中国物理B

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Soliton-cnoidal interactional wave solutions for the reduced Maxwell-Bloch equations

黄丽丽, 乔志军, 陈勇

2018 (2): 20201-020201. doi: 10.1088/1674-1056/27/2/020201

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In this paper, we study soliton-cnoidal wave solutions for the reduced Maxwell-Bloch equations. The truncated Painlevé analysis is utilized to generate a consistent Riccati expansion, which leads to solving the reduced Maxwell-Bloch equations with solitary wave, cnoidal periodic wave, and soliton-cnoidal interactional wave solutions in an explicit form. Particularly, the soliton-cnoidal interactional wave solution is obtained for the first time for the reduced Maxwell-Bloch equations. Finally, we present some figures to show properties of the explicit soliton-cnoidal interactional wave solutions as well as some new dynamical phenomena.

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A local energy-preserving scheme for Zakharov system

洪旗, 汪佳玲, 王雨顺

2018 (2): 20202-020202. doi: 10.1088/1674-1056/27/2/020202

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In this paper, we propose a local conservation law for the Zakharov system. The property is held in any local time-space region which is independent of the boundary condition and more essential than the global energy conservation law. Based on the rule that the numerical methods should preserve the intrinsic properties as much as possible, we propose a local energy-preserving (LEP) scheme for the system. The merit of the proposed scheme is that the local energy conservation law can be conserved exactly in any time-space region. With homogeneous Dirchlet boundary conditions, the proposed LEP scheme also possesses the discrete global mass and energy conservation laws. The theoretical properties are verified by numerical results.

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Energy states of the Hulthen plus Coulomb-like potential with position-dependent mass function in external magnetic fields

M Eshghi,R Sever,S M Ikhdair

2018 (2): 20301-020301. doi: 10.1088/1674-1056/27/2/020301

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We need to solve a suitable exponential form of the position-dependent mass (PDM) Schrödinger equation with a charged particle placed in the Hulthen plus Coulomb-like potential field and under the actions of the external magnetic and Aharonov-Bohm (AB) flux fields. The bound state energies and their corresponding wave functions are calculated for the spatially-dependent mass distribution function of interest in physics. A few plots of some numerical results with respect to the energy are shown.

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Arbitrated quantum signature scheme with continuous-variable squeezed vacuum states

冯艳艳, 施荣华, 郭迎

2018 (2): 20302-020302. doi: 10.1088/1674-1056/27/2/020302

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We propose an arbitrated quantum signature (AQS) scheme with continuous variable (CV) squeezed vacuum states, which requires three parties, i.e., the signer Alice, the verifier Bob and the arbitrator Charlie trusted by Alice and Bob, and three phases consisting of the initial phase, the signature phase and the verification phase. We evaluate and compare the original state and the teleported state by using the fidelity and the beam splitter (BS) strategy. The security is ensured by the CV-based quantum key distribution (CV-QKD) and quantum teleportation of squeezed states. Security analyses show that the generated signature can be neither disavowed by the signer and the receiver nor counterfeited by anyone with the shared keys. Furthermore, the scheme can also detect other manners of potential attack although they may be successful. Also, the integrality and authenticity of the transmitted messages can be guaranteed. Compared to the signature scheme of CV-based coherent states, our scheme has better encoding efficiency and performance. It is a potential high-speed quantum signature scheme with high repetition rate and detection efficiency which can be achieved by using the standard off-the-shelf components when compared to the discrete-variable (DV) quantum signature scheme.

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Quantum light storage in rare-earth-ion-doped solids

华怡林, 周宗权, 李传锋, 郭光灿

2018 (2): 20303-020303. doi: 10.1088/1674-1056/27/2/020303

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The reversible transfer of unknown quantum states between light and matter is essential for constructing large-scale quantum networks. Over the last decade, various physical systems have been proposed to realize such quantum memory for light. The solid-state quantum memory based on rare-earth-ion-doped solids has the advantages of a reduced setup complexity and high robustness for scalable application. We describe the methods used to spectrally prepare the quantum memory and release the photonic excitation on-demand. We will review the state of the art experiments and discuss the perspective applications of this particular system in both quantum information science and fundamental tests of quantum physics.

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Quantum information processing with nitrogen-vacancy centers in diamond

刘刚钦, 潘新宇

2018 (2): 20304-020304. doi: 10.1088/1674-1056/27/2/020304

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Nitrogen-vacancy (NV) center in diamond is one of the most promising candidates to implement room temperature quantum computing. In this review, we briefly discuss the working principles and recent experimental progresses of this spin qubit. These results focus on understanding and prolonging center spin coherence, steering and probing spin states with dedicated quantum control techniques, and exploiting the quantum nature of these multi-spin systems, such as superposition and entanglement, to demonstrate the superiority of quantum information processing. Those techniques also stimulate the fast development of NV-based quantum sensing, which is an interdisciplinary field with great potential applications.

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Qubits based on semiconductor quantum dots

张鑫, 李海欧, 王柯, 曹刚, 肖明, 郭国平

2018 (2): 20305-020305. doi: 10.1088/1674-1056/27/2/020305

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Semiconductor quantum dots are promising hosts for qubits to build a quantum processor. In the last twenty years, intensive researches have been carried out and diverse kinds of qubits based on different types of semiconductor quantum dots were developed. Recent advances prove high fidelity single and two qubit gates, and even prototype quantum algorithms. These breakthroughs motivate further research on realizing a fault tolerant quantum computer. In this paper we review the main principles of various semiconductor quantum dot based qubits and the latest associated experimental results. Finally the future trends of those qubits will be discussed.

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Detecting high-dimensional multipartite entanglement via some classes of measurements

刘璐, 高亭, 闫凤利

2018 (2): 20306-020306. doi: 10.1088/1674-1056/27/2/020306

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Mutually unbiased bases, mutually unbiased measurements and general symmetric informationally complete measurements are three related concepts in quantum information theory. We investigate multipartite systems using these notions and present some criteria detecting entanglement of arbitrary high dimensional multi-qudit systems and multipartite systems of subsystems with different dimensions. It is proved that these criteria can detect the k-nonseparability (k is even) of multipartite qudit systems and arbitrary high dimensional multipartite systems of m subsystems with different dimensions. We show that they are more efficient and wider of application range than the previous ones. They provide experimental implementation in detecting entanglement without full quantum state tomography.

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Entangled-photons generation with quantum dots

李远, 丁飞

2018 (2): 20307-020307. doi: 10.1088/1674-1056/27/2/020307

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Entanglement between particles is a crucial resource in quantum information processing, an important example of which is the exploitation of entangled photons in quantum communication protocols. Among the different available sources of entangled photons, semiconductor quantum dots (QDs) excel owing to their deterministic emission properties, potential for electrical injections, and direct compatibility with semiconductor manufacturing techniques. Despite the great promises, QD-based sources are far from being ideal. In particular, such sources present several critical issues, which require the overcoming of challenges pertaining to spectral tunability, entanglement fidelity, photon indistinguishability and brightness. In this article, we will discuss the potential solutions to these problems and review the recent progress in the field.

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Nuclear magnetic resonance for quantum computing: Techniques and recent achievements

辛涛, 王碧雪, 李可仁, 孔祥宇, 魏世杰, 王涛, 阮东, 龙桂鲁

2018 (2): 20308-020308. doi: 10.1088/1674-1056/27/2/020308

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Rapid developments in quantum information processing have been made, and remarkable achievements have been obtained in recent years, both in theory and experiments. Coherent control of nuclear spin dynamics is a powerful tool for the experimental implementation of quantum schemes in liquid and solid nuclear magnetic resonance (NMR) system, especially in liquid-state NMR. Compared with other quantum information processing systems, the NMR platform has the advantages such as the long coherence time, the precise manipulation, and well-developed quantum control techniques, which make it possible to accurately control a quantum system with up to 12-qubits. Extensive applications of liquid-state NMR spectroscopy in quantum information processing such as quantum communication, quantum computing, and quantum simulation have been thoroughly studied over half a century. This article introduces the general principles of NMR quantum information processing, and reviews the new-developed techniques. The review will also include the recent achievements of the experimental realization of quantum algorithms for machine learning, quantum simulations for high energy physics, and topological order in NMR. We also discuss the limitation and prospect of liquid-state NMR spectroscopy and the solid-state NMR systems as quantum computing in the article.

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Destroying MTZ black holes with test particles

宋宇, 唐浩, 邹德成, 孙成一, 岳瑞宏

2018 (2): 20401-020401. doi: 10.1088/1674-1056/27/2/020401

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Neglecting the self-force and radiative effects, we follow the spirit of Wald's gedanken experiment and discuss whether a (2+1)-dimensional Martinez-Teitelboim-Zanelli (MTZ) black hole can turn into a naked singularity by capturing a charged and massive particle. We find that after capturing a charged and massive test particle, an extremal or near-extremal MTZ black hole could turn into naked singularity, leading to a possible violation of the cosmic censorship. There exist ranges of the test particles' energies △E which allow the appearance of naked singularities from both extremal and near extremal MTZ black holes.

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Current loss of magnetically insulated coaxial diode with cathode negative ion

朱丹妮, 张军, 钟辉煌, 高景明, 白珍

2018 (2): 20501-020501. doi: 10.1088/1674-1056/27/2/020501

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Current loss without an obvious impedance collapse in the magnetically insulated coaxial diode (MICD) is studied through experiment and particle-in-cell (PIC) simulation when the guiding magnetic field is strong enough. Cathode negative ions are clarified to be the predominant reason for it. Theoretical analysis and simulation both indicate that the velocity of the negative ion reaches up to 1 cm/ns due to the space potential between the anode and cathode gap (A-C gap). Accordingly, instead of the reverse current loss and the parasitic current loss, the negative ion loss appears during the whole pulse. The negative ion current loss is determined by its ionization production rate. It increases with diode voltage increasing. The smaller space charge effect caused by the beam thickening and the weaker radial restriction both promote the negative ion production under a lower magnetic field. Therefore, as the magnetic field increases, the current loss gradually decreases until the beam thickening nearly stops.

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Generalized Chaplygin equations for nonholonomic systems on time scales

金世欣, 张毅

2018 (2): 20502-020502. doi: 10.1088/1674-1056/27/2/020502

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The generalized Chaplygin equations for nonholonomic systems on time scales are proposed and studied. The Hamilton principle for nonholonomic systems on time scales is established, and the corresponding generalized Chaplygin equations are deduced. The reduced Chaplygin equations are also presented. Two special cases of the generalized Chaplygin equations on time scales, where the time scales are equal to the set of real numbers and the integer set, are discussed. Finally, several examples are given to illustrate the application of the results.

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Optimizing the atom types of proteins through iterative knowledge-based potentials

汪心享, 黄胜友

2018 (2): 20503-020503. doi: 10.1088/1674-1056/27/2/020503

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Knowledge-based scoring functions have been widely used for protein structure prediction, protein-small molecule, and protein-nucleic acid interactions, in which one critical step is to find an appropriate representation of protein structures. A key issue is to determine the minimal protein representations, which is important not only for developing of scoring functions but also for understanding the physics of protein folding. Despite significant progresses in simplifying residues into alphabets, few studies have been done to address the optimal number of atom types for proteins. Here, we have investigated the atom typing issue by classifying the 167 heavy atoms of proteins through 11 schemes with 1 to 20 atom types based on their physicochemical and functional environments. For each atom typing scheme, a statistical mechanics-based iterative method was used to extract atomic distance-dependent potentials from protein structures. The atomic distance-dependent pair potentials for different schemes were illustrated by several typical atom pairs with different physicochemical properties. The derived potentials were also evaluated on a high-resolution test set of 148 diverse proteins for native structure recognition. It was found that there was a crossover around the scheme of four atom types in terms of the success rate as a function of the number of atom types, which means that four atom types may be used when investigating the basic folding mechanism of proteins. However, it was revealed by a close examination of typical potentials that 14 atom types were needed to describe the protein interactions at atomic level. The present study will be beneficial for the development of protein related scoring functions and the understanding of folding mechanisms.

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Performance study of aluminum shielded room for ultra-low-field magnetic resonance imaging based on SQUID: Simulations and experiments

李波, 董慧, 黄小磊, 邱阳, 陶泉, 朱建明

2018 (2): 20701-020701. doi: 10.1088/1674-1056/27/2/020701

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The aluminum shielded room has been an important part of ultra-low-field magnetic resonance imaging (ULF MRI) based on the superconducting quantum interference device (SQUID). The shielded room is effective to attenuate the external radio-frequency field and keep the extremely sensitive detector, SQUID, working properly. A high-performance shielded room can increase the signal-to-noise ratio (SNR) and improve image quality. In this study, a circular coil with a diameter of 50 cm and a square coil with a side length of 2.0 m was used to simulate the magnetic fields from the nearby electric apparatuses and the distant environmental noise sources. The shielding effectivenesses (SE) of the shielded room with different thicknesses of aluminum sheets were calculated and simulated. A room using 6-mm-thick aluminum plates with a dimension of 1.5 m×1.5 m×2.0 m was then constructed. The SE was experimentally measured by using three-axis SQUID magnetometers, with tranisent magnetic field induced in the aluminum plates by the strong pre-polarization pulses. The results of the measured SE agreed with that from the simulation. In addition, the introduction of a 0.5-mm gap caused the obvious reduction of SE indicating the importance of door design. The nuclear magnetic resonance (NMR) signals of water at 5.9 kHz were measured in free space and in a shielded room, and the SNR was improved from 3 to 15. The simulation and experimental results will help us design an aluminum shielded room which satisfies the requirements for future ULF human brain imaging. Finally, the cancellation technique of the transient eddy current was tried, the simulation of the cancellation technique will lead us to finding an appropriate way to suppress the eddy current fields.

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Theoretical analysis of suppressing Dick effect in Ramsey-CPT atomic clock by interleaving lock

孙晓林, 张建伟, 程鹏飞, 左娅妮, 王力军

2018 (2): 23101-023101. doi: 10.1088/1674-1056/27/2/023101

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For most pulsed atomic clocks, the Dick effect is one of the main limits to reach its frequency stability limitation due to quantum projection noise. In this paper, we measure the phase noise of the local oscillator in the Ramsey-CPT atomic clock and calculate the Dick effect induced Allan deviation based on a three-level atomic model, which is quite different from typical atomic clocks. We further present a detailed analysis of optimizing the sensitivity function and minimizing the Dick effect by interleaving lock. By optimizing the duty circle of laser pulses, average time during detection and optical intensity of laser beam, the Dick effect induced Allan deviation can be reduced to the level of 10^-14.

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State-to-state dynamics of F(²P)+HO(²Π) →O(³P)+HF(¹∑⁺) reaction on 1³A" potential energy surface

赵娟, 吴慧, 孙海波, 王立飞

2018 (2): 23102-023102. doi: 10.1088/1674-1056/27/2/023102

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State-to-state time-dependent quantum dynamics calculations are carried out to study F(²P)+HO(²Π)→O(³P)+HF(¹∑⁺) reaction on 1³A" ground potential energy surface (PES). The vibrationally resolved reaction probabilities and the total integral cross section agree well with the previous results. Due to the heavy-light-heavy (HLH) system and the large exoergicity, the obvious vibrational inversion is found in a state-resolved integral cross section. The total differential cross section is found to be forward-backward scattering biased with strong oscillations at energy lower than a threshold of 0.10 eV, which is the indication of the indirect complex-forming mechanism. When the collision energy increases to greater than 0.10 eV, the angular distribution of the product becomes a strong forward scattering, and almost all the products are distributed at θ_t=0°. This forward-peaked distribution can be attributed to the larger J partial waves and the property of the F atom itself, which make this reaction a direct abstraction process. The state-resolved differential cross sections are basically forward-backward symmetric for v'=0, 1, and 2 at a collision energy of 0.07 eV; for a collision energy of 0.30 eV, it changes from backward/sideward scattering to forward peaked as v' increasing from 0 to 3. These results indicate that the contribution of differential cross sections with more highly vibrational excited states to the total differential cross sections is principal, which further verifies the vibrational inversion in the products.

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Excited state intramolecular proton transfer mechanism of o-hydroxynaphthyl phenanthroimidazole

刘爽, 马艳珍, 杨云帆, 刘松松, 李永庆, 宋玉志

2018 (2): 23103-023103. doi: 10.1088/1674-1056/27/2/023103

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By utilizing the density functional theory (DFT) and the time-dependent density functional theory (TDDFT), the excited state intramolecular proton transfer (ESIPT) mechanism of o-hydroxynaphthyl phenanthroimidazole (HNPI) is studied in detail. Upon photo is excited, the intramolecular hydrogen bond is obviously enhanced in the S₁ state, which thus promotes the ESIPT process. Hydrogen bond is shown to be strengthened via comparing the molecular structures and the infrared vibration spectra of the S₀ and S₁ states. Through analyzing the frontier molecular orbitals, we can conclude that the excitation is a type of the intramolecular charge transfer excitation, which also indicates the trend of proton transfer in S₁ state. The vertical excitation based on TDDFT calculation can effectively repeat the absorption and fluorescence spectra of the experiment. However, the fluorescence spectrum of normal structure, which is similar to the spectrum of isomer structure is not detected in the experiment. It can be concluded that the fluorescence measured in the experiment is attributed to both structures. In addition, by analyzing the potential energy curves (PECs) calculated by the B3LYP functional method, it can be derived that since the molecule to cross the potential barrier in the S₁ state is smaller than in the S₀ state and the reverse proton transfer process in the S₁ state is more difficult than in the S₀ state, the ESIPT occurs in the S₁ state.

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Comparisons of electrical and optical properties between graphene and silicene-A review

Wirth-Lima A J,Silva M G,Sombra A S B

2018 (2): 23201-023201. doi: 10.1088/1674-1056/27/2/023201

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Two-dimensional (2D) metamaterials are considered to be of enormous relevance to the progress of all exact sciences. Since the discovery of graphene, researchers have increasingly investigated in depth the details of electrical/optical properties pertinent to other 2D metamaterials, including those relating to the silicene. In this review are included the details and comparisons of the atomic structures, energy diagram bands, substrates, charge densities, charge mobilities, conductivities, absorptions, electrical permittivities, dispersion relations of the wave vectors, and supported electromagnetic modes related to graphene and silicene. Hence, this review can help readers to acquire, recover or increase the necessary technological basis for the development of more specific studies on graphene and silicene.

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Temporal interference driven by an oscillating electric field in photodetachment of H^- ion

王德华, 李梦芝, 宋鸿娜, 任笑笑

2018 (2): 23202-023202. doi: 10.1088/1674-1056/27/2/023202

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The real time domain interferometry for the photodetachment dynamics driven by the oscillating electric field has been studied for the first time. Both the geometry of the detached electron trajectories and the electron probability density are shown to be different from those in the photodetachment dynamics in a static electric field. The influence of the oscillating electric field on the detached electron leads to a surprisingly intricate shape of the electron waves, and multiple interfering trajectories generate complex interference patterns in the electron probability density. Using the semiclassical open-orbit theory, we calculate the interference patterns in the time-dependent electron probability density for different electric field strengths, different frequencies and phases in the oscillating electric field. This method is universal, and can be extended to study the photoionization dynamics of the atoms in the time-dependent electric field. Our study can guide the future experimental researches in the photodetachment or photoionization microscopy of negative ions and atoms in the oscillating electric field.

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Temperature dependence of line parameters of ¹²C¹⁶O₂ near 2.004 μm studied by tunable diode laser spectroscopy

马宏亮, 孙明国, 査申龙, 刘强, 曹振松, 黄印博, 朱柱, 饶瑞中

2018 (2): 23301-023301. doi: 10.1088/1674-1056/27/2/023301

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The absorption spectrum of carbon dioxide at 2.004 μm has been recorded at sample temperatures between 218.0 K and room temperature, by using a high-resolution tunable diode laser absorption spectrometer (TDLAS) combined with a temperature controlled cryogenically cooled absorption cell. The self-, N₂-, and air-broadening coefficients for nine transitions of ¹²C¹⁶O₂ belonging to the 20012 ← 00001 band in the 4987 cm^-1-4998 cm^-1 region have been measured at different temperatures. From these measurements, we have further determined the temperature dependence exponents of the pressure-broadening coefficients. To the best of our knowledge, the temperature dependence parameters of the collisional broadening coefficients are reported experimentally for the first time for these nine transitions. The measured halfwidth coefficients and the air temperature dependence exponents of these transitions are compared with the available values reported in the literature and HITRAN 2012 database. Agreements and discrepancies are also discussed.

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Responsive mechanism and molecular design of di-2-picolylamine-based two-photon fluorescent probes for zinc ions

朱美玉, 赵珂, 宋军, 王传奎

2018 (2): 23302-023302. doi: 10.1088/1674-1056/27/2/023302

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The properties of one-photon absorption (OPA), emission and two-photon absorption (TPA) of a di-2-picolylamine-based zinc ion sensor are investigated by employing the density functional theory in combination with response functions. The responsive mechanism is explored. It is found that the calculated OPA and TPA properties are quite consistent with experimental data. Because the intra-molecular charge transfer (ICT) increases upon zinc ion binding, the TPA intensity is enhanced dramatically. According to the model sensor, we design a series of zinc ion probes which differ by conjugation center, acceptor and donor moieties. The properties of OPA, emission and TPA of the designed molecules are calculated at the same computational level. Our results demonstrate that the OPA and emission wavelengths of the designed probes have large red-shifts after zinc ions have been bound. Comparing with the model sensor, the TPA intensities of the designed probes are enhanced significantly and the absorption positions are red-shifted to longer wavelength range. Furthermore, the TPA intensity can be improved greatly upon zinc ion binding due to the increased ICT mechanism. These compounds are potential excellent candidates for two-photon fluorescent zinc ion probes.

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Exploring the methane combustion reaction: A theoretical contribution

彭亚, 蒋仲安, 陈举师

2018 (2): 23401-023401. doi: 10.1088/1674-1056/27/2/023401

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This paper represents an attempt to extend the mechanisms of reactions and kinetics of a methane combustion reaction. Three saddle points (SPs) are identified in the reaction CH₄⁺O(³P) → OH ⁺CH₃ using the complete active space selfconsistent field and the multireference configuration interaction methods with a proper active space. Our calculations give a fairly accurate description of the regions around the twin first-order SPs (³A' and ³A") along the direction of O(³P) attacking a near-collinear H-CH₃. One second-order SP^2nd (³E) between the above twin SPs is the result of the C_3v symmetry Jahn-Teller coupling within the branching space. Further kinetic calculations are performed with the canonical unified statistical theory method with the temperature ranging from 298 K to 1000 K. The rate constants are also reported. The present work reveals the reaction mechanism of hydrogen-abstraction by the O(³P) from methane, and develops a better understanding for the role of SPs. In addition, a comparison of the reactions of O(³P) with methane through different channels allows a molecule-level discussion of the reactivity and mechanism of the title reaction.

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Strontium optical lattice clock at the National Time Service Center

王叶兵, 尹默娟, 任洁, 徐琴芳, 卢本全, 韩建新, 郭阳, 常宏

2018 (2): 23701-023701. doi: 10.1088/1674-1056/27/2/023701

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We report the ⁸⁷Sr optical lattice clock developed at the National Time Service Center. We achieved a closed-loop operation of the optical lattice clock based on ⁸⁷Sr atoms. The linewidth of the spin-polarized clock peak is 3.9 Hz with a clock laser pulse length of 300 ms, which corresponds to a Fourier-limited linewidth of 3 Hz. The fitting of the in-loop error signal data shows that the instability is approximately 5×10^-15τ^-1/2, affected primarily by the white noise. The fractional frequency difference averages down to 5.7×10^-17 for an averaging time of 3000 s.

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Higher order harmonics suppression in extreme ultraviolet and soft x-ray

陈勇, 魏来, 钱凤, 杨祖华, 王少义, 巫殷忠, 张强强, 范全平, 曹磊峰

2018 (2): 24101-024101. doi: 10.1088/1674-1056/27/2/024101

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The extreme ultraviolet and soft x-ray sources are widely used in various domains. Suppressing higher order harmonics and improving spectral purity are significant. This paper describes a novel method of higher order harmonics suppression with single order diffraction gratings in extreme ultraviolet and soft x-ray. The principle of harmonic suppression with single order diffraction grating is described, and an extreme ultraviolet and soft x-ray non-harmonics grating monochromator is designed based on the single order diffraction grating. The performance is simulated by an optical design software. The emergent beams of a monochromator with different gratings are measured by a transmission grating spectrometer. The results show that the single order diffraction grating can suppress higher order harmonics effectively, and it is expected to be widely used in synchrotron radiation, diagnostics of laser induced plasma, and astrophysics.

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Sub-external cavity effect and elimination method in laser self-mixing interference wave plate measurement system

牛海莎, 牛燕雄, 宋建军

2018 (2): 24201-024201. doi: 10.1088/1674-1056/27/2/024201

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Laser self-mixing interference (SMI) wave plate measurement method is a burgeoning technique for its simplicity and efficiency. But for the non-coated sample, the reflected light from the surface can seriously affect the measurement results. To analyze the reason theoretically, a self-consistent model for laser operation with a sub-external and an external cavity is established, and the sub-external cavity formed by the sample and a cavity mirror is proved to be the main error source. A synchronous tuning method is proposed to eliminate the sub-external cavity effect. Experiments are carried out on the synchronously tuning double external cavities self-mixing interference system, and the error of the system is in the range of -0.435°~0.387° compared with the ellipsometer. The research plays an important role in improving the performance and enlarging the application range of the laser self-mixing interference system.

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Double-rod metasurface for mid-infrared polarization conversion

蒲洋, 罗意, 刘路, 何德, 徐洪艳, 景洪伟, 蒋亚东, 刘志军

2018 (2): 24202-024202. doi: 10.1088/1674-1056/27/2/024202

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Resonant responses of metasurface enable effective control over the polarization properties of lights. In this paper, we demonstrate a double-rod metasurface for broadband polarization conversion in the mid-infrared region. The metasurface consists of a metallic double-rod array separated from a reflecting ground plane by a film of zinc selenide. By superimposing three localized resonances, cross polarization conversion is achieved over a bandwidth of 16.9 THz around the central frequency at 34.6 THz with conversion efficiency exceeding 70%. The polarization conversion performance is in qualitative agreement with simulation. The surface current distributions and electric field profiles of the resonant modes are discussed to analyze the underlying physical mechanism. Our demonstrated broadband polarization conversion has potential applications in the area of mid-infrared spectroscopy, communication, and sensing.

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Quantum state transfer via a hybrid solid-optomechanical interface

裴培, 黄鹤飞, 郭彦青, 张兴远, 戴佳峰

2018 (2): 24203-024203. doi: 10.1088/1674-1056/27/2/024203

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We propose a scheme to implement quantum state transfer between two distant quantum nodes via a hybrid solid-optomechanical interface. The quantum state is encoded on the native superconducting qubit, and transferred to the microwave photon, then the optical photon successively, which afterwards is transmitted to the remote node by cavity leaking, and finally the quantum state is transferred to the remote superconducting qubit. The high efficiency of the state transfer is achieved by controllable Gaussian pulses sequence and numerically demonstrated with theoretically feasible parameters. Our scheme has the potential to implement unified quantum computing-communication-computing, and high fidelity of the microwave-optics-microwave transfer process of the quantum state.

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Cavity optomechanics: Manipulating photons and phonons towards the single-photon strong coupling

刘玉龙, 王冲, 张靖, 刘玉玺

2018 (2): 24204-024204. doi: 10.1088/1674-1056/27/2/024204

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Cavity optomechanical systems provide powerful platforms to manipulate photons and phonons, open potential applications for modern optical communications and precise measurements. With the refrigeration and ground-state cooling technologies, studies of cavity optomechanics are making significant progress towards the quantum regime including nonclassical state preparation, quantum state tomography, quantum information processing, and future quantum internet. With further research, it is found that abundant physical phenomena and important applications in both classical and quantum regimes appeal as they have a strong optomechanical nonlinearity, which essentially depends on the single-photon optomechanical coupling strength. Thus, engineering the optomechanical interactions and improving the single-photon optomechanical coupling strength become very important subjects. In this article, we first review several mechanisms, theoretically proposed for enhancing optomechanical coupling. Then, we review the experimental progresses on enhancing optomechanical coupling by optimizing its structure and fabrication process. Finally, we review how to use novel structures and materials to enhance the optomechanical coupling strength. The manipulations of the photons and phonons at the level of strong optomechanical coupling are also summarized.

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Absorption linewidth inversion with wavelength modulation spectroscopy

颜悦, 杜振辉, 李金义, 王瑞雪

2018 (2): 24205-024205. doi: 10.1088/1674-1056/27/2/024205

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For absorption linewidth inversion with wavelength modulation spectroscopy (WMS), an optimized WMS spectral line fitting method was demonstrated to infer absorption linewidth effectively, and the analytical expressions for relationships between Lorentzian linewidth and the separations of first harmonic peak-to-valley and second harmonic zero-crossing were deduced. The transition of CO₂ centered at 4991.25 cm^-1 was used to verify the optimized spectral fitting method and the analytical expressions. Results showed that the optimized spectra fitting method was able to infer absorption accurately and compute more than 10 times faster than the commonly used numerical fitting procedure. The second harmonic zero-crossing separation method calculated an even 6 orders faster than the spectra fitting without losing any accuracy for Lorentzian dominated cases. Additionally, linewidth calculated through second harmonic zero-crossing was preferred for much smaller error than the first harmonic peak-to-valley separation method. The presented analytical expressions can also be used in on-line optical sensing applications, electron paramagnetic resonance, and further theoretical characterization of absorption lineshape.

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Spectral redshift of high-order harmonics by adding a weak pulse in the falling part of the trapezoidal laser pulse

潘雪飞, 张军, 贲帅, 徐彤彤, 刘学深

2018 (2): 24206-024206. doi: 10.1088/1674-1056/27/2/024206

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We investigate the spectral redshift of high-order harmonics of the H₂⁺ (D₂⁺) molecule by numerically solving the non-Born-Oppenheimer time-dependent Schrödinger equation (TDSE). The results show that the spectral redshift of high-order harmonics can be observed by adding a weak pulse in the falling part of the trapezoidal laser pulses. Comparing with the H₂⁺ molecule, the shift of high-order harmonic generation (HHG) spectrum for the D₂⁺ molecule is more obvious. We employ the spatial distribution in HHG and time-frequency analysis to illustrate the physical mechanism of the spectral redshift of high-order harmonics.

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Influence of intra-cavity loss on transmission characteristics of fiber Bragg grating Fabry-Perot cavity

王迪, 丁孟, 皮浩洋, 李璇, 杨飞, 叶青, 蔡海文, 魏芳

2018 (2): 24207-024207. doi: 10.1088/1674-1056/27/2/024207

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A theoretical model of the fiber Bragg grating Fabry-Perot (FBG-FP) transmission spectrum considering loss of FBG and intra-cavity fiber is presented. Several types of FBG-FPs are inscribed experimentally, and their spectra are measured. The results confirm that weak intra-cavity loss is enhanced at the resonance transmission peak, that is, loss of transmission peaks is observably larger than other wavelengths. For FBG-FPs with multi resonance peaks, when the resonance peak wavelength is closer to the Bragg wavelength, the more significant loss effect of resonance transmission peak is exhibited. The measured spectra are fitted with the presented theoretical model. The fitted coefficient of determinations are near 1, which proves the validity of the theoretical model. This study can be applied to measure FBG loss more accurately, without a reference light. It can play an important role in FBG and FBG-FP writing process optimization and application parameter optimization.

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Fabrication of mixed perovskite organic cation thin films via controllable cation exchange

赵宇龙, 王进峰, 赵本广, 贾晨晨, 牟俊朋, 朱磊, 宋健, 顾修全, 强颖怀

2018 (2): 24208-024208. doi: 10.1088/1674-1056/27/2/024208

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Here in this paper, we demonstrate a facile technique for creating the mixed formamidinium (HN=CHNH₃⁺, FA⁺) and methylammonium (CH₃NH₃⁺, MA⁺) cations in the lead iodide perovskite. This technique entails a facile drop-casting of formamidinium iodide (FAI) solutions on as-prepared MAPbI₃ perovskite thin films under the controlled conditions, which leads to controllable displacement of the MA⁺ cations by FA⁺ cations in the perovskite structure at room temperature. Uniform and controllable mixed organic cation perovskite thin films without a “bi-layered” or graded structure are achieved. By applying this approach to photovoltaic devices, we are able to improve the performances of devices through extending their optical-absorption onset further into the infrared region to enhance solar-light harvesting. Additionally, this work provides a simple and efficient technique to tune the structural, electrical, and optoelectronic properties of the light-harvesting materials for high-performance perovskite solar cells.

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Multiple off-axis acoustic vortices generated by dual coaxial vortex beams

李雯, 戴思捷, 马青玉, 郭各朴, 丁鹤平

2018 (2): 24301-024301. doi: 10.1088/1674-1056/27/2/024301

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As a kind of special acoustic field, the helical wavefront of an acoustic vortex (AV) beam is demonstrated to have a pressure zero with phase singularity at the center in the transverse plane. The orbital angular momentum of AVs can be applied to the field of particle manipulation, which attracts more and more attention in acoustic researches. In this paper, by using the simplified circular array of point sources, dual coaxial AV beams are excited by the even-and odd-numbered sources with the topological charges of l_E and l_O based on the phase-coded approach, and the composite acoustic field with an on-axis center-AV and multiple off-axis sub-AVs can be generated by the superimposition of the AV beams for|l_E|≠|l_O|. The generation of edge phase dislocation is theoretically derived and numerically analyzed for l_E=-l_O. The numbers and the topological charges as well as the locations of the center-AV and sub-AVs are demonstrated, which are proved to be determined by the topological charges of the coaxial AV beams. The proposed approach breaks through the limit of only one on-axis AV with a single topological charge along the beam axis, and also provides the feasibility of off-axis particle trapping with multiple AVs in object manipulation.

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Influence of mode conversions in the skull on transcranial focused ultrasound and temperature fields utilizing the wave field separation method: A numerical study

王祥达, 林伟军, 苏畅, 王秀明

2018 (2): 24302-024302. doi: 10.1088/1674-1056/27/2/024302

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Transcranial focused ultrasound is a booming noninvasive therapy for brain stimuli. The Kelvin-Voigt equations are employed to calculate the sound field created by focusing a 256-element planar phased array through a monkey skull with the time-reversal method. Mode conversions between compressional and shear waves exist in the skull. Therefore, the wave field separation method is introduced to calculate the contributions of the two waves to the acoustic intensity and the heat source, respectively. The Pennes equation is used to depict the temperature field induced by ultrasound. Five computational models with the same incident angle of 0° and different distances from the focus for the skull and three computational models at different incident angles and the same distance from the focus for the skull are studied. Numerical results indicate that for all computational models, the acoustic intensity at the focus with mode conversions is 12.05% less than that without mode conversions on average. For the temperature rise, this percentage is 12.02%. Besides, an underestimation of both the acoustic intensity and the temperature rise in the skull tends to occur if mode conversions are ignored. However, if the incident angle exceeds 30°, the rules of the over-and under-estimation may be reversed. Moreover, shear waves contribute 20.54% of the acoustic intensity and 20.74% of the temperature rise in the skull on average for all computational models. The percentage of the temperature rise in the skull from shear waves declines with the increase of the duration of the ultrasound.

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Thin film dynamics in coating problems using Onsager principle

邸亚娜, 许现民, 周嘉嘉

2018 (2): 24501-024501. doi: 10.1088/1674-1056/27/2/024501

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A new variational method is proposed to investigate the dynamics of the thin film in a coating flow where a liquid is delivered through a fixed slot gap onto a moving substrate. A simplified ODE system has also been derived for the evolution of the thin film whose thickness h_f is asymptotically constant behind the coating front. We calculate the phase diagram as well as the film profiles and approximate the film thickness theoretically, and agreement with the well-known scaling law as Ca^2/3 is found.

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Capillary filling in closed-end nanotubes

赵晨, 周嘉嘉

2018 (2): 24701-024701. doi: 10.1088/1674-1056/27/2/024701

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Capillary filling in small length scale is an important process in nanotechnology and microfabrication. When one end of the tube or channel is sealed, it is important to consider the escape of the trapped gas. We develop a dynamic model on capillary filling in closed-end tubes, based on the diffusion-convection equation and Henry's law of gas dissolution. We systematically investigate the filling dynamics for various sets of parameters, and compare the results with a previous model which assumes a linear density profile of dissolved gas and neglect the convective term.

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Theoretical studies and molecular dynamics simulations on ion transport properties in nanochannels and nanopores

肖克, 李典杰, 吴晨旭

2018 (2): 24702-024702. doi: 10.1088/1674-1056/27/2/024702

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Control of ion transport and fluid flow through nanofluidic devices is of primary importance for energy storage and conversion, drug delivery and a wide range of biological processes. Recent development of nanotechnology, synthesis techniques, purification technologies, and experiment have led to rapid advances in simulation and modeling studies on ion transport properties. In this review, the applications of Poisson-Nernst-Plank (PNP) equations in analyzing transport properties are presented. The molecular dynamics (MD) studies of transport properties of ion and fluidic flow through nanofluidic devices are reported as well.

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Numerical study on discharge characteristics influenced by secondary electron emission in capacitive RF argon glow discharges by fluid modeling

赵璐璐, 刘悦

2018 (2): 25201-025201. doi: 10.1088/1674-1056/27/2/025201

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A one-dimensional (1D) fluid model of capacitive RF argon glow discharges between two parallel-plate electrodes at low pressure is employed. The influence of the secondary electron emission on the plasma characteristics in the discharges is investigated numerically by the model. The results show that as the secondary electron emission coefficient increases, the cycle-averaged electric field has almost no change; the cycle-averaged electron temperature in the bulk plasma almost does not change, but it increases in the two sheath regions; the cycle-averaged ionization rate, electron density, electron current density, ion current density, and total current density all increase. Also, the cycle-averaged secondary electron fluxes on the surfaces of the electrodes increase as the secondary electron emission coefficient increases. The evolutions of the electron flux, the secondary electron flux and the ion flux on the powered electrode increase as the secondary electron emission coefficient increases. The cycle-averaged electron pressure heating, electron Ohmic heating, electron heating, and ion heating in the two sheath regions increase as the secondary electron emission coefficient increases. The cycle-averaged electron energy loss increases with increasing secondary electron emission coefficient.

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Electric field in two-dimensional complex plasma crystal: Simulated lattices

Behnam Bahadory

2018 (2): 25202-025202. doi: 10.1088/1674-1056/27/2/025202

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We focus on molecular dynamics simulated two-dimensional complex plasma crystals. We use rigid walls as a confinement force and produce square and rectangular crystals. We report various types of two-row crystals. The narrow and long crystals are likely to be used as wigglers; therefore, we simulate such crystals. Also, we analyze the electric fields of simulated crystals. A bit change in lattice parameters can change the internal structures of crystals and their electric fields notably. These parameters are the number of grains, grains charge, length, and width of the crystal. With the help of electric fields, we show the details of crystal structures.

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Schamel equation in an inhomogeneous magnetized sheared flow plasma with q-nonextensive trapped electrons

Shaukat Ali Shan,Qamar-ul-Haque

2018 (2): 25203-025203. doi: 10.1088/1674-1056/27/2/025203

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An investigation is carried out for understanding the properties of ion-acoustic (IA) solitary waves in an inhomogeneous magnetized electron-ion plasma with field-aligned sheared flow under the impact of q-nonextensive trapped electrons. The Schamel equation and its stationary solution in the form of solitary waves are obtained for this inhomogeneous plasma. It is shown that the amplitude of IA solitary waves increases with higher trapping efficiency (β), while the width remains almost the same. Further, it is found that the amplitude of the solitary waves decreases with enhanced normalized drift speed, shear flow parameter and the population of the energetic particles. The size of the nonlinear solitary structures is calculated to be a few hundred meters and it is pointed out that the present results are useful to understand the solar wind plasma.

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Dust charging and levitating in a sheath of plasma containing energetic particles

欧靖, 赵晓云, 林滨滨

2018 (2): 25204-025204. doi: 10.1088/1674-1056/27/2/025204

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The structure of the sheath in the presence of energetic particles is investigated in the multi-fluid framework. Based on the orbital motion limited (OML) theory, the dust grain charging inside the sheath of plasma containing energetic particles is examined for the carbon wall, and then the effect of the energetic particles on the stationary dust particle inside the sheath is discussed through the trapping potential energy. It is found that with the increase of energetic ion concentration or energy, the size of dust staying in levitation equilibrium decreases and the levitating position is much closer to the wall. In the case of deuterium ions as energetic ions, the bigger dust particle can be trapped by the sheath than in the case of hydrogen ions as energetic ions. When the energetic electron component is present, the levitating position of dust particle in the sheath depends strongly on the energetic electron. The levitating dust particle is closer to the wall as the energetic electron energy or concentration is increased. In addition, with the increase of temperature of thermal background ion, the size of dust particle trapped by the sheath decreases and the levitating positions of dust particles with the same size radius inside the sheath move toward the wall. Our results can be helpful in investigating the property of the sheath where the energetic particle component is present.

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A fast emittance measurement unit for high intensity DC beam

张艾霖, 任海涛, 彭士香, 张滔, 徐源, 张景丰, 温佳美, 武文斌, 郭之虞, 陈佳洱

2018 (2): 25205-025205. doi: 10.1088/1674-1056/27/2/025205

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A combined unit, which has the ability to measure the current and emittance of the high intensity direct current (DC) ion beam, is developed at Peking University (PKU). It is a multi-slit single-wire (MSSW)-type beam emittance meter combined with a water-cooled Faraday Cup, named high intensity beam emittance measurement unit-6 (HIBEMU-6). It takes about 15 seconds to complete one measurement of the beam current and its emittance. The emittance of a 50-mA@50-kV DC proton beam is measured.

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Rayleigh-Taylor instability at spherical interfaces of incompressible fluids

郭宏宇, 王立锋, 叶文华, 吴俊峰, 李英骏, 张维岩

2018 (2): 25206-025206. doi: 10.1088/1674-1056/27/2/025206

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Rayleigh-Taylor instability (RTI) of three incompressible fluids with two interfaces in spherical geometry is derived analytically. The growth rate on the two interfaces and the perturbation feedthrough coefficients between two spherical interfaces are derived. For low-mode perturbation, the feedthrough effect from outer interface to inner interface is much more severe than the corresponding planar case, while the feedback from inner interface to the outer interface is smaller than that in planar geometry. The low-mode perturbations lead to the pronounced RTI growth on the inner interface of a spherical shell that are larger than the cylindrical and planar results. It is the low-mode perturbation that results in the difference between the RTI growth in spherical and cylindrical geometry. When the mode number of the perturbation is large enough, the results in cylindrical geometry are recovered.

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Analytical studies on the evolution processes of rarefied deuterium plasma shell Z-pinch by PIC and MHD simulations

宁成, 张小强, 张扬, 孙顺凯, 薛创, 丰志兴, 李百文

2018 (2): 25207-025207. doi: 10.1088/1674-1056/27/2/025207

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In this paper, we analytically explore the magnetic field and mass density evolutions obtained in particle-in-cell (PIC) and magnetohydrodynamics (MHD) simulations of a rarefied deuterium shell Z-pinch and compare those results, and also we study the effects of artificially increased Spitzer resistivity on the magnetic field evolution and Z-pinch dynamic process in the MHD simulation. There are significant differences between the profiles of mass density in the PIC and MHD simulations before 45 ns of the Z-pinch in this study. However, after the shock formation in the PIC simulation, the mass density profile is similar to that in the MHD simulation in the case of using multiplier 2 to modify the Spitzer resistivity. Compared with the magnetic field profiles of the PIC simulation of the shell, the magnetic field diffusion has still not been sufficiently revealed in the MHD simulation even though their convergence ratios become the same by using larger multipliers in the resistivity. The MHD simulation results suggest that the magnetic field diffusion is greatly enhanced by increasing the Spitzer resistivity used, which, however, causes the implosion characteristic to change from shock compression to weak shock, even shockless evolution, and expedites the expansion of the shell. Too large a multiplier is not suggested to be used to modify the resistivity in some Z-pinch applications, such as the Z-pinch driven inertial confinement fusion (ICF) in a dynamic hohlraum. Two-fluid or Hall MHD model, even the PIC/fluid hybrid simulation would be considered as a suitable physical model when there exist the plasma regions with very low density in the simulated domain.

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Effect of actuating frequency on plasma assisted detonation initiation

周思引, 车学科, 王迪, 聂万胜

2018 (2): 25208-025208. doi: 10.1088/1674-1056/27/2/025208

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Aiming at studying the influence of actuating frequency on plasma assisted detonation initiation by alternating current dielectric barrier discharge, a loosely coupled method is used to simulate the detonation initiation process of a hydrogen-oxygen mixture in a detonation tube at different actuating frequencies. Both the discharge products and the detonation forming process which is assisted by the plasma are analyzed. It is found that the patterns of the temporal and spatial distributions of discharge products in one cycle are not changed by the actuating frequency. However, the concentration of every species decreases as the actuating frequency rises, and atom O is the most sensitive to this variation, which is related to the decrease of discharge power. With respect to the reaction flow of the detonation tube, the deflagration-to-detonation transition (DDT) time and distance both increase as the actuating frequency rises, but the degree of effect on DDT development during flow field evolution is erratic. Generally, the actuating frequency affects none of the amplitude value of the pressure, temperature, species concentration of the flow field, and the combustion degree within the reaction zone.

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Structural, magnetic properties, and electronic structure of hexagonal FeCoSn compound

李勇, 代学芳, 刘国栋, 魏志阳, 刘恩克, 韩小磊, 杜志伟, 郗学奎, 王文洪, 吴光恒

2018 (2): 26101-026101. doi: 10.1088/1674-1056/27/2/026101

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The structural, magnetic properties, and electronic structures of hexagonal FeCoSn compounds with as-annealed bulk and ribbon states were investigated by x-ray powder diffraction (XRD), differential scanning calorimetry (DSC), transmission electron microscope (TEM), scanning electron microscope (SEM), magnetic measurements, and first-principles calculations. Results indicate that both states of FeCoSn show an Ni₂In-type hexagonal structure with a small amount of FeCo-rich secondary phase. The Curie temperatures are located at 257 K and 229 K, respectively. The corresponding magnetizations are 2.57 μ_B/f.u. and 2.94 μ_B/f.u. at 5 K with a field of 50 kOe (1 Oe=79.5775 A·m^-1). The orbital hybridizations between 3d elements are analyzed from the distribution of density of states (DOS), showing that Fe atoms carry the main magnetic moments and determine the electronic structure around Fermi level. A peak of DOS at Fermi level accounts for the presence of the FeCo-rich secondary phase. The Ni₂In-type hexagonal FeCoSn compound can be used during the isostructural alloying for tuning phase transitions.

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Light trapping and optical absorption enhancement in vertical semiconductor Si/SiO₂ nanowire arrays

王莹, 李新化

2018 (2): 26102-026102. doi: 10.1088/1674-1056/27/2/026102

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The full potential of optical absorption property must be further cultivated before silicon (Si) semiconductor nanowire (NW) arrays become available for mainstream applications in optoelectronic devices. In this paper, we demonstrate both experimentally and theoretically that an SiO₂ coating can substantially improve the absorption of light in Si NW arrays. When the transparent SiO₂ shell is coated on the outer layer of Si NW, the incident light penetrates better into the absorbing NW core. We provide the detailed theoretical analysis by a combination of finite-difference time-domain (FDTD) analysis. It is demonstrated that increasing the thickness of the dielectric shell, we achieve 1.72 times stronger absorption in the NWs than in uncoated NWs.

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Theoretical study on electronic structure and thermoelectric properties of PbS_xTe_1-x (x=0.25, 0.5, and 0.75) solid solution

鲁勇, 李开跃, 张晓林, 黄艳, 邵晓红

2018 (2): 26103-026103. doi: 10.1088/1674-1056/27/2/026103

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The electronic structure and thermoelectric (TE) properties of PbSxTe_1-x (x=0.25, 0.5, and 0.75) solid solution have been studied by combining the first-principles calculations and semi-classical Boltzmann theory. The special quasi-random structure (SQS) method is used to model the solid solutions of PbSxTe_1-x, which can produce reasonable electronic structures with respect to experimental results. The maximum zT value can reach 1.67 for p-type PbS_0.75Te_0.25 and 1.30 for PbS_0.5Te_0.5 at 800 K, respectively. The performance of p-type PbSxTe_1-x is superior to the n-type ones, mainly attributed to the higher effective mass of the carriers. The zT values for PbSxTe_1-x solid solutions are higher than that of pure PbTe and PbS, in which the combination of low thermal conductivity and high power factor play important roles.

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Neutron powder diffraction and high-pressure synchrotron x-ray diffraction study of tantalum nitrides

冯雷豪, 胡启威, 雷力, 房雷鸣, 戚磊, 张雷雷, 蒲梅芳, 寇自力, 彭放, 陈喜平, 夏元华, 小岛洋平, 大藤宏明, 贺端威, 陈波, 入舩徹男

2018 (2): 26201-026201. doi: 10.1088/1674-1056/27/2/026201

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Tantalum nitride (TaN) compact with a Vickers hardness of 26 GPa is prepared by a high-pressure and high-temperature (HPHT) method. The crystal structure and atom occupations of WC-type TaN have been investigated by neutron powder diffraction, and the compressibility of WC-type TaN has been investigated by using in-situ high-pressure synchrotron x-ray diffraction. The third-order Birch-Murnaghan equation of state fitted to the x-ray diffraction pressure-volume (P-V) sets of data, collected up to 41 GPa, yields ambient pressure isothermal bulk moduli of B₀=369(2) GPa with pressure derivatives of B₀'=4 for the WC-type TaN. The bulk modulus of WC-type TaN is not in good agreement with the previous result (B₀=351 GPa), which is close to the recent theoretical calculation result (B₀=378 GPa). An analysis of the experiment results shows that crystal structure of WC-type TaN can be viewed as alternate stacking of Ta and N layers along the c direction, and the covalent Ta-N bonds between Ta and N layers along the c axis in the crystal structure play an important role in the incompressibility and hardness of WC-type TaN.

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Thermal conductivity of carbon nanotube superlattices: Comparative study with defective carbon nanotubes

周魁葵, 徐宁, 谢国锋

2018 (2): 26501-026501. doi: 10.1088/1674-1056/27/2/026501

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We use molecular dynamics simulation to calculate the thermal conductivities of (5, 5) carbon nanotube superlattices (CNTSLs) and defective carbon nanotubes (DCNTs), where CNTSLs and DCNTs have the same size. It is found that the thermal conductivity of DCNT is lower than that of CNTSL at the same concentration of Stone-Wales (SW) defects. We perform the analysis of heat current autocorrelation functions and observe the phonon coherent resonance in CNTSLs, but do not observe the same effect in DCNTs. The phonon vibrational eigen-mode analysis reveals that all modes of phonons are strongly localized by SW defects. The degree of localization of CNTSLs is lower than that of DCNTs, because the phonon coherent resonance results in the phonon tunneling effect in the longitudinal phonon mode. The results are helpful in understanding and tuning the thermal conductivity of carbon nanotubes by defect engineering.

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Effect of isotope doping on phonon thermal conductivity of silicene nanoribbons: A molecular dynamics study

徐润峰, 韩奎, 李海鹏

2018 (2): 26801-026801. doi: 10.1088/1674-1056/27/2/026801

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Silicene, a silicon analogue of graphene, has attracted increasing research attention in recent years because of its unique electrical and thermal conductivities. In this study, phonon thermal conductivity and its isotopic doping effect in silicene nanoribbons (SNRs) are investigated by using molecular dynamics simulations. The calculated thermal conductivities are approximately 32 W/mK and 35 W/mK for armchair-edged SNRs and zigzag-edged SNRs, respectively, which show anisotropic behaviors. Isotope doping induces mass disorder in the lattice, which results in increased phonon scattering, thus reducing the thermal conductivity. The phonon thermal conductivity of isotopic doped SNR is dependent on the concentration and arrangement pattern of dopants. A maximum reduction of about 15% is obtained at 50% randomly isotopic doping with ³⁰Si. In addition, ordered doping (i.e., isotope superlattice) leads to a much larger reduction in thermal conductivity than random doping for the same doping concentration. Particularly, the periodicity of the doping superlattice structure has a significant influence on the thermal conductivity of SNR. Phonon spectrum analysis is also used to qualitatively explain the mechanism of thermal conductivity change induced by isotopic doping. This study highlights the importance of isotopic doping in tuning the thermal properties of silicene, thus guiding defect engineering of the thermal properties of two-dimensional silicon materials.

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Thermoelectric properties of two-dimensional hexagonal indium-VA

毕京云, 韩利红, 王倩, 伍力源, 屈贺如歌, 芦鹏飞

2018 (2): 26802-026802. doi: 10.1088/1674-1056/27/2/026802

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The electrical properties and thermoelectric (TE) properties of monolayer In-VA are investigated theoretically by combining first-principles method with Boltzmann transport theory. The ultralow intrinsic thermal conductivities of 2.64 W·m^-1·K^-1 (InP), 1.31 W·m^-1·K^-1 (InAs), 0.87 W·m^-1·K^-1 (InSb), and 0.62 W·m^-1 K^-1 (InBi) evaluated at room temperature are close to typical thermal conductivity values of good TE materials (κ < 2 W·m^-1·K^-1). The maximal ZT values of 0.779, 0.583, 0.696, 0.727, and 0.373 for InN, InP, InAs, InSb, and InBi at p-type level are calculated at 900 K, which makes In-VA potential TE material working at medium-high temperature.

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Electronic structures and optical properties of HfO₂-TiO₂ alloys studied by first-principles GGA+ U approach

李金平, 孟松鹤, 杨程, 陆汉涛, 遠山貴巳

2018 (2): 27101-027101. doi: 10.1088/1674-1056/27/2/027101

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The phase diagram of HfO₂-TiO₂ system shows that when Ti content is less than 33.0 mol%, HfO₂-TiO₂ system is monoclinic; when Ti content increases from 33.0 mol% to 52.0 mol%, it is orthorhombic; when Ti content reaches more than 52.0 mol%, it presents rutile phase. So, we choose the three phases of HfO₂-TiO₂ alloys with different Ti content values. The electronic structures and optical properties of monoclinic, orthorhombic and rutile phases of HfO₂-TiO₂ alloys are obtained by the first-principles generalized gradient approximation (GGA)+U approach, and the effects of Ti content and crystal structure on the electronic structures and optical properties of HfO₂-TiO₂ alloys are investigated. By introducing the Coulomb interactions of 5d orbitals on Hf atom (U₁^d), those of 3d orbitals on Ti atom (U₂^d), and those of 2p orbitals on O atom (U^p) simultaneously, we can improve the calculation values of the band gaps, where U₁^d, U₂^d, and Up values are 8.0 eV, 7.0 eV, and 6.0 eV for both the monoclinic phase and orthorhombic phase, and 8.0 eV, 7.0 eV, and 3.5 eV for the rutile phase. The electronic structures and optical properties of the HfO₂-TiO₂ alloys calculated by GGA+U₁^d (U₁^d=8.0 eV)+U₂^d (U₂^d=7.0 eV)+U^p (U^p=6.0 eV or 3.5 eV) are compared with available experimental results.

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Computational mechanistic investigation of radiation damage of adenine induced by hydroxyl radicals

谈荣日, 刘慧宣, 寻大毛, 宗文军

2018 (2): 27102-027102. doi: 10.1088/1674-1056/27/2/027102

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The radiation damage of adenine base was studied by B3LYP and MP2 methods in the presence of hydroxyl radicals to probe the reactivities of five possible sites of an isolated adenine molecule. Both methods predict that the C8 site is the more vulnerable than the other sites. For its bonding covalently with the hydroxyl radicals, B3LYP predicts a barrierless pathway, while MP2 finds a transition state with an energy of 106.1 kJ/mol. For the hydroxylation at the C2 site, the barrier was calculated to be 165.3 kJ/mol using MP2 method. For the dehydrogenation reactions at five sites of adenine, B3LYP method predicts that the free energy barrier decreases in the order of H8 > H2 > HN62 > HN61 > HN9.

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Intersubband optical absorption of electrons in double parabolic quantum wells of Al_xGa_1-xAs/Al_yGa_1-yAs

马淑芳, 屈媛, 班士良

2018 (2): 27103-027103. doi: 10.1088/1674-1056/27/2/027103

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Some realizable structures of double parabolic quantum wells (DPQWs) consisting of Al_xGa_1-xAs/Al_yGa_1-y As are constructed to discuss theoretically the optical absorption due to the intersubband transition of electrons for both symmetric and asymmetric cases with three energy levels of conduction bands. The electronic states in these structures are obtained using a finite element difference method. Based on a compact density matrix approach, the optical absorption induced by intersubband transition of electrons at room temperature is discussed. The results reveal that the peak positions and heights of intersubband optical absorption coefficients (IOACs) of DPQWs are sensitive to the barrier thickness, depending on Al component. Furthermore, external electric fields result in the decrease of peak, and play an important role in the blue shifts of absorption spectra due to electrons excited from ground state to the first and second excited states. It is found that the peaks of IOACs are smaller in asymmetric DPQWs than in symmetric ones. The results also indicate that the adjustable extent of incident photon energy for DPQW is larger than for a square one of a similar size. Our results are helpful in experiments and device fabrication.

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Characteristic modification by inserted metal layer and interface graphene layer in ZnO-based resistive switching structures

刘浩男, 索晓霞, 张林奥, 张端, 吴汉春, 赵宏康, 江兆潭, 李英兰, 王志

2018 (2): 27104-027104. doi: 10.1088/1674-1056/27/2/027104

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ZnO-based resistive switching device Ag/ZnO/TiN, and its modified structure Ag/ZnO/Zn/ZnO/TiN and Ag/graphene/ZnO/TiN, were prepared. The effects of inserted Zn layers in ZnO matrix and an interface graphene layer on resistive switching characteristics were studied. It is found that metal ions, oxygen vacancies, and interface are involved in the RS process. A thin inserted Zn layer can increase the resistance of HRS and enhance the resistance ratio. A graphene interface layer between ZnO layer and top electrode can block the carrier transport and enhance the resistance ratio to several times. The results suggest feasible routes to tailor the resistive switching performance of ZnO-based structure.

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Observation of nonconservation characteristics of radio frequency noise mechanism of 40-nm n-MOSFET

王军, 彭小梅, 刘志军, 王林, 罗震, 王丹丹

2018 (2): 27201-027201. doi: 10.1088/1674-1056/27/2/027201

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Bias non-conservation characteristics of radio-frequency noise mechanism of 40-nm n-MOSFET are observed by modeling and measuring its drain current noise. A compact model for the drain current noise of 40-nm MOSFET is proposed through the noise analysis. This model fully describes three kinds of main physical sources that determine the noise mechanism of 40-nm MOSFET, i.e., intrinsic drain current noise, thermal noise induced by the gate parasitic resistance, and coupling thermal noise induced by substrate parasitic effect. The accuracy of the proposed model is verified by noise measurements, and the intrinsic drain current noise is proved to be the suppressed shot noise, and with the decrease of the gate voltage, the suppressed degree gradually decreases until it vanishes. The most important findings of the bias non-conservative nature of noise mechanism of 40-nm n-MOSFET are as follows. (i) In the strong inversion region, the suppressed shot noise is weakly affected by the thermal noise of gate parasitic resistance. Therefore, one can empirically model the channel excess noise as being like the suppressed shot noise. (ii) In the middle inversion region, it is almost full of shot noise. (iii) In the weak inversion region, the thermal noise is strongly frequency-dependent, which is almost controlled by the capacitive coupling of substrate parasitic resistance. Measurement results over a wide temperature range demonstrate that the thermal noise of 40-nm n-MOSFET exists in a region from the weak to strong inversion, contrary to the predictions of suppressed shot noise model only suitable for the strong inversion and middle inversion region. These new findings of the noise mechanism of 40-nm n-MOSFET are very beneficial for its applications in ultra low-voltage and low-power RF, such as novel device electronic structure optimization, integrated circuit design and process technology evaluation.

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Highly stable two-dimensional graphene oxide: Electronic properties of its periodic structure and optical properties of its nanostructures

张琴, 张红, 程新路

2018 (2): 27301-027301. doi: 10.1088/1674-1056/27/2/027301

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According to first principle simulations, we theoretically predict a type of stable single-layer graphene oxide (C₂O). Using density functional theory (DFT), C₂O is found to be a direct gap semiconductor. In addition, we obtain the absorption spectra of the periodic structure of C₂O, which show optical anisotropy. To study the optical properties of C₂O nanostructures, time-dependent density functional theory (TDDFT) is used. The C₂O nanostructure has a strong absorption near 7 eV when the incident light polarizes along the armchair-edge. Besides, we find that the optical properties can be controlled by the edge configuration and the size of the C₂O nanostructure. With the elongation strain increasing, the range of light absorption becomes wider and there is a red shift of absorption spectrum.

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A transparent electromagnetic-shielding film based on one-dimensional metal-dielectric periodic structures

赵亚丽, 马富花, 李旭峰, 马江将, 贾琨, 魏学红

2018 (2): 27302-027302. doi: 10.1088/1674-1056/27/2/027302

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In this study, we designed and fabricated optical materials consisting of alternating ITO and Ag layers. This approach is considered to be a promising way to obtain a light-weight, ultrathin and transparent shielding medium, which not only transmits visible light but also inhibits the transmission of microwaves, despite the fact that the total thickness of the Ag film is much larger than the skin depth in the visible range and less than that in the microwave region. Theoretical results suggest that a high dielectric/metal thickness ratio can enhance the broadband and improve the transmittance in the optical range. Accordingly, the central wavelength was found to be red-shifted with increasing dielectric/metal thickness ratio. A physical mechanism behind the controlling transmission of visible light is also proposed. Meanwhile, the electromagnetic shielding effectiveness of the prepared structures was found to exceed 40 dB in the range from 0.1 GHz to 18 GHz, even reaching up to 70 dB at 0.1 GHz, which is far higher than that of a single ITO film of the same thickness.

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Superconducting quantum bits

刘伟洋, 郑东宁, 赵士平

2018 (2): 27401-027401. doi: 10.1088/1674-1056/27/2/027401

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Superconducting quantum bits (qubits) and circuits are the leading candidate for the implementation of solid-state quantum computation. They have also been widely used in a variety of studies of quantum physics, atomic physics, quantum optics, and quantum simulation. In this article, we will present an overview of the basic principles of the superconducting qubits, including the phase, flux, charge, and transmon (Xmon) qubits, and the progress achieved so far concerning the improvements of the device design and quantum coherence property. Experimental studies in various research fields using the superconducting qubits and circuits will be briefly reviewed.

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Chiral p-wave pairing of ultracold fermionic atoms due to a quadratic band touching

王海啸, 刘子衡, 蒋建华

2018 (2): 27402-027402. doi: 10.1088/1674-1056/27/2/027402

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We study the superfuild ground state of ultracold fermions in optical lattices with a quadratic band touching. Examples are a checkerboard lattice around half filling and a kagome lattice above one third filling. Instead of pairing between spin states, here we focus on pairing interactions between different orbital states. We find that our systems have only odd-parity (orbital) pairing instability while the singlet (orbital) pairing instability vanishes thanks to the quadratic band touching. In the mean field level, the ground state is found to be a chiral p-wave pairing superfluid (mixed with finite f-wave pairing order-parameters) which supports Majorana fermions.

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Magnetocaloric effect in the layered organic-inorganic hybrid (CH₃NH₃)₂CuCl₄

马怡妮娜, 翟昆, 闫丽琴, 柴一晟, 尚大山, 孙阳

2018 (2): 27501-027501. doi: 10.1088/1674-1056/27/2/027501

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We present a study of magnetocaloric effect of the quasi-two-dimensional (2D) ferromagnet (CH₃NH₃)₂CuCl₄ in ab plane (easy-plane). From the measurements of magnetic field dependence of magnetization at various temperatures, we have discovered a large magnetic entropy change associated with the ferromagnetic-paramagnetic transition. The heat capacity measurements reveal an abnormal adiabatic change below the Curie temperature T_c~8.9 K, which is caused by the nature of quasi-2D layered crystal structure. These results suggest that perovskite organic-inorganic hybrids with a layered structure are suitable candidates as working substances in magnetic refrigeration technology.

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First-principles study of polarization and piezoelectricity behavior in tetragonal PbTiO₃-based superlattices

朱振业

2018 (2): 27701-027701. doi: 10.1088/1674-1056/27/2/027701

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Using first-principles calculation, the contribution of A-site and B-site atoms to polarization and piezoelectricity d₃₃ in the tetragonal PbTiO₃/KNbO₃ and PbTiO₃/LaAlO₃ superlattices is investigated in this paper. It is shown that PbTiO₃/KNbO₃ superlattice has larger polarization and d₃₃ than PbTiO₃/LaAlO₃ superlattice, because there is stronger charge transfer between A(B)-site atoms and oxygen atom in PbTiO₃/KNbO₃ superlattice. In PbTiO₃/KNbO₃ superlattice, B-site atoms (Ti, Nb) make larger contribution to the total polarization and d₃₃ than the A-site atoms (Pb, K) because of the strong covalent interactions between the transition metal (Ti, Nb) and the oxygen atoms, while piezoelectricity in PbTiO₃/LaAlO₃ superlattice mainly ascribes to piezoelectric contribution of Pb atom and Ti atom in PbTiO₃ component. Furthermore, by calculating the proportion of the piezoelectric contribution from PbTiO₃ component in superlattices, we find there is different response of strain to piezoelectric contribution from PbTiO₃ component in two superlattices but still with a value larger than 50%. In PbTiO₃/KNbO₃ superlattice, the c-axis strain reduces the proportion, especially under tensile condition. Meanwhile in PbTiO₃/LaAlO₃ superlattice, PbTiO₃ plays a leading role to the total d₃₃, especially under compressive condition, and the proportion decreases as the tensile strain increases.

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Multiple broadband magnetoelectric response in Terfenol-D/PZT structure

文建彪, 张娟娟, 高原文

2018 (2): 27702-027702. doi: 10.1088/1674-1056/27/2/027702

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In this paper, a novel magnetoelectric (ME) composite structure is proposed, and the ME response in the structure is measured at the bias magnetic field up to 2000 Oe (1 Oe=79.5775 A·m^-1) and the excitation frequency of alternating magnetic field ranging from 1 kHz to 200 kHz. The ME voltage of each PZT layer is detected. According to the measurement results, the phase differences are observed among three channels and the multi-peak phenomenon appears in each channel. Meanwhile, the results show that the ME structure can stay a relatively high ME response within a wide bandwidth. Besides, the hysteretic loops of three PZT layers are observed. When the frequency of alternating current (AC) magnetic field changes, the maximum value of ME coefficient appears in different layers due to the multiple vibration modes of the structure. Moreover, a finite element analysis is performed to evaluate the resonant frequency of the structure, and the theoretical calculating results accord well with the experimental results. The experiment results suggest that the proposed structure may be a good candidate for designing broadband magnetic field sensors.

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Optimizing effective phase modulation in coupled double quantum well Mach-Zehnder modulators

王光辉, 张金珂

2018 (2): 27801-027801. doi: 10.1088/1674-1056/27/2/027801

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We report optimal phase modulation based on enhanced electro-optic effects in a Mach-Zehnder (MZ) modulator constructed by AlGaAs/GaAs coupled double quantum well (CDQW) waveguides with optical gain. The net change of refractive indexes between two arms of the CDQW MZ modulator is derived by both the electronic polarization method and the normal-surface method. The numerical results show that very large refractive index change over 10^-1 can be obtained, making the phase modulation in the CDQW MZ modulator very highly efficient. It is desirable and important that a very small voltage-length product for π phase shift, V_π×L₀=0.0226 V·mm, is obtained by optimizing bias electric field and CDQW structural parameters, which is about seven times smaller than that in single quantum-well MZ modulators. These properties open an avenue for CDQW nanostructures in device applications such as electro-optical switches and phase modulators.

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Optically induced abnormal terahertz absorption in black silicon

翟东为, 刘海玲, 杨玉平

2018 (2): 27802-027802. doi: 10.1088/1674-1056/27/2/027802

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The absorption responses of blank silicon and black silicon (silicon with micro/nano-conical surface structures) wafers to an 808-nm continuous-wave (CW) laser are investigated at room temperature by terahertz time-domain spectroscopy. The transmission of the blank silicon shows an appreciable change, from ground state to the pump state, with amplitude varying up to 50%, while that of the black silicon (BS) with different cone sizes is observed to be more stable. Furthermore, the terahertz transmission through BS is observed to be strongly dependent on the size of the conical structure geometry. The conductivities of blank silicon and BS are extracted from the experimental data with and without pumping. The non-photo-excited conductivities increase with increasing frequency and agree well with the Lorentz model, whereas the photo-excited conductivities decrease with increasing frequency and fit well with the Drude-Smith model. Indeed, for BS, the conductivity, electron density and mobility are found to correlate closely with the size of the conical structure. This is attributed to the influence of space confinement on the carrier excitation, that is, the carriers excited at the BS conical structure surface have a stronger localization effect with a backscattering behavior in small-sized microstructures and a higher recombination rate due to increased electron interaction and collision with electrons, interfaces and grain boundaries.

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Investigation of europium(Ⅲ)-doped ZnS for immunoassay

朱超凡, 沙雪, 楚学影, 李金华, 徐铭泽, 金芳军, 徐志堃

2018 (2): 27803-027803. doi: 10.1088/1674-1056/27/2/027803

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Biofunctional europium (Ⅲ)-doped ZnS (ZnS:Eu) nanocrystals are prepared by a sol-gel method. The characteristic luminescence of ZnS:Eu is used as a probe signal to realize sensitive immunoassay. The luminescence intensity of the Eu³⁺ in the ZnS matrix shows strong concentration dependence, and the optimal doping concentration is 4%. However, the emission wavelengths of the ZnS:Eu nanocrystals are not dependent on doping concentration nor the temperature (from 100 K to 300 K). Our results show that these features allow for reliable immunoassay. Human immunoglobulin, used as a target analyte, is captured by antibody modified ZnS:Eu probe and is finally enriched on gold substrate for detection. High specificity of the assay is demonstrated by control experiments. The linear detection range is 10 nM-800 nM, and the detection limit is about 9.6 nM.

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Magneto-optical properties of self-assembled InAs quantum dots for quantum information processing

唐静, 许秀来

2018 (2): 27804-027804. doi: 10.1088/1674-1056/27/2/027804

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Semiconductor quantum dots have been intensively investigated because of their fundamental role in solid-state quantum information processing. The energy levels of quantum dots are quantized and can be tuned by external field such as optical, electric, and magnetic field. In this review, we focus on the development of magneto-optical properties of single InAs quantum dots embedded in GaAs matrix, including charge injection, relaxation, tunneling, wavefunction distribution, and coupling between different dimensional materials. Finally, the perspective of coherent manipulation of quantum state of single self-assembled quantum dots by photocurrent spectroscopy with an applied magnetic field is discussed.

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Magnetic field aligned orderly arrangement of Fe₃O₄ nanoparticles in CS/PVA/Fe₃O₄ membranes

杜萌, 曹兴忠, 夏锐, 周忠坡, 靳硕学, 王宝义

2018 (2): 27805-027805. doi: 10.1088/1674-1056/27/2/027805

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The CS/PVA/Fe₃O₄ nanocomposite membranes with chainlike arrangement of Fe₃O₄ nanoparticles are prepared by a magnetic-field-assisted solution casting method. The aim of this work is to investigate the relationship between the microstructure of the magnetic anisotropic CS/PVA/Fe₃O₄ membrane and the evolved macroscopic physicochemical property. With the same doping content, the relative crystallinity of CS/PVA/Fe₃O₄-M is lower than that of CS/PVA/Fe₃O₄. The Fourier transform infrared spectroscopy (FT-TR) measurements indicate that there is no chemical bonding between polymer molecule and Fe₃O₄ nanoparticle. The Fe₃O₄ nanoparticles in CS/PVA/Fe₃O₄ and CS/PVA/Fe₃O₄-M are wrapped by the chains of CS/PVA, which is also confirmed by scanning electron microscopy (SEM) and x-ray diffraction (XRD) analysis. The saturation magnetization value of CS/PVA/Fe₃O₄-M obviously increases compared with that of non-magnetic aligned membrane, meanwhile the transmittance decreases in the UV-visible region. The o-Ps lifetime distribution provides information about the free-volume nanoholes present in the amorphous region. It is suggested that the microstructure of CS/PVA/Fe₃O₄ membrane can be modified in its curing process under a magnetic field, which could affect the magnetic properties and the transmittance of nanocomposite membrane. In brief, a full understanding of the relationship between the microstructure and the macroscopic property of CS/PVA/Fe₃O₄ nanocomposite plays a vital role in exploring and designing the novel multifunctional materials.

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Suppression of electron and hole overflow in GaN-based near-ultraviolet laser diodes

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

2018 (2): 28101-028101. doi: 10.1088/1674-1056/27/2/028101

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In order to suppress the electron leakage to p-type region of near-ultraviolet GaN/In_xGa_1-xN/GaN multiple-quantum-well (MQW) laser diode (LD), the Al composition of inserted p-type Al_xGa_1-xN electron blocking layer (EBL) is optimized in an effective way, but which could only partially enhance the performance of LD. Here, due to the relatively shallow GaN/In_0.04Ga_0.96N/GaN quantum well, the hole leakage to n-type region is considered in the ultraviolet LD. To reduce the hole leakage, a 10-nm n-type Al_xGa_1-xN hole blocking layer (HBL) is inserted between n-type waveguide and the first quantum barrier, and the effect of Al composition of Al_xGa_1-xN HBL on LD performance is studied. Numerical simulations by the LASTIP reveal that when an appropriate Al composition of Al_xGa_1-xN HBL is chosen, both electron leakage and hole leakage can be reduced dramatically, leading to a lower threshold current and higher output power of LD.

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Robust stability characterizations of active metamaterials with non-Foster loads

范逸风, 孙永志

2018 (2): 28102-028102. doi: 10.1088/1674-1056/27/2/028102

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Active metamaterials incorporating with non-Foster elements have been considered as one of the means of overcoming inherent limitations of the passive counterparts, thus achieving broadband or gain metamaterials. However, realistic active metamaterials, especially non-Foster loaded medium, would face the challenge of the possibility of instability. Moreover, they normally appear to be time-variant and in unsteady states, which leads to the necessity of a stability method to cope with the stability issue considering the system model uncertainty. In this paper, we propose an immittance-based stability method to design a non-Foster loaded metamaterial ensuring robust stability. First, the principle of this stability method is introduced after comparing different stability criteria. Based on the equivalent system model, the stability characterization is used to give the design specifications to achieve an active metamaterial with robust stability. Finally, it is applied to the practical design of active metamaterial with non-Foster loaded loop arrays. By introducing the disturbance into the non-Foster circuit (NFC), the worst-case model uncertainty is considered during the design, and the reliability of our proposed method is verified. This method can also be applied to other realistic design of active metamaterials.

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Observation of oscillations in the transport for atomic layer MoS₂

解晓强, 彭英姿, 郑奇烨, 李源, 陈吉

2018 (2): 28103-028103. doi: 10.1088/1674-1056/27/2/028103

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In our experiment, an atomic layer MoS₂ structure grown on SiO₂/Si substrates is used in transport test. The voltage U_14,23 oscillates and the corresponding period varies with applied current. The largest period appears at 45 μA. The oscillation periods are different when samples are under laser radiation or in darkness. We discover that under the laser irradiation, the oscillation period occurs at lower current than in the darkness case. Meanwhile, the drift velocity is estimated at~10⁷ cm/s. Besides, by studying the envelope of U_14,23 versus applied current, we see a beating phenomenon at a certain current value. The beating period in darkness is larger than under laser irradiation. The difference between beating periods reveals the energy difference of electrons. Similar results are obtained by using different laser power densities and different light sources. The possible mechanism behind the oscillation period is discussed.

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Influences of substrate temperature on microstructure and corrosion behavior of APS Ni₅₀Ti₂₅Al₂₅ inter-metallic coating

Sh Khandanjou,M Ghoranneviss,Sh Saviz,M Reza Afshar

2018 (2): 28104-028104. doi: 10.1088/1674-1056/27/2/028104

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In the present investigation, Ni₅₀Ti₂₅Al₂₅ (at.%) mechanically alloyed powder is deposited on carbon steel substrate. Before the coating process, the substrate is heated to temperature ranging from room temperature to 400℃. The microstructure, porosity, microhardness, adhesion strength, and corrosion behavior of the coating are investigated at different substrate temperatures. Results show that coating porosity is lower on high temperature surface. Microhardness and adhesion strength of the deposition layer on the substrate without preheating have lower values than with preheating. The polarization test result shows that corrosion performance of the coating is dependent on micro cracks and porosities and the increasing of substrate temperature can improve the quality of coating and corrosion performance.

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Monitoring the formation of oil-water emulsions with a fast spatially resolved NMR spectroscopy method

游梦婷, 韦芝良, 杨健, 崔晓红, 陈忠

2018 (2): 28201-028201. doi: 10.1088/1674-1056/27/2/028201

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In the present study, a fast chemical shift imaging (CSI) method has been used to dynamically monitor the formation of oil-water emulsions and the phase separation process of the emulsion phase from the excessive water or oil phase on the molecular level. With signals sampled from series of small voxels simultaneously within a few seconds, high-resolution one-dimensional (1D) ¹H nuclear magnetic resonance (NMR) spectra from different spatial positions for inhomogeneous emulsion systems induced by susceptibility differences among components can be obtained independently. On the basis of integrals from these ¹H NMR spectra, profiles obtained explicitly demonstrate the spatial and temporal variations of oil concentrations. Furthermore, the phase separation time and the length of the oil-water emulsion phase are determined. In addition, effects of oil types and proportions of the emulsifier on the emulsification states are also inspected. Experimental results indicate that 1D PHASICS (Partial Homogeneity Assisted Inhomogeneity Correction Spectroscopy) provides a helpful and promising alternative to research on dynamic processes or chemical reactions.

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A low-outgassing-rate carbon fiber array cathode

李安昆, 樊玉伟, 钱宝良, 张自成, 荀涛

2018 (2): 28401-028401. doi: 10.1088/1674-1056/27/2/028401

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In this paper, a new carbon fiber based cathode-a low-outgassing-rate carbon fiber array cathode-is investigated experimentally, and the experimental results are compared with those of a polymer velvet cathode. The carbon fiber array cathode is constructed by inserting bunches of carbon fibers into the cylindrical surface of the cathode. In experiment, the diode base pressure is maintained at 1×10^-2 Pa-2×10^-2 Pa, and the diode is driven by a compact pulsed power system which can provide a diode voltage of about 100 kV and pulse duration of about 30 ns at a repetition rate of tens of Hz. Real-time pressure data are measured by a magnetron gauge. Under the similar conditions, the experimental results show that the outgassing rate of the carbon fiber array cathode is an order smaller than that of the velvet cathode and that this carbon fiber array cathode has better shot-to-shot stability than the velvet cathode. Hence, this carbon fiber array cathode is demonstrated to be a promising cathode for the radial diode, which can be used in magnetically insulated transmission line oscillator (MILO) and relativistic magnetron (RM).

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Enhanced radiation-induced narrow channel effects in 0.13-μm PDSOI nMOSFETs with shallow trench isolation

张梦映, 胡志远, 毕大炜, 戴丽华, 张正选

2018 (2): 28501-028501. doi: 10.1088/1674-1056/27/2/028501

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Total ionizing dose responses of different transistor geometries after being irradiated by ⁶⁰Co γ-rays, in 0.13-μm partially-depleted silicon-on-insulator (PD SOI) technology are investigated. The negative threshold voltage shift in an n-type metal-oxide semiconductor field effect transistor (nMOSFET) is inversely proportional to the channel width due to radiation-induced charges trapped in trench oxide, which is called the radiation-induced narrow channel effect (RINCE). The analysis based on a charge sharing model and three-dimensional technology computer aided design (TCAD) simulations demonstrate that phenomenon. The radiation-induced leakage currents under different drain biases are also discussed in detail.

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Effects of proton irradiation at different incident angles on InAlAs/InGaAs InP-based HEMTs

孙树祥, 魏志超, 夏鹏辉, 王文斌, 段智勇, 李玉晓, 钟英辉, 丁芃, 金智

2018 (2): 28502-028502. doi: 10.1088/1674-1056/27/2/028502

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InP-based high electron mobility transistors (HEMTs) will be affected by protons from different directions in space radiation applications. The proton irradiation effects on InAlAs/InGaAs hetero-junction structures of InP-based HEMTs are studied at incident angles ranging from 0 to 89.9° by SRIM software. With the increase of proton incident angle, the change trend of induced vacancy defects in the InAlAs/InGaAs hetero-junction region is consistent with the vacancy energy loss trend of incident protons. Namely, they both have shown an initial increase, followed by a decrease after incident angle has reached 30°. Besides, the average range and ultimate stopping positions of incident protons shift gradually from buffer layer to hetero-junction region, and then go up to gate metal. Finally, the electrical characteristics of InP-based HEMTs are investigated after proton irradiation at different incident angles by Sentaurus-TCAD. The induced vacancy defects are considered self-consistently through solving Poisson's and current continuity equations. Consequently, the extrinsic transconductance, pinch-off voltage and channel current demonstrate the most serious degradation at the incident angle of 30°, which can be accounted for the most severe carrier sheet density reduction under this condition.

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Application of microdosimetry on biological physics for ionizing radiation

陈丹丹, 孙亮

2018 (2): 28701-028701. doi: 10.1088/1674-1056/27/2/028701

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Stochastic characterization of radiation interaction is of importance to cell damage. Microdosimetry is to investigate the random structures of particle tracks in order to understand the dose-effect in cellular scales. In the review, we introduced the basic concepts of microdosimetry as well as the experimental methods (TEPC) and Monte Carlo simulations. Three basic biophysical models are interpreted and compared, including the target model, linear-quadratic model, and microdosimetric-kinetic model. The bottlenecks in the current microdosimetry research are also discussed, which need the interdisciplinary contributions from biology, physics, mathematics, computer science and electric engineering.

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Lipoprotein in cholesterol transport: Highlights and recent insights into its structural basis and functional mechanism

陈淑玉, 李娜, 金桃丽, 缑璐, 郝东晓, 田芷淇, 张胜利, 张磊

2018 (2): 28702-028702. doi: 10.1088/1674-1056/27/2/028702

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Lipoproteins are protein-lipid macromolecular assemblies which are used to transport lipids in circulation and are key targets in cardiovascular disease (CVD). The highly dynamic lipoprotein molecules are capable of adopting an array of conformations that is crucial to lipid transport along the cholesterol transport pathway, among which high-density lipoprotein (HDL) and low-density lipoprotein (LDL) are major players in plasma cholesterol metabolism. For a more detailed illustration of cholesterol transport process, as well as the development of therapies to prevent CVD, here we review the functional mechanism and structural basis of lipoproteins in cholesterol transport, as well as their structural dynamics in the plasma lipoprotein (HDL and LDL) elevations, in order to obtain better quantitative understandings on structure-function relationship of lipoproteins. Finally, we also provide an approach for further research on the lipoprotein in cholesterol transport.

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Influence of anisotropy on the electrical conductivity and diffusion coefficient of dry K-feldspar: Implications of the mechanism of conduction

代立东, 胡海英, 李和平, 孙文清, 蒋建军

2018 (2): 28703-028703. doi: 10.1088/1674-1056/27/2/028703

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The electrical conductivities of single-crystal K-feldspar along three different crystallographic directions are investigated by the Solartron-1260 Impedance/Gain-phase analyzer at 873 K-1223 K and 1.0 GPa-3.0 GPa in a frequency range of 10^-1 Hz-10⁶ Hz. The measured electrical conductivity along the ⊥[001] axis direction decreases with increasing pressure, and the activation energy and activation volume of charge carriers are determined to be 1.04 ±0.06 eV and 2.51 ±0.19 cm³/mole, respectively. The electrical conductivity of K-feldspar is highly anisotropic, and its value along the ⊥[001] axis is approximately three times higher than that along the ⊥[100] axis. At 2.0 GPa, the diffusion coefficient of ionic potassium is obtained from the electrical conductivity data using the Nernst-Einstein equation. The measured electrical conductivity and calculated diffusion coefficient of potassium suggest that the main conduction mechanism is of ionic conduction, therefore the dominant charge carrier is transferred between normal lattice potassium positions and adjacent interstitial sites along the thermally activated electric field.

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Protection-against-water-attack determined difference between strengths of backbone hydrogen bonds in kinesin's neck zipper region

覃静宇, 耿轶钊, 吕刚, 纪青, 方海平

2018 (2): 28704-028704. doi: 10.1088/1674-1056/27/2/028704

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Docking of the kinesin's neck linker (NL) to the motor domain is the key force-generation process of the kinesin. In this process, NL's β 10 portion forms four backbone hydrogen bonds (HBs) with the motor domain. These backbone hydrogen bonds show big differences in their effective strength. The origins of these strength differences are still unclear. Using molecular dynamics method, we investigate the stability of the backbone HBs in explicit water environment. We find that the strength differences of these backbone HBs mainly arise from their relationships with water molecules which are controlled by arranging the surrounding residue sidechains. The arrangement of the residues in the C-terminal part of β 10 results in the existence of the water-attack channels around the backbone HBs in this region. Along these channels the water molecules can directly attack the backbone HBs and make these HBs relatively weak. In contrast, the backbone HB at the N-terminus of β 10 is protected by the surrounding hydrophobic and hydrophilic residues which cooperate positively with the central backbone HB and make this HB highly strong. The intimate relationship between the effective strength of protein backbone HB and water revealed here should be considered when performing mechanical analysis for protein conformational changes.

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Diffusional inhomogeneity in cell cultures

张佳政, 李娜, 陈唯

2018 (2): 28705-028705. doi: 10.1088/1674-1056/27/2/028705

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Cell migrations in the cell cultures are found to follow non-Gaussian statistics. We recorded long-term cell migration patterns with more than six hundred cells located in 28 mm². Our experimental data support the claim that an individual cell migration follows Gaussian statistics. Because the cell culture is inhomogeneous, the statistics of the cell culture exhibit a non-Gaussian distribution. We find that the normalized histogram of the diffusion velocity follows an exponential tail. A simple model is proposed based on the diffusional inhomogeneity to explain the exponential distribution of locomotion activity in this work. Using numerical calculation, we prove that our model is in great agreement with the experimental data.

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Noise decomposition algorithm and propagation mechanism in feed-forward gene transcriptional regulatory loop

桂容, 李治泓, 胡丽君, 程光晖, 刘泉, 熊娟, 贾亚, 易鸣

2018 (2): 28706-028706. doi: 10.1088/1674-1056/27/2/028706

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Feed-forward gene transcriptional regulatory networks, as a set of common signal motifs, are widely distributed in the biological systems. In this paper, the noise characteristics and propagation mechanism of various feed-forward gene transcriptional regulatory loops are investigated, including (i) coherent feed-forward loops with AND-gate, (ii) coherent feed-forward loops with OR-gate logic, and (iii) incoherent feed-forward loops with AND-gate logic. By introducing logarithmic gain coefficient and using linear noise approximation, the theoretical formulas of noise decomposition are derived and the theoretical results are verified by Gillespie simulation. From the theoretical and numerical results of noise decomposition algorithm, three general characteristics about noise transmission in these different kinds of feed-forward loops are observed. i) The two-step noise propagation of upstream factor is negative in the incoherent feed-forward loops with AND-gate logic, that is, upstream factor can indirectly suppress the noise of downstream factors. ii) The one-step propagation noise of upstream factor is non-monotonic in the coherent feed-forward loops with OR-gate logic. iii) When the branch of the feed-forward loop is negatively controlled, the total noise of the downstream factor monotonically increases for each of all feed-forward loops. These findings are robust to variations of model parameters. These observations reveal the universal rules of noise propagation in the feed-forward loops, and may contribute to our understanding of design principle of gene circuits.

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Quantitative and sensitive detection of prohibited fish drugs by surface-enhanced Raman scattering

林世超, 张鑫, 赵伟臣, 陈朝阳, 杜攀, 赵永梅, 吴正龙, 许海军

2018 (2): 28707-028707. doi: 10.1088/1674-1056/27/2/028707

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Rapid and simple detections of two kinds of prohibited fish drugs, crystal violet (CV) and malachite green (MG), were accomplished by surface-enhanced Raman scattering (SERS). Based on the optimized Au/cicada wing, the detectable concentration of CV/MG can reach 10^-7 M, and the linear logarithmic quantitative relationship curves between logI and logC allows for the determination of the unknown concentration of CV/MG solution. The detection of these two analytes in real environment was also achieved, demonstrating the application potential of SERS in the fast screening of the prohibited fish drugs, which is of great benefit for food safety and environmental monitoring.

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Bio-macromolecular dynamic structures and functions, illustrated with DNA, antibody, and lipoprotein

缑璐, 金桃丽, 陈淑玉, 李娜, 郝东晓, 张胜利, 张磊

2018 (2): 28708-028708. doi: 10.1088/1674-1056/27/2/028708

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Bio-macromolecules, such as proteins and nucleic acids, are the basic materials that perform fundamental activities required for life. Their structural heterogeneities and dynamic personalities are vital to understand the underlying functional mechanisms of bio-macromolecules. With the rapid development of advanced technologies such as single-molecule technologies and cryo-electron microscopy (cryo-EM), an increasing number of their structural details and mechanics properties at molecular level have significantly raised awareness of basic life processes. In this review, firstly the basic principles of single-molecule method and cryo-EM are summarized, to shine a light on the development in these fields. Secondly, recent progress driven by the above two methods are underway to explore the dynamic structures and functions of DNA, antibody, and lipoprotein. Finally, an outlook is provided for the further research on both the dynamic structures and functions of bio-macromolecules, through single-molecule method and cryo-EM combining with molecular dynamics simulations.

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Generation of optimal persistent formations for heterogeneous multi-agent systems with a leader constraint

王国强, 罗贺, 胡笑旋

2018 (2): 28901-028901. doi: 10.1088/1674-1056/27/2/028901

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In this study, we consider the generation of optimal persistent formations for heterogeneous multi-agent systems, with the leader constraint that only specific agents can act as leaders. We analyze three modes to control the optimal persistent formations in two-dimensional space, thereby establishing a model for their constrained generation. Then, we propose an algorithm for generating the optimal persistent formation for heterogeneous multi-agent systems with a leader constraint (LC-HMAS-OPFGA), which is the exact solution algorithm of the model, and we theoretically prove its validity. This algorithm includes two kernel sub-algorithms, which are optimal persistent graph generating algorithm based on a minimum cost arborescence and the shortest path (MCA-SP-OPGGA), and the optimal persistent graph adjusting algorithm based on the shortest path (SP-OPGAA). Under a given agent formation shape and leader constraint, LC-HMAS-OPFGA first generates the network topology and its optimal rigid graph corresponding to this formation shape. Then, LC-HMAS-OPFGA uses MCA-SP-OPGGA to direct the optimal rigid graph to generate the optimal persistent graph. Finally, LC-HMAS-OPFGA uses SP-OPGAA to adjust the optimal persistent graph until it satisfies the leader constraint. We also demonstrate the algorithm, LC-HMAS-OPFGA, with an example and verify its effectiveness.

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Another look at the moist baroclinic Ertel-Rossby invariant with mass forcing

杨帅, 高守亭, 陈斌

2018 (2): 29201-029201. doi: 10.1088/1674-1056/27/2/029201

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Due to the importance of the mass forcing induced by precipitation and condensation in moist processes, the Lagrangian continuity equation without a source/sink term utilized to prove the Ertel-Rossby invariant (ERI) and its conservation property is re-derived considering the mass forcing. By introducing moist enthalpy and moisture entropy, the baroclinic ERI could be adapted to moist flow. After another look at the moist ERI, it is deployed as the dot product between the generalized velocity and the generalized vorticity in moist flow, which constitutes a kind of generalized helicity. Thus, the baroclinic ERI is further extended to the moist case. Moreover, the derived moist ERI forumla remains formally consistent with the dry version, no matter whether mass forcing is present. By using the Weber transformation and the Lagrangian continuity equation with a source/sink effect, the conservation property of the baroclinic ERI in moist flow is revisited. The presence or absence of mass forcing in the Lagrangian continuity equation determines whether or not the baroclinic ERI in moist flow is materially conserved. In other words, it would be qualified as a quasi-invariant but only being dependent on the circumstances. By another look at the moist baroclinic ERI, it is surely a neat formalism with a simple physical explanation, and the usefulness of its anomaly in diagnosing atmospheric flow is demonstrated by case study.

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Surface-tension-confined droplet microfluidics

陈新莲, 伍罕, 巫金波

2018 (2): 29202-029202. doi: 10.1088/1674-1056/27/2/029202

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This article is a concise overview about the developing microfluidic systems named surface-tension-confined droplet microfluidics (STORMs). Different from traditional complexed droplet microfluidics which generated and confined the droplets by three-dimensional (3D) poly(dimethylsiloxane)-based microchannels, STORM systems provide twodimensional (2D) platforms for control of droplets. STORM devices utilize surface energy, with methods such as surface chemical modification and mechanical processing, to control the movement of fluid droplets. Various STORM devices have been readily prepared, with distinct advantages over conventional droplet microfluidics, which generated and confined the droplets by 3D poly(dimethylsiloxane)-based microchannels, such as significant reduction of energy consumption necessary for device operation, facile or even direct introduction of droplets onto patterned surface without external driving force such as a micropump, thus increased frequency or efficiency of droplets generation of specific STORM device, among others. Thus, STORM devices can be excellent alternatives for majority areas in droplet microfluidics and irreplaceable choices in certain fields by contrast. In this review, fabrication methods or strategies, manipulation methods or mechanisms, and main applications of STORM devices are introduced.

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