitude by depressing the surface trapping states of the core ZnCuInS QDs at room temperature. However, the PL measurements at the elevated temperature reveal that the core-shell nanocrystals remain temperature-sensitive with respect to their relatively thin shells. The temperature sensitivity of these small-sized single-layered core-shell nanocrystals may find applications as effective thermometers for the in vivo detection of biological reactions within cells.
CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

High-Quality and Strain-Relaxation GaN Epilayer Grown on SiC Substrates Using AlN Buffer and AlGaN Interlayer

Bo-Ting Liu, Shi-Kuan Guo, Ping Ma, Jun-Xi Wang, Jin-Min Li
Chin. Phys. Lett. 2017, 34 (04): 048101 doi: 10.1088/0256-307X/34/4/048101
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We study the effect of the AlGaN interlayer on structural quality and strain engineering of the GaN films grown on SiC substrates with an AlN buffer layer. Improved structural quality and tensile stress releasing are realized in unintentionally doped GaN thin films grown on 6H–SiC substrates by metal organic chemical vapor deposition. Using the optimized AlGaN interlayer, we find that the full width at half maximum of x-ray diffraction peaks for GaN decreases dramatically, indicating an improved crystalline quality. Meanwhile, it is revealed that the biaxial tensile stress in the GaN film is significantly reduced from the Raman results. Photoluminescence spectra exhibit a shift of the peak position of the near-band-edge emission, as well as the integrated intensity ratio variation of the near-band-edge emission to the yellow luminescence band. Thus by optimizing the AlGaN interlayer, we could acquire the high-quality and strain-relaxation GaN epilayer with large thickness on SiC substrates.

Kinetics of Spherical Interface in Crystal Growth

Mei-Qin Fu, Qing-Ling Bi, Yong-Jun Lü
Chin. Phys. Lett. 2017, 34 (04): 048102 doi: 10.1088/0256-307X/34/4/048102
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The growth kinetics of spherical NiAl and CuZr crystals are studied by using molecular dynamics simulations. The growth rates of crystals are found to increase with the grain radius. The simulations show that the interface thickness and the Jackson $\alpha$-factor increase as the growth proceeds, indicating that the interface becomes increasingly rough during growth. Due to the increasing interface roughening, the fraction of repeatable growth sites at interface $f$ is proposed to actually increase in growth. An attachment rate, which is defined as the fraction of atoms that join the crystal interface without leaving, is used to approximate $f$, displaying a linear increase. With this approximation, we predict the growth rates as a function of the crystal radius, and the results qualitatively agree with those from the direct simulations.

Research of Trap and Electron Density Distributions in the Interface of Polyimide/Al$_{2}$O$_{3}$ Nanocomposite Films Based on IDC and SAXS

Yuan-Yuan Liu, Jing-Hua Yin, Xiao-Xu Liu, Duo Sun, Ming-Hua Chen, Zhong-Hua Wu, Bo Su
Chin. Phys. Lett. 2017, 34 (04): 048201 doi: 10.1088/0256-307X/34/4/048201
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The distributions of traps and electron density in the interfaces between polyimide (PI) matrix and Al$_{2}$O$_{3}$ nanoparticles are researched using the isothermal decay current and the small-angle x-ray scattering (SAXS) tests. According to the electron density distribution for quasi two-phase mixture doped by spherical nanoparticles, the electron densities in the interfaces of PI/Al$_{2}$O$_{3}$ nanocomposite films are evaluated. The trap level density and carrier mobility in the interface are studied. The experimental results show that the distribution and the change rate of the electron density in the three layers of interface are different, indicating different trap distributions in the interface layers. There is a maximum trap level density in the second layer, where the maximum trap level density for the nanocomposite film doped by 25 wt% is $1.054\times10^{22}$ eV$\cdot$m$^{-3}$ at 1.324 eV, resulting in the carrier mobility reducing. In addition, both the thickness and the electron density of the nanocomposite film interface increase with the addition of the doped Al$_{2}$O$_{3}$ contents. Through the study on the trap level distribution in the interface, it is possible to further analyze the insulation mechanism and to improve the performance of nano-dielectric materials.

Information Capacity and Transmission in a Courbage–Nekorkin–Vdovin Map-Based Neuron Model

Yuan Yue, Yu-Jiang Liu, Ya-Lei Song, Yong Chen, Lian-Chun Yu
Chin. Phys. Lett. 2017, 34 (04): 048701 doi: 10.1088/0256-307X/34/4/048701
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The map-based neuron models have received attention as valid phenomenological neuron models due to their computational efficiency and flexibility to generate rich patterns. Here we evaluate the information capacity and transmission of the Courbage–Nekorkin–Vdovin (CNV) map-based neuron model with a bursting and tonic firing mode in response to external pulse inputs, in both temporal and rate coding schemes. We find that for both firing modes, the CNV model could capture the essential behavior of the stochastic Hodgkin–Huxley model in information transmission for the temporal coding scheme, with regard to the dependence of total entropy, noise entropy, information rate, and coding efficiency on the strength of the input signal. However, in tonic firing mode, it fails to replicate the input strength-dependent information rate in the rate coding scheme. Our results suggest that the CNV map-based neuron model could capture the essential behavior of information processing of typical conductance-based neuron models.

Auditory Hopf Amplification Revealed by an Energy Method

Lin Tian, Zhang-Cai Long
Chin. Phys. Lett. 2017, 34 (04): 048702 doi: 10.1088/0256-307X/34/4/048702
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We report on the auditory Hopf amplification contributed by the electrical energy of the hair cell during its bundle deflecting. An energy method to calculate the active force is adopted according to the electrical energy consumption of the hair cell. After some experimental data was analyzed and simulated, we find that the electrical energy determines the value of the active force and enlarges the mechanical response of the hair bundle. This amplification is controlled by the cell voltage and makes the sensor a Hopf vibrator with hearing nonlinear characteristics. A velocity-dependent active force derived previously from the force-gating channel operation strongly reinforces our conclusion.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

Nucleosynthesis in Advection-Dominated Accretion Flow onto a Black Hole

Jiang Zhang, Ren-Yi Ma, Hong-Jie Li, Bo Zhang
Chin. Phys. Lett. 2017, 34 (04): 049701 doi: 10.1088/0256-307X/34/4/049701
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Nucleosynthesis in advection-dominated accretion flow (ADAF) onto a black hole is proposed to be an important role in chemical evolution around compact stars. We investigate the nucleosynthesis in ADAF relevant for a black hole of low mass, different from that of the self-similar solution. In particular, the presence of supersolar metal mass fractions of some isotopes seems to be associated with the known black hole nucleosynthesis in ADAF, which offers further evidence of diversity of the chemical enrichment.
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