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Chin. Phys. Lett.  
  Chin. Phys. Lett.--2016, 33 (02)   Published: 27 January 2016
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The $SO(3,1)$-Gauge Invariant Approach to Fermions on Rindler Spacetime

Ciprian Dariescu, Marina-Aura Dariescu
Chin. Phys. Lett. 2016, 33 (02): 020201 doi: 10.1088/0256-307X/33/2/020201
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We try to explicitly derive the Lorentz-gauge covariant Dirac equation, in terms of pseudo-orthonormal bases, on Rindler spacetime and to work out, with all the necessary coefficients, the respective closed-form solutions, in both Dirac and Weyl representations.

Giant Enhancement of Diffusion in a Tilted Egg-Carton Potential

Yang Song, Jing-Dong Bao
Chin. Phys. Lett. 2016, 33 (02): 020202 doi: 10.1088/0256-307X/33/2/020202
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Diffusion of a particle on a tilted periodic surface such as the egg-carton potential is investigated using Langevin Monte Carlo simulations. It is found that the effective diffusion coefficient of the particle related to the one-dimensional case can be greatly enhanced, when the local minima of such potential along the $x$ and $y$ directions are close to vanishing. A relation between the group diffusion and the phase diffusion is used to analyze the enhancement mechanism of the diffusion.

Scalable Quantum Information Transfer between Individual Nitrogen-Vacancy Centers by a Hybrid Quantum Interface

Pei Pei, He-Fei Huang, Yan-Qing Guo, He-Shan Song
Chin. Phys. Lett. 2016, 33 (02): 020301 doi: 10.1088/0256-307X/33/2/020301
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We develop a design of a hybrid quantum interface for quantum information transfer (QIT), adopting a nanomechanical resonator as the intermedium, which is magnetically coupled with individual nitrogen-vacancy centers as the solid qubits, while capacitively coupled with a coplanar waveguide resonator as the quantum data bus. We describe the Hamiltonian of the model, and analytically demonstrate the QIT for both the resonant interaction and large detuning cases. The hybrid quantum interface allows for QIT between arbitrarily selected individual nitrogen-vacancy centers, and has advantages of the scalability and controllability. Our methods open an alternative perspective for implementing QIT, which is important during quantum storing or processing procedures in quantum computing.

Transportation of Two Coupled Particles in an Asymmetric Saw-Tooth Potential

Ling-Wei Kong, Rong-Zheng Wan, Hai-Ping Fang
Chin. Phys. Lett. 2016, 33 (02): 020501 doi: 10.1088/0256-307X/33/2/020501
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Based on a simple model, we theoretically show the transport behaviors of two harmonically coupled Brownian particles in an asymmetric saw-tooth potential with two slopes. The coupled particles are subject to stochastic fluctuations. It is found that when the equilibrium distance of the coupled particles is between the two slopes of the potential, the transport direction of the coupled particles will be reversed with a certain harmonic coupling strength. This current reversal can be easily understood with the near rigid approximation, where the two coupled particles can be regarded as a single particle in an effective potential. Compared with the original saw-tooth potential, the asymmetry of the effective potential could be reversed when the equilibrium distance is between the two slopes of the original potential, which results in the current reversal.

Electronic States of Difluorocarbene Calculated by Multireference Configuration Interaction Method

Er-Ping Sun, Ting-Qi Ren, Qi-Xin Liu, Quan Miao, Jin-Juan Zhang, Hai-Feng Xu, Bing Yan
Chin. Phys. Lett. 2016, 33 (02): 023101 doi: 10.1088/0256-307X/33/2/023101
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We investigate the geometries and energies of seven electronic states $\tilde {X}$$^{1}\!A_{1}$, $\tilde {A}$$^{1}\!B_{1}$, $\tilde {a}$$^{3}\!B_{1}$, $\tilde {B}$$^{1}\!A_{2}$, $\tilde {b}$$^{3}\!A_{2}$, $\tilde {C}$$^{1}\!B_{2}$ and $\tilde {c}$$^{3}\!B_{2}$ of CF$_{2}$ carbene using internally contracted multireference configuration interaction methods including Davidson correction (icMRCI+Q) with different basis sets aug-cc-pVXZ (X=T, Q, 5). For the first time, the potential energy curves of electronic states of CF$_{2}$ related to the lowest dissociation limit are calculated at the icMRCI+Q/aug-cc-pVTZ level. The ab initio results will further increase our understanding of the structures and dynamics of electronic states of CF$_{2}$ radical.

Molecular Application of a State Specific Multi-Reference Brillouin–Wigner Perturbation Theory

H. Aksu
Chin. Phys. Lett. 2016, 33 (02): 023102 doi: 10.1088/0256-307X/33/2/023102
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The single reference second order Brillouin–Wigner perturbation theory recently developed, which eliminates its size-extensivity error, has been generalized to state-specific, multi-reference (SS-MR), BWPT2 providing a size-extensive correction to the electron correlation problem for systems that demand the use of a multi-reference function. Illustrative numerical tests of the size-extensivity corrections are made for widely used molecules in their ground states, which are pronounced multi-reference characteristics. We have implemented two-reference and three-reference cases for CH$_{2}$, BH and bond breaking process in the ground states of HF molecules. The results are compared with the rigorously size-extensive methods such as the Møller–Plesset perturbation theory, i.e., MP2, full configuration interaction (Full-CI) and allied methods using the same basis sets.

Two-Photon Transitions of $^{85}$Rb 5$D_{5/2}$ State by Using an Optical Frequency Comb and a Continuous-Wave Laser

Shu-Kai Cao, Peng-Rui Fan, Yi-Chi Zhang, Li-Rong Wang, Lian-Tuan Xiao, Suo-Tang Jia
Chin. Phys. Lett. 2016, 33 (02): 023201 doi: 10.1088/0256-307X/33/2/023201
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A high-resolution two-photon spectrum of 5$S_{1/2}\to5P_{3/2}\to5D_{5/2}$ transitions in a thermal $^{85}$Rb vapor cell is presented by using an optical frequency comb and a cw laser. The fluorescence of 6$P_{3/2}\to5S_{1/2}$ spontaneous emission is detected when the cw laser frequency is scanned from the 5$S_{1/2}$ ground state to 5$P_{3/2}$ hyperfine levels and the optical frequency comb repetition rate is fixed. The hyperfine splittings ($F_{\rm f}=2$–5) of the 5$D_{5/2}$ excited state are well resolved. The dependences of fluorescence intensities on the cw laser intensity and temperature of $^{85}$Rb vapor cell are studied, respectively. The experimental results are in good agreement with the theoretical analyses.

High-Power Passively Q-Switched Nd:YAG Laser at 1112nm with a Cr$^{4+}$:YAG Saturable Absorber

Yang-Yang Dun, Ping Li, Xiao-Han Chen, Bao-Min Ma
Chin. Phys. Lett. 2016, 33 (02): 024201 doi: 10.1088/0256-307X/33/2/024201
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A high-power passively Q-switched Nd:YAG laser operating at 1112 nm with Cr$^{4+}$:YAG as a saturable absorber is demonstrated. Under 808 nm diode-direct pumping, the maximum average output power of 2.73 W is achieved at the pump power of 16.65 W, corresponding to an optical-to-optical conversion efficiency of 16.4%. At the same time, the pulse width, pulse repetition rate, single pulse energy and peak power are 27.2 ns, 9 kHz, 303.3 µJ and 11.2 kW, respectively. As far as we know, the result gives the highest average output power at 1112 nm generated by an 808 nm diode-end-pumped Nd:YAG laser.

Generating Squeezed States of Nanomechanical Resonator via a Flux Qubit in a Hybrid System

Chao-Quan Wang, Jian Zou, Zhi-Ming Zhang
Chin. Phys. Lett. 2016, 33 (02): 024202 doi: 10.1088/0256-307X/33/2/024202
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We propose a scheme for generating squeezed states based on a superconducting hybrid system. Our system consists of a nanomechanical resonator, a superconducting flux qubit, and a superconducting transmission line resonator. Using our proposal, one can easily generate the squeezed states of the nanomechanical resonator. In our scheme, the nonlinear interaction between the nanomechanical resonator and the superconducting transmission line resonator can be implemented by the flux qubit as 'nonlinear media' with a tunable Josephson energy. The realization of the nonlinearity does not need any operations on the flux qubit and just needs to adiabatically keep it at the ground state, which can greatly decrease the effect of the decoherence of the flux qubit on the squeezed efficiency.

Two-Mode Converters at 1.3µm Based on Multimode Interference Couplers on InP Substrates

Fei Guo, Dan Lu, Rui-Kang Zhang, Hui-Tao Wang, Wei Wang, Chen Ji
Chin. Phys. Lett. 2016, 33 (02): 024203 doi: 10.1088/0256-307X/33/2/024203
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Two-mode converters at 1.3 µm, aiming at applications in mode-division multiplexing in Ethernet systems, are proposed and experimentally demonstrated. Based on multimode interference couplers, the two-mode converters with 50% and 66% mode conversion efficiencies are designed and fabricated on InP substrates. Mode conversion from the fundamental mode (TE$_{0})$ to the first order mode (TE$_{1})$ is successfully demonstrated within the wavelength range of 1280–1320 nm. The 1.3-µm mode converters should be important devices in mode-division multiplexing systems in Ethernet systems.

Numerical Evaluation of Effect of Motion of Samples on Ptychographic Imaging and Solution with a Random Phase Modulator

Zhao-Hui Li, Jian-Qi Zhang, De-Lian Liu, Xiao-Rui Wang
Chin. Phys. Lett. 2016, 33 (02): 024204 doi: 10.1088/0256-307X/33/2/024204
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The retrieval of ptychographical imaging encounters a degradation produced by motion of samples. The mechanism of capturing the diffractive patterns of a sample which is motile is simulated numerically. The relation between the retrieval degradation and the amplitude of motion is evaluated quantitatively. Experiments indicate that the reliability and resolution of the complex amplitude retrieval of a sample is inversely proportional to its vibratory amplitude. A random phase modulated aperture is employed to cure the degradation produced by the motion of samples to a certain extent.

Single Photon Scattering in a Pair of Waveguides Coupled by a Whispering-Gallery Resonator Interacting with a Semiconductor Quantum Dot

Mu-Tian Cheng, Gen-Long Ye, Wei-Wei Zong, Xiao-San Ma
Chin. Phys. Lett. 2016, 33 (02): 024205 doi: 10.1088/0256-307X/33/2/024205
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The single photon scattering properties in a pair of waveguides coupled by a whispering-gallery resonator interacting with a semiconductor quantum dot are investigated theoretically. The two waveguides support four possible ports for an incident single photon. The quantum dot is considered a V-type system. The incident direction-dependent single photon scattering properties are studied and equal-output probability from the four ports for a single photon incident is discussed. The influences of backscattering between the two modes of the whispering-gallery resonator for incident direction-dependent single photon scattering properties are also presented.

Anomalous Variation of Beat Frequency in a Dual Frequency He–Ne Laser

Wei-Xin Liu, Ming-Zhe Sun
Chin. Phys. Lett. 2016, 33 (02): 024206 doi: 10.1088/0256-307X/33/2/024206
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The beat frequency in a dual frequency He–Ne laser varies while the resonant cavity length is tuned. As to the laser with two longitudinal modes, the variation amplitude is commonly less than 500 kHz, proven by experiments and theories. This study reveals an anomalous variation of the beat frequency when a piece of element is put into the cavity and is aligned with the laser axis. Consequently the variation amplitude could reach 22 MHz, several dozen times larger than that without the intra-cavity element. This cannot be explained only by laser mode pulling and pushing effects. Some influencing factors are investigated experimentally, including the tilted angle of the element and the distance between its surface and cavity mirror. The qualitative analysis is discussed, which agrees with the experimental results.

A Broadband Pulsed External-Cavity Quantum Cascade Laser Operating near 6.9µm

Wei Luo, Chuan-Xi Duan
Chin. Phys. Lett. 2016, 33 (02): 024207 doi: 10.1088/0256-307X/33/2/024207
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We report an external cavity quantum cascade laser (EC-QCL) operating near 6.9 µm using the Littman–Metcalf configuration. The EC-QCL works in a pulsed mode and can be tuned continuously from 1340 to 1640 cm$^{-1}$ by only tilting the tuning mirror. The fine tuning ability of the EC-QCL is demonstrated by measuring the absorption spectrum of water in the ambient air with a lock-in amplifier.

Effect of Quench Treatment on Fe/Mo Order and Magnetic Properties of Double Perovskite Sr$_{2}$FeMoO$_{6}$

Yan-Chun Hu, Ya-Wen Cui, Xian-Wei Wang, Yi-Pu Liu
Chin. Phys. Lett. 2016, 33 (02): 026101 doi: 10.1088/0256-307X/33/2/026101
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A quench-treatment technique is used to prepare a high-quality polycrystalline sample of double perovskite Sr$_{2}$FeMoO$_{6}$ (SFMO). X-ray powder diffraction analysis reveals that the sample has a single phase and exhibits I4/m symmetry. The cation order $\eta$ of the sample increases to 98.9(2)% from 94.2(3)%, which is prepared by the traditional sol-gel method. The initial magnetization isotherm of the sample is detected at 300 K. Unit-cell magnetization for the current sample is 1.332 $\mu_{\rm B}$ at 300 K, and the one for the traditional sol-gel method sample is 0.946 $\mu_{\rm B}$. Unit-cell magnetization is enhanced to 40.80% by the quench-treatment technique. Quench treatment is an effective method of enhancing the Fe/Mo order and magnetic properties of double perovskite SFMO.

Atomistic Simulations of the Effect of Helium on the Dissociation of Screw Dislocations in Nickel

Jian Xu, Cheng-Bin Wang, Wei Zhang, Cui-Lan Ren, Heng-Feng Gong, Ping Huai
Chin. Phys. Lett. 2016, 33 (02): 026102 doi: 10.1088/0256-307X/33/2/026102
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The interactions of He with dissociated screw dislocations in face-centered-cubic (fcc) Ni are investigated by using molecular dynamics simulations based on an embedded-atom method model. The binding and formation energies of interstitial He in and near Shockley partial cores are calculated. The results show that interstitial He atoms at tetrahedral sites in the perfect fcc lattice and atoms occupying sites one plane above or below one of the two Shockley partial cores exhibit the strongest binding energy. The attractive or repulsive nature of the interaction between interstitial He and the screw dislocation depends on the relative position of He to these strong binding sites. In addition, the effect of He on the dissociation of screw dislocations are investigated. It is found that He atoms homogeneously distributed in the glide plane can reduce the stacking fault width.

Supersaturating Silicon with Titanium by Continuous-Wave Laser Irradiation of Sputtered Titanium Film on Silicon

Bao-Dian Fan, Yu Qiu, Rong Chen, Miao Pan, Li-Han Cai, Jiang-Hui Zheng, Chao Chen
Chin. Phys. Lett. 2016, 33 (02): 026103 doi: 10.1088/0256-307X/33/2/026103
Full Text: [PDF 547 KB] (10)
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A method of magnetron sputtering followed by continuous-wave (cw) laser irradiation is developed to prepare crystalline silicon supersaturated with titanium. The irradiation of single crystalline Si samples sputtered with a thin layer of Ti is carried out under the 1064 nm cw laser in a specially designed home-made facility. The thickness of the Si layer, within which the concentration of Ti surpasses the Mott limit, reaches 365 nm and the maximum concentration of Ti reaches $1.83\times10^{21}$ cm$^{-3}$. The crystalline structure of the Si samples is kept unchanged after cw laser irradiation. These results show that the current method can be an efficient way to obtain an intermediate band semiconductor material for solar cells.

The Stable or Metastable Phases in Compressed Zn-O Systems

Guang-Lin Sun, Hong-Mei Huang, Yan-Ling Li
Chin. Phys. Lett. 2016, 33 (02): 026104 doi: 10.1088/0256-307X/33/2/026104
Full Text: [PDF 1276 KB] (32)
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Variable-composition evolutionary structure searches are used to explore stable stoichiometries for the Zn-O system below 300 GPa. Our results confirm the previous structural phase transition sequence of pressurised ZnO. ZnO is thermodynamically stable up to 300 GPa and zinc peroxide (ZnO$_{2}$, space group $Pa\bar{3}$) is metastable under lower pressure. Insulating $I4/mcm$-ZnO$_{2}$ is thermodynamically stable between 128.3–300 GPa. Insulated metastable $P3_{1}21$-ZnO$_{2}$, controlling the pressure range of 51.5–128.3 GPa, has a wide band gap compared to the $Pa\bar{3}$-ZnO$_{2}$ and $I4/mcm$-ZnO$_{2}$. Phonon and elastic constant calculations conclude the dynamical and mechanical stability for the explored thermodynamically stable or metastable structures.

Generation of Nitrogen-Vacancy Center Pairs in Bulk Diamond by Molecular Nitrogen Implantation

Zhao-Jun Gong, Xiang-Dong Chen, Cong-Cong Li, Shen Li, Bo-Wen Zhao, Fang-Wen Sun
Chin. Phys. Lett. 2016, 33 (02): 026105 doi: 10.1088/0256-307X/33/2/026105
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The coupled negatively charged nitrogen-vacancy (NV$^{-}$) center system is a promising candidate for scalable quantum information techniques. In this work, ionized nitrogen molecules are implanted into bulk diamond to generate coupled NV$^{-}$ center pairs. The two-photon autocorrelation measurement and optically detected magnetic resonance measurement are carried out to confirm the production of the NV$^{-}$ center pair. Also, both 1.3 µs decoherence time and 4.9 kHz magnetic coupling strength of the NV$^{-}$ center pair are measured by controlling and detecting the spin states. Along with nanoscale manipulation and detection methods, such coupled NV$^{-}$ centers through short distance dipole–dipole interaction would show high potential in scalable quantum information processes.

The Mechanism of Critical Strain of Serrated Yielding in Strain Rate Domain

Shi-Hua Fu, Yu-Long Cai, Su-Li Yang, Qing-Chuan Zhang, Xiao-Ping Wu
Chin. Phys. Lett. 2016, 33 (02): 026201 doi: 10.1088/0256-307X/33/2/026201
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The mechanism of the critical strain of serrated yielding is studied via tension tests at various strain rates. Before the critical strain, it is deduced that dislocations are not pinned at high strain rates, and dislocations at low strain rates are pinned but cannot escape. The critical strain depends on the first pinning process at high strain rates and on the first unpinning process at low strain rates. The calculated results based on the two criteria are in good consistency with the experiment.

Pressure and Time Dependences of the Supercooled Liquid-to-Liquid Transition in Sulfur

Dou-Dou Zhang, Xiu-Ru Liu, Zhu He, Shi-Ming Hong
Chin. Phys. Lett. 2016, 33 (02): 026301 doi: 10.1088/0256-307X/33/2/026301
Full Text: [PDF 507 KB] (10)
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Thermal behavior of bulk amorphous sulfur is investigated by in situ temperature measurements at high pressures of 0.9, 1.4 and 2.1 GPa, and under different heating rates of 8, 10 and 12 K/min at 0.9 GPa. The results show that the onset temperature of the transition from the supercooled liquid to the liquid state for sulfur increases with the pressure and the heating rate. It is deduced that the transition does not follow the Clapeyron equation, indicating considerable coupling of the molecular structure change in the transition. Along with the data at ambient pressure and high pressure, we present a dynamic diagram to demonstrate the relationship between the amorphous solid, supercooled liquid, liquid, and crystal phases of sulfur, and suggest an experimental approach to establish pressure–temperature–time transition diagrams for supercooled liquid and liquid.

First-Principles Study of Properties of Strained PbTiO$_{3}$/KTaO$_{3}$ Superlattice

Zhen-Ye Zhu, Si-Qi Wang, Yan-Ming Fu
Chin. Phys. Lett. 2016, 33 (02): 026302 doi: 10.1088/0256-307X/33/2/026302
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The impacts of strain and polar discontinuities on the performance of superlattices have attracted widespread attention. Using first-principles calculation, we study the polarization and piezoelectricity of PbTiO$_{3}$/KTaO$_{3}$ (PTO/KTO) superlattices with strain and polar discontinuities. The strain caused by lattice mismatch between the superlattice and the substrate induces lattice distortion, the displacement of each atom and dynamical charge transfer between the Ti atom or Ta atom and the O atoms in the PTO/KTO superlattice. With more compressive or less tensile strain, the polarization value increases linearly, piezoelectric tensor $e_{31}$ ($e_{32}$) increases while $e_{33}$ and $e_{25}$ ($e_{16}$) increase negatively. Polarity discontinuity caused by the interfacial charge will produce large irreversible polarization. Proved by ${\it \Gamma}$-point phonons of PTO/KTO superlattices of different strain values, the polar discontinuity and the piezoelectric properties are just weakly dependent on temperature as found in PTO/KTO superlattices.

Effect of Chromium on Structure and Tribological Properties of Hydrogenated Cr/a-C:H Films Prepared via a Reactive Magnetron Sputtering System

Long Liu, Sheng-Guo Zhou, Zheng-Bing Liu, Yue-Chen Wang, Li-Qiu Ma
Chin. Phys. Lett. 2016, 33 (02): 026801 doi: 10.1088/0256-307X/33/2/026801
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Hydrogenated Cr-incorporated carbon films (Cr/a-C:H) are deposited successfully by using a dc reactive magnetron sputtering system. The structure and mechanical properties of the as-deposited Cr/a-C:H films are characterized systematically by field-emission scanning electron microscope, x-ray diffraction, Raman spectra, nanoindentation and scratch. It is shown that optimal Cr metal forms nanocrystalline carbide to improve the hardness, toughness and adhesion strength in the amorphous carbon matrix, which possesses relatively higher nano-hardness of 15.7 GPa, elastic modulus of 126.8 GPa and best adhesion strength with critical load ($L_{\rm C})$ of 36 N for the Cr/a-C:H film deposited at CH$_{4}$ flow rate of 20 sccm. The friction and wear behaviors of as-deposited Cr/a-C:H films are evaluated under both the ambient air and deionized water conditions. The results reveal that it can achieve superior low friction and anti-wear performance for the Cr/a-C:H film deposited at CH$_{4}$ flow rate of 20 sccm under the ambient air condition, and the friction coefficient and wear rate tested in deionized water condition are relatively lower compared with those tested under the ambient air condition for each film. Superior combination of mechanical and tribological properties for the Cr/a-C:H film should be a good candidate for engineering applications.

Absorption Range and Energy Shift of Surface Plasmon in Au Monomer and Dimer

Xiao-Kun Zhao, Yuan Yao, Pei-Lin Lang, Hong-Lian Guo, Xi Shen, Yan-Guo Wang, Ri-Cheng Yu
Chin. Phys. Lett. 2016, 33 (02): 026802 doi: 10.1088/0256-307X/33/2/026802
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The resonance behaviors of local surface plasmon resonance in Au monomer and dimer are characterized systemically by electron energy loss spectroscopy in a scanning transmission electron microscope. The measured absorption range is about 20 nm larger than the physical size of the Au nanoparticles and the resonance peak energy shows a red shift when the electron beam passes off the nanoparticles. The Au dimer displays similar behaviors. Numerical simulation also reproduces those experimental results.

Effect of Si $\delta$-Doping on the Linear and Nonlinear Optical Absorptions and Refractive Index Changes in InAlN/GaN Single Quantum Wells

Shaffa Almansour, Hassen Dakhlaoui, Emane Algrafy
Chin. Phys. Lett. 2016, 33 (02): 027301 doi: 10.1088/0256-307X/33/2/027301
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In the framework of effective mass approximation, we theoretically investigate the electronic structure of the Si $\delta$-doped InAlN/GaN single quantum well by solving numerically the coupled equations Schrödinger–Poisson self-consistently. The linear, nonlinear optical absorption coefficients and relative refractive index changes are calculated as functions of the doping concentration and its thickness. The obtained results show that the position and the amplitude of the linear and total optical absorption coefficients and the refractive index changes can be modified by varying the doping concentration and its thickness. In addition, it is found that the maximum of the optical absorption can be red-shifted or blue-shifted by varying the doping concentration. The obtained results are important for the design of various electronic components such as high-power FETs and infrared photonic devices.

The Hole Transport Characteristics of 1, 4, 5, 8, 9 and 11-Hexaazatriphenylene-Hexacarbonitrile by Blending

Yan-Ping Wang, Jin-Ying Huang, Jiang-Shan Chen, Xian-Feng Qiao, De-Zhi Yang, Dong-Ge Ma, Li-Song Dong
Chin. Phys. Lett. 2016, 33 (02): 027302 doi: 10.1088/0256-307X/33/2/027302
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The hole transport characteristics of molecule blends of 1, 4, 5, 8, 9 and 11-hexaazatriphenylene-hexacarbonitrile (HAT-CN): N,N'-di(naphthalene-1-yl)-N,N'-diphenyl-benzidine (NPB) and HAT-CN: 4,4'-cyclohexylidenebis[N,N-bis(4-methylphenyl)benzenamine] (TAPC) with various NPB and TAPC mixing concentrations (5–90 wt%) are studied. When the concentration is in the range of 5–80 wt%, it is found that the hole conductions in the two blends are space-charge-limited current (SCLC) with free trap distributions. The current–voltage characteristics of the two blends show SCLC with exponential trap distributions at the concentration of 90 wt%. The hole mobilities of the two blends are very close (10$^{-4}$–10$^{-3}$ cm$^{2}$V$^{-1}$s$^{-1}$), the dependence of electric field and temperature can be described by the modified Poole–Frenkel model. The hole mobility and activation energy of the two blends depending on concentration are similar.

Electron-Elastic-Wave Interaction in a Two-Dimensional Topological Insulator Hot!

Xiao-Guang Wu
Chin. Phys. Lett. 2016, 33 (02): 027303 doi: 10.1088/0256-307X/33/2/027303
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The interaction between an electron and an elastic wave is investigated for HgTe and InAs-GaSb quantum wells. The well-known Bernevig–Hughes–Zhang model, i.e., the $4\times 4$ model for a two-dimensional (2D) topological insulator (TI), is extended to include the terms that describe the coupling between the electron and the elastic wave. The influence of this interaction on the transport properties of the 2DTI and of the edge states is discussed. As the electron-like and hole-like carriers interact with the elastic wave differently due to the crystal symmetry of the 2DTI, one may utilize the elastic wave to tune/control the transport property of charge carriers in the 2DTI. The extended 2DTI model also provides the possibility to investigate the backscattering of edge states of a 2DTI more realistically.

Spin-Split Joint Density of States in GdN

Muhammad Azeem
Chin. Phys. Lett. 2016, 33 (02): 027501 doi: 10.1088/0256-307X/33/2/027501
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We present an investigation of the optical constants of the near stoichiometric GdN films. Transmission and reflection spectra are collected for the paramagnetic and the ferromagnetic GdN in the photon energy range of 0.5–5.5 eV. In the ferromagnetic phase, behaviors of minority and majority spin states are specifically focussed on, which indicate spin-split joint density of states. The results confirm the LSDA+$U$ estimates of energy gap associated with the majority-spins and also the magnitude of spin splitting.

Analyzing Bandwidth on the Microwave Absorber by the Interface Reflection Model

Liang Qiao, Tao Wang, Zhong-Lei Mei, Xi-Ling Li, Wen-Bo Sui, Li-Yun Tang, Fa-Shen Li
Chin. Phys. Lett. 2016, 33 (02): 027502 doi: 10.1088/0256-307X/33/2/027502
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Metallic flaky sendust particles are prepared for use as fillers in electromagnetic attenuation composites. We report the interface reflection model to divide the broad bandwidth into electromagnetic loss and quarter-wavelength ($\lambda/4$) cancelation. Combining with the face reflection calculation, we identify the electromagnetic loss originated from skin effect, which is used to explain over half of the absorbed energy in high frequency band. Most importantly, the unique electromagnetic loss cannot generate the reflection loss (RL) peak. Using the phase relation of face reflection, we show evidence that the $\lambda/4$ cancelation is vital to generate the RL peak. The calculated energy loss agrees well with the experimental data and lays the foundation for further research.

Nanosecond Characterization of Regional Domain Imprint from Fast Domain Switching Currents in Pb(Zr,Ti)O$_{3}$ Thin Films

Jun Jiang, An-Quan Jiang
Chin. Phys. Lett. 2016, 33 (02): 027701 doi: 10.1088/0256-307X/33/2/027701
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The traditional imprint characterization of ferroelectric thin films estimates imprint time dependence of the mean coercive voltage of all domains from a polarization-voltage hysteresis loop, which shows a semilogarithmic time dependence above an initial imprint time of $\tau _{0}> 1$ µs at room temperature. Below $\tau _{0}$, the imprint effect is believed to be weak. In consideration of region-by-region domain reversal under a rising pulsed voltage with ordered coercive voltages increasing from zero up to the maximum applied voltage during capacitor charging time, we can estimate the imprinted coercive voltage of each domain from domain switching current transient separately with imprint time as short as 20 ns. In disagreement with the previous observations, all imprinted coercive voltages for the domains in Pt/Pb(Zr$_{0.4}$Ti$_{0.6})$O$_{3}$/Pt thin-film capacitors show step-like increases at two characteristic times of 300 ns and 0.27 s. The imprint effect is surprisingly strong enough even at shortened time down to 20 ns without any evidence of weakening.

Structural Design and Experiment of Narrow-Band Response GaAlAs Photocathodes

Jing Zhao, Jian Zhang, Cui Qin, Hui-Long Yu, Yi-Jun Zhang, Xin-Long Chen, Ben-Kang Chang
Chin. Phys. Lett. 2016, 33 (02): 027801 doi: 10.1088/0256-307X/33/2/027801
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To obtain the peak response at 532 nm, narrow-band response GaAlAs photocathodes with two GaAlAs active layers of different aluminum compositions are designed in consideration of the maximum absorptivity and quantum efficiency. The transmission-mode and the corresponding reflective-mode photocathodes are grown by metalorganic chemical vapor deposition. The results indicate that the peak response and the cut-off wavelength occur at 532 nm for the two kinds of photocathodes respectively. The response of the reflection-mode photocathode is an order of magnitude higher than that of the transmission-mode photocathode, whereas the better growth quality and the thicker second GaAlAs active layer can improve the transmission-mode response.

Scattering of Circularly Polarized Terahertz Waves on a Graphene Nanoantenna

Zhi-Kun Liu, Ya-Nan Xie, Li Geng, Deng-Ke Pan, Pan Song
Chin. Phys. Lett. 2016, 33 (02): 027802 doi: 10.1088/0256-307X/33/2/027802
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We present a surface current method to model the graphene rectangular nanoantenna scattering in the terahertz band with Comsol. Compared with the equivalent thin slab method, the results obtained by the surface current method are more accurate and efficient. Then the electromagnetic scattering of circularly polarized terahertz waves on graphene nanoantennas is numerically analyzed by utilizing the surface current method. The dependences of the antenna resonant frequency with the circularly polarized wave on width and length are consistent with those for the linear polarized waves. These results are proved to be useful to design efficient nanoantennas in terahertz wireless communications.

Characteristics of Laser-Induced Surface and Bulk Damage of Large-Aperture Deuterated Potassium Dihydrogen Phosphate at 351nm

Wei Han, Li-Dan Zhou, Yong Xiang, Ye Tian, Fang Wang, Fu-Quan Li, Li-Quan Wang, Bin Feng, Jun-Pu Zhao, Kui-Xing Zheng, Qi-Hua Zhu, Xiao-Feng Wei, Wan-Guo Zheng, Ma-Li Gong
Chin. Phys. Lett. 2016, 33 (02): 027803 doi: 10.1088/0256-307X/33/2/027803
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Deuterated potassium dihydrogen phosphate damage performance at 351 nm is studied on a large-aperture laser system. Bulk and rear-surface damage are initiated under the 3$\omega$ fluences of 6.7 J/cm$^{2}$ and 3 J/cm$^{2}$, and show different growth characteristics under multiple laser irradiations with the fluence of 6 J/cm$^{2}$. The size and number of bulk damage keep unchanged once initiated. However, surface damage size also does not grow, while surface damage number increases linearly with laser shots. Different damage thresholds and growth behaviors suggest different formations of bulk and surface damage precursors. The cause of surface damage is supposed to be near-surface absorbing particles buried under the sol-gel coating.

B–C Bond in Diamond Single Crystal Synthesized with h-BN Additive at High Pressure and High Temperature

Yong Li, Zhen-Xiang Zhou, Xue-Mao Guan, Shang-Sheng Li, Ying Wang, Xiao-Peng Jia, Hong-An Ma
Chin. Phys. Lett. 2016, 33 (02): 028101 doi: 10.1088/0256-307X/33/2/028101
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The synthesis of diamond single crystal in the Fe$_{64}$Ni$_{36}$-C system with h-BN additive is investigated at pressure 6.5 GPa and temperature range of 1300–1400$^{\circ}\!$C. The color of the obtained diamond crystals translates from yellow to dark green with increasing the h-BN addition. Fourier-transform infrared (FTIR) results indicate that $sp^{2}$ hybridization B-N-B and B-N structures generate when the additive content reaches a certain value in the system. The two peaks are located at 745 and 1425 cm$^{-1}$, respectively. Furthermore, the FTIR characteristic peak resulting from nitrogen pairs is noticed and it tends to vanish when the h-BN addition reaches 1.1 wt%. Furthermore, Raman peak of the synthesized diamond shifts down to a lower wavenumber with increasing the h-BN addition content in the synthesis system.

Influence of Blocking Interlayer in Blue Organic Light-Emitting Diodes with Different Thicknesses of Emitting Layer and Interlayer

Shuang Cheng, Jian-Qi Shen, Zhi-Qi Kou, Xiao-Ping Wang
Chin. Phys. Lett. 2016, 33 (02): 028501 doi: 10.1088/0256-307X/33/2/028501
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A series of blue organic light-emitting diodes with electron or hole blocking interlayer are fabricated. Different structures of blocking interlayers can influence the position of the recombination zone due to the fact that they confine carriers in different ways. We find that the double hole blocking interlayer structure can balance carrier injection more effectively. Its power and current efficiency are more stable and the current efficiency value is 30.2 cd/A at 1000 cd/m$^2$. Decreasing the thicknesses of the emitting layer and interlayers is in favor of the power efficiency. The performance of the device is also affected by changing the interlayer position when we use hole and electron blocking material as interlayers simultaneously.

The Structural Stability of Alpha-Helix Determined by the Preference of Amino Acids

Xiao-Xiao Xie, Jun-Wei Li, Shao-Ying Xiao, Yu-Zhi Liu, Hui Liu, Jin-Peng Geng, Su-Hua Zhang, Hui Yu, Yong Zhan, Hai-Long An
Chin. Phys. Lett. 2016, 33 (02): 028701 doi: 10.1088/0256-307X/33/2/028701
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To accomplish their functions, proteins have to achieve different conformations accompanied by conformational transitions. However, the relationship between the preference of amino acids and the stability of the secondary structure is still unclear. Here we perform molecular simulations on a series of helical structures. Our data show that the dissociation energy of the helical structure is related to the preference of amino acids, and the electrostatic repulsion of the residue $i$ and $i+3/4$ with the same sign of charge destabilizes the alpha helix.

Identifying Influence of Nodes in Complex Networks with Coreness Centrality: Decreasing the Impact of Densely Local Connection

Yi-Run Ruan, Song-Yang Lao, Yan-Dong Xiao, Jun-De Wang, Liang Bai
Chin. Phys. Lett. 2016, 33 (02): 028901 doi: 10.1088/0256-307X/33/2/028901
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Ranking nodes by their spreading ability has been a fundamental issue related to many real applications, such as information and disease control. In the well-known coreness centrality measure, nodes' influence is ranked only by summing all neighbors' $k$-shell values while the effect of the topological connections among them on the nodes' spreading ability are ignored. In this work, we propose an improved coreness measure by decreasing the impact of densely local connections. Comparing the results from a series of susceptible-infected-recovered simulations on real networks, we show that our improved method can rank the nodes' spreading ability more accurately than other ranking measures such as $k$-shell, distance based method, mixed degree decomposition and coreness centrality method.
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