中国物理B

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Localized waves of the coupled cubic-quintic nonlinear Schrödinger equations in nonlinear optics

徐涛, 陈勇, 林机

2017 (12): 120201-120201. doi: 10.1088/1674-1056/26/12/120201

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We investigate some novel localized waves on the plane wave background in the coupled cubic-quintic nonlinear Schrödinger (CCQNLS) equations through the generalized Darboux transformation (DT). A special vector solution of the Lax pair of the CCQNLS system is elaborately constructed, based on the vector solution, various types of higher-order localized wave solutions of the CCQNLS system are constructed via the generalized DT. These abundant and novel localized waves constructed in the CCQNLS system include higher-order rogue waves, higher-order rogues interacting with multi-soliton or multi-breather separately. The first-and second-order semi-rational localized waves including several free parameters are mainly discussed:(i) the semi-rational solutions degenerate to the first-and second-order vector rogue wave solutions; (ii) hybrid solutions between a first-order rogue wave and a dark or bright soliton, a second-order rogue wave and two dark or bright solitons; (iii) hybrid solutions between a first-order rogue wave and a breather, a second-order rogue wave and two breathers. Some interesting and appealing dynamic properties of these types of localized waves are demonstrated, for example, these nonlinear waves merge with each other markedly by increasing the absolute value of α. These results further uncover some striking dynamic structures in the CCQNLS system.

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Temperature dependence of migration features of self-interstitials in zirconium

钟睿, 侯氢, 马超琼, 付宝勤, 汪俊

2017 (12): 120202-120202. doi: 10.1088/1674-1056/26/12/120202

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Molecular dynamics simulations are conducted to study self-interstitial migration in zirconium. By defining crystal lattice points where more than one atom is present in corresponding Wigner-Seitz cells, as the locations of self-interstitial atoms (LSIAs), three types of events are identified as LSIA migrations:the jump remaining in one 〈1120〉 direction (ILJ), the jump from one 〈1120〉 to another 〈1120〉 direction in the same basal plane (OLJ), and the jump from one basal plane to an adjacent basal plane (OPJ). The occurrence frequencies of the three types are calculated. ILJ is found to be a dominant event in a temperature range from 300 K to 1200 K, but the occurrence frequencies of OLJ and OPJ increase with temperature increasing. The total occurrence frequency of all jump types has a good linear dependence on temperature. Moreover, the migration trajectories of LSIAs in the hcp basal-plane is not what is observed if only conventional one-or two-dimensional migrations exists; rather, they exhibit the feature that we call fraction-dimensional. Using Monte Carlo simulations, the potential kinetic effects of fraction-dimensional migration, which is measured by the average number of lattice sites visited per jump event (denoted by n_SPE), are analysed. The significant differences between the n_SPE value of the fraction-dimensional migration and those of conventional one-and two-dimensional migrations suggest that the conventional diffusion coefficient cannot give an accurate description of the underlying kinetics of SIAs in Zr. This conclusion could be generally meaningful for the cases where the low-dimensional migration of defects are observed.

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Analytical and numerical investigations of displaced thermal state evolutions in a laser process

杜传勋, 孟祥国, 张冉, 王继锁

2017 (12): 120301-120301. doi: 10.1088/1674-1056/26/12/120301

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We investigate how displaced thermal states (DTSs) evolve in a laser channel. Remarkably, the initial DTS, an example of a mixed state, still remains mixed and thermal. At long times, they finally decay to a highly classical thermal field only related to the laser parameters κ and g. The normal ordering product of density operator of the DTS in the laser channel leads to obtaining the analytical time-evolution expressions of the photon number, Wigner function, and von Neumann entropy. Also, some interesting results are presented via numerically investigating these explicit time-dependent expressions.

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Decoy-state reference-frame-independent quantum key distribution with both source errors and statistical fluctuations

刘康, 李剑, 朱建荣, 张春梅, 王琴

2017 (12): 120302-120302. doi: 10.1088/1674-1056/26/12/120302

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Reference-frame-independent quantum key distribution (RFI QKD) can generate secret keys without the alignment of reference frames, which is very robust in real-life implementations of QKD systems. However, the performance of decoy-state RFI QKD with both source errors and statistical fluctuations is still missing until now. In this paper, we investigate the performance of decoy-state RFI QKD in practical scenarios with two kinds of light sources, the heralded single photon source (HSPS) and the weak coherent source (WCS), and also give clear comparison results of decoy-state RFI QKD with WCS and HSPS. Simulation results show that the secret key rates of decoy-state RFI QKD with WCS are higher than those with HSPS in short distance range, but the secret key rates of RFI QKD with HSPS outperform those with WCS in long distance range.

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Monogamy relations of quantum entanglement for partially coherently superposed states

石现

2017 (12): 120303-120303. doi: 10.1088/1674-1056/26/12/120303

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Monogamy is a fundamental property of multi-partite entangled states. Recently, Kim J S[Phys. Rev. A 93 032331] showed that a partially coherent superposition (PCS) of a generalized W-class state and the vacuum saturates the strong monogamy inequality proposed by Regula B et al.[Phys. Rev. Lett. 113 110501] in terms of squared convex roof extended negativity; and this fact may present that this class of states are good candidates for studying the monogamy of entanglement. Hence in this paper, we will investigate the monogamy relations for the PCS states. We first present some properties of the PCS states that are useful for providing our main theorems. Then we present several monogamy inequalities for the PCS states in terms of some entanglement measures.

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Topological superfluid in a two-dimensional polarized Fermi gas with spin-orbit coupling and adiabatic rotation

乔雷, 迟诚

2017 (12): 120304-120304. doi: 10.1088/1674-1056/26/12/120304

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We study the properties of superfluid in a two-dimensional (2D) polarized Fermi gas with spin-orbit coupling and adiabatic rotation which are trapped in a harmonic potential. Due to the competition between polarization, spin-orbit coupling, and adiabatic rotation, the Fermi gas exhibits many intriguing phenomena. By using the Bardeen-Cooper-Schrieffer (BCS) mean-field method with local density approximation, we investigate the dependence of order parameter solution on the spin-orbit coupling strength and the rotation velocity. The energy spectra with different rotation velocities are studied in detail. Besides, the conditions for the zero-energy Majorana fermions in topological superfluid phase to be observed are obtained. By investigating distributions of number density, we find that the rotation has opposite effect on the distribution of number density with different spins, which leads to the enhancement of the polarization of Fermi gas. Here, we focus on the region of BCS pairing and ignore the Fulde-Ferrell-Larkin-Ovchinnikov state.

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Linear synchronization and circuit implementation of chaotic system with complete amplitude control

李春彪, 张若洵, 陆天爱

2017 (12): 120501-120501. doi: 10.1088/1674-1056/26/12/120501

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Although chaotic signals are considered to have great potential applications in radar and communication engineering, their broadband spectrum makes it difficult to design an applicable amplifier or an attenuator for amplitude conditioning. Moreover, the transformation between a unipolar signal and a bipolar signal is often required. In this paper, a more intelligent hardware implementation based on field programmable analog array (FPAA) is constructed for chaotic systems with complete amplitude control. Firstly, two chaotic systems with complete amplitude control are introduced, one of which has the property of offset boosting with total amplitude control, while the other has offset boosting and a parameter for partial control. Both cases can achieve complete amplitude control including amplitude rescaling and offset boosting. Secondly, linear synchronization is established based on the special structure of chaotic system. Finally, experimental circuits are constructed on an FPAA where the predicted amplitude control is realized through only two independent configurable analog module (CAM) gain values.

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Parameter analysis of chaotic superlattice true random number source

刘延飞, 杨东东, 郑浩, 汪立新

2017 (12): 120502-120502. doi: 10.1088/1674-1056/26/12/120502

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Superlattices in chaotic state can be used as a key part of a true random number generator. The chaotic characteristics of the signal generated in the superlattice are mostly affected by the parameters of the superlattice and the applied voltage, while the latter is easier to adjust. In this paper, the model of the superlattice is first established. Then, based on this model, the chaotic characteristics of the generated signal are studied under different voltages. The results demonstrate that the onset of chaos in the superlattice is typically accompanied by the mergence of multistability, and there are voltage intervals in each of which the generated signal is chaotic.

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Asymmetric W-shaped and M-shaped soliton pulse generated from a weak modulation in an exponential dispersion decreasing fiber

刘祥树, 赵立臣, 段亮, 杨战营, 杨文力

2017 (12): 120503-120503. doi: 10.1088/1674-1056/26/12/120503

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We study localized waves on continuous wave background in an exponential dispersion decreasing fiber with two orthogonal polarization states. We demonstrate that asymmetric W-shaped and M-shaped soliton pulse can be generated from a weak modulation on continuous wave background. The numerical simulation results indicate that the generated asymmetric soliton pulses are robust against small noise or perturbation. In particular, the asymmetric degree of the asymmetric soliton pulse can be effectively controlled by changing the relative frequency of the two components. This character can be used to generate other nonlinear localized waves, such as dark-antidark and antidark-dark soliton pulse pair, symmetric W-shaped and M-shaped soliton pulse. Furthermore, we find that the asymmetric soliton pulse possesses an asymmetric discontinuous spectrum.

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A novel image encryption scheme based on Kepler's third law and random Hadamard transform

罗玉玲, 周戎龙, 刘俊秀, 丘森辉, 曹弋

2017 (12): 120504-120504. doi: 10.1088/1674-1056/26/12/120504

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In this paper, a novel image encryption scheme based on Kepler's third law and random Hadamard transform is proposed to ensure the security of a digital image. First, a set of Kepler periodic sequences is generated to permutate image data, which is characteristic of the plain-image and the Kepler's third law. Then, a random Hadamard matrix is constructed by combining the standard Hadamard matrix with the hyper-Chen chaotic system, which is used to further scramble the image coefficients when the image is transformed through random Hadamard transform. In the end, the permuted image presents interweaving diffusion based on two special matrices, which are constructed by Kepler periodic sequence and chaos system. The experimental results and performance analysis show that the proposed encrypted scheme is highly sensitive to the plain-image and external keys, and has a high security and speed, which are very suitable for secure real-time communication of image data.

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Role of entropy generation minimization in thermal optimization

程雪涛, 梁新刚

2017 (12): 120505-120505. doi: 10.1088/1674-1056/26/12/120505

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Thermal optimization is very important for improving the performances of thermal systems. In engineering, the entropy generation minimization (EGM) has been widely used to optimize and evaluate the performances of thermal systems. However, the consistency between the EGM and the optimization objective should be specified when the EGM is used. In this paper, we discuss the view angle of irreversibility of entropy generation, and show that entropy generation directly reflects the exergy destruction or the ability loss of doing work. As the design objective in a thermal system is not often consistent with the view angle of irreversibility of entropy generation, the EGM may not lead to the optimal value of the design objective. In heat transfer and heat-work conversion, the inconsistence between the design objectives and the EGM is shown with some examples, and the applicability of the EGM is found to be conditional. The “entropy generation paradox” in heat exchanger analyses is also discussed, and it is shown that there is no direct monotonic relation between the minimum entropy generation rate and the best heat transfer performance of heat exchangers.

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Constant evacuation time gap:Experimental study and modeling

郭宁, 姜锐, 胡茂彬, 丁建勋

2017 (12): 120506-120506. doi: 10.1088/1674-1056/26/12/120506

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In this paper, the evacuation dynamics in an artificial room with only one exit is investigated via experiments and modeling. Two sets of experiments are implemented, in which pedestrians are asked to escape individually. It is found that the average evacuation time gap is essentially constant. To model the evacuation dynamics, an improved social force model is proposed, in which it is assumed that the driving force of a pedestrian cannot be performed when the resultant physical force exceeds a threshold. Simulation results are in good agreement with the experimental ones.

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Signal-to-noise ratio comparison of angular signal radiography and phase stepping method

朱佩平, 胡仁芳, 高昆, 吴朝, 鲍园, 田扬超

2017 (12): 120601-120601. doi: 10.1088/1674-1056/26/12/120601

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Grating-based x-ray phase contrast imaging has the potential to be applied in future medical applications as it is compatible with both laboratory and synchrotron source. However, information retrieval methods are important because acquisition speed, scanning mode, image quality, and radiation dose depend on them. Phase-stepping (PS) is a widely used method to retrieve information, while angular signal radiography (ASR) is a newly established method. In this manuscript, signal-to-noise ratios (SNRs) of ASR are compared with that of PS. Numerical experiments are performed to validate theoretical results. SNRs comparison shows that for refraction and scattering images ASR has higher SNR than PS method, while for absorption image both methods have same SNR. Therefore, our conclusions would have guideline in future preclinical and clinical applications.

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Investigation on the dynamic behaviors of the coupled memcapacitor-based circuits

周知, 于东升, 王晓媛

2017 (12): 120701-120701. doi: 10.1088/1674-1056/26/12/120701

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In this paper, by referring to the concept of coupled memristors (MRs) and considering the flux coupling connection, the constitutive relations for describing the coupled memcapacitors (MCs) are theoretically deduced. The dynamic behaviors of dual coupled MCs in serial and parallel connections are analyzed in terms of identical or opposite polarities for the first time. Based on the derived constitutive relations of the two coupled MCs, the modified relaxation oscillators (ROs) are obtained with the purpose of achieving controllable oscillation frequency and duty cycle. In consideration of different parameter configurations, the experimental investigation is carried out by using practical off-the-shelf circuit components to verify the correction of the theoretical calculation with numerical simulation of the coupled MCs and its application in ROs.

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A dual-axis, high-sensitivity atomic magnetometer

李茹杰, 全伟, 范文峰, 邢力, 王卓, 翟跃阳, 房建成

2017 (12): 120702-120702. doi: 10.1088/1674-1056/26/12/120702

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Atomic magnetometer (AM) operated in a spin-exchange relaxation-free (SERF) regime features superior sensitivity and non-cryogenic operation, and thus is competitive with the best superconducting quantum interference devices. Previously, SERF AM with fT/Hz^1/2 level sensitivity commonly acted as a single-axis sensor. Here we demonstrate a dual-axis SERF AM capable of simultaneously and independently detecting x-and y-field components with a sensitivity of 20 fT/Hz^1/2. As there is no necessity to worry about the cross-talk effects arising from field modulations, the dual-axis scheme proposed here is of particular interest to AM array and hence the biomagnetic applications.

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Improvement of the thermoelectric efficiency of pyrene-based molecular junction with doping engineering

Mohammad Farid Jamali,Meysam Bagheri Tagani,Hamid Rahimpour Soleimani

2017 (12): 123101-123101. doi: 10.1088/1674-1056/26/12/123101

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In this study, the thermoelectric properties of pyrene molecule doped with boron and nitrogen atom at different sites of molecule are investigated using density functional theory and none-equilibrium Green's function formalism in the linear response regime. Our calculations show that when the impurities are added to the edge of the molecule, the anti-resonant peaks will appear in the transmission diagram in the vicinity of the Fermi energy level. So it increases the thermoelectric figure of merit of the system in comparison with the one that the impurity is located in the center of molecule. Additionally, the seebeck coefficient signs are not the same among the B, N, and N & B doped devices, indicating that the types of the carriers can be changed with different types of doping.

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CN bond orientation in metal carbonitride endofullerenes:A density functional theory study

张竹霞, 张勇, 薛文华, 贾伟, 张彩丽, 李春霞, 崔鹏

2017 (12): 123102-123102. doi: 10.1088/1674-1056/26/12/123102

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The geometric and electronic structures of scandium carbonitride endofullerene Sc₃CN@C_2n (2n=68, 78, 80, 82, and 84) and Sc(Y)NC@C₇₆ have been systematically investigated to identify the preferred position of internal C and N atoms by density functional theory (DFT) calculations combined with statistical mechanics treatments. The CN bond orientation can generally be inferred from the molecule stability and electronic configuration. It is found that Sc₃CN@C_2n molecules have the most stable structure with C atom locating at the center of Sc₃CN cluster. The CN bond has trivalent form of[CN]^3- and connects with adjacent three Sc atoms tightly. However, in Sc(Y)NC@C₇₆ with[NC]^-, the N atom always resides in the center of the whole molecule. In addition, the stability of Sc₃CN@C_2n has been further compared in terms of the organization of the corresponding molecular energy level. The structural differences between Sc₃CN@C_2n and Sc₃NC@C_2n are highlighted by their respected infrared spectra.

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Effects of temperature and pressure on thermodynamic properties of Cd_0.25Zn_0.75 alloy

Najm Ul Aarifeen,A Afaq

2017 (12): 123103-123103. doi: 10.1088/1674-1056/26/12/123103

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Thermodynamic properties of Cd_0.25Zn_0.75Se alloy are studied using quasi harmonic model for pressure range of 0 GPa-10 GPa and temperature range 0 K-1000 K. The structural optimization is obtained by self-consistent field calculations and full-potential linearized muffin-tin orbital method with GGA+U as an exchange correlation functional where U=2.3427 eV is Hubbard potential. The effects of temperature and pressure on bulk modulus, Helmholtz free energy, internal energy, entropy, Debye temperature, Grüneisen parameter, thermal expansion coefficient, and heat capacities of the material are observed and discussed. The bulk modulus, Helmholtz free energy, and Debye temperature are found to be decreased on increasing temperature while there is an increasing behavior with rise of the pressure. Whereas the internal energy has increasing trend with the rise in temperature and it almost remains insensitive to pressure. The entropy of the system increases (decreases) with rise of pressure (temperature).

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Anisotropic self-diffusion of fluorinated poly(methacrylate) in metal-organic frameworks assessed with molecular dynamics simulation

鲁桃, 徐彪, 叶飞宏, 周馨慧, 陆云清, 王瑾

2017 (12): 123104-123104. doi: 10.1088/1674-1056/26/12/123104

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Utilizing the periodically structured metal-organic framework (MOF) as the reaction vessel is a promising technique to achieve the aligned polymer molecular chains, where the diffusion procedure of the polymer monomer inside MOF is one of the key mechanisms. To investigate the diffusion mechanism of fluorinated polymer monomers in MOFs, in this paper the molecular dynamics simulations combined with the density functional theory and the Monte Carlo method are used and the all-atom models of TFMA (trifluoroethyl methacrylate) monomer and two types of MOFs,[Zn₂(BDC)₂(TED)]_n and[Zn₂(BPDC)₂(TED)]_n, are established. The diffusion behaviors of TFMA monomer in these two MOFs are simulated and the main influencing factors are analyzed. The obtained results are as follows. First, the electrostatic interactions between TFMA monomers and MOFs cause the monomers to concentrate in the MOF channel, which slows down the monomer diffusion. Second, the anisotropic shape of the one-dimensional MOF channel leads to different diffusion speeds of monomers in different directions. Third, MOF with a larger pore diameter due to a longer organic ligand,[Zn₂(BPDC)₂(TED)]_n in this paper, facilitates the diffusion of monomers in the MOF channel. Finally, as the number of monomers increases, the self-diffusion coefficient is reduced by the steric effect.

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Enhancement of signal-to-noise ratio of ultracold polar NaCs molecular spectra by phase locking detection

王文浩, 刘文良, 武寄洲, 李玉清, 王晓锋, 刘艳艳, 马杰, 肖连团, 贾锁堂

2017 (12): 123701-123701. doi: 10.1088/1674-1056/26/12/123701

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We report a method of high-sensitively detecting the weak signal in photoassociation (PA) spectra of ultracold NaCs molecules by phase sensitive-demodulated trap-loss spectra of Na atoms from a photomultiplier tube. We find that the signal-to-noise ratio (SNR) of the PA spectra is strongly dependent on the integration time and the sensitivity of the lock-in amplifier, and our results show reasonable agreement with the theoretical analyses of the SNR with the demodulation parameters. Meanwhile, we investigate the effect of the interaction time of the PA laser with the colliding Na-Cs atom pairs on the SNR of the PA spectra. The atom loss rate is dependent on both the PA-induced atom loss and the loading of the MOT. The high-sensitive detection of the excited ultracold NaCs molecules lays a solid foundation for further study of the formation and application of ultracold NaCs molecules.

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Highly sensitive photoassociation spectroscopy of ultracold ²³Na¹³³Cs molecular long-range states below the 3S_1/2+6P_3/2 limit

刘艳艳, 武寄洲, 刘文良, 王晓锋, 王文浩, 马杰, 肖连团, 贾锁堂

2017 (12): 123702-123702. doi: 10.1088/1674-1056/26/12/123702

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We present high resolution photoassociation spectroscopy of ultracold ²³Na¹³³Cs molecules in a long-range c³∑⁺ state below the (3S_1/2 + 6P_3/2) asymptote. We perform photoassociation spectroscopy in a dual-species magneto-optical trap (MOT) and detect the photoassociation resonances using trap-loss spectroscopy. By fitting the experimental data with the semi-classical LeRoy-Bernstein formula, we deduce the long-range molecular coefficient C₆ and derive the empirical potential energy curve in the long-range region.

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Studies on convergence and scaling law of Thomson backscattering spectra in strong fields

谢含章, 蒋纯, 谢柏松

2017 (12): 124101-124101. doi: 10.1088/1674-1056/26/12/124101

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With the saddle point analysis method for the Bessel function structure and property, the convergence problem and the scaling laws of Thomson backscattering spectra are solved and studied in both cases that are for the plane wave laser field without and with applied external constant magnetic field. Some unclear points appeared in previous work are clarified. The extension of the method to a general situation for the laser field with an arbitrary polarization is discussed. We also make a simple analysis and discussion about the optimal spectra dependence of field parameters and its implication to practical applications.

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Error analysis and Stokes parameter measurement of rotating quarter-wave plate polarimeter

支丹丹, 李健军, 高冬阳, 翟文超, 黄雄豪, 郑小兵

2017 (12): 124201-124201. doi: 10.1088/1674-1056/26/12/124201

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In this paper, we present a simple Stokes parameter measurement method for a rotating quarter-wave plate polarimeter. This method is used to construct a model to describe the principle of how the magnitudes of errors influence the deviation of the output light Stokes parameter, on the basis of accuracy analysis of the retardance error of the quarter-wave plate, the misalignment of the analyzing polarizer, and the phase shift of the measured signals, which will help us to determine the magnitudes of these errors and then to acquire the correct results of Stokes parameters. The method is validated by the experiments on left-handed circularly polarized and linear horizontal polarization beams. With the improved method, the maximum measurement deviations of Stokes parameters for these two different polarized states are reduced from 2.72% to 2.68%, and from 3.83% to 1.06% respectively. Our results demonstrate that the proposed method can be used as a promising approach to Stokes parameter measurement for a rotating quarter-wave plate polarimeter.

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(3+1)-dimensional localized self-accelerating Airy elegant Ince-Gaussian wave packets and their radiation forces in free space

李冬冬, 彭喜, 彭玉莲, 张丽萍, 陈星宇, 庄经立, 赵方, 杨湘波, 邓冬梅

2017 (12): 124202-124202. doi: 10.1088/1674-1056/26/12/124202

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We construct analytically linear self-accelerating Airy elegant Ince-Gaussian wave packet solutions from (3+1)-dimensional potential-free Schrödinger equation. These wave packets have elliptical geometry and show different characteristics when the parameters (p, m) and ellipticity ε are adjusted. We investigate these characteristics both analytically and numerically and give the 3-dimensional intensity and phase distribution of these wave packets. Lastly, we analyze the radiation forces on a Rayleigh dielectric particle. In addition, we also find an interesting phenomenon that if the energy distribution between every part of wave packets is uneven at the input plane, the energy will be transferred between every part in the process of transmission.

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High efficiency terahertz diffraction grating with trapezoidal elements

巫殷忠, 范全平, 张强强, 魏来, 陈勇, 杨祖华, 曹磊峰

2017 (12): 124203-124203. doi: 10.1088/1674-1056/26/12/124203

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A newly designed grating used in terahertz region is proposed, which is composed of the trapezoidal elements repeated successively along one dimension of the substrate, and uniform interval (the grating period) repeated along the other dimension. The transmission of the grating owns a designable trapezoidal profile dependent on the geometric dimensions of the element. The far-field diffraction patterns of a designed grating at incident broadband terahertz frequencies, with element dimensions of upper, lower side and period of 50, 250, and 300 μm, respectively, are simulated by the scalar diffraction theory. The simulation results indicate that the terahertz grating exhibits a property of single-order diffraction, and the diffraction efficiency of the first order reaches 6.6%, exceeding that of a traditional sinusoidal amplitude grating with identical period and duty cycle. Owing to the regular architecture and the high single-order diffraction efficiency, the grating is easy to fabricate and shows great potential applications in single-shot spectral measurements of weak broadband terahertz pulse.

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Reconfigurable dynamic all-optical chaotic logic operations in an optically injected VCSEL

钟东洲, 许葛亮, 罗伟, 肖珍珍

2017 (12): 124204-124204. doi: 10.1088/1674-1056/26/12/124204

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In a chaotic system of vertical cavity surface emitting laser (VCSEL) with external optical-injection, we propose a novel implementation scheme for reconfigurable dynamic all-optical chaotic logic operations (AOCLOs). Under different key parameters, such as the bias current, the injection strength and the frequency detuning of the injected light field and the VCSEL, we also explore the evolutions of the polarization-bistability with the amplitude of the injected light field when the output of VCSEL is chaotic wave. According to the dynamic evolutions, we find out the optimal value of the frequency detuning that is considered as a control logic signal, and further implement different AOCLOs, such as AND, NAND, OR, NOR, XOR, and XNOR, by controlling the logic operation of the control logic signal between two logic inputs. Moreover, the ability to reconstruct these logic operations is demonstrated under relatively low noise strength of the spontaneous emission.

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Parallel generation of 31 tripartite entangled states based on optical frequency combs

张静, 王艳芳, 刘晓宇, 杨荣国

2017 (12): 124205-124205. doi: 10.1088/1674-1056/26/12/124205

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Quantum entangled states, especially those having particular properties, are key resources for quantum information and quantum computation. In this paper, we put forward a new scheme to produce 31 continuous-variable (CV) tripartite entanglement fields based on three optical frequency combs via cascade nonlinear processes in an optical parametric cavity, and investigate the spectral characteristics of three frequency combs. The center wavelengths of the three combs are designed as 852 nm, 780 nm (atomic transition lines), and 1550 nm (fiber communication wavelength). The positivity under partial transposition (PPT) criterion, which is sufficient and necessary, is used to evaluate the entanglement in each group of comb lines. This scheme is experimentally feasible and valuable for constructing quantum information networks in future.

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Generation of squeezed vacuum on cesium D2 line down to kilohertz range

田剑锋, 左冠华, 张玉驰, 李刚, 张鹏飞, 张天才

2017 (12): 124206-124206. doi: 10.1088/1674-1056/26/12/124206

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We report the experimental generation of a squeezed vacuum at frequencies ranging from 2.5 kHz to 200 kHz that is resonant on the cesium D2 line by using a below-threshold optical parametric oscillator (OPO). The OPO is based on a periodically-poled KTiOPO₄ (PPKTP) crystal that is pumped using a bow-tie four-mirror ring frequency doubler. The phase of the squeezed light is controlled using a quantum noise locking technique. At a pump power of 115 mW, maximum quadrature phase squeezing of 3.5 dB and anti-squeezing of 7.5 dB are detected using a home-made balanced homodyne detector. This squeezed vacuum at an atomic transition in the kilohertz range is an ideal quantum source for quantum metrology of enhancing measurement precision, especially for ultra-sensitive measurement of weak magnetic fields when using a Cs atomic magnetometer in the audio frequency range.

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Broadrange tunable slow and fast light in quantum dot photonic crystal structure

Alireza Lotfian,Reza Yadipour,Hamed Baghban

2017 (12): 124207-124207. doi: 10.1088/1674-1056/26/12/124207

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Slow and fast light processes, based on both structural and material dispersions, are realized in a wide tuning range in this article. Coherent population oscillations (CPO) in electrically tunable quantum dot semiconductor optical amplifiers lead to a variable group index ranging from the background index (n_bgd) to~30. A photonic crystal waveguide is then dispersion engineered and a group index of 260 with the normalized delay-bandwidth product (NDBP) of 0.65 is achieved in the proposed waveguide. Using comprehensive numerical simulations, we show that a considerable enhancement of slow light effect can be achieved by combining both the material and the structural dispersions in the proposed active QDPCW structure. We compare our developed FDTD results with analytical results and show that there is good agreement between the results, which demonstrates that the proposed electrically-tunable slow light idea is obtainable in the QDPCW structure. We achieve a total group index in a wide tuning range from n_bgd to~1500 at the operation bandwidth, which shows a significant enhancement compared with the schemes based only on material or structural dispersions. The tuning range and also NDBP of the slow light scheme are much larger than those of the electrically tunable CPO process.

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Time-resolved spectroscopy for 5s'⁴D_7/2 state transitions undergoing electron-ion recombination in femtosecond laser-produced copper plasma

宋海英, 李辉, 张艳杰, 谷鹏, 刘海云, 李维, 刘勋, 刘世炳

2017 (12): 124208-124208. doi: 10.1088/1674-1056/26/12/124208

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In the femtosecond laser-produced Cu-plasma, the transient transition dynamics that the excited state 5s'⁴D_7/2 via electron-ion recombination transfers to 4p'⁴F_9/2⁰ (465.11 nm, Λ₁ line) and 4p'⁴D_7/2⁰ (529.25 nm, Λ₂ line) states are investigated by using the time-resolved spectroscopy. The occupation number and relevant lifetime of the excited state 5s'⁴D_7/2, the temporal evolutions of spectral intensities for Λ₁ line and Λ₂ line emissions are demonstrated to be in direct proportion to the employed laser intensity, which reveals the transient features of transition dynamics clearly differing from that resulted in the traditional collision excitation. Furthermore, some unique characteristics for Λ₁ and Λ₂ transitions stemming from electron-ion recombination are examined in detail.

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Coherently induced grating in refractive index enhanced medium

刘撰撰, 陈煜远, 原佳宇, 万仁刚

2017 (12): 124209-124209. doi: 10.1088/1674-1056/26/12/124209

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We demonstrate a scheme for coherently induced grating based on a mixture of two three-level atomic species interacting with two standing-wave fields. As a result of interaction between the absorptive and amplified Raman resonances, the refractive index of the medium can be enhanced and modulated periodically. Then a sinusoidal grating, which can diffract the probe field into high-order directions, is coherently formed in the medium. The proposed scheme is theoretically investigated in a mixture of atomic isotopes of rubidium. The results show that the diffraction efficiency depends strongly on the two two-photon detunings of the two Raman transitions and the intensities of the two driving standing-wave fields. The proposed electromagnetically induced grating scheme may be applied to the all-optical switching and beam splitting in optical networking and communication.

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Output light power of InGaN-based violet laser diodes improved by using a u-InGaN/GaN/AlGaN multiple upper waveguide

梁锋, 赵德刚, 江德生, 刘宗顺, 朱建军, 陈平, 杨静, 刘炜, 刘双韬, 邢瑶, 张立群, 王文杰, 李沫, 张源涛, 杜国同

2017 (12): 124210-124210. doi: 10.1088/1674-1056/26/12/124210

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The upper waveguide (UWG) has direct influences on the optical and electrical characteristics of the violet laser diode (LD) by changing the optical field distribution or barrier of the electron blocking layer (EBL). In this study, a series of InGaN-based violet LDs with different UWGs are investigated systematically with LASTIP software. It is found that the output light power (OLP) under an injecting current of 120 mA or the threshold current (I_th) is deteriorated when the UWG is u-In_0.02Ga_0.98N/GaN or u-In_0.02Ga_0.98N/Al_xGa_1-xN (0 ≤ x ≤ 0.1), which should be attributed to small optical confinement factor (OCF) or severe electron leakage. Therefore, a new violet LD structure with u-In_0.02Ga_0.98N/GaN/Al_0.05Ga_0.95N multiple layer UWG is proposed to reduce the optical loss and increase the barrier of EBL. Finally, the output light power under an injecting current of 120 mA is improved to 176.4 mW.

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Optical properties of a three-dimensional chiral metamaterial

郭娟娟, 汪茂胜, 黄万霞

2017 (12): 124211-124211. doi: 10.1088/1674-1056/26/12/124211

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A three-dimensional chiral metamaterial with four-fold rotational symmetry is designed, and its optical properties are investigated by numerical simulations. The results show that this chiral metamaterial has the following features:high polarization conversion, perfect circular dichroism, and asymmetric transmission of circularly polarized light. A comparison of the results of chiral metamaterials without and with weak coupling between the constituent nanostructures enables us to confirm that the optical properties of our proposed nanostructure are closely related to the coupling between the single nanoparticles. This means that the coupling between nanoparticles can enhance the polarization conversion, circular dichroism, and asymmetric transmission. Due to the excellent optical properties, our metamaterial might have potential applications in the development of future multi-functional optical devices.

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Plasmonically induced reflection in metal-insulator-metal waveguides with two silver baffles coupled square ring resonator

张志东, 马连俊, 高飞, 张彦军, 唐军, 曹慧亮, 张斌珍, 王继成, 闫树斌, 薛晨阳

2017 (12): 124212-124212. doi: 10.1088/1674-1056/26/12/124212

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A plasmonic waveguide coupled system that is composed of a square ring cavity and a metal-insulator-metal (MIM) waveguide with two silver baffles is proposed. The transmission and reflection properties of the proposed plasmonic system are investigated numerically using the finite element method. The normalized H_z field distributions are calculated to analyze the transmission mode in the plasmonic system. The extreme destructive interference between light mode and dark mode causes plasmonically induced reflection (PIR) window in the transmission spectrum. The PIR window is fitted using the coupled mode theory. The analytical result agrees with the simulation result approximately. In addition, the PIR window can be controlled by adjusting structural parameters and filling different dielectric into the MIM waveguide and the square ring cavity. The results provide a new approach to designing plasmonic devices.

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Performance analysis of surface plasmon resonance sensor with high-order absentee layer

孟庆卿, 赵鑫, 陈淑静, 林承友, 丁迎春, 陈朝阳

2017 (12): 124213-124213. doi: 10.1088/1674-1056/26/12/124213

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A surface plasmon resonance (SPR) sensor with a high-order absentee layer on the top of metallic film is proposed. The performance of the SPR sensor with NaCl, MgO, TiO₂ or AlAs high-order absentee layer is analyzed theoretically. The results indicate that the sensitivity and the full width at half maximum of those SPR sensors decrease with the increasing of the order of absentee layer, but the variation of the figure of merit (FOM) depends on the refractive index of absentee layer. By improving the order of absentee layer with high-refractive-index, the FOM of the SPR sensor can be enhanced. The maximum value of FOM for the SPR sensor with high-order TiO₂ (or AlAs) absentee layer is 1.059% (or 2.587%) higher than the one with one-order absentee layer. It is believed the proposed SPR sensor with high-order absentee layer will be helpful for developing the high-performance SPR sensors.

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Geometrical representation of coherent tunneling process in two-waveguide and three-waveguide coupler

时坚, 马瑞琼, 段作梁, 梁猛, 柴宝玉, 董军

2017 (12): 124214-124214. doi: 10.1088/1674-1056/26/12/124214

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We propose an identical geometrical representation scheme for both Landau-Zener (LZ) tunneling process in two-waveguide coupler with a cubically bent structure and stimulated Raman adiabatic passage (STIRAP) in three-waveguide coupler, similar to the geometrical representation of sum frequency process. The results show that although the two-waveguide coupler with a cubically bent axis has not aperiodic structure, it acts as a chirped quasi-phase-matching (QPM) grating and corrects the relative phase between the two supermodes in the curved coupler system. We present a scheme about how to choose the parameters to design the curved beam splitter.

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All polymer asymmetric Mach-Zehnder interferometer waveguide sensor by imprinting bonding and laser polishing

刘豫, 孙月, 衣云骥, 田亮, 曹悦, 陈长鸣, 孙小强, 张大明

2017 (12): 124215-124215. doi: 10.1088/1674-1056/26/12/124215

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We present an all polymer asymmetric Mach-Zehnder interferometer (AMZI) waveguide sensor based on imprinting bonding and laser polishing method. The fabrication methods are compatible with high accuracy waveguide sensing structure. The rectangle waveguide structure of this sensor has three sensing surfaces contacting the test media, and its sensing accuracy can be increased 5 times compared with that of one surface sensing structure. An AMZI device structure is designed. The single mode condition, the length of the sensing arm, and the length deviation between the sensing arm and the reference arm are optimized. The length deviation is optimized to be 19.8 μm in a refractive index range between 1.470 and 1.545. We fabricate the AMZI waveguide by lithography and wet etching method. The imprinting bonding and laser polishing method is proposed and investigated. The insertion loss is between-80.36 dB and-10.63 dB. The average and linear sensitivity are 768.1 dB/RIU and 548.95 dB/RIU, respectively. And the average and linear detection resolution of the sensor are 1.30×10^-6 RIU (RIU:refractive index unit) and 1.82×10^-5 RIU, respectively. This sensor has a fast and cost-effective fabrication process which can be used in the cases of requiring portability and disposability.

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Ultra-broadband polarization splitter based on graphene layer-filled dual-core photonic crystal fiber

邹辉, 熊慧, 张云山, 马勇, 郑加金

2017 (12): 124216-124216. doi: 10.1088/1674-1056/26/12/124216

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An ultra-broadband polarization splitter based on graphene layer-filled dual-core photonic crystal fiber (GDC-PCF) that can work in a wavelength range from 1120 nm to 1730 nm is proposed in this paper. Through optimizing fiber configuration, the polarization splitter has an extinction ratio of-56.3 dB at 1.55 μm with a fiber length of 4.8 mm. Compared with the photonic crystal fiber reported splitters, to our knowledge, the GDC-PCF splitter with the extinction ratio below-20 dB has a super wide bandwidth of 610 nm. Due to the excellent splitting characteristics, the GDC-PCF will be used in coherent optical communication systems in a wavelength range from infrared to mid-infraed.

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Seismoelectric wave propagation modeling in a borehole in water-saturated porous medium having an electrochemical interface

丁浩然, 刘金霞, 崔志文

2017 (12): 124301-124301. doi: 10.1088/1674-1056/26/12/124301

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Water-saturated porous media often exhibit a seismoelectric effect due to the existence of an electrical double layer and a relative flow of pore fluid. Here we consider the seismoelectric waves in an open borehole surrounded by water-saturated porous formation which exhibits discontinuity of electrochemical properties at a cylindrical interface. We carefully analyze the seismoelectric interface response since these signals show sensitivity to contrasts in electrochemical properties across an interface. Both coupled and approximate methods are used to compute borehole seismoelectric fields. The simulation results show that the radiated electromagnetic wave from the electrochemical interface is generated due to the change of salinity in pore fluid in the porous formation. However, the elastic properties of the formation remain unchanged across such an electrochemical interface. As a result it is difficult to recognize such a change in electrochemical properties using only elastic waves. Therefore, the seismoelectric interface response is potentially used to detect the changes of the electrochemical properties in the formation.

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Lorentz force electrical impedance tomography using pulse compression technique

孙直申, 刘国强, 夏慧

2017 (12): 124302-124302. doi: 10.1088/1674-1056/26/12/124302

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Lorentz force electrical impedance tomography (LFEIT) combines ultrasound stimulation and electromagnetic field detection with the goal of creating a high contrast and high resolution hybrid imaging modality. In this study, pulse compression working together with a linearly frequency modulated ultrasound pulse was investigated in LFEIT. Experiments were done on agar phantoms having the same level of electrical conductivity as soft biological tissues. The results showed that:(i) LFEIT using pulse compression could detect the location of the electrical conductivity variations precisely; (ii) LFEIT using pulse compression could get the same performance of detecting electrical conductivity variations as the traditional LFEIT using high voltage narrow pulse but reduce the peak stimulating power to the transducer by 25.5 dB; (iii) axial resolution of 1 mm could be obtained using modulation frequency bandwidth 2 MHz.

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Effects of gas pressure on plasma characteristics in dual frequency argon capacitive glow discharges at low pressure by a self-consistent fluid model

赵璐璐, 刘悦

2017 (12): 125201-125201. doi: 10.1088/1674-1056/26/12/125201

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A self-consistent fluid model for dual radio frequency argon capacitive glow discharges at low pressure is established. Numerical results are obtained by using a finite difference method to solve the model numerically, and the results are analyzed to study the effect of gas pressure on the plasma characteristics. It shows that when the gas pressure increases from 0.3 Torr (1 Torr=1.33322×10² Pa) to 1.5 Torr, the cycle-averaged plasma density and the ionization rate increase; the cycle-averaged ion current densities and ion energy densities on the electrodes electrode increase; the cycle-averaged electron temperature decreases. Also, the instantaneous electron density in the powered sheath region is presented and discussed. The cycle-averaged electric field has a complex behavior with the increasing of gas pressure, and its changes take place mainly in the two sheath regions. The cycle-averaged electron pressure heating, electron ohmic heating, electron heating, and electron energy loss are all influenced by the gas pressure. Two peaks of the electron heating appear in the sheath regions and the two peaks become larger and move to electrodes as the gas pressure increases.

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Rayleigh-Taylor instability of multi-fluid layers in cylindrical geometry

郭宏宇, 王立锋, 叶文华, 吴俊峰, 张维岩

2017 (12): 125202-125202. doi: 10.1088/1674-1056/26/12/125202

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Rayleigh-Taylor instability of three fluid layers with two interfaces in cylindrical geometry is investigated analytically. The growth rates and the amplitudes of perturbation on the two interfaces are obtained. The feedback factor from outer to inner interface is larger than that from inner to outer interface under the same conditions. The growth rate on the initially unstable interface is larger than the corresponding result in planar geometry for low mode perturbation. The two interfaces are decoupled for a larger mode number perturbation. The dependencies of the amplitudes of perturbation on different initial conditions are analyzed. The negative feedback effect from initially stable interface to another unstable interface is observed. In the limit of infinity inner radius and finite shell thickness, the results in planar geometry are recovered.

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Structural and size evolution of indium nanoparticles embedded in aluminum synthesized by ion implantation

晏艳霞, 刘孟, 胡梅娟, 朱宏志, 王欢

2017 (12): 126101-126101. doi: 10.1088/1674-1056/26/12/126101

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The structural and the size evolution of embedded In nanoparticles in Al synthesized by ion implantation and subsequent annealing are experimentally investigated. The average radius r of In nanoparticles is determined as a function of annealing time in a temperature range between 423 K and 453 K. The structural transition of In nanoparticles with the crystallographic orientation In (200)[002]||Al (200)[002] is observed to change into In (111)[110]||Al (002)[110] with a critical particle radius between 2.3 nm and 2.6 nm. In addition, the growth of In nanoparticles in the annealing process is evidently governed by the diffusion limited Ostwald ripening. By further analyzing the experimental data, values of diffusion coefficient and activation energy are obtained.

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Finite element analysis of ionic liquid gel soft actuator

何斌, 张成红, 丁安

2017 (12): 126102-126102. doi: 10.1088/1674-1056/26/12/126102

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A new type of soft actuator material-ionic liquid gel (ILG), which consists of HEMA, BMIMBF₄, and TiO₂, can be transformed into gel state under the irradiation of ultraviolet (UV) light. In this paper, Mooney-Rivlin hyperelastic model of finite element method is proposed for the first time to study the properties of the ILG. It has been proved that the content of TiO₂ has a great influence on the properties of the gel, and Young's modulus of the gel increases with the increase of its content, despite of reduced tensile deformation. The results in this work show that when the TiO₂ content is 1.0 wt%, a large tensile deformation and a strong Young's modulus can be obtained to be 325% and 7.8 kPa, respectively. The material parameters of ILG with TiO₂ content values of 0.2 wt%, 0.5 wt%, 1.0 wt%, and 1.5 wt% are obtained, respectively, through uniaxial tensile tests, including C₁₀, C₀₁, C₂₀, C₁₁, C₀₂, C₃₀, C₂₁, C₁₂, and C₀₃ elements. In this paper, the large-scaled general finite element software ANSYS is used to simulate and analyze the ILG, which is based on SOLID186 element and nonlinear hyperelastic Mooney-Rivlin model. The finite element simulation analysis based stress-strain curves are almost consistent with the experimental stress-strain curves, and hence the finite element analysis of ILG is feasible and credible. This work presents a new direction for studying the performance of soft actuator for the ILG, and also contributes to the design of soft robot actuator.

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First-principles calculations of structure and elasticity of hydrous fayalite under high pressure

张传瑜, 王绪本, 赵晓凤, 陈星润, 虞游, 田晓峰

2017 (12): 126103-126103. doi: 10.1088/1674-1056/26/12/126103

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The structures, elasticities, sound velocities, and electronic properties of anhydrous and hydrous fayalite (Fe₂SiO₄ and Fe_1.75H_0.5SiO₄) under high pressure have been investigated by means of the density functional theory within the generalized gradient approximation (GGA) with the on-site Coulomb energy being taken into account (GGA+U). The optimized results show that H atoms prefer to substitute Fe atoms in the Fe1 site. Compared with the anhydrous fayalite Fe₂SiO₄, the mass density, elastic moduli, and sound velocities of Fe_1.75H_0.5SiO₄ slightly decrease. According to our data, adding 2.3 wt% water into fayalite leads to reductions of compressional and shear wave velocities (V_P and V_S) by 3.4%-7.5% and 0.3%-3.4% at pressures from 0 GPa to 25 GPa, respectively, which are basically in agreement with the 2%-5% reductions of sound velocity obtained by the experimental measurement in the low velocity zones (LVZ). Based on the electronic structure, the valence and conduction bands are slightly broader for hydrous fayalite. However, hydrous fayalite keeps the insulation characteristics under the pressures up to 30 GPa, which indicates that hydration has little effect on its electronic structure.

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Zn-Cu-codoped SnO₂ nanoparticles:Structural, optical, and ferromagnetic behaviors

吕建国

2017 (12): 126104-126104. doi: 10.1088/1674-1056/26/12/126104

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Zn-Cu-codoped SnO₂ nanoparticles have been synthesized by chemical precipitation method. All nanoparticles are crystalline, with the average size increases from 2.55 nm to 4.13 nm as the calcination temperature increases from 400℃ to 600℃. The high calcination temperature can enhance the crystalline quality and grain growth. The oxygen content decreases with decreasing calcination temperature; at a low temperature of 400℃, Zn-Cu-codoped SnO₂ nanoparticles are in a rather oxygen-poor state having many oxygen vacancies. The optical band gap energies of Zn-Cu-codoped SnO₂ nanoparticles calcined at 400℃ and 600℃ are decreased from 3.93 eV to 3.62 eV due to quantum confinement effects. Both samples exhibit room-temperature ferromagnetism, with a larger saturation magnetization at 400℃ due to the presence of large density of defects such as oxygen vacancies. Zn-Cu-codoped SnO₂ nanoparticles exhibit large optical band gap energies and room temperature ferromagnetism, which make them potential candidates for applications in optoelectronics and spintronics.

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Mechanical, elastic, anisotropy, and electronic properties of monoclinic phase of m-Si_xGe_3-xN₄

马振洋, 阎芳, 王苏鑫, 贾琼琼, 于新海, 史春蕾

2017 (12): 126105-126105. doi: 10.1088/1674-1056/26/12/126105

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The structural, mechanical, elastic anisotropic, and electronic properties of the monoclinic phase of m-Si₃N₄, m-Si₂GeN₄, m-SiGe₂N₄, and m-Ge₃N₄ are systematically investigated in this work. The calculated results of lattice parameters, elastic constants and elastic moduli of m-Si₃N₄ and m-Ge₃N₄ are in good agreement with previous theoretical results. Using the Voigt-Reuss-Hill method, elastic properties such as bulk modulus B and shear modulus G are investigated. The calculated ratio of B/G and Poisson's ratio v show that only m-SiGe₂N₄ should belong to a ductile material in nature. In addition, m-SiGe₂N₄ possesses the largest anisotropic shear modulus, Young's modulus, Poisson's ratio, and percentage of elastic anisotropies for bulk modulus A_B and shear modulus A_G, and universal anisotropic index A_U among m-Si_xGe_3-xN₄ (x=0, 1, 2, 3.) The results of electronic band gap reveal that m-Si₃N₄, m-Si₂GeN₄, m-SiGe₂N₄, and m-Ge₃N₄ are all direct and wide band gap semiconducting materials.

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Negative linear compressibility of generic rotating rigid triangles

周晓勤, 张磊, 杨璐

2017 (12): 126201-126201. doi: 10.1088/1674-1056/26/12/126201

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The compressibility properties of systems consisting of generic rotating rigid triangles are analyzed and discussed. It is shown that these systems which are usually associated with auxeticity can exhibit strongly anisotropic properties for certain conformations, which may give rise to the anomalous property of negative linear compressibility (NLC), that is, the system with particular geometry will expand along one direction when loaded hydrostatically. It is also shown that through carefully choosing the geometric features (i.e. the dimensions and the alignment of the rotating triangles as well as the angles between them) and the direction along which the linear compressibility is measured, one may control the magnitude and range of the NLC. All this provides a novel but effective method of manufacturing the systems which can be tailored to achieve particular values of NLC to fit particular practical applications.

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Effects of alloying element on stabilities, electronic structures, and mechanical properties of Pd-based superalloys

闫佩, 种晓宇, 蒋业华, 冯晶

2017 (12): 126202-126202. doi: 10.1088/1674-1056/26/12/126202

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The thermodynamic stabilities, electronic structures, and mechanical properties of the Pd-based superalloys are studied by first principles calculations. In this work, we discuss the effect of Pd-based superalloys made from Al, Si, Sc, Ti, V, Cr, Mn, Fe, Cu, Zn, Y, Zr, Nb, Mo, Tc, Hf, Ta, W, Re, Os, Ir and Pt, and we also calculate a face centered cubic (fcc) structure 2×2×2 superalloy including 31 Pd atoms and one alloying element TM (Pd₃₁TM). The mixing energies of these Pd-Based superalloys are negative, indicating that all Pd-based superalloys are thermodynamically stable. The Pd₃₁Mn has the lowest mixing energy with a value of-0.97 eV/atom. The electronic structures of the Pd-based superalloys are also studied, the densities of states, elastic constants and moduli of the mechanical properties of the Pd-based superalloys are determined by the stress-strain method and Voigt-Reuss-Hill approximation. It is found that Pd₃₁TM is mechanically stable, and Pd₃₁Tc has the largest C₁₁, with a value 279.7 GPa. The Pd₃₁Cr has the highest bulk modulus with a value of 299.8 GPa. The Pd₃₁Fe has the largest shear modulus and Young's modulus with the values of 73.8 GPa and 195.2 GPa, respectively. By using the anisotropic index, the anisotropic mechanical properties of the Pd₃₁TM are discussed, and three-dimensional (3D) surface contours and the planar projections on (001) and (110) planes are also investigated by the Young modulus.

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Variations in defect substructure and fracture surface of commercially pure aluminum under creep in weak magnetic field

陈希章

2017 (12): 126203-126203. doi: 10.1088/1674-1056/26/12/126203

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Commercially pure polycrystalline aluminum of grade A85, as a test material, is investigated. Using scanning and transmission electron microscopy the aluminum fine structure and fracture surface are analyzed. Fractures are studied in the regime of creep with and without a simultaneous effect of 0.3-T magnetic field. It is found that the application of a magnetic field in a linear stage of creep leads to substructure imperfection increasing. Furthermore, the magnetic field effect on aluminum in the process of creep causes the average scalar density of dislocations to increase and induces the process of dislocation loop formation to strengthen. Fractographic investigation of the fracture surface shows that in the fibrous fracture zone the average size of plastic fracture pits decreases more than twice under creep in the condition of external magnetic field compared with in the conventional experimental condition. In a shear zone, the magnetic field causes the average size of fracture pits to decrease. Experimental data obtained in the research allow us to conclude that the magnetic field effect on aluminum in the process of creep leads to the fracture toughness value of the material decreasing, which will affect the state of defect substructure of the volume and surface layer of the material. The influence of the magnetic field is analyzed on the basis of the magneto-plasticity effect.

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A diffusion model for solute atoms diffusing and aggregating in nuclear structural materials

宋泉, 孟繁新, 宁博元, 庄军, 宁西京

2017 (12): 126601-126601. doi: 10.1088/1674-1056/26/12/126601

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In nuclear structural materials, the nuclear irradiations induce the precipitations of soluble elements or produce the insoluble elements such as He atoms that may form clusters, heavily shortening the service life-times of the materials. In the present work, a diffusion model is developed to predict where and how fast the solute atoms (either soluble or insoluble) aggregate, and this model is applied to the study of the formation and growth of He bubbles in metal tritides (PdT_0.6, ErT₂, NbT_0.0225, VT_0.5, TaT_0.097, TiT_1.5, ZrT_1.6) within one thousand days. The results are in good agreement with the available experimental observations and suggest that searching for metals with a barrier of more than 1.1 eV for a single He atom diffusion and making more defects in metal tritides can significantly reduce the growth of He bubbles and extend the service time of the metals.

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Segregations and desorptions of Ge atoms in nanocomposite Si_1-xGe_x films during high-temperature annealing

汪煜, 杨濛, 王刚, 魏晓旭, 王军转, 李昀, 左则文, 郑有炓, 施毅

2017 (12): 126801-126801. doi: 10.1088/1674-1056/26/12/126801

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Nanocomposite Si_1-xGe_x films are deposited by dual-source jet-type inductively coupled plasma chemical vapor deposition (jet-ICPCVD). The segregations and desorptions of Ge atoms, which dominate the structural evolutions of the films during high-temperature annealing, are investigated. When the annealing temperature (T_a) is 900℃, the nanocomposite Si_1-xGe_x films are well crystallized, and nanocrystals (NCs) with the core-shell structure form in the films. After being annealed at 1000℃ (above the melting point of bulk Ge), Ge atoms accumulate on the surfaces of Ge-rich films, whereas pits appear on films with lower Ge content, resulting from desorption. Meanwhile, voids are observed in the films. A cone-like structure involving the percolation of the homogeneous clusters and the crystallization of NCs enhances Ge segregation.

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Molecular dynamics study of plastic deformation mechanism in Cu/Ag multilayers

田圆圆, 李甲, 胡泽英, 王志鹏, 方棋洪

2017 (12): 126802-126802. doi: 10.1088/1674-1056/26/12/126802

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The plastic deformation mechanism of Cu/Ag multilayers is investigated by molecular dynamics (MD) simulation in a nanoindentation process. The result shows that due to the interface barrier, the dislocations pile-up at the interface and then the plastic deformation of the Ag matrix occurs due to the nucleation and emission of dislocations from the interface and the dislocation propagation through the interface. In addition, it is found that the incipient plastic deformation of Cu/Ag multilayers is postponed, compared with that of bulk single-crystal Cu. The plastic deformation of Cu/Ag multilayers is affected by the lattice mismatch more than by the difference in stacking fault energy (SFE) between Cu and Ag. The dislocation pile-up at the interface is determined by the obstruction of the mismatch dislocation network and the attraction of the image force. Furthermore, this work provides a basis for further understanding and tailoring metal multilayers with good mechanical properties, which may facilitate the design and development of multilayer materials with low cost production strategies.

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Tuning electronic properties of the S₂/graphene heterojunction by strains from density functional theory

雷军辉, 王秀峰, 林建国

2017 (12): 127101-127101. doi: 10.1088/1674-1056/26/12/127101

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Based on the density functional calculations, the structural and electronic properties of the WS₂/graphene heterojunction under different strains are investigated. The calculated results show that unlike the free mono-layer WS₂, the monolayer WS₂ in the equilibrium WS₂/graphene heterojunctionis characterized by indirect band gap due to the weak van der Waals interaction. The height of the schottky barrier for the WS₂/graphene heterojunction is 0.13 eV, which is lower than the conventional metal/MoS₂ contact. Moreover, the band properties and height of schottky barrier for WS₂/graphene heterojunction can be tuned by strain. It is found that the height of the schottky barrier can be tuned to be near zero under an in-plane compressive strain, and the band gap of the WS₂ in the heterojunction is turned into a direct band gap from the indirect band gap with the increasing schottky barrier height under an in-plane tensile strain. Our calculation results may provide a potential guidance for designing and fabricating the WS₂-based field effect transistors.

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Effects of post-annealed floating gate on the performance of AlGaN/GaN heterostructure field-effect transistors

崔鹏, 林兆军, 付晨, 刘艳, 吕元杰

2017 (12): 127102-127102. doi: 10.1088/1674-1056/26/12/127102

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AlGaN/GaN heterostructure field-effect transistors (HFETs) with different floating gate lengths and floating gates annealed at different temperatures, are fabricated. Using the measured capacitance-voltage curves of the gate Shottky contacts for the AlGaN/GaN HFETs, we find that after floating gate experiences 600℃ rapid thermal annealing, the larger the floating gate length, the larger the two-dimensional electron gas electron density under the gate region is. Based on the measured capacitance-voltage and current-voltage curves, the strain of the AlGaN barrier layer in the gate region is calculated, which proves that the increased electron density originates from the increased strain of the AlGaN barrier layer.

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Characteristics and mechanism analysis of Fano resonances in Π-shaped gold nano-trimer

钟汉华, 周见红, 顾辰杰, 王勉, 方云团, 许田, 周骏

2017 (12): 127301-127301. doi: 10.1088/1674-1056/26/12/127301

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Fano interference of metallic nanostructure is an effective way to reduce the irradiation loss and improve the spectral resolution. A Π-shaped gold nano-trimer, which is composed of a gold nanorod and two gold nanorices, is presented to investigate the properties of Fano resonances in the visible spectrum by using the finite element method (FEM). The theoretical analysis demonstrates that the Fano resonance of the Π-shaped gold nano-trimer is attributed to the near-field interaction between the bright mode of the nanorice pair and the dark quadrupole mode of the nanorod. Furthermore, by breaking the geometric symmetry of the nanostructure the line-shape spectrum with double Fano resonances of Π-shaped gold nano-trimer is obtained and exhibits structure-dependent and medium-dependent characteristics. It is a helpful strategy to design a plasmonic nanostructure for implementing multiple Fano resonances in practical applications.

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Capacitance extraction method for a gate-induced quantum dot in silicon nanowire metal-oxide-semiconductor field-effect transistors

徐雁冰, 杨红官

2017 (12): 127302-127302. doi: 10.1088/1674-1056/26/12/127302

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An improved method of extracting the coupling capacitances of quantum dot structure is reported. This method is based on measuring the charge transfer current in the silicon nanowire metal-oxide-semiconductor field-effect transistor (MOSFET), in which the channel closing and opening are controlled by applying alternating-current biases with a half period phase shift to the dual lower gates. The capacitances around the dot, including fringing capacitances and barrier capacitances, are obtained by analyzing the relation between the transfer current and the applied voltage. This technique could be used to extract the capacitance parameters not only from the bulk silicon devices, but also from the silicon-on-insulator (SOI) MOSFETs.

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Spin-valley-dependent transport and giant tunneling magnetoresistance in silicene with periodic electromagnetic modulations

刘一曼, 邵怀华, 周光辉, 朴红光, 潘礼庆, 刘敏

2017 (12): 127303-127303. doi: 10.1088/1674-1056/26/12/127303

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The transport property of electrons tunneling through arrays of magnetic and electric barriers is studied in silicene. In the tunneling transmission spectrum, the spin-valley-dependent filtered states can be achieved in an incident energy range which can be controlled by the electric gate voltage. For the parallel magnetization configuration, the transmission is asymmetric with respect to the incident angle θ, and electrons with a very large negative incident angle can always transmit in propagating modes for one of the spin-valley filtered states under a certain electromagnetic condition. But for the antiparallel configuration, the transmission is symmetric about θ and there is no such transmission channel. The difference of the transmission between the two configurations leads to a giant tunneling magnetoresistance (TMR) effect. The TMR can reach to 100% in a certain Fermi energy interval around the electrostatic potential. This energy interval can be adjusted significantly by the magnetic field and/or electric gate voltage. The results obtained may be useful for future valleytronic and spintronic applications, as well as magnetoresistance device based on silicene.

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Quantum spin Hall and quantum valley Hall effects in trilayer graphene and their topological structures

Majeed Ur Rehman,A A Abid

2017 (12): 127304-127304. doi: 10.1088/1674-1056/26/12/127304

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The present study pertains to the trilayer graphene in the presence of spin orbit coupling to probe the quantum spin/valley Hall effect. The spin Chern-number C_s for energy-bands of trilayer graphene having the essence of intrinsic spin-orbit coupling is analytically calculated. We find that for each valley and spin, C_s is three times larger in trilayer graphene as compared to single layer graphene. Since the spin Chern-number corresponds to the number of edge states, consequently the trilayer graphene has edge states, three times more in comparison to single layer graphene. We also study the trilayer graphene in the presence of both electric-field and intrinsic spin-orbit coupling and investigate that the trilayer graphene goes through a phase transition from a quantum spin Hall state to a quantum valley Hall state when the strength of the electric field exceeds the intrinsic spin coupling strength. The robustness of the associated topological bulk-state of the trilayer graphene is evaluated by adding various perturbations such as Rashba spin-orbit (RSO) interaction α_R, and exchange-magnetization M. In addition, we consider a theoretical model, where only one of the outer layers in trilayer graphene has the essence of intrinsic spin-orbit coupling, while the other two layers have zero intrinsic spin-orbit coupling. Although the first Chern number is non-zero for individual valleys of trilayer graphene in this model, however, we find that the system cannot be regarded as a topological insulator because the system as a whole is not gaped.

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Quantum oscillations and nontrivial transport in (Bi_0.92In_0.08)₂Se₃

张敏昊, 李焱, 宋凤麒, 王学锋, 张荣

2017 (12): 127305-127305. doi: 10.1088/1674-1056/26/12/127305

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Quantum phase transition in topological insulators has drawn heightened attention in condensed matter physics and future device applications. Here we report the magnetotransport properties of single crystalline (Bi_0.92In_0.08)₂Se₃. The average mobility of~1000 cm²·V^-1·s^-1 is obtained from the Lorentz law at the low field (< 3 T) up to 50 K. The quantum oscillations rise at a field of~5 T, revealing a high mobility of~1.4×10⁴ cm²·V^-1·s^-1 at 2 K. The Dirac surface state is evident by the nontrivial Berry phase in the Landau-Fan diagram. The properties make the (Bi_0.92In_0.08)₂Se₃ a promising platform for the investigation of quantum phase transition in topological insulators.

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Effects of rapid thermal annealing on crystallinity and Sn surface segregation of Ge_1-xSn_x films on Si (100) and Si (111)

苗渊浩, 胡辉勇, 宋建军, 宣荣喜, 张鹤鸣

2017 (12): 127306-127306. doi: 10.1088/1674-1056/26/12/127306

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Germanium-tin films with rather high Sn content (28.04% and 29.61%) are deposited directly on Si (100) and Si (111) substrates by magnetron sputtering. The mechanism of the effect of rapid thermal annealing on the Sn surface segregation of Ge_1-xSn_x films is investigated by x-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The x-ray diffraction (XRD) is also performed to determine the crystallinities of the Ge_1-xSn_x films. The experimental results indicate that root mean square (RMS) values of the annealed samples are comparatively small and have no noticeable changes for the as-grown sample when annealing temperature is below 400℃. The diameter of the Sn three-dimensional (3D) island becomes larger than that of an as-grown sample when the annealing temperature is 700℃. In addition, the Sn surface composition decreases when annealing temperature ranges from 400℃ to 700℃. However, Sn bulk compositions in samples A and B are kept almost unchanged when the annealing temperature is below 600℃. The present investigation demonstrates that the crystallinity of Ge_1-xSn_x/Si (111) has no obvious advantage over that of Ge_1-xSn_x/Si (100) and the selection of Si (111) substrate is an effective method to improve the surface morphologies of Ge_1-xSn_x films. We also find that more severe Sn surface segregation occurs in the Ge_1-xSn_x/Si (111) sample during annealing than in the Ge_1-xSn_x/Si (100) sample.

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Macro-performance of multilayered thermoelectric medium

宋坤, 宋豪鹏, 高存法

2017 (12): 127307-127307. doi: 10.1088/1674-1056/26/12/127307

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The effective properties of thermoelectric composites are well known to depend on boundary conditions, which causes the macro performance of thermoelectric composite to be difficult to assess. The overall macro-performance of multilayered thermoelectric medium is discussed in this paper. The analytical solutions are obtained, including the heat flux, temperature, electric potential, and the overall energy conversion efficiency. The results show that there are unique relationships between the temperature/electric potential and the electric current/energy flux in the material, and whether the material is independent of or embedded in thermoelectric composites. Besides, the Peltier effect at the interface can significantly improve the overall energy conversion efficiency of thermoelectric composites. These results provide a powerful tool to analyze the effective behaviors of thermoelectric composites.

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Dynamic localization of two electrons in AC-driven triple quantum dots and quantum dot shuttles

屈晋先, 段素青, 杨宁

2017 (12): 127308-127308. doi: 10.1088/1674-1056/26/12/127308

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We analyze the dynamic localization of two interacting electrons induced by alternating current electric fields in triple quantum dots and triple quantum dot shuttles. The calculation of the long-time averaged occupation probability shows that both the intra-and inter-dot Coulomb interaction can increase the localization of electrons even when the AC field is not very large. The mechanical oscillation of the quantum dot shuttles may keep the localization of electrons at a high level within a range if its frequency is quite a bit smaller than the AC field. However, the localization may be depressed if the frequency of the mechanical oscillation is the integer times of the frequency of the AC field. We also derive the analytical condition of two-electron localization both for triple quantum dots and quantum dot shuttles within the Floquet formalism.

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Evaluation of threading dislocation density of strained Ge epitaxial layer by high resolution x-ray diffraction

苗渊浩, 胡辉勇, 李鑫, 宋建军, 宣荣喜, 张鹤鸣

2017 (12): 127309-127309. doi: 10.1088/1674-1056/26/12/127309

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The analysis of threading dislocation density (TDD) in Ge-on-Si layer is critical for developing lasers, light emitting diodes (LEDs), photodetectors (PDs), modulators, waveguides, metal oxide semiconductor field effect transistors (MOSFETs), and also the integration of Si-based monolithic photonics. The TDD of Ge epitaxial layer is analyzed by etching or transmission electron microscope (TEM). However, high-resolution x-ray diffraction (HR-XRD) rocking curve provides an optional method to analyze the TDD in Ge layer. The theory model of TDD measurement from rocking curves was first used in zinc-blende semiconductors. In this paper, this method is extended to the case of strained Ge-on-Si layers. The HR-XRD 2θ/ω scan is measured and Ge (004) single crystal rocking curve is utilized to calculate the TDD in strained Ge epitaxial layer. The rocking curve full width at half maximum (FWHM) broadening by incident beam divergence of the instrument, crystal size, and curvature of the crystal specimen is subtracted. The TDDs of samples A and B are calculated to be 1.41×10⁸ cm^-2 and 6.47×10⁸ cm^-2, respectively. In addition, we believe the TDDs calculated by this method to be the averaged dislocation density in the Ge epitaxial layer.

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One-dimensional method of investigating the localized states in armchair graphene-like nanoribbons with defects

谢阳, 胡智健, 丁文浩, 吕小龙, 谢航

2017 (12): 127310-127310. doi: 10.1088/1674-1056/26/12/127310

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In this paper we propose a type of new analytical method to investigate the localized states in the armchair graphene-like nanoribbons. The method is based on the tight-binding model and with a standing wave assumption. The system of armchair graphene-like nanoribbons includes the armchair supercells with arbitrary elongation-type line defects and the semi-infinite nanoribbons. With this method, we analyze many interesting localized states near the line defects in the graphene and boron-nitride nanoribbons. We also derive the analytical expressions and the criteria for the localized states in the semi-infinite nanoribbons.

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Comparison of band structure and superconductivity in FeSe_0.5Te_0.5 and FeS

杨阳, 冯世全, 向圆圆, 路洪艳, 王万胜

2017 (12): 127401-127401. doi: 10.1088/1674-1056/26/12/127401

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The isovalent iron chalcogenides, FeSe_0.5Te_0.5 and FeS, share similar lattice structures but behave very differently in superconducting properties. We study the underlying mechanism theoretically. By first principle calculations and tight-binding fitting, we find the spectral weight of the d_X²-Y² orbital changes remarkably in these compounds. While there are both electron and hole pockets in FeSe_0.5Te_0.5 and FeS, a small hole pocket with a mainly d_X²-Y² character is absent in FeS. We find the spectral weights of d_X²-Y² orbital change remarkably, which contribute to electron and hole pockets in FeSe_0.5Te_0.5 but only to electron pockets in FeS. We then perform random-phase-approximation and unbiased singular-mode functional renormalization group calculations to investigate possible superconducting instabilities that may be triggered by electron-electron interactions on top of such bare band structures. For FeSe_0.5Te_0.5, we find a fully gapped s^±-wave pairing that can be associated with spin fluctuations connecting electron and hole pockets. For FeS, however, a nodal d_xy (or d_x²-y² in an unfolded Broullin zone) is favorable and can be related to spin fluctuations connecting the electron pockets around the corner of the Brillouin zone. Apart from the difference in chacogenide elements, we propose the main source of the difference is from the d_X²-Y² orbital, which tunes the Fermi surface nesting vector and then influences the dominant pairing symmetry.

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A hybrid functional first-principles study on the band structure of non-strained Ge_1-xSn_x alloys

王小怀, 陈城钊, 冯胜奇, 魏心源, 李云

2017 (12): 127402-127402. doi: 10.1088/1674-1056/26/12/127402

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Using hybrid-functional first-principles calculation combined with the supercell method and band unfolding technique we investigate the band structure of non-strained Ge_1-xSn_x alloys with various Sn concentrations. The calculations show that at the Sn concentration of~3.1 mol% the GeSn alloy presents a direct band gap. The variation of the band structure are ascribed to the weaker electro-negativity of Sn atoms and a slight charge transfer from Sn atoms to Ge atoms.

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Random crystal field effect on hysteresis loops and compensation behavior of mixed spin-(1,3/2) Ising system

K Htoutou,Y Benhouria,A Oubelkacem,R Ahl laamara,L B Drissi

2017 (12): 127501-127501. doi: 10.1088/1674-1056/26/12/127501

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Magnetic hysteresis and compensation behavior of a mixed spin-(1, 3/2) Ising model on a square lattice are investigated in the framework of effective field theory based on a probability distribution technique. The effect of random crystal field, ferromagnetic and ferrimagnetic exchange interaction on hysteresis loops and compensation phenomenon are discussed. A number of characteristic phenomena have been reported such as the observation of triple hysteresis loops at low temperatures and for negative values of random crystal field. Critical and double compensation temperatures have been also found. The obtained results are also compared to some previous works.

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Low temperature magnetic and magnetostrictive properties in Pr(Fe_1-xCo_x)_1.9 cubic Laves alloys

唐妍梅, 徐行祤, 黄业, 唐志雄, 唐少龙

2017 (12): 127502-127502. doi: 10.1088/1674-1056/26/12/127502

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The structures, spin reorientations, magnetic, and magnetostrictive properties of the polycrystalline Pr(Fe_1-xCo_x)_1.9 (x=0-1.0) cubic laves phase alloys between 5 K and 300 K are investigated. Large low-field magnetostrictions are observed at 5 K in the alloys with x=0.2 and 0.4 due to the low magnetic anisotropies of these two alloys. A large negative magnetostriction of about-1130 ppm is found in PrCo_1.9 alloy at 5 K. The magnetizations of the alloys with 0 ≤ x ≤ 0.6 decrease abnormally at the spin reorientation temperature T_sr, and an abnormity is detected in the alloy with x=1.0 at its Curie temperature T_c (45 K). The substitution of Fe by Co increases the value of T_sr in the alloy with x value increasing from 0.0 to 0.4, and then reduces the value of T_sr with x value further increasing to 0.6.

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Modeling of LiFePO4 battery open circuit voltage hysteresis based on recursive discrete Preisach model

孙维毅, 闵海涛, 郭冬妮, 于远彬

2017 (12): 127503-127503. doi: 10.1088/1674-1056/26/12/127503

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This paper focuses on the modeling of LiFePO4 battery open circuit voltage (OCV) hysteresis. There exists obvious hysteresis in LiFePO4 battery OCV, which makes it complicated to model the LiFePO4 battery. In this paper, the recursive discrete Preisach model (RDPM) is applied to the modeling of LiFePO4 battery OCV hysteresis. The theory of RDPM is illustrated in detail and the RDPM on LiFePO4 battery OCV hysteresis modeling is verified in experiment. The robust of RDPM under different working conditions are also demonstrated in simulation and experiment. The simulation and experimental results show that the proposed method can significantly improve the accuracy of LiFePO4 battery OCV hysteresis modeling when the battery OCV characteristic changes, which conduces to the online state estimation of LiFePO4 battery.

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Near-interface oxide traps in 4H-SiC MOS structures fabricated with and without annealing in NO

孙秋杰, 张玉明, 宋庆文, 汤晓燕, 张艺蒙, 李诚瞻, 赵艳黎, 张义门

2017 (12): 127701-127701. doi: 10.1088/1674-1056/26/12/127701

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Near-interface oxide traps (NIOTs) in 4H-SiC metal-oxide-semiconductor (MOS) structures fabricated with and without annealing in NO are systematically investigated in this paper. The properties of NIOTs in SiC MOS structures prepared with and without annealing in NO are studied and compared in detail. Two main categories of the NIOTs, the “slow” and “fast” NIOTs, are revealed and extracted. The densities of the “fast” NIOTs are determined to be 0.76×10¹¹ cm^-2 and 0.47×10¹¹ cm^-2 for the N₂ post oxidation annealing (POA) sample and NO POA sample, respectively. The densities of “slow” NIOTs are 0.79×10¹¹ cm^-2 and 9.44×10¹¹ cm^-2 for the NO POA sample and N₂ POA sample, respectively. It is found that the NO POA process only can significantly reduce “slow” NIOTs. However, it has a little effect on “fast” NIOTs. The negative and positive constant voltage stresses (CVS) reveal that electrons captured by those “slow” NIOTs and bulk oxide traps (BOTs) are hardly emitted by the constant voltage stress.

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Singular variation property of elastic constants of piezoelectric ceramics shunted to negative capacitance

胡吉英, 李朝晖, 李启虎

2017 (12): 127702-127702. doi: 10.1088/1674-1056/26/12/127702

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Piezoelectric shunt damping has been widely used in vibration suppression, sound absorption, noise elimination, etc. In such applications, the variant elastic constants of piezoelectric materials are the essential parameters that determine the performances of the systems, when piezoelectric materials are shunted to normal electrical elements, i.e., resistance, inductance and capacitance, as well as their combinations. In recent years, many researches have demonstrated that the wideband sound absorption or vibration suppression can be realized with piezoelectric materials shunted to negative capacitance. However, most systems using the negative-capacitance shunt circuits show their instabilities in the optimal condition, which are essentially caused by the singular variation properties of elastic constants of piezoelectric materials when shunted to negative capacitance. This paper aims at investigating the effects of negative-capacitance shunt circuits on elastic constants of a piezoelectric ceramic plate through theoretical analyses and experiments, which gives an rational explanation for why negative capacitance shunt circuit is prone to make structure instable. First, the relationships between the elastic constants c₁₁, c₃₃, c₅₅ of the piezoelectric ceramic and the shunt negative capacitance are derived with the piezoelectric constitutive law theoretically. Then, an experimental setup is established to verify the theoretical results through observing the change of elastic constant c₅₅ of the shunted piezoelectric plate with the variation of negative capacitance. The experimental results are in good agreement with the theoretical analyses, which reveals that the instability of the shunt damping system is essentially caused by the singular variation property of the elastic constants of piezoelectric material shunted to negative capacitance.

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Design and theoretical study of a polarization-insensitive multiband terahertz metamaterial bandpass filter

李海鹏, 付文悦, 沈晓鹏, 韩奎, 王伟华

2017 (12): 127801-127801. doi: 10.1088/1674-1056/26/12/127801

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We report the design of a novel multiband metamaterial bandpass filter (BPF) in the terahertz (THz)-wave region. The designed BPF is composed of a metal-dielectric-metal sandwiched structure with three nested rings on the top surface and a cross structure on the bottom surface. Full-wave simulation results show that the designed BPF has three transmission peaks at frequencies of 0.42, 1.27, and 1.86 THz with transmission rates of-0.87,-1.85, and-1.83 dB, respectively. Multi-reflection interference theory is introduced to explain the transmission mechanism of the designed triple-band BPF. The theoretical transmission spectrum is in good agreement with the full-wave simulated results. The designed BPF can maintain a stable performance as the incident angle varies from 0° to 30° for both transverse electric and transverse magnetic polarizations of the incident wave. The designed BPF can be potentially used in THz devices due to its multiband transmissions, polarization insensitivity, and stable wide-angle response in the THz region.

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Modeling for multi-resonant behavior of broadband metamaterial absorber with geometrical substrate

张凯伦, 侯志灵, 毕松, 房惠敏

2017 (12): 127802-127802. doi: 10.1088/1674-1056/26/12/127802

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Despite widespread use for extending absorption bandwidth, the coexistence and coupling mechanism of multiple resonance is not well understood. We propose two models to describe the multi-resonant behavior of a broadband metamaterial absorber with geometrical-array substrate (GAS). The multi-resonance coupling of GAS is well described by logarithmic law. The interaction between metasurface and GAS can further broaden the absorption bandwidth by generating a new resonance which coexists with original resonances in substrate. The proposed models can thoroughly describe this multiple-resonance behavior, highlighting guidelines for designing broadband absorbers.

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Positive gate bias stress-induced hump-effect in elevated-metal metal-oxide thin film transistors

齐栋宇, 张冬利, 王明湘

2017 (12): 128101-128101. doi: 10.1088/1674-1056/26/12/128101

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Under the action of a positive gate bias stress, a hump in the subthreshold region of the transfer characteristic is observed for the amorphous indium-gallium-zinc oxide thin film transistor, which adopts an elevated-metal metal-oxide structure. As stress time goes by, both the on-state current and the hump shift towards the negative gate-voltage direction. The humps occur at almost the same current levels for devices with different channel widths, which is attributed to the parasitic transistors located at the channel width edges. Therefore, we propose that the positive charges trapped at the back-channel interface cause the negative shift, and the origin of the hump is considered as being due to more positive charges trapped at the edges along the channel width direction. On the other hand, the hump-effect becomes more significant in a short channel device (L=2 μm). It is proposed that the diffusion of oxygen vacancies takes place from the high concentration source/drain region to the intrinsic channel region.

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Nucleation mechanism and morphology evolution of MoS₂ flakes grown by chemical vapor deposition

许贺菊, 米建松, 李云, 张彬, 丛日东, 傅广生, 于威

2017 (12): 128102-128102. doi: 10.1088/1674-1056/26/12/128102

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We study the nucleation mechanism and morphology evolution of MoS₂ flakes grown by chemical vapor deposition (CVD) on SiO₂/Si substrates with using S and MoO₃ powders. The MoS₂ flake is of monolayer with triangular nucleation, which might arise from the initial MoO_3-x that is deposited on the substrate, and then bonded with S to form MoS₂ flake. The ratio of Mo and S is higher than 1:2 at the beginning with Mo terminated triangular nucleation formed. After that, the morphology of MoS₂ flake evolves from triangle to similar hexagon, then to truncated triangle which is determined by the faster growth speed of Mo termination than that of S termination under the S rich environment. The nucleation density does not increase linearly with the increase of reactant concentration, which could be explained by the two-dimensional nucleation theory.

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Optical properties of wavelength-tunable green-emitting color conversion glass ceramics

李杨, 胡丽丽, 杨波波, 石明明, 邹军

2017 (12): 128103-128103. doi: 10.1088/1674-1056/26/12/128103

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Color conversion glass ceramics are prepared by cosintering borosilicate glass frits and green 0.06Ce:Y_2.94(Al_1-xGa_x)₅O₁₂ phosphors. The crystal structures, the influence of Ga concentration on the photoluminescence (PL), and reliability properties of the color conversion glass ceramics are investigated. The PL emission wavelengths of 0.06Ce:Y_2.94(Al_1-xGa_x)₅O₁₂ glass ceramics show blue shift from 545 nm to 525 nm with increasing Ga content (x value) under excited at 460 nm. Reliability test results show that the quantum yield (QY) of 0.06Ce:Y_2.94(Al_1-xGa_x)₅O₁₂ glass ceramics decreases from 70.60% to 59.06% with x value increasing from 0.15 to 0.35 under the ambient condition of 85℃/RH85% for the exposure time of 168 h. And the quantum yield (QY) of 0.06Ce:Y_2.94(Al_1-xGa_x)₅O₁₂ glass ceramics decreases from 65.13% to 52.23% after being soaked into boiled water for 4 h. The finding reveals that the addition of Ga can deteriorate the reliability of the color conversion glass ceramics.

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Effect of elastic strain energy on grain growth and texture in AZ31 magnesium alloy by phase-field simulation

何日, 王明涛, 金剑锋, 宗亚平

2017 (12): 128201-128201. doi: 10.1088/1674-1056/26/12/128201

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A phase-field model is modified to investigate the grain growth and texture evolution in AZ31 magnesium alloy during stressing at elevated temperatures. The order parameters are defined to represent a physical variable of grain orientation in terms of three angles in spatial coordinates so that the grain volume of different order parameters can be used to indicate the texture of the alloy. The stiffness tensors for different grains are different because of elastic anisotropy of the magnesium lattice. The tensor is defined by transforming the standard stiffness tensor according to the angle between the (0001) plane of a grain and the direction of applied stress. Therefore, different grains contribute to different amounts of work under applied stress. The simulation results are well-explained by using the limited experimental data available, and the texture results are in good agreement with the experimental observations. The simulation results reveal that the applied stress strongly influences AZ31 alloy grain growth and that the grain-growth rate increases with the applied stress increasing, particularly when the stress is less than 400 MPa. A parameter (△d) is introduced to characterize the degree of grain-size variation due to abnormal grain growth; the △d increases with applied stress increasing and becomes considerably large only when the stress is greater than 800 MPa. Moreover, the applied stress also results in an intensive texture of the 〈0001〉 axis parallel to the direction of compressive stress in AZ31 alloy after growing at elevated temperatures, only when the applied stress is greater than 500 MPa.

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Bursting oscillations in a hydro-turbine governing system with two time scales

韩青爽, 陈帝伊, 张浩

2017 (12): 128202-128202. doi: 10.1088/1674-1056/26/12/128202

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A fast-slow coupled model of the hydro-turbine governing system (HTGS) is established by introducing frequency disturbance in this paper. Based on the proposed model, the performances of two time scales for bursting oscillations in the HTGS are investigated and the effect of periodic excitation of frequency disturbance is analyzed by using the bifurcation diagrams, time waveforms and phase portraits. We find that stability and operational characteristics of the HTGS change with the value of system parameter k_d. Furthermore, the comparative analyses for the effect of the bursting oscillations on the system with different amplitudes of the periodic excitation a are carried out. Meanwhile, we obtain that the relative deviation of the mechanical torque m_t rises with the increase of a. These methods and results of the study, combined with the performance of two time scales and the fast-slow coupled engineering model, provide some theoretical bases for investigating interesting physical phenomena of the engineering system.

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Compact superconducting single-and dual-band filter design using multimode stepped-impedance resonator

王翔, 魏斌, 陆喜龙, 郭旭波, 曹必松

2017 (12): 128501-128501. doi: 10.1088/1674-1056/26/12/128501

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This study presents two multimode stepped-impedance structures to design single-and dual-band filters. Transmission zeroes are introduced for the single-band filter by using dual-mode stepped-impedance resonators. The single-band filter with high selectivity is centered at 6.02 GHz and has a fractional bandwidth (FBW) of 25.6%. Four stubs (two low frequency and two high frequency ones) are connected to the rectangular patch in the center to construct a quadruple-mode resonator. The independent conditions of the center frequencies of the high and low bands of the resonator are analyzed. A dual-band filter, which operates at 1.53 GHz and 2.44 GHz with FWBs of 12.1% and 14.1%, respectively is designed. The single-and dual-band filters are both fabricated with double-sided YBCO films and they can be used in mobile and satellite communications.

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Electrically controlled optical switch in the hybrid opto-electromechanical system

秦立国, 王中阳, 马鸿洋, 王淑梅, 龚尚庆

2017 (12): 128502-128502. doi: 10.1088/1674-1056/26/12/128502

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To promote the future quantum information technologies, we demonstrate an electrically driven optical switch based on quantum interference in a hybrid opto-electromechanical system, which consists of an opto-mechanical cavity and an external electric circuit. The key element of our scheme is a moveable mirror of cavity as a charged mechanical oscillator capacitively coupled to a fixed charged plate in a variable capacitor. By adjusting the voltage of the capacitor, the displacement of the moveable mirror is modulated, then the cavity field can be electrically turned on or off due to the detuning of the cavity. Based on the cavity induced transparency, the transparency window can be electrically switched on or off by turning on or off the cavity field. Therefore, the susceptibility of the medium in the cavity can be electrically controlled, i.e., the scheme of the electrically controlled absorption switching can be demonstrated. This electrically driven optical switch will excite a development trend and implementation prospect towards the integration and miniaturization of quantum module device in a chip.

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Anisotropic formation mechanism and nanomechanics for the self-assembly process of cross-β peptides

邓礼, 赵玉荣, 周鹏, 徐海, 王延颋

2017 (12): 128701-128701. doi: 10.1088/1674-1056/26/12/128701

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Nanostructures self-assembled by cross-β peptides with ordered structures and advantageous mechanical properties have many potential applications in biomaterials and nanotechnologies. Quantifying the intra-and inter-molecular driving forces for peptide self-assembly at the atomistic level is essential for understanding the formation mechanism and nanomechanics of various morphologies of self-assembled peptides. We investigate the thermodynamics of the intra-and inter-sheet structure formations in the self-assembly process of cross-β peptide KⅢIK by means of steered molecular dynamics simulation combined with umbrella sampling. It is found that the mechanical properties of the intra-and inter-sheet structures are highly anisotropic with their intermolecular bond stiffness at the temperature of 300 K being 5.58 N/m and 0.32 N/m, respectively. This mechanical anisotropy comes from the fact that the intra-sheet structure is stabilized by enthalpy but the inter-sheet structure is stabilized by entropy. Moreover, the formation process of KⅢIK intra-sheet structure is cooperatively driven by the van der Waals (VDW) interaction between the hydrophobic side chains and the electrostatic interaction between the hydrophilic backbones, but that of the inter-sheet structure is primarily driven by the VDW interaction between the hydrophobic side chains. Although only peptide KⅢIK is studied, the qualitative conclusions on the formation mechanism should also apply to other cross-β peptides.

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Computational study of non-catalytic T-loop pocket on CDK proteins for drug development

王慧雯, 王凯丽, 管泽雨, 简弋人, 贾亚, 曾辰, 赵蕴杰

2017 (12): 128702-128702. doi: 10.1088/1674-1056/26/12/128702

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Cyclin-dependent kinases (CDKs) are critical to the cell cycle and many other biological processes, and as such, are considered as one of the promising targets for therapy against cancer and other diseases. Most pan-CDK inhibitors bind to the highly conserved catalytic ATP-binding pocket and therefore lack the specificity to prevent side effects. It is desirable to develop drugs targeting non-catalytic pockets for specificity towards individual CDKs. Here we performed a systematic analysis of non-catalytic pockets on CDKs and identified a region underneath the T-loop, which we term TL pocket, for potential inhibitor development. Specifically, we compared the TL pockets of human CDK2 and CDK7-homolog Pfmrk of Plasmodium falciparum, a malaria-causing parasite. Molecular dynamics simulations of several short peptides revealed that this less conserved TL pocket could be used to design potentially specific inhibitors against malaria disease.

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Biexponential distribution of open times of a toy channel model

李翔, 钟金金, 高学娟, 吴宇宁, 帅建伟, 祁宏

2017 (12): 128703-128703. doi: 10.1088/1674-1056/26/12/128703

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The biexponential distributions of open times are observed in various types of ion channels. In this paper, by discussing a simple channel model, we show that there are two different schemes to understand the biexponential distribution of open times. One scheme is mathematically strict based on generator matrix theory, while the other one has a clear physical explanation according to an approximation process with numerical simulation of Markovian channel dynamics. Our comparison results suggest that even for biologically complex channels, in addition to carrying out a stochastic simulation, the strict theoretical analysis should be considered to understand the multiple exponential distributions of open times.

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Enhanced effect of dimension of receptor-ligand complex and depletion effect on receptor-mediated endocytosis of nanoparticles

刘野, 高庆庆, 刘益军, 赵闯, 毛宗良, 胡林, 刘艳辉

2017 (12): 128704-128704. doi: 10.1088/1674-1056/26/12/128704

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We present an extended analytical model including the depletion effect and the dimension of ligand-receptor complex, aiming to elucidate their influences on endocytosis of spherocylindrical nanoparticles (NPs). It is found that the dimension of ligand-receptor complex (δ) and the depletion effect interrelatedly govern the optimal conditions of NP endocytosis. The endocytosis phase diagram constructed in the space of NP radius and relative aspect ratio indicates that the endocytosis of NP is enhanced evidently by reducing the optimal radius and the threshold radius of endocytosed NP. Meanwhile, through thermodynamic and kinetic analysis of the diffusion of receptors, the dependence of diffusion length on depletion effect and the dimension of ligand-receptor complex can be identified in great detail. For small aspect ratio, diffusion length decreases with increasing concentration c of small bioparticles in cellular environment. Endocytosis speed corresponding to large radius R and high concentration c of small bioparticles strongly depends on the increasing (2r-δ). These results may show some highlights into the conscious design of NPs for diagnostic agents and therapeutic drug delivery applications.

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Molecular dynamic simulation of the thermodynamic and kinetic properties of nucleotide base pair

王宇杰, 王珍, 王晏莉, 张文炳

2017 (12): 128705-128705. doi: 10.1088/1674-1056/26/12/128705

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A nucleotide base pair is the basic unit of RNA structures. Understanding the thermodynamic and kinetic properties of the closing and opening of a base pair is vital for quantitative understanding the biological functions of many RNA molecules. Due to the fast transition rate, it is difficult to directly observe opening and closing of single nucleic acid base pair in experiments. This review will provide a brief summary of the studies about the thermodynamic and kinetic properties of a base pair opening and closing by using molecular dynamic simulation methods.

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Modulation and control of DNA charge inversion

王艳伟, 杨光参

2017 (12): 128706-128706. doi: 10.1088/1674-1056/26/12/128706

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DNA is one of most important biological polyelectrolytes, which is negatively charged in physiological condition. Most of Its charge is neutralized by attracting cations in solution. In some conditions, the effective charge of DNA switches its sign from negative to positive, implying charge inversion of DNA. The underlying microscopic mechanism of the counterintuitive phenomenon is still not fully understood although specific chemical affinity and electrostatic ion correlation are considered as two possible driving forces. In this review, we present some recent experimental progress in the modulation and control of DNA charge by single molecular techniques. It has been shown that DNA charge inversion can be modulated bidirectionly by decreasing or increasing the dielectric constant of solution to make the electrophoretic mobility of DNA increase from a negative value to a positive value. In this meanwhile, charge inversion and condensation of DNA in solution of trivalent and quadrivalent counterions are significantly influenced by pH value of the solution. When mixing quadrivalent counterion with mono-, di-and tri-valent counterions in solution, suppression and promotion of DNA charge inversion can be observed. In addition, hydrophobic effect can play an important role in DNA charge inversiton and compaction. We show that the organic monovalent ions of tetraphenyl chloride arsenic (Ph₄As⁺) can induce DNA compaction and even invert its electrophoretic mobility. Thus, hydrophobic effect can be the main driving force of DNA charge inversion and compaction by the organic monovalent ion.

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Derivation of persistent time for anisotropic migration of cells

刘艳平, 张晓翠, 吴宇宁, 刘雯, 李翔, 刘如川, 刘雳宇, 帅建伟

2017 (12): 128707-128707. doi: 10.1088/1674-1056/26/12/128707

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Cell migration plays an essential role in a wide variety of physiological and pathological processes. In this paper we numerically discuss the properties of an anisotropic persistent random walk (APRW) model, in which two different and independent persistent times are assumed for cell migrations in the x-and y-axis directions. An intrinsic orthogonal coordinates with the primary and non-primary directions can be defined for each migration trajectory based on the singular vector decomposition method. Our simulation results show that the decay time of single exponential distribution of velocity auto-correlation function (VACF) in the primary direction is actually the large persistent time of the APRW model, and the small decay time of double exponential VACF in the non-primary direction equals the small persistent time of the APRW model. Thus, we propose that the two persistent times of anisotropic migration of cells can be properly estimated by discussing the VACFs of trajectory projected to the primary and non-primary directions.

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Protein-membrane interactions investigated with surface-induced fluorescence attenuation

马丽, 李颖, 李明, 胡书新

2017 (12): 128708-128708. doi: 10.1088/1674-1056/26/12/128708

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Research on protein-membrane interactions has been undeveloped due to the lack of proper techniques to detect the position of proteins at membranes because membranes are usually only about 4-nm thick. We have recently developed a new method named surface-induced fluorescence attenuation (SIFA) to track both vertical and lateral kinetics of a single labelling dye in supported lipid bilayers. It takes advantage of strong interaction between a light-emitting dye and a partially reflecting surface. By applying the technique to membrane proteins being fluorescently labelled at different residues, here we show that SIFA can measure not only the insertion depth of a dye inside a lipid bilayer, but also the position of a dye in solution near the surface. SIFA can therefore be used to study membrane proteins of various types.

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The birhythmicity increases the diversity of p53 oscillation induced by DNA damage

王道光, 周春红, 张小鹏

2017 (12): 128709-128709. doi: 10.1088/1674-1056/26/12/128709

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The tumor suppressor p53 mediates the cellular response to various stresses. It was experimentally shown that the concentration of p53 can show oscillations with short or long periods upon DNA damage. The underlying mechanism for this phenomenon is still not fully understood. Here, we construct a network model comprising the ATM-p53-Wip1 and p53-Mdm2 negative feedback loops and ATM autoactivation. We recapitulate the typical features of p53 oscillations including p53 birhythmicity. We show the dependence of p53 birhythmicity on various factors such as the phosphorylation status of ATM. We also perform stochastic simulation and find the noise-induced transitions between two modes of p53 oscillation, which increases the p53 variability in both the amplitude and period. These results suggest that p53 birhythmicity enhances the responsiveness of p53 network, which may facilitate its tumor suppressive function.

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Importance of PbI₂ morphology in two-step deposition of CH₃NH₃PbI₃ for high-performance perovskite solar cells

韦慧, 汤洋, 冯波, 尤晖

2017 (12): 128801-128801. doi: 10.1088/1674-1056/26/12/128801

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Controlling the morphology of the perovskite film is an effective way to improve the photoelectric conversion efficiency of solar cell devices. In this work, we study the influence of the crystallization condition on PbI₂ morphology and the performances of resulting perovskite solar cells. The PbI₂ morphologies and coverage rates under different formation conditions such as solvent effect, slow crystallization at room temperature and substrate-preheating, are found to be of crucial importance for preparing high-quality perovskite. The generation of loosely packed disk-like PbI₂ film with interpenetrating nanopores promotes the penetration of methyl ammonium iodide (MAI), leading to a better crystallinity of the perovskite film, and a best repeatable power conversion efficiency of 11.59% is achieved when methyl ammonium lead triiodide (CH₃NH₃PbI₃, MAPbI₃) is employed. In addition, an excellent device is also obtained with an efficiency of more than 93% to remain after working for 43 days.

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A uniform framework of projection and community detection for one-mode network in bipartite networks

吴果林, 顾长贵, 邱路, 杨会杰

2017 (12): 128901-128901. doi: 10.1088/1674-1056/26/12/128901

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Projection is a widely used method in bipartite networks. However, each projection has a specific application scenario and differs in the forms of mapping for bipartite networks. In this paper, inspired by the network-based information exchange dynamics, we propose a uniform framework of projection. Subsequently, an information exchange rate projection based on the nature of community structures of a network (named IERCP) is designed to detect community structures of bipartite networks. Results from the synthetic and real-world networks show that the IERCP algorithm has higher performance compared with the other projection methods. It suggests that the IERCP may extract more information hidden in bipartite networks and minimize information loss.

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