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CN 11-5639/O4
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  • Pressure effect in the Kondo semimetal CeRu4Sn6 with nontrivial topology

    Jiahao Zhang(张佳浩), Shuai Zhang(张帅), Ziheng Chen(陈子珩), Meng Lv(吕孟), Hengcan Zhao(赵恒灿), Yi-feng Yang(杨义峰), Genfu Chen(陈根富), Peijie Sun(孙培杰)
    Chin. Phys. B 2018, 27 (9): 097103
    Kondo semimetal CeRu4Sn6 is attracting renewed attention due to the theoretically predicted nontrivial topology in its electronic band structure. We report hydrostatic and chemical pressure effects on the transport properties of single-and poly-crystalline samples. The electrical resistivity ρ(T...

  • 0-π transition induced by the barrier strength in spin superconductor Josephson junctions

    Wen Zeng(曾文), Rui Shen(沈瑞)
    Chin. Phys. B 2018, 27 (9): 097401
    The Andreev-like levels and the free energy of the spin superconductor/insulator/spin superconductor junction are obtained by using the Bogoliubov-de Gennes equation. The phase dependence of the spin supercurrents exhibits a 0-π transition by changing the barrier strength. The dependences of the ...

  • Visualizing light-to-electricity conversion process in InGaN/GaN multi-quantum wells with a p-n junction

    Yangfeng Li(李阳锋), Yang Jiang(江洋), Junhui Die(迭俊珲), Caiwei Wang(王彩玮), Shen Yan(严珅), Haiyan Wu(吴海燕), Ziguang Ma(马紫光), Lu Wang(王禄), Haiqiang Jia(贾海强), Wenxin Wang(王文新), Hong Chen(陈弘)
    Chin. Phys. B 2018, 27 (9): 097104
    Absorption and carrier transport behavior plays an important role in the light-to-electricity conversion process, which is difficult to characterize. Here we develop a method to visualize such a conversion process in the InGaN/GaN multi-quantum wells embedded in a p-n junction. Under non-resonant ab...

  • Potentials of classical force fields for interactions between Na+ and carbon nanotubes

    De-Yuan Li(李德远), Guo-Sheng Shi(石国升), Feng Hong(洪峰), Hai-Ping Fang(方海平)
    Chin. Phys. B 2018, 27 (9): 098801
    Carbon nanotubes (CNTs) have long been expected to be excellent nanochannels for use in desalination membranes and other bio-inspired human-made channels owing to their experimentally confirmed ultrafast water flow and theoretically predicted ion rejection. The correct classical force field potentia...

Chin. Phys. B  
  Chin. Phys. B--2018, Vol.27, No.9
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TOPICAL REVIEW—Spin manipulation in solids

Spin manipulation in semiconductor quantum dots qubit

Ke Wang(王柯), Hai-Ou Li(李海欧), Ming Xiao(肖明), Gang Cao(曹刚), Guo-Ping Guo(郭国平)
Chin. Phys. B, 2018, 27 (9): 090308 doi: 10.1088/1674-1056/27/9/090308
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Thirty years of effort in semiconductor quantum dots has resulted in significant developments in the control of spin quantum bits (qubits). The natural two-energy level of spin states provides a path toward quantum information processing. In particular, the experimental implementation of spin control with high fidelity provides the possibility of realizing quantum computing. In this review, we will discuss the basic elements of spin qubits in semiconductor quantum dots and summarize some important experiments that have demonstrated the direct manipulation of spin states with an applied electric field and/or magnetic field. The results of recent experiments on spin qubits reveal a bright future for quantum information processing.

Electrical spin polarization through spin-momentum locking in topological-insulator nanostructures

Minhao Zhang(张敏昊), Xuefeng Wang(王学锋), Fengqi Song(宋凤麒), Rong Zhang(张荣)
Chin. Phys. B, 2018, 27 (9): 097307 doi: 10.1088/1674-1056/27/9/097307
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Recently, spin-momentum-locked topological surface states (SSs) have attracted significant attention in spintronics. Owing to spin-momentum locking, the direction of the spin is locked at right angles with respect to the carrier momentum. In this paper, we briefly review the exotic transport properties induced by topological SSs in topological-insulator (TI) nanostructures, which have larger surface-to-volume ratios than those of bulk TI materials. We discuss the electrical spin generation in TIs and its effect on the transport properties. A current flow can generate a pure in-plane spin polarization on the surface, leading to a current-direction-dependent magnetoresistance in spin valve devices based on TI nanostructures. A relative momentum shift of two coupled topological SSs also generates net spin polarization and induces an in-plane anisotropic negative magnetoresistance. Therefore, the spin-momentum locking can enable the broad tuning of the spin transport properties of topological devices for spintronic applications.

Progress of novel diluted ferromagnetic semiconductors with decoupled spin and charge doping: Counterparts of Fe-based superconductors

Shengli Guo(郭胜利), Fanlong Ning(宁凡龙)
Chin. Phys. B, 2018, 27 (9): 097502 doi: 10.1088/1674-1056/27/9/097502
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Diluted ferromagnetic semiconductors (DMSs) that combine the properties of semiconductors with ferromagnetism have potential application in spin-sensitive electronic (spintronic) devices. The search for DMS materials exploded after the observation of ferromagnetic ordering in Ⅲ-V (Ga,Mn)As films. Recently, a series of DMS compounds isostructural to iron-based superconductors have been reported. Among them, the highest Curie temperature TC of 230 K has been achieved in (Ba,K)(Zn,Mn)2As2. However, most DMSs, including (Ga,Mn)As, are p-type, i.e., the carriers that mediate the ferromagnetism are holes. For practical applications, DMSs with n-type carriers are also advantageous. Very recently, a new DMS Ba(Zn,Co)2As2 with n-type carriers has been synthesized. Here we summarize the recent progress on this research stream. We will show that the homogeneous ferromagnetism in these bulk form DMSs has been confirmed by microscopic techniques, i.e., nuclear magnetic resonance (NMR) and muon spin rotation (μSR).

Voltage control of ferromagnetic resonance and spin waves

Xinger Zhao(赵星儿), Zhongqiang Hu(胡忠强), Qu Yang(杨曲), Bin Peng(彭斌), Ziyao Zhou(周子尧), Ming Liu(刘明)
Chin. Phys. B, 2018, 27 (9): 097505 doi: 10.1088/1674-1056/27/9/097505
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The voltage control of magnetism has attracted intensive attention owing to the abundant physical phenomena associated with magnetoelectric coupling. More importantly, the techniques to electrically manipulate spin dynamics, such as magnetic anisotropy and ferromagnetic resonance, are of great significance because of their potential applications in high-density memory devices, microwave signal processors, and magnetic sensors. Recently, voltage control of spin waves has also been demonstrated in several multiferroic heterostructures. This development provides new platforms for energy-efficient, tunable magnonic devices. In this review, we focus on the most recent advances in voltage control of ferromagnetic resonance and spin waves in magnetoelectric materials and discuss the physical mechanisms and prospects for practical device applications.

Magnetism manipulation in ferromagnetic/ferroelectric heterostructures by electric field induced strain

Xiaobin Guo(郭晓斌), Dong Li(李栋), Li Xi(席力)
Chin. Phys. B, 2018, 27 (9): 097506 doi: 10.1088/1674-1056/27/9/097506
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Magnetization manipulation by an electric field (E-field) in ferromagnetic/ferroelectric heterostructures has attracted increasing attention because of the potential applications in novel magnetoelectric devices and spintronic devices, due to the ultra-low power consumption of the process. In this review, we summarize the recent progress in E-field controlled magnetism in ferromagnetic/ferroelectric heterostructures with an emphasis on strain-mediated converse magnetoelectric coupling. Firstly, we briefly review the history, the underlying theory of the magnetoelectric coupling mechanism, and the current status of research. Secondly, we illustrate the competitive energy relationship and volatile magnetization switching under an E-field. We then discuss E-field modified ferroelastic domain states and recent progress in non-volatile manipulation of magnetic properties. Finally, we present the pure E-field controlled 180° in-plane magnetization reversal and both E-field and current modified 180° perpendicular magnetization reversal.

TOPICAL REVIEW—Nanophotonics

Etching-assisted femtosecond laser microfabrication

Monan Liu(刘墨南), Mu-Tian Li(李木天), Han Yang(杨罕), Hong-Bo Sun(孙洪波)
Chin. Phys. B, 2018, 27 (9): 094212 doi: 10.1088/1674-1056/27/9/094212
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Although femtosecond laser microfabrication is one of the most promising three-dimensional (3D) fabrication techniques, it could suffer from low fabrication efficiency for structures with high 3D complexities. By using etching as a main assistant technique, the processing can be speeded up and an improved structure surface quality can be provided. However, the assistance of a single technique cannot satisfy the increasing demands of fabrication and integration of highly functional 3D microstructures. Therefore, a multi-technique-based 3D microfabrication method is required. In this paper, we briefly review the recent development on etching-assisted femtosecond laser microfabrication (EAFLM). Various processing approaches have been proposed to further strengthen the flexibilities of the EAFLM. With the use of the multi-technique-based microfabrication method, 3D microstructure arrays can be rapidly defined on planar or curved surfaces with high structure qualities.

Two-dimensional materials-decorated microfiber devices for pulse generation and shaping in fiber lasers

Zhi-Chao Luo(罗智超), Meng Liu(刘萌), Ai-Ping Luo(罗爱平), Wen-Cheng Xu(徐文成)
Chin. Phys. B, 2018, 27 (9): 094215 doi: 10.1088/1674-1056/27/9/094215
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Two-dimensional (2D) materials have been regarded as a promising nonlinear optical medium for fabricating versatile optical and optoelectronic devices. Among the various photonic applications, the employment of 2D materials as nonlinear optical devices such as saturable absorbers for ultrashort pulse generation and shaping in ultrafast lasers is one of the most striking aspects in recent years. In this paper, we review the recent progress of 2D materials based pulse generation and soliton shaping in ultrafast fiber lasers, and particularly in the context of 2D materials-decorated microfiber photonic devices. The fabrication of 2D materials-decorated microfiber photonic devices, high performance mode-locked pulse generation, and the nonlinear soliton dynamics based on pulse shaping method are discussed. Finally, the challenges and the perspective of the 2D materials-based photonic devices as well as their applications are also discussed.

Surface plasmon polariton waveguides with subwavelength confinement

Longkun Yang(杨龙坤), Pan Li(李盼), Hancong Wang(汪涵聪), Zhipeng Li(李志鹏)
Chin. Phys. B, 2018, 27 (9): 094216 doi: 10.1088/1674-1056/27/9/094216
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Surface plasmon polaritons (SPPs) are evanescent waves propagating along metal-dielectric interfaces, which provide an effective way to realize optical wave guiding with subwavelength confinement. Metallic nanostructures supporting SPPs, that is, plasmonic waveguides, are considered as required components to construct nanophotonic devices and circuits with a high degree of miniaturization and integration. In this paper, various types of plasmonic waveguides operating in the visible, infrared, and terahertz regions are reviewed, and the status of the research on their fundamentals, fabrications, and applications is provided as well. First, we discuss the mechanisms of SPPs beyond the diffraction limit, and their launching methods. Then, the characteristics of SPPs on various plasmonic waveguides are reviewed, including top-down and bottom-up fabricated types. Considering applications, certain prototypes of plasmonic devices and circuits constructed by plasmonic waveguides for bio/chemo sensing, router, and light modulation are demonstrated. Finally, a summary and future outlook of plasmonic waveguides are given.

Intrinsic luminescence from metal nanostructures and its applications

Weidong Zhang(张威东), Te Wen(温特), Yuqing Cheng(程宇清), Jingyi Zhao(赵静怡), Qihuang Gong(龚旗煌), Guowei Lü(吕国伟)
Chin. Phys. B, 2018, 27 (9): 097302 doi: 10.1088/1674-1056/27/9/097302
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Intrinsic luminescence from metal nanostructures complements conventional scattering and absorption behaviors and has many interesting and unique features. This phenomenon has attracted considerable research attention in recent years because of its various potential applications. In this review, we discuss recent advances in this field, summarize potential applications for this type of luminescence, and compare theoretical models to describe the phenomena. On the basis of the excitation process, the characteristic features and corresponding applications are summarized briefly in three parts, namely, continuous-wave light, pulsed laser, and electron excitation. A universal physical mechanism likely operates in all these emission processes regardless of differences in the excitation processes; however, there remains some debate surrounding the details of the theoretical model. Further insight into these luminescence phenomena will not only provide a deeper fundamental understanding of plasmonic nanostructures but will also advance and extend their applications.

Recent progress on photoluminescence from plasmonic nanostructures: Phenomenon, mechanism, and application

Tingting Yin(尹婷婷), Liyong Jiang(蒋立勇), Zexiang Shen(申泽骧)
Chin. Phys. B, 2018, 27 (9): 097803 doi: 10.1088/1674-1056/27/9/097803
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Photoluminescence (PL) from bulk noble metals arises from the interband transition of bound electrons. Plasmonic nanostructures can greatly enhance the quantum yield of noble metals through the localized surface plasmon. In this work, we briefly review recent progress on the phenomenon, mechanism, and application of one-photon PL from plasmonic nanostructures. Particularly, our recent efforts in the study of the PL peak position, partial depolarization, and mode selection from plasmonic nanostructures can bring about a relatively complete and deep understanding of the physical mechanism of one-photon PL from plasmonic nanostructures, paving the way for future applications in plasmonic imaging, plasmonic nanolasing, and surface enhanced fluorescence spectra.

SPECIAL TOPIC—Nanophotonics

Ultra-compact graphene plasmonic filter integrated in a waveguide

Baoxin Liao(廖宝鑫), Xiangdong Guo(郭相东), Hai Hu(胡海), Ning Liu(刘宁), Ke Chen(陈科), Xiaoxia Yang(杨晓霞), Qing Dai(戴庆)
Chin. Phys. B, 2018, 27 (9): 094101 doi: 10.1088/1674-1056/27/9/094101
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Graphene plasmons have become promising candidates for deep-subwavelength nanoscale optical devices due to their strong field confinement and low damping. Among these nanoscale optical devices, band-pass filter for wavelength selection and noise filtering are key devices in an integrated optical circuit. However, plasmonic filters are still oversized because large resonant cavities are needed to perform frequency selection. Here, an ultra-compact filter integrated in a graphene plasmonic waveguide was designed, where a rectangular resonant cavity is inside a graphene nanoribbon waveguide. The properties of the filter were studied using the finite-difference time-domain method and demonstrated using the analytical model. The results demonstrate the band-pass filter has a high quality factor (20.36) and electrically tunable frequency response. The working frequency of the filter could also be tuned by modifying the cavity size. Our work provides a feasible structure for a graphene plasmonic nano-filter for future use in integrated optical circuits.

Observation of 550 MHz passively harmonic mode-locked pulses at L-band in an Er-doped fiber laser using carbon nanotubes film

Qianqian Huang(黄千千), Chuanhang Zou(邹传杭), Tianxing Wang(王天行), Mohammed Al Araimi, Aleksey Rozhin, Chengbo Mou(牟成博)
Chin. Phys. B, 2018, 27 (9): 094210 doi: 10.1088/1674-1056/27/9/094210
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We demonstrate a passively harmonic mode-locked (PHML) fiber laser operating at the L-band using carbon nanotubes polyvinyl alcohol (CNTs-PVA) film. Under suitable pump power and an appropriate setting of the polarization controller (PC), the 54th harmonic pulses at the L-band are generated with the side mode suppression ratio (SMSR) better than 44 dB and a repetition frequency of 503.37 MHz. Further increasing the pump power leads to a higher frequency of 550 MHz with compromised stability of 38.5 dB SMSR. To the best of our knowledge, this is the first demonstration on the generation of L-band PHML pulses from an Er-doped fiber laser based on CNTs.

Enhancement and control of the Goos-Hänchen shift bynonlinear surface plasmon resonance in graphene

Qi You(游琪), Leyong Jiang(蒋乐勇), Xiaoyu Dai(戴小玉), Yuanjiang Xiang(项元江)
Chin. Phys. B, 2018, 27 (9): 094211 doi: 10.1088/1674-1056/27/9/094211
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The Goos-Hänchen (GH) shift of graphene in the terahertz frequency range is investigated, and an extremely high GH shift is obtained owing to the excitation of surface plasmon resonance in graphene in the modified Otto configuration. It is shown that the GH shift can be positive or negative, and can be enhanced by introducing a nonlinearity in the substrate. Large and bistable GH shifts are demonstrated to be due to the hysteretic behavior of the reflectance phase. The bistable GH shift can be manipulated by changing the thickness of the air gap and the Fermi level or relaxation time of graphene.

MXene Ti3C2Tx saturable absorber for pulsed laser at 1.3 μm

Cong Wang(王聪), Qian-Qian Peng(彭倩倩), Xiu-Wei Fan(范秀伟), Wei-Yuan Liang(梁维源), Feng Zhang(张峰), Jie Liu(刘杰), Han Zhang(张晗)
Chin. Phys. B, 2018, 27 (9): 094214 doi: 10.1088/1674-1056/27/9/094214
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The excellent optical properties of MXene provide new opportunities for short-pulse lasers. A diode-pumped passively Q-switched laser at 1.3 μm wavelength with MXene Ti3C2Tx as saturable absorber was achieved for the first time. The stable passively Q-switched laser has 454 ns pulse width and 162 kHz repetition rate at 4.5 W incident pumped power. The experimental results show that the MXene Ti3C2Tx saturable absorber can be used as an optical modulator to generate short pulse lasers in a solid-state laser field.

Ultrasonic sensitivity-improved fiber-optic Fabry-Perot interferometer using a beam collimator and its application for ultrasonic imaging of seismic physical models

Zhi-Hua Shao(邵志华), Xue-Guang Qiao(乔学光), Feng-Yi Chen(陈凤仪), Qiang-Zhou Rong(荣强周)
Chin. Phys. B, 2018, 27 (9): 094218 doi: 10.1088/1674-1056/27/9/094218
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An ultrasonic sensitivity-improved fiber-optic Fabry-Perot interferometer (FPI) is proposed and employed for ultrasonic imaging of seismic physical models (SPMs). The FPI comprises a flexible ultra-thin gold film and the end face of a graded-index multimode fiber (MMF), both of which are enclosed in a ceramic tube. The MMF in a specified length can collimate the diverged light beam and compensate for the light loss inside the air cavity, leading to an increased spectral fringe visibility and thus a steeper spectral slope. By using the spectral sideband filtering technique, the collimated FPI shows an improved ultrasonic response. Moreover, two-dimensional images of two SPMs are achieved in air by reconstructing the pulse-echo signals through using the time-of-flight approach. The proposed sensor with easy fabrication and compact size can be a good candidate for high-sensitivity and high-precision nondestructive testing of SPMs.

Femtosecond Tm-Ho co-doped fiber laser using a bulk-structured Bi2Se3 topological insulator

Jinho Lee(李珍昊), Ju Han Lee(李周翰)
Chin. Phys. B, 2018, 27 (9): 094219 doi: 10.1088/1674-1056/27/9/094219
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We experimentally demonstrate a femtosecond mode-locked thulium-holmium (Tm-Ho) co-doped fiber laser incorporating a saturable absorber (SA) based on a bulk-structured bismuth selenide (Bi2Se3) topological insulator (TI). The SA was prepared by depositing a mechanically exfoliated Bi2Se3 TI layer onto a side-polished optical fiber platform. Unlike high-quality nano-structured Bi2Se3 TI-based SA, bulk-structured Bi2Se3 with non-negligible oxidation was used as a saturable absorption material for this experimental demonstration due to its easy fabrication process. The saturation power and modulation depth of the prepared SA were measured to be ~28.6 W and ~13.4%, respectively. By incorporating the prepared SA into a Tm-Ho co-doped fiber ring cavity, stable soliton pulses with a temporal width of ~853 fs could be generated at 1912.12 nm. The 3-dB bandwidth of the mode-locked pulse was measured to be ~4.87 nm. This experimental demonstration reaffirms that Bi2Se3 is a superb base material for mid-infrared passive mode-locking even under oxidation.

Room-temperature strong coupling between dipolar plasmon resonance in single gold nanorod and two-dimensional excitons in monolayer WSe2

Jinxiu Wen(温锦秀), Hao Wang(汪浩), Huanjun Chen(陈焕君), Shaozhi Deng(邓少芝), Ningsheng Xu(许宁生)
Chin. Phys. B, 2018, 27 (9): 096101 doi: 10.1088/1674-1056/27/9/096101
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All-solid-state strong coupling systems with large vacuum Rabi splitting energy have great potential applications in future quantum information technologies, such as quantum manipulations, quantum information storage and processing, and ultrafast optical switches. Monolayer transition metal dichalcogenides (TMDs) have recently been explored as excellent candidates for the observation of solid-state strong coupling phenomena. In this work, from both experimental and theoretical aspects, we explored the strong coupling effect by integrating an individual plasmonic gold nanorod into the monolayer tungsten diselenide (WSe2). Evident anti-crossing behavior was observed from the coupled energy diagram at room temperature; a Rabi splitting energy of 98 meV was extracted.

Selective enhancement of green upconversion luminescence of Er-Yb: NaYF4 by surface plasmon resonance of W18O49 nanoflowers and applications in temperature sensing

Ang Li(李昂), Jin-Lei Wu(吴金磊), Xue-Song Xu(许雪松), Yang Liu(刘洋), Ya-Nan Bao(包亚男), Bin Dong(董斌)
Chin. Phys. B, 2018, 27 (9): 097301 doi: 10.1088/1674-1056/27/9/097301
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The W18O49 nanoflowers with a diameter of 500 nm are prepared by a facile hydrothermal method. The Er-Yb:NaYF4 nanoparticles are adsorbed on the petals (the position of the strongest local electric field on W18O49 nanoflowers). With a 976 nm laser diode (LD) as an excitation source, the selectively green upconversion luminescence (UCL) is observed to be enhanced by two orders of magnitude in Er-Yb:NaYF4/W18O49 nanoflowers heterostructures. It suggests that the near infrared (NIR)-excited localized surface plasmon resonance (LSPR) of W18O49 is primarily responsible for the enhanced UCL, which could be partly reabsorbed by the W18O49, thus leading to the selective enhancement of green UCL for the Er-Yb:NaYF4. The fluorescence intensity ratio is investigated as a function of temperature based on the intense green UCL, which indicates that Er-Yb:NaYF4/W18O49 nanoflower heterostructures have good potential for developing into temperature sensors.


Dynamical behaviors of traveling wave solutions to a Fujimoto-Watanabe equation

Zhen-Shu Wen(温振庶), Li-Juan Shi(师利娟)
Chin. Phys. B, 2018, 27 (9): 090201 doi: 10.1088/1674-1056/27/9/090201
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We study dynamical behaviors of traveling wave solutions to a Fujimoto-Watanabe equation using the method of dynamical systems. We obtain all possible bifurcations of phase portraits of the system in different regions of the three-dimensional parameter space. Then we show the required conditions to guarantee the existence of traveling wave solutions including solitary wave solutions, periodic wave solutions, kink-like (antikink-like) wave solutions, and compactons. Moreover, we present exact expressions and simulations of these traveling wave solutions. The dynamical behaviors of these new traveling wave solutions will greatly enrich the previews results and further help us understand the physical structures and analyze the propagation of nonlinear waves.

Quantum uncertainty relations of quantum coherence and dynamics under amplitude damping channel

Fugang Zhang(张福刚), Yongming Li(李永明)
Chin. Phys. B, 2018, 27 (9): 090301 doi: 10.1088/1674-1056/27/9/090301
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In this paper, we discuss quantum uncertainty relations of quantum coherence through a different method from Ref. [52]. Some lower bounds with parameters and their minimal bounds are obtained. Moreover, we find that for two pairs of measurement bases with the same maximum overlap, quantum uncertainty relations and lower bounds with parameters are different, but the minimal bounds are the same. In addition, we discuss the dynamics of quantum uncertainty relations of quantum coherence and their lower bounds under the amplitude damping channel (ADC). We find that the ADC will change the uncertainty relations and their lower bounds, and their tendencies depend on the initial state.

Decoherence for a two-qubit system in a spin-chain environment

Yang Yang(杨阳), An-Min Wang(王安民), Lian-Zhen Cao(曹连振), Jia-Qiang Zhao(赵加强), Huai-Xin Lu(逯怀新)
Chin. Phys. B, 2018, 27 (9): 090302 doi: 10.1088/1674-1056/27/9/090302
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The quantum coherence and correlation dynamics for a two-qubit system in the Ising spin-chain environment are studied. A sudden change of coherence is found near the critical point, which provides us with an effective way to detect the quantum phase transition. By studying the relationship between quantum discord and coherence, we find that coherence displays the behavior of classical correlation for t<t0, and of quantum discord for t>t0, where t0 is the time-point of a sudden transition between classical and quantum decoherence.

Entropy of field interacting with two two-qubit atoms

Tang-Kun Liu(刘堂昆), Yu Tao(陶宇), Chuan-Jia Shan(单传家), Ji-Bing Liu(刘继兵)
Chin. Phys. B, 2018, 27 (9): 090303 doi: 10.1088/1674-1056/27/9/090303
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We use quantum field entropy to measure the degree of entanglement for a coherent state light field interacting with two atoms that are initially in an arbitrary two-qubit state. The influence of different mean photon number of the coherent field on the entropy of the field is discussed in detail when the two atoms are initially in one superposition state of the Bell states. The results show that the mean photon number of the light field can regulate the quantum entanglement between the atoms and light field.

Deterministic hierarchical joint remote state preparation with six-particle partially entangled state

Na Chen(陈娜), Bin Yan(颜斌), Geng Chen(陈赓), Man-Jun Zhang(张曼君), Chang-Xing Pei(裴昌幸)
Chin. Phys. B, 2018, 27 (9): 090304 doi: 10.1088/1674-1056/27/9/090304
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In this paper, we present a novel scheme for hierarchical joint remote state preparation (HJRSP) in a deterministic manner, where two senders can jointly and remotely prepare an arbitrary single-qubit at three receivers' port. A six-particle partially entangled state is pre-shared as the quantum channel. There is a hierarchy among the receivers concerning their powers to reconstruct the target state. Due to various unitary operations and projective measurements, the unit success probability can always be achieved irrespective of the parameters of the pre-shared partially entangled state.

Demonstration of quantum anti-Zeno effect with a single trapped ion

Man-Chao Zhang(张满超), Wei Wu(吴伟), Lin-Ze He(何林泽), Yi Xie(谢艺), Chun-Wang Wu(吴春旺), Quan Li(黎全), Ping-Xing Chen(陈平形)
Chin. Phys. B, 2018, 27 (9): 090305 doi: 10.1088/1674-1056/27/9/090305
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We experimentally demonstrate the quantum anti-Zeno effect in a two-level system based on a single trapped ion 40Ca+. In the large detuning regime, we show that the transfer from the ground state to the excited state can be remarkably enhanced by the inserted projection measurements. The inserted measurements in our experiment are realized by the electron shelving technique. Compared to the ideal projection measurement, which makes the quantum state collapse instantaneously, a practical electron shelving process needs a finite time duration. The minimum time for this collapse process is shown to be inversely proportional to the square of the coupling strength between the measurement laser and the system.

Thermal quantum correlations of a spin-1/2 Ising-Heisenberg diamond chain with Dzyaloshinskii-Moriya interaction

Yidan Zheng(郑一丹), Zhu Mao(毛竹), Bin Zhou(周斌)
Chin. Phys. B, 2018, 27 (9): 090306 doi: 10.1088/1674-1056/27/9/090306
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We investigate the properties of thermal quantum correlations in an infinite spin-1/2 Ising-Heisenberg diamond chain with Dzyaloshinskii-Moriya (DM) interaction. The thermal quantum discord (TQD) and the thermal entanglement (TE) are discussed as two kinds of important methods to measure the quantum correlation, respectively. It is found that DM interaction plays an important role in the thermal quantum correlations of the system. It can enhance the thermal quantum correlations by increasing DM interaction. Furthermore, the thermal quantum correlations can be promoted by tuning the external magnetic field and the Heisenberg coupling parameter in the antiferromagnetic system. It is shown that the behaviors of TQD differ from those of TE. TQD is more robust against decoherence than TE. For the measurement of TQD, the “regrowth” phenomenon occurs in the ferromagnetic system. We also find that the anisotropy favors the thermal quantum correlations of the system with weak DM interaction.

Finite-size analysis of eight-state continuous-variable quantum key distribution with the linear optics cloning machine

Hang Zhang(张航), Yu Mao(毛宇), Duan Huang(黄端), Ying Guo(郭迎), Xiaodong Wu(吴晓东), Ling Zhang(张玲)
Chin. Phys. B, 2018, 27 (9): 090307 doi: 10.1088/1674-1056/27/9/090307
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We propose a method to improve the secret key rate of an eight-state continuous-variable quantum key distribution (CVQKD) by using a linear optics cloning machine (LOCM). In the proposed scheme, an LOCM is exploited to compensate for the imperfections of Bob's apparatus, so that the generated secret key rate of the eight-state protocol could be well enhanced. We investigate the security of our proposed protocol in a finite-size scenario so as to further approach the practical value of a secret key rate. Numeric simulation shows that the LOCM with reasonable tuning gain λ and transmittance τ can effectively improve the secret key rate of eight-state CVQKD in both an asymptotic limit and a finite-size regime. Furthermore, we obtain the tightest bound of the secure distance by taking the finite-size effect into account, which is more practical than that obtained in the asymptotic limit.

Nonlinear suboptimal tracking control of spacecraft approaching a tumbling target

Zhan-Peng Xu(许展鹏), Xiao-Qian Chen(陈小前), Yi-Yong Huang(黄奕勇), Yu-Zhu Bai(白玉铸), Wen Yao(姚雯)
Chin. Phys. B, 2018, 27 (9): 090501 doi: 10.1088/1674-1056/27/9/090501
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We investigate the close-range relative motion and control of a spacecraft approaching a tumbling target. Unlike the traditional rigid-body dynamics with translation and rotation about the center of mass (CM), the kinematic coupling between translation and rotation is taken into consideration to directly describe the motion of the spacecraft's sensors or devices which are not coincident with the CM. Thus, a kinematically coupled 6 degrees-of-freedom (DOF) relative motion model for the instrument (feature point) is set up. To make the chaser spacecraft's feature point track the target's, an optimal tracking problem is defined and a control law with a feedback-feedforward structure is designed. With quasi-linearization of the nonlinear dynamical system, the feedforward term is computed from a specified constraint about the dynamical system and the reference model, and the feedback action is derived starting from the state-dependent Ricca equation (SDRE). The proposed controller is compared with an existing suboptimal tracking controller, and numerical simulations are presented to illustrate the effectiveness and superiority of the proposed method.

Conservation laws for Birkhoffian systems of Herglotz type

Yi Zhang(张毅), Xue Tian(田雪)
Chin. Phys. B, 2018, 27 (9): 090502 doi: 10.1088/1674-1056/27/9/090502
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Conservation laws for the Birkhoffian system and the constrained Birkhoffian system of Herglotz type are studied. We propose a new differential variational principle, called the Pfaff-Birkhoff-d'Alembert principle of Herglotz type. Birkhoff's equations for both the Birkhoffian system and the constrained Birkhoffian system of Herglotz type are obtained. According to the relationship between the isochronal variation and the nonisochronal variation, the conditions of the invariance for the Pfaff-Birkhoff-d'Alembert principle of Herglotz type are given. Then, the conserved quantities for the Birkhoffian system and the constrained Birkhoffian system of Herglotz type are deduced. Furthermore, the inverse theorems of the conservation theorems are also established.

Damage and recovery of fiber Bragg grating under radiation environment

Shi-Zhe Wen(温世喆), Wei-Chen Xiong(熊伟晨), Li-Ping Huang(黄力平), Zhen-Rui Wang(王镇锐), Xing-Bin Zhang(张兴斌), Zhen-Hui He(何振辉)
Chin. Phys. B, 2018, 27 (9): 090701 doi: 10.1088/1674-1056/27/9/090701
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To develop the application of fiber Bragg gratings as temperature and strain sensors in space environments, it is necessary to understand the effect of high-energy radiation on the performance of the fiber Bragg grating. We performed an experiment involving Co60-γ ionizing irradiation with a total dose of 1.01×106 rad on two Ge-doped single-mode fiber Bragg gratings with central wavelengths of 825 and 835 nm, respectively. We found that, with the increase of radiation dose, the redshift of the peak wavelength of the reflection spectrum of the fiber Bragg gratings indicated the increase of the refractive index and the number of color centers. After irradiation, the refractive index decreased with the decreasing number of color centers. We analyzed the influence of ionizing irradiation on the transmission performance of the fiber Bragg gratings using a color-center model, which explained the experimental results. The proposed model was used to determine the creation rate and annihilation rates of the color center, which are foundational data for using the fiber Bragg gratings in space applications.


Visualizing light-to-electricity conversion process in InGaN/GaN multi-quantum wells with a p-n junction Hot!

Yangfeng Li(李阳锋), Yang Jiang(江洋), Junhui Die(迭俊珲), Caiwei Wang(王彩玮), Shen Yan(严珅), Haiyan Wu(吴海燕), Ziguang Ma(马紫光), Lu Wang(王禄), Haiqiang Jia(贾海强), Wenxin Wang(王文新), Hong Chen(陈弘)
Chin. Phys. B, 2018, 27 (9): 097104 doi: 10.1088/1674-1056/27/9/097104
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Absorption and carrier transport behavior plays an important role in the light-to-electricity conversion process, which is difficult to characterize. Here we develop a method to visualize such a conversion process in the InGaN/GaN multi-quantum wells embedded in a p-n junction. Under non-resonant absorption conditions, a photocurrent was generated and the photoluminescence intensity decayed by more than 70% when the p-n junction out-circuit was switched from open to short. However, when the excitation photon energy decreased to the resonant absorption edge, the photocurrent dropped drastically and the photoluminescence under open and short circuit conditions showed similar intensity. These results indicate that the escaping of the photo-generated carriers from the quantum wells is closely related to the excitation photon energy.


Ground-state energy of beryllium atom with parameter perturbation method

Feng Wu(吴锋), Lijuan Meng(孟丽娟)
Chin. Phys. B, 2018, 27 (9): 093101 doi: 10.1088/1674-1056/27/9/093101
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We present a perturbation study of the ground-state energy of the beryllium atom by incorporating double parameters in the atom's Hamiltonian. The eigenvalue of the Hamiltonian is then solved with a double-fold perturbation scheme, where the spin-spin interaction of electrons from different shells of the atom is also considered. Calculations show that the obtained ground-state energy is in satisfactory agreement with experiment. It is found that the Coulomb repulsion of the inner-shell electrons enhances the effective nuclear charge seen by the outer-shell electrons, and the shielding effect of the outer-shell electrons to the nucleus is also notable compared with that of the inner-shell electrons.

Diffusion Monte Carlo calculations on LaB molecule

Nagat Elkahwagy, Atif Ismail, S M A Maize, K R Mahmoud
Chin. Phys. B, 2018, 27 (9): 093102 doi: 10.1088/1674-1056/27/9/093102
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Potential energy curves for the lowest electronic states of LaB and LaB- have been calculated by ab initio calculations. The diffusion Monte Carlo method has been employed in combination with three different trial functions. Spectroscopic constants have also been numerically derived for the neutral molecule and compared with the only available theoretical work;[19] however, predictions are provided for the corresponding constants for the anionic species which have not been reported yet. Our calculations suggest the high spin quintet state of LaB as the ground state with the triplet state higher in energy irrespective of the type of the functional used. This suggestion is in good accordance with the previous theoretical results calculated at B3LYP/LANL2DZ level of theory, whereas it contradicts with the prediction based upon B3LYP/SDD calculations in the same study. Moreover, variations of the permanent dipole moments as a function of the internuclear separations for the two electronic states of the neutral molecule have been studied and analyzed.

Effect of elliptical polarizations on nonsequential double ionization in two-color elliptically polarized laser fields

Tong-Tong Xu(徐彤彤), Jia-He Chen(陈佳贺), Xue-Fei Pan(潘雪飞), Hong-Dan Zhang(张宏丹), Shuai Ben(贲帅), Xue-Shen Liu(刘学深)
Chin. Phys. B, 2018, 27 (9): 093201 doi: 10.1088/1674-1056/27/9/093201
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Using the classical ensemble model, we investigate the nonsequential double ionization (NSDI) of Ar and Mg in the two-color elliptically polarized laser pulse for different elliptical polarizations. Numerical results show that for Ar atoms the NSDI yield increases as the ellipticity increases, which is different from the case of Mg atoms. Moreover, the correlated behavior in the correlated electron momentum along the x direction and ion momentum distributions of Ar atoms are influenced by the ellipticity. By statistical analysis of different times, we can conclude that the ellipticity may be responsible for the NSDI processes. The correlated momenta distributions along the x direction at the recollision time are demonstrated and the results show that the travelling time and ellipticity can affect the emitted directions of both electrons.

Numerical tests of theoretical models describing ionization of H(1s) atom by linearly polarized flat pulse of laser radiation

Jarosław H Bauer, Min Deng(邓敏)
Chin. Phys. B, 2018, 27 (9): 093202 doi: 10.1088/1674-1056/27/9/093202
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We derive the well-known Coulomb correction factor for the Gordon-Volkov wave function describing an outgoing electron in the process of ionization in an intense laser field. Although rigorous treatment would limit its use only to laser fields much lower than the so-called barrier-suppression field, it appears that in practice the correction factor may be used also close to and even above this critical value of the laser field. We compare predictions of several analytical expressions describing ionization rate of the hydrogen atom in its ground state in the strong linearly polarized laser field. We also compare ionization probabilities obtained by integrating these ionization rates over a temporal envelope of the laser pulse with predictions based on the exact numerical solution to the time-dependent Schrödinger equation.

Density functional study on the bimetallic TimZrn (n+m ≤ 5) clusters and their interactions with H2

Ge Zhang(张鸽), Yong Sheng(盛勇)
Chin. Phys. B, 2018, 27 (9): 093601 doi: 10.1088/1674-1056/27/9/093601
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Equilibrium geometries, stabilities, and electronic properties of small TimZrn (n+m ≤ 5) clusters were investigated using the density functional method. The ground states were determined, and it was found that the larger clusters and those consisting of more Zr atoms are more stable. The electronic properties of the clusters were discussed based on HOMO-LUMO gaps, vertical ionization potentials (VIP), and vertical electron affinities (VEA). Furthermore, we studied the interactions between those clusters and molecular hydrogen, and found that in all the cases dissociative chemisorptions occurred. According to the chemisorption energies, the pure Zr clusters are relatively more active towards H2 when compared with the others except Ti3Zr, which shows the highest activity. The magnetic moments of TimZrn and TimZrnH2 were also compared, and the results show that the hydrogenated clusters have the same or decreased total magnetic moments with respect to the bare clusters except for Ti3Zr2.


Two-frequency amplification in a semiconductor tapered amplifier for cold atom experiments

Zhi-Xin Meng(孟至欣), Yu-Hang Li(李宇航), Yan-Ying Feng(冯焱颖)
Chin. Phys. B, 2018, 27 (9): 094201 doi: 10.1088/1674-1056/27/9/094201
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Simultaneous two-frequency amplification is highly desirable in cold atom experiments. The nonlinear response would appear in the two-frequency amplification with a semiconductor tapered amplifier (TA) and has a direct influence on the experimental result. We investigated in detail the effects of frequency difference, total power, and power ratio of two seeding lasers on the output components based on a simplified theoretical model. The simulation results showed that the multiple sideband generation in the amplifier due to self-phase and amplitude modulation could be suppressed and the TA tended to linearly amplify the power ratio between two-frequency components, when the two seeding lasers had a large frequency difference. This was verified experimentally in the output power ratio measurement via a calibrated Fabry-Perot interferometer method with a good linearity and an uncertainty of 1%. We also discussed the consequences of power ratio responses in the amplification in light of cold atom experiments, especially in the ac Stark shift related phase error of Raman-type atom interferometers (AIs). It was shown that the fluctuation of intensity ratio of Raman beams may induce significant systematic errors for an AI gyroscope.

Lensless two-color ghost imaging from the perspective of coherent-mode representation

Bin Luo(罗斌), Guohua Wu(吴国华), Longfei Yin(尹龙飞)
Chin. Phys. B, 2018, 27 (9): 094202 doi: 10.1088/1674-1056/27/9/094202
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The coherent-mode representation theory is firstly used to analyze lensless two-color ghost imaging. A quite complicated expression about the point-spread function (PSF) needs to be given to analyze which wavelength has a stronger affect on imaging quality when the usual integral representation theory is used to ghost imaging. Unlike this theory, the coherent-mode representation theory shows that imaging quality depends crucially on the distribution of the decomposition coefficients of the object imaged in a two-color ghost imaging. The analytical expression of the decomposition coefficients of the object is unconcerned with the wavelength of the light used in the reference arm, but has relevance with the wavelength in the object arm. In other words, imaging quality of two-color ghost imaging depends primarily on the wavelength of the light illuminating the object. Our simulation results also demonstrate this conclusion.

Nonuniform sampled angular spectrum method by using trigonometric interpolation

Qiu-Hu Cheng(程秋虎), Shi-Yu Wang(王石语), Meng-Yao Wu(吴梦瑶), Zhen Guo(过振), De-Fang Cai(蔡德芳), Bing-Bin Li(李兵斌)
Chin. Phys. B, 2018, 27 (9): 094203 doi: 10.1088/1674-1056/27/9/094203
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The angular spectrum method (ASM) is a popular numerical approach for scalar diffraction calculations. However, traditional ASM has an inherent problem in that nonuniform sampling is precluded. In an attempt to address this limitation, an improved trigonometric interpolation ASM (TIASM) is proposed, in which the fast Fourier transform (FFT) is replaced by a trigonometric interpolation. The results show that TIASM is more suitable to situations in which the source field has a simple and strong frequency contrast, irrespective of whether the original phase distribution is a plane wave or a Fresnel zone plate phase distribution.

Effect of residual Doppler averaging on the probe absorption in cascade type system: A comparative study

Suman Mondal, Arindam Ghosh, Khairul Islam, Dipankar Bhattacharyya, Amitava Bandyopadhyay
Chin. Phys. B, 2018, 27 (9): 094204 doi: 10.1088/1674-1056/27/9/094204
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Effect of residual Doppler averaging on the probe absorption in an alkali vapor medium in the presence of a coherent pump beam is studied analytically for the Ξ type system. A coherent probe field is assumed to connect the ground level with the intermediate level whereas a coherent control beam is supposed to act between the intermediate energy level and the uppermost level. Optical Bloch equations (OBE) for a three-level Ξ type system and a four-level Ξ type system are derived by using density matrix formalism. These equations are solved by an analytic method to determine the probe response, which not only depends on the wavelength difference between the control (pump) field and the probe field but shows substantially different features depending on whether the wavelength of the control field is greater than that of the probe field or the reverse. The effect of temperature on probe response is also shown. Enhancement in probe absorption and additional features are noticed under a strong probe limit at room temperature. The four-level Ξ type system has two ground levels and this leads to substantial modification in the simulated probe absorption as compared to the three-level system.

Laser frequency offset-locking using electromagnetically induced transparency spectroscopy of 85Rb in magnetic field

Han-Mu Wang(王汉睦), Hong Cheng(成红), Shan-Shan Zhang(张珊珊), Pei-Pei Xin(辛培培), Zi-Shan Xu(徐子珊), Hong-Ping Liu(刘红平)
Chin. Phys. B, 2018, 27 (9): 094205 doi: 10.1088/1674-1056/27/9/094205
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We have experimentally offset-locked the frequencies of two lasers using electromagnetically induced transparency (EIT) spectroscopy of 85Rb vapor with a buffer gas in a magnetic field at room temperature. The magnetic field is generated by a permanent magnet mounted on a translation stage and its field magnitude can be varied by adjusting the distance between the magnet and Rb cell, which maps the laser locking frequency to the space position of the magnet. This frequency-space mapping technique provides an unambiguous daily laser frequency detuning operation with high accuracy. A repeatability of less than 0.5 MHz is achieved with the locking frequency detuned up to 184 MHz when the magnetic field varies from 0 up to 80 G.

Fractional squeezing-Hankel transform based on the induced entangled state representations

Cui-Hong Lv(吕翠红), Su-Qing Zhang(张苏青), Wen Xu(许雯)
Chin. Phys. B, 2018, 27 (9): 094206 doi: 10.1088/1674-1056/27/9/094206
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Based on the fact that the quantum mechanical version of Hankel transform kernel (the Bessel function) is just the transform between |q,r> angle and (s,r'|, two induced entangled state representations are given, and working with them we derive fractional squeezing-Hankel transform (FrSHT) caused by the operator e-iα(a1a2+a1a2)e-iπa2a2, which is an entangled fractional squeezing transform operator. The additive rule of the FrSHT can be explicitly proved.

High-power and high optical conversion efficiency diode-end-pumped laser with multi-segmented Nd: YAG/Nd: YVO4

Meng-Yao Wu(吴梦瑶), Peng-Fei Qu(屈鹏飞), Shi-Yu Wang(王石语), Zhen Guo(过振), De-Fang Cai(蔡德芳), Bing-Bin Li(李兵斌)
Chin. Phys. B, 2018, 27 (9): 094207 doi: 10.1088/1674-1056/27/9/094207
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A novel flat-flat resonator consisting of two crystals (Nd:YAG+Nd:YVO4) is established for power scaling in a diode-end-pumped solid-state laser. We systematically compare laser characteristics between multi-segmented (Nd:YAG+Nd:YVO4) and conventional composite (Nd:YAG+Nd:YAG) crystals to demonstrate the feasibility of spectral line matching for output power scale-up in end-pumped lasers. A maximum continuous-wave output power of 79.2 W is reported at 1064 nm, with Mx2=4.82, My2=5.48, and a pumping power of 136 W in the multi-segmented crystals (Nd:YAG+Nd:YVO4). Compared to conventional composite crystals (Nd:YAG+Nd:YAG), the optical-optical conversion efficiency of multi-segmented crystals (Nd:YAG+Nd:YVO4) from 808 nm to 1064 nm is enhanced from 30% to 58.8%, while the laser output sensitivity as affected by the diode-laser temperature is reduced from 55% to 9%.

Thermal analysis of GaN-based laser diode mini-array

Jun-Jie Hu(胡俊杰), Shu-Ming Zhang(张书明), De-Yao Li(李德尧), Feng Zhang(张峰), Mei-Xin Feng(冯美鑫), Peng-Yan Wen(温鹏雁), Jian-Pin Liu(刘建平), Li-Qun Zhang(张立群), Hui Yang(杨辉)
Chin. Phys. B, 2018, 27 (9): 094208 doi: 10.1088/1674-1056/27/9/094208
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Thermal characteristics of multiple laser stripes integrated into one chip is investigated theoretically in this paper. The temperature pattern of the laser diode mini-array packaged in a TO-can is analyzed and optimized to achieve a uniform temperature distribution among the laser stripes and along the cavity direction. The temperature among the laser stripes varies by more than 5 K if the stripes are equally arranged, and can be reduced to less than 0.4 K if proper arrangement is designed. For conventional submount structure, the temperature variation along the cavity direction is as high as 7 K, while for an optimized trapezoid submount structure, the temperature varies only within 0.5 K.

High-power linearly-polarized tunable Raman fiber laser

Jiaxin Song(宋家鑫), Hanshuo Wu(吴函烁), Jiangming Xu(许将明), Hanwei Zhang(张汉伟), Jun Ye(叶俊), Jian Wu(吴坚), Pu Zhou(周朴)
Chin. Phys. B, 2018, 27 (9): 094209 doi: 10.1088/1674-1056/27/9/094209
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In this study, we demonstrate an all-fiber high-power linearly-polarized tunable Raman fiber laser system. An in-house high-power tunable fiber laser was employed as the pump source. A fiber loop mirror (FLM) serving as a high reflectivity mirror and a flat-cut endface serving as an output coupler were adopted to provide broadband feedback. A piece of 59-m commercial passive fiber was used as the Raman gain medium. The Raman laser had a 27.6 nm tuning range from 1112 nm to 1139.6 nm and a maximum output power of 125.3 W, which corresponds to a conversion efficiency of 79.4%. The polarization extinction ratio (PER) at all operational wavelengths was measured to be over 21 dB. To the best of our knowledge, this is the first report on a hundred-watt level linearly-polarized tunable Raman fiber laser.

Detection performance improvement of photon counting chirped amplitude modulation lidar with response probability correction

Yi-Fei Sun(孙怿飞), Zi-Jing Zhang(张子静), Li-Yuan Zhao(赵丽媛), Wei-Min Sun(孙伟民), Yuan Zhao(赵远)
Chin. Phys. B, 2018, 27 (9): 094213 doi: 10.1088/1674-1056/27/9/094213
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Geiger mode avalanche photodiode detector (Gm-APD) possesses the ultra-high sensitivity. Photon counting chirped amplitude modulation (PCCAM) light detection and ranging (lidar) uses the counting results of the returned signal detected by Gm-APD to mix with the reference signal, which makes PCCAM lidar capable of realizing the ultra-high sensitivity, and this is very important for detecting the remote and weak signal. However, Gm-APD is a nonlinear device, different from traditional linear detectors. Due to the nonlinear response of Gm-APD, the counting results of the returned signal detected by Gm-APD are different from those of both the original modulation signal and the reference signal. This will affect the mixing effect and thus degrade the detection performance of PCCAM lidar. In this paper, we propose a response probability correction method. First, the response probability correction model is established on the basis of Gm-APD Poisson probability response model. Then, the response probability correction model is used to adjust the original modulation signal that is used to drive laser, in order to make the counting results of the returned signal detected by Gm-APD better mix with the local reference signal in the same form. Through this method, the detection performance of PCCAM lidar is enhanced efficiently.

Compact and high-efficient wavelength demultiplexing coupler based on high-index dielectric nanoantennas

Jingfeng Tan(谭敬丰), Hua Pang(庞画), Fengkai Meng(孟凤凯), Jin Jiang(蒋进)
Chin. Phys. B, 2018, 27 (9): 094217 doi: 10.1088/1674-1056/27/9/094217
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Wavelength demultiplexing waveguide couplers have important applications in integrated nanophotonic devices. Two of the most important indicators of the quality of a wavelength demultiplexing coupler are coupling efficiency and splitting ratio. In this study, we utilize two asymmetric high-index dielectric nanoantennas directly positioned on top of a silicon-on insulator waveguide to realize a compact wavelength demultiplexing coupler in a communication band, which is based on the interference of the waveguide modes coupled by the two nanoantennas. We add a Au substrate for further increasing the coupling efficiency. This has constructive and destructive influences on the antenna's in-coupling efficiency owing to the Fabry-Perot (FP) resonance in the SiO2 layer. Therefore, we can realize a wavelength demultiplexing coupler with compact size and high coupling efficiency. This coupler has widespread applications in the areas of wavelength filters, on-chip signal processing, and integrated nanophotonic circuits.

Anti-detection technology of cat eye target based on decentered field lens

Da-Lin Song(宋大林), Jun Chang(常军), Yi-Fei Zhao(赵一菲), Ze-Xia Zhang(张泽霞)
Chin. Phys. B, 2018, 27 (9): 094220 doi: 10.1088/1674-1056/27/9/094220
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Optoelectronic imaging equipment is easy to expose to active laser detection devices because of “cat eye” effect. In this paper, we propose a new structure of optical system to reduce the retroreflector effect of a cat eye target. Decentered field lens structure is adopted in the design without sacrificing imaging quality and clear aperture. An imaging system with ±30° field of view is taken for example. The detailed design and simulation results are presented. The results indicate that this kind of optical system can reduce the retroreflection signal substantially and maintain acceptable imaging performance.

Pressure dependent modulation instability in photonic crystal fiber filled with argon gas

He-Lin Wang(王河林), Ai-Jun Yang(杨爱军), XiaoLong Wang(王肖隆), Bin Wu(吴彬), Yi Ruan(阮乂)
Chin. Phys. B, 2018, 27 (9): 094221 doi: 10.1088/1674-1056/27/9/094221
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By using the designed photonic crystal fiber filled with argon gas, the effect of gas pressure on modulation instability (MI) gain is analyzed in detail. The MI gain bandwidth increases gradually as the argon gas pressure rises from 1P0 to 400P0 (P0 is one standard atmosphere), while its gain amplitude slightly decreases. Moreover, the increase of the incident light power also results in the increase of MI gain bandwidth in the Stokes or anti-Stokes region when the incident power increases from 1 W to 200 W. Making use of the optimal parameters including the higher argon gas pressure (400P0) and the incident light power (200 W), we finally obtain a 100 nm broadband MI gain. These results indicate that controlling the MI gain characteristic by changing the argon gas pressure in PCF is an effective way when the incident light source is not easy to satisfy the requirement of practical application. This method of controlling MI gain can be used in optical communication and laser shaping.

Influence of temperature on the properties of one-dimensional piezoelectric phononic crystals

Ahmed Nagaty, Ahmed Mehaney, Arafa H Aly
Chin. Phys. B, 2018, 27 (9): 094301 doi: 10.1088/1674-1056/27/9/094301
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The current study investigates the influence of temperature on a one-dimensional piezoelectric phononic crystal using tunable resonant frequencies. Analytical and numerical examples are introduced to emphasize the influence of temperature on the piezoelectric phononic crystals. It was observed that the transmission spectrum of a one-dimensional phononic crystal containing a piezoelectric material (0.7 PMN-0.3PT) can be changed drastically by an increase in temperature. The resonant peak can be shifted toward high or low frequencies by an increase or decrease in temperature, respectively. Therefore, we deduced that temperature can exhibit a large tuning in the phononic band gaps and in the local resonant frequencies depending on the presence of a piezoelectric material. Such result can enhance the harvesting energy from piezoelectric materials, especially those that are confined in a phononic crystal.

Performance improvement of magneto-acousto-electrical tomography for biological tissues with sinusoid-Barker coded excitation

Zheng-Feng Yu(余正风), Yan Zhou(周), Yu-Zhi Li(李禹志), Qing-Yu Ma(马青玉), Ge-Pu Guo(郭各朴), Juan Tu(屠娟), Dong Zhang(章东)
Chin. Phys. B, 2018, 27 (9): 094302 doi: 10.1088/1674-1056/27/9/094302
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By combining magnetics, acoustics and electrics, the magneto-acoustic-electrical tomography (MAET) proves to possess the capability of differentiating electrical impedance variation and thus improving the spatial resolution. However, the signal-to-noise ratio (SNR) of the collected MAET signal is still unsatisfactory for biological tissues with low-level electrical conductivity. In this study, the formula of MAET measurement with sinusoid-Barker coded excitation is derived and simplified for a planar piston transducer. Numerical simulations are conducted for a four-layered gel phantom with the 13-bit sinusoid-Barker coded excitation, and the performances of wave packet recovery with side-lobe suppression are improved by using the mismatched compression filter, which is also demonstrated by experimentally measuring a three-layered gel phantom. It is demonstrated that comparing with the single-cycle sinusoidal excitation, the amplitude of the driving signal can be reduced greatly with an SNR enhancement of 10 dB using the 13-bit sinusoid-Barker coded excitation. The amplitude and polarity of the wave packet filtered from the collected MAET signal can be used to achieve the conductivity derivative at the tissue boundary. In this study, we apply the sinusoid-Barker coded modulation method and the mismatched suppression scheme to MAET measurement to ensure the safety for biological tissues with improved SNR and spatial resolution, and suggest the potential applications in biomedical imaging.

Contribution of terahertz waves to near-field radiative heat transfer between graphene-based hyperbolic metamaterials

Qi-Mei Zhao(赵启梅), Tong-Biao Wang(王同标), De-Jian Zhang(张德建), Wen-Xing Liu(刘文兴), Tian-Bao Yu(于天宝), Qing-Hua Liao(廖清华), Nian-Hua Liu(刘念华)
Chin. Phys. B, 2018, 27 (9): 094401 doi: 10.1088/1674-1056/27/9/094401
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Hyperbolic metamaterials alternately stacked by graphene and silicon (Si) are proposed and theoretically studied to investigate the contribution of terahertz (THz) waves to near-field radiative transfer. The results show that the heat transfer coefficient can be enhanced several times in a certain THz frequency range compared with that between graphene-covered Si bulks because of the presence of a continuum of hyperbolic modes. Moreover, the radiative heat transfer can also be enhanced remarkably for the proposed structure even in the whole THz range. The hyperbolic dispersion of the graphene-based hyperbolic metamaterial can be tuned by varying the chemical potential or the thickness of Si, with the tunability of optical conductivity and the chemical potential of graphene fixed. We also demonstrate that the radiative heat transfer can be actively controlled in the THz frequency range.

Physical and chemical effects of phosphorus-containing compounds on laminar premixed flame

Yongfeng Yin(殷永丰), Yong Jiang(蒋勇), Rong Qiu(邱榕), Caiyi Xiong(熊才溢)
Chin. Phys. B, 2018, 27 (9): 094701 doi: 10.1088/1674-1056/27/9/094701
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Phosphorus-containing compounds are the promising halon alternatives for flame inhibitions.However,some literatures suggested that the phosphorus-related inhibitors may behave as the unfavorable ones that will increase the burning velocity under lean-burn conditions,and this indeed posed potential threats to the fire prevention and fighting.To seek deeper insights into the reaction process,a numerical investigation was actualized to study the phosphorus-related effects on methane-air flames.By replacing a phosphorus-related inhibitor with the corresponding decomposed molecules,the detailed promoting and inhibiting effects of combustion were separated from the general chemical effect.A comparative study was carried out to identify the interaction between the two effects under different combustion conditions.It is observed that the promoting effect becomes the dominant factor during the reaction process when the equivalence ratio is smaller than 0.60.In this lean-burn condition,the exothermic reactions were faster than the others within the reaction chains due to the reduction of radical recombination in hydrocarbon oxidation.The results are believed to be useful for the further application and improvement of flame inhibitors.

Hopf bifurcation control of a Pan-like chaotic system

Liang Zhang(张良), JiaShi Tang(唐驾时), Qin Han(韩芩)
Chin. Phys. B, 2018, 27 (9): 094702 doi: 10.1088/1674-1056/27/9/094702
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This paper is concerned with the Hopf bifurcation control of a modified Pan-like chaotic system. Based on the Routh-Hurwtiz theory and high-dimensional Hopf bifurcation theory, the existence and stability of the Hopf bifurcation depending on selected values of the system parameters are studied. The region of the stability for the Hopf bifurcation is investigated. By the hybrid control method, a nonlinear controller is designed for changing the Hopf bifurcation point and expanding the range of the stability. Discussions show that with the change of parameters of the controller, the Hopf bifurcation emerges at an expected location with predicted properties and the range of the Hopf bifurcation stability is expanded. Finally, numerical simulation is provided to confirm the analytic results.

Cavity formation during water entry of heated spheres

Jia-Chuan Li(李佳川), Ying-Jie Wei(魏英杰), Cong Wang(王聪), Wei-Xue Xia(夏维学)
Chin. Phys. B, 2018, 27 (9): 094703 doi: 10.1088/1674-1056/27/9/094703
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We experimentally study the cavity formation when heated spheres impact onto water at low and high subcooling. The observations present that the formation and appearance of the cavity are affected by the boiling modes and the heat transfer intensity. In the nucleate-boiling regime, a rough cavity can be formed at a rather low impact velocity, while at the same velocity, the cavity formed in the film-boiling regime may have a very smooth interface with a stable vapor layer around the sphere. We discuss the effects of the impact speed, water and sphere temperatures on the stability of the vapor layer. For low subcooled water, the stable vapor layer will be disturbed when increasing the impact velocity, leading to a disturbed cavity. For high subcooled water, the film boiling has a particular boiling model in which the vapor layer around the sphere cannot keep its stability. In this particular film-boiling regime, no cavities can be formed at low impact velocities and only broken cavities can be formed at high impact velocities.

Phase field simulation of single bubble behavior under an electric field

Chang-Sheng Zhu(朱昶胜), Dan Han(韩丹), Sheng Xu(徐升)
Chin. Phys. B, 2018, 27 (9): 094704 doi: 10.1088/1674-1056/27/9/094704
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Based on the Cahn-Hilliard phase field model, a three-dimensional multiple-field coupling model for simulating the motion characteristics of a rising bubble in a liquid is established in a gas-liquid two-phase flow. The gas-liquid interface motion is simulated by using a phase-field method, and the effect of the electric field intensity on bubble dynamics is studied without electric field, or with vertical electric field or horizontal electric field. Through the coupling effect of electric field and flow field, the deformation of a single rising bubble and the formation of wake vortices under the action of gravity and electric field force are studied in detail. The correctness of the results is verified by mass conservation, and the influences of different electric field directions and different voltages on the movement of bubbles in liquid are considered. The results show that the ratio of the length to axis is proportional to the strength of the electric field when the air bubble is stretched into an ellipsoid along the electric field line under the action of electrostatic gravity and surface tension. In addition, the bubble rising speed is affected by the electric field, the vertical electric field accelerates the bubble rise, and the horizontal direction slows it down.

Shock oscillation in highly underexpanded jets

Xiao-Peng Li(李晓鹏), Rui Zhou(周蕊), Xiao-Ping Chen(陈小平), Xue-Jun Fan(范学军), Guo-Shan Xie(谢国山)
Chin. Phys. B, 2018, 27 (9): 094705 doi: 10.1088/1674-1056/27/9/094705
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The oscillatory motions of shocks in highly underexpanded jets with nozzle pressure ratios of 5.60, 7.47, 9.34, and 11.21 are quantitatively studied by using large eddy simulation. Two types of shock oscillations are observed:one is the Mach disk oscillation in the streamwise direction and the other is the shock oscillation in the radial direction. It is found that the Mach disk moves quickly in the middle of the oscillatory region but slowly at the top or bottom boundaries. The oscillation cycles of Mach disk are the same for different cases, and are all dominated by an axisymmetric mode of 5.298 kHz. For the oscillation in the radial direction, the shocks oscillate more toward the jet centerline but less in the jet shear layer, and the oscillation magnitude is an increasing function of screech amplitude. The cycles of the radial shock oscillation switch randomly between the two screech frequencies for the first two cases. However, the oscillation periodicity is more complex for the jets with high nozzle pressure ratios of 9.34 and 11.21 than for the jets with the low nozzle pressure ratios of 5.6 and 7.47. In addition, the shock oscillation characteristics are also captured by coarse mesh and Smagorinsky model, but the coarse mesh tends to predict a slower and weaker shock oscillation.


Theoretical derivation of the crystallographic parameters of polytypes of long-period stacking ordered structures with the period of 13 and 14 in hexagonal close-packed system

Li Ye(叶礼), Dong-Shan Zhao(赵东山), Yuan-Lin Zhuang(庄园林), Shuang-Feng Jia(贾双凤), Jia-Ping Zhou(周嘉萍), Jia-Nian Gui(桂嘉年), Jian-Bo Wang(王建波)
Chin. Phys. B, 2018, 27 (9): 096102 doi: 10.1088/1674-1056/27/9/096102
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Based on crystallographic theory, there are 63 kinds of polytypes of 13H long-period stacking order (LPSO) structure, 126 kinds of polytypes of 14H LPSO structure, 120 kinds of polytypes of 39R LPSO structure, and 223 kinds of polytypes of 42R LPSO structure in a hexagonal close-packed (HCP) system, and their stacking sequences and space groups have been derived in detail. The result provides a theoretical explanation for the various polytypes of the LPSO structure.

Effect of microstructure on 3He migration in TiT1.9 films

Haifeng Wang(王海峰), Shuming Peng(彭述明), Wei Ding(丁伟), Huahai Shen(申华海), Weidu Wang(王维笃), Xiaosong Zhou(周晓松), Xinggui Long(龙兴贵)
Chin. Phys. B, 2018, 27 (9): 096103 doi: 10.1088/1674-1056/27/9/096103
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Two kinds of films were prepared to study the effect of microstructure on helium migration in Ti tritides. Both films showed different release behaviors and helium bubble distributions. In the film consisting of columnar grains, a two-layered structure was observed. Inclusions with a strip feature were found at the grain boundary, and no helium bubbles were distributed in these inclusions. However, helium preferred to migrate to the boundaries of these inclusions. Bubble linkage as a ribbon-like feature developed parallel to the film surface in the film consisting of columnar grains. More cracks were developed at the grain boundaries of the film consisting of columnar grains, although the helium content in the film consisting of columnar grains was less than that in the film consisting of equiaxed grains. A surface region with a small number of bubbles, or “depleted zone”, was observed near the surface. The cracks extending to the film surface were the pathways of the critical helium released from the film. The helium migration was strongly influenced by the grain microstructure.

Structural and electrical properties of carbon-ion-implanted ultrananocrystalline diamond films

Hui Xu(徐辉), Jian-Jun Liu(刘建军), Hai-Tao Ye(叶海涛), D J Coathup, A V Khomich, Xiao-Jun Hu(胡晓君)
Chin. Phys. B, 2018, 27 (9): 096104 doi: 10.1088/1674-1056/27/9/096104
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We investigate the structural and electrical properties of carbon-ion-implanted ultrananocrystalline diamond (UNCD) films. Impedance spectroscopy measurements show that the impedance of diamond grains is relatively stable, while that of grain boundaries (GBs) (Rb) significantly increases after the C+ implantation, and decreases with the increase in the annealing temperature (Ta) from 650 ℃ to 1000 ℃. This implies that the C+ implantation has a more significant impact on the conductivity of GBs. Conductive atomic force microscopy demonstrates that the number of conductive sites increases in GB regions at Ta above 900 ℃, owing to the formation of a nanographitic phase confirmed by high-resolution transmission electronic microscopy. Visible-light Raman spectra show that resistive trans-polyacetylene oligomers desorb from GBs at Ta above 900 ℃, which leads to lower Rb of samples annealed at 900 and 1000 ℃. With the increase in Ta to 1000 ℃, diamond grains become smaller with longer GBs modified by a more ordered nanographitic phase, supplying more conductive sites and leading to a lower Rb.

Exact transverse solitary and periodic wave solutions in a coupled nonlinear inductor-capacitor network

Serge Bruno Yamgoué, Guy Roger Deffo, Eric Tala-Tebue, François Beceau Pelap
Chin. Phys. B, 2018, 27 (9): 096301 doi: 10.1088/1674-1056/27/9/096301
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Through two methods, we investigate the solitary and periodic wave solutions of the differential equation describing a nonlinear coupled two-dimensional discrete electrical lattice. The fixed points of our model equation are examined and the bifurcations of phase portraits of this equation for various values of the front wave velocity are presented. Using the sine-Gordon expansion method and classic integration, we obtain exact transverse solutions including breathers, bright solitons, and periodic solutions.

Properties of negative thermal expansion β-eucryptite ceramics prepared by spark plasma sintering

Li-Min Zhao(赵利敏), Yong-Guang Cheng(程永光), Hao-Shan Hao(郝好山), Jiao Wang(王娇), Shao-Hui Liu(刘少辉), Bao-Sen Zhang(张宝森)
Chin. Phys. B, 2018, 27 (9): 096501 doi: 10.1088/1674-1056/27/9/096501
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β-eucryptite powders are prepared by the sol-gel method through using tetraethoxysilane lithium nitrate and aluminum isopropoxide as starting materials. β-eucryptite ceramics are prepared by spark plasma sintering. The effects of sintering temperature on the negative thermal expansion properties of the β-eucryptite are investigated by x-ray diffraction (XRD), scanning electron microscopy, and thermal expansion test. The XRD results exhibit no change in the crystal structure of the sample prepared by different sintering processes. The negative thermal expansion properties increase with the increase of the sintering temperature. The coefficient of thermal expansion of β-eucryptite ceramics sintered at 1100 ℃ is calculated to be -4.93×10-6-1. Crystallization behaviors of the ceramics may play an important role in the increase of negative thermal expansion of β-eucryptite. High sintering temperature could improve the crystallization behaviors of the ceramics and reduce the residue glass phase, which can improve the negative thermal expansion properties of β-eucryptite ceramics.

Microdroplet targeting induced by substrate curvature

Hongguang Zhang(张红光), Zhenjiang Guo(郭振江), Shan Chen(陈珊), Bo Zhang(张博), Xianren Zhang(张现仁)
Chin. Phys. B, 2018, 27 (9): 096801 doi: 10.1088/1674-1056/27/9/096801
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Fundamental understanding of the wettability of curved substrates is crucial for the applications of microdroplets in colloidal science, microfluidics, and heat exchanger technologies. Here we report via lattice Boltzmann simulations and energetic analysis that microdroplets show an ability of transporting selectively to appropriate substrates solely according to substrate shape (curvature), which is called the substrate-curvature-dependent droplet targeting because of its similarity to protein targeting by which proteins are transported to the appropriate destinations in the cell. Two dynamic pathways of droplet targeting are identified:one is the Ostwald ripening-like liquid transport between separated droplets via evaporating droplets on more curved convex (or less curved concave) surfaces and growing droplets on less curved convex (or more curved concave) surfaces, and the other is the directional motion of a droplet through contacting simultaneously substrates of different curvatures. Then we demonstrate analytically that droplet targeting is a thermodynamically driven process. The driving force for directional motion of droplets is the surface-curvature-induced modulation of the work of adhesion, while the Ostwald ripening-like transport is ascribed to the substrate-curvature-induced change of droplet curvature radius. Our findings of droplet targeting are potentially useful for a tremendous range of applications, such as microfluidics, thermal control, and microfabrication.

Nondestructive determination of film thickness with laser-induced surface acoustic waves

Xiao Xia(肖夏), Kong Tao(孔涛), Qi Hai Yang(戚海洋), Qing Hui Quan(秦慧全)
Chin. Phys. B, 2018, 27 (9): 096802 doi: 10.1088/1674-1056/27/9/096802
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The application of surface acoustic waves (SAWs) for thickness measurement is presented. By studying the impact of film thickness h on the dispersion phenomenon of surface acoustic waves, a method for thickness determination based on theoretical dispersion curve v (fh) and experimental dispersion curve v (f) is developed. The method provides a series of thickness values at different frequencies f, and the mean value is considered as the final result of the measurement. The thicknesses of six interconnect films are determined by SAWs, and the results are compared with the manufacturer's data. The relative differences are in the range from 0.4% to 2.18%, which indicates that the surface acoustic wave technique is reliable and accurate in the nondestructive thickness determination for films. This method can be generally used for fast and direct determination of film thickness.


Electronic properties of defects in Weyl semimetal tantalum arsenide

Yan-Long Fu(付艳龙), Chang-Kai Li(李长楷), Zhao-Jun Zhang(张昭军), Hai-Bo Sang(桑海波), Wei Cheng(程伟), Feng-Shou Zhang(张丰收)
Chin. Phys. B, 2018, 27 (9): 097101 doi: 10.1088/1674-1056/27/9/097101
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The tantalum arsenide (TaAs) is a topological Weyl semimetal which is a class of materials of gapless with three-dimensional topological structure. In order to develop a comprehensive description of the topological properties of the Weyl semimetal, we use the density functional theory to study several defects of TaAs after H irradiation and report the electronic dispersion curves and the density of states of these defects. We find that various defects have different influences on the topological properties. Interstitial H atom can shift the Fermi level. Both Ta vacancy with a concentration of 1/64 and As vacancy with a concentration of 1/64 destruct a part of the Weyl points. The substitutional H atom on a Ta site could repair only a part of the Weyl points, while H atom on an As site could repair all the Weyl points.

Site preferences of alloying transition metal elements in Ni-based superalloy: A first-principles study

Baokun Lu(路宝坤), Chong-Yu Wang(王崇愚), Zhihui Du(都志辉)
Chin. Phys. B, 2018, 27 (9): 097102 doi: 10.1088/1674-1056/27/9/097102
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Atomistic characterization of chemical element distribution is crucial to understanding the role of alloying elements for strengthening mechanism of superalloy. In the present work, the site preferences of two alloying elements X-Y in γ-Ni of Ni-based superalloy are systematically studied using first-principles calculations with and without spin-polarization. The doping elements X and Y are chosen from the 27 kinds of 3d, 4d, 5d group transition metals (Sc, Ti, V, Cr, Mn, Fe, Co, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Os, Ir, Pt, Au) and Al. We find that the spin-polarized calculations for Re-Re, Re-Ru, Re-Cr, Ru-Cr show a strong chemical binding affinity between the solute elements and are more consistent with the experimental results. The binding energies of pairs between the 28 elements have an obvious periodicity and are closely related the electronic configuration of the elements. When the d-electrons of the element are close to the half full-shell state, two alloying elements possess attractive binding energies, reflecting the effect of the Hund's rule. The combinations of early transition metals (Sc, Ti, V, Y, Zr, Nb, Hf, Ta) have a repulsive interaction in γ-Ni. These results offer insights into the role of alloying elements for strengthening mechanism of superalloy.

Pressure effect in the Kondo semimetal CeRu4Sn6 with nontrivial topology Hot!

Jiahao Zhang(张佳浩), Shuai Zhang(张帅), Ziheng Chen(陈子珩), Meng Lv(吕孟), Hengcan Zhao(赵恒灿), Yi-feng Yang(杨义峰), Genfu Chen(陈根富), Peijie Sun(孙培杰)
Chin. Phys. B, 2018, 27 (9): 097103 doi: 10.1088/1674-1056/27/9/097103
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Kondo semimetal CeRu4Sn6 is attracting renewed attention due to the theoretically predicted nontrivial topology in its electronic band structure. We report hydrostatic and chemical pressure effects on the transport properties of single-and poly-crystalline samples. The electrical resistivity ρ(T) is gradually enhanced by applying pressure over a wide temperature range from room temperature down to 25 mK. Two thermal activation gaps estimated from high-and low-temperature windows are found to increase with pressure. A flat ρ(T) observed at the lowest temperatures below 300 mK appears to be robust against both pressure and field. This feature as well as the increase of the energy gaps calls for more intensive investigations with respect to electron correlations and band topology.

Multiscale energy density algorithm and application to surface structure of Ni matrix of superalloy

Min Sun(孙敏), Chong-Yu Wang(王崇愚), Ji-Ping Liu(刘吉平)
Chin. Phys. B, 2018, 27 (9): 097105 doi: 10.1088/1674-1056/27/9/097105
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Multiscale materials modeling as a new technique could offer more accurate predictive capabilities. The most active area of research for multiscale modeling focuses on the concurrent coupling by considering models on disparate scales simultaneously. In this paper, we present a new concurrent multiscale approach, the energy density method (EDM), which couples the quantum mechanical (QM) and the molecular dynamics (MD) simulations simultaneously. The coupling crossing different scales is achieved by introducing a transition region between the QM and MD domains. In order to construct the energy formalism of the entire system, concept of site energy and weight parameters of disparate scales are introduced. The EDM is applied to the study of the multilayer relaxation of the Ni (001) surface structure and is validated against the periodic density functional theory (DFT) calculations. The results show that the concurrent EDM could combine the accuracy of the DFT description with the low computational cost of the MD simulation and is suitable to the study of the local defects subjected to the influence of the long-range environment.

Temperature dependence on the electrical and physical performance of InAs/AlSb heterojunction and high electron mobility transistors

Jing Zhang(张静), Hongliang Lv(吕红亮), Haiqiao Ni(倪海桥), Zhichuan Niu(牛智川), Yuming Zhang(张玉明)
Chin. Phys. B, 2018, 27 (9): 097201 doi: 10.1088/1674-1056/27/9/097201
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In this report, the effect of temperature on the InAs/AlSb heterojunction and high-electron-mobility transistors (HEMTs) with a gate length of 2 μ are discussed comprehensively. The results indicate that device performance is greatly improved at cryogenic temperatures. It is also observed that the device performance at 90 K is significantly improved with 27% lower gate leakage current, 12% higher maximum drain current, and 22.5% higher peak transconductance compared to 300 K. The temperature dependence of mobility and the two-dimensional electron gas concentration in the InAs/AlSb heterojunction for the temperature range 90 K-300 K is also investigated. The electron mobility at 90 K (42560 cm2/V·s) is 2.5 times higher than its value at 300 K (16911 cm2/V·s) because of the weaker lattice vibration and the impurity ionization at cryogenic temperatures, which corresponds to a reduced scattering rate and higher mobility. We also noted that the two-dimensional electron gas concentration decreases slightly from 1.99×1012 cm-2 at 300 K to 1.7×1012 cm-2 at 90 K with a decrease in temperature due to the lower ionization at cryogenic temperature and the nearly constant ΔEc.

Thermal stability of the spin injection in Co/Ag/Co lateral spin valves

Le Wang(王乐), Lu-Chen Chen(陈鹭琛), Wen-Yu Liu(刘雯雨), Shuo Han(韩烁), Weiwei Wang(王伟伟), Zhanjie Lu(卢占杰), Shan-Shan Chen(陈珊珊)
Chin. Phys. B, 2018, 27 (9): 097202 doi: 10.1088/1674-1056/27/9/097202
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Spin injection, spin diffusion, and spin detection are investigated in Co/Ag/Co lateral spin valves at room temperature. Clear spin accumulation signals are detected by the non-local measurement. By fitting the results to the one-dimensional diffusion equation,~8.6% spin polarization of the Co/Ag interface and ~180 nm spin diffusion length in Ag are obtained. Thermal treatment results show that the spin accumulation signal drastically decreases after 100 ℃ annealing, and disappears under 200 ℃ annealing. Our results demonstrate that, compared to the spin diffusion length, the decrease and the disappearance of the spin accumulation signal are mainly dominated by the variation of the interfacial spin polarization of the Co/Ag interface.

Modeling capacitance–voltage characteristic of TiW/p-InP Schottky barrier diode

Yi-Dong Wang(王一栋), Jun Chen(陈俊)
Chin. Phys. B, 2018, 27 (9): 097203 doi: 10.1088/1674-1056/27/9/097203
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The capacitance-voltage (C-V) characteristic of the TiW/p-InP Schottky barrier diodes (SBDs) is analyzed considering the effects of the interface state (Nss), series resistance (Rs), and deep level defects. The C-V of the Schottky contact is modeled based on the physical mechanism of the interfacial state and series resistance effect. The fitting coefficients α and β are used to reflect the Nss and Rs on the C-V characteristics, respectively. The α decreases with the increase of frequency, while β increases with the increase of frequency. The capacitance increases with the increase of α and the decrease of β. From our model, the peak capacitance and its position can be estimated. The experimental value is found to be larger than the calculated one at the lower voltage. This phenomenon can be explained by the effect of deep level defects.

The magneto-thermoelectric effect of graphene with intra-valley scattering

Wenye Duan(段文晔), Junfeng Liu(刘军丰), Chao Zhang(张潮), Zhongshui Ma(马中水)
Chin. Phys. B, 2018, 27 (9): 097204 doi: 10.1088/1674-1056/27/9/097204
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We present a qualitative and quantitative study of the magneto-thermoelectric effect of graphene. In the limit of impurity scattering length being much longer than the lattice constant, the intra-valley scattering dominates the charge and thermal transport. The self-energy and the Green's functions are calculated in the self-consistent Born approximation. It is found that the longitudinal thermal conductivity splits into double peaks at high Landau levels and exhibits oscillations which are out of phase with the electric conductivity. The chemical potential-dependent electrical resistivity, the thermal conductivities, the Seebeck coefficient, and the Nernst coefficient are obtained. The results are in good agreement with the experimental observations.

Ab initio study of H/O trapping and clustering on U/Al interface

Wenhong Ouyang(欧阳文泓), Wensheng Lai(赖文生), Zhengjun Zhang(张政军)
Chin. Phys. B, 2018, 27 (9): 097303 doi: 10.1088/1674-1056/27/9/097303
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Al coating on U surfaces is one of the methods to protect U against environmental corrosion. The behaviors of hydrogen and oxygen impurities near the Al/α-U interface have been studied in the density functional theory framework. It turns out that U vacancies tend to segregate to the interface with segregation energies of around 0.5-0.8 eV. The segregated U vacancy can act as a sink for H and O impurities, which is saturated when filled with 8 H or 6 O atoms, respectively. Moreover, the O impurities tend to stay in the Al layer while the H impurities prefer to diffuse into the U lattice, suggesting that the Al coating can play a significant role against oxidation but not against hydrogenation of U.

Electric field manipulation of multiple nonequivalent Dirac cones in the electronic structures of hexagonal CrB4 sheet

Jinkun Wang(王锦坤), Yajiao Ke(柯亚娇), Qingxing Xie(谢晴兴), Yanli Li(李艳丽), Jiafu Wang(王嘉赋)
Chin. Phys. B, 2018, 27 (9): 097304 doi: 10.1088/1674-1056/27/9/097304
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Two-dimensional materials with Dirac cones have significant applications in photoelectric technology. The origin and manipulation of multiple Dirac cones need to be better understood. By first-principle calculations, we study the influence of external fields on the electronic structure of the hexagonal CrB4 sheet with double nonequivalent Dirac cones. Our results show that the two cones are not sensitive to tensile strain and out-of-plane electric field, but present obviously different behaviors under the in-plane external electric field (along the B-B direction), i.e., one cone holds while the other vanishes with a gap opening. More interestingly, a new nonequivalent cone emerges under a proper in-plane electric field. We also discuss the origin of the cones in CrB4 sheet. Our study provides a new method on how to obtain Dirac cones by the external field manipulation, which may motivate potential applications in nanoelectronics.

Analysis of the inhomogeneous barrier and phase composition of W/4H-SiC Schottky contacts formed at different annealing temperatures

Sheng-Xu Dong(董升旭), Yun Bai(白云), Yi-Dan Tang(汤益丹), Hong Chen(陈宏), Xiao-Li Tian(田晓丽), Cheng-Yue Yang(杨成樾), Xin-Yu Liu(刘新宇)
Chin. Phys. B, 2018, 27 (9): 097305 doi: 10.1088/1674-1056/27/9/097305
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The electrical characteristics of W/4H-SiC Schottky contacts formed at different annealing temperatures have been measured by using current-voltage-temperatures (I-V-T) and capacitance-voltage-temperatures (C-V-T) techniques in the temperature range of 25 ℃-175 ℃. The testing temperature dependence of the barrier height (BH) and ideality factor (n) indicates the presence of inhomogeneous barrier. Tung's model has been applied to evaluate the degree of inhomogeneity, and it is found that the 400 ℃ annealed sample has the lowest T0 of 44.6 K among all the Schottky contacts. The barrier height obtained from C-V-T measurement is independent of the testing temperature, which suggests a uniform BH. The x-ray diffraction (XRD) analysis shows that there are two kinds of space groups of W when it is deposited or annealed at lower temperature (≤ 500 ℃). The phase of W2C appears in the sample annealed at 600 ℃, which results in the low BH and the high T0. The 500 ℃ annealed sample has the highest BH at all testing temperatures, indicating an optimal annealing temperature for the W/4H-SiC Schottky rectifier for high-temperature application.

Key technologies for dual high-k and dual metal gate integration

Yong-Liang Li(李永亮), Qiu-Xia Xu(徐秋霞), Wen-Wu Wang(王文武)
Chin. Phys. B, 2018, 27 (9): 097306 doi: 10.1088/1674-1056/27/9/097306
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The key technologies for the dual high-k and dual metal gate, such as the electrical optimization of metal insert poly-Si stack structure, the separating of high-k and metal gate of n/pMOS in different regions of the wafer, and the synchronous etching of n/pMOS gate stack, are successfully developed. First, reasonable flat-band voltage and equivalent oxide thickness of pMOS MIPS structure are obtained by further optimizing the HfSiAlON dielectric through incorporating more Al-O dipole at interface between HfSiAlON and bottom SiOx. Then, the separating of high-k and metal gate for n/pMOS is achieved by SC1 (NH4OH:H2O2:H2O=1:1:5) and DHF-based solution for the selective removing of nMOS TaN and HfSiON and by BCl3-based plasma and DHF-based solution for the selective removing of pMOS TaN/Mo and HfSiAlON. After that, the synchronous etching of n/pMOS gate stack is developed by utilizing optimized BCl3/SF6/O2/Ar plasma to obtain a vertical profile for TaN and TaN/Mo and by utilizing BCl3/Ar plasma combined with DHF-based solution to achieve high selectivity to Si substrate. Finally, good electrical characteristics of CMOS devices, obtained by utilizing these new developed technologies, further confirm that they are practicable technologies for DHDMG integration.

Characteristics and threshold voltage model of GaN-based FinFET with recessed gate

Chong Wang(王冲), Xin Wang(王鑫), Xue-Feng Zheng(郑雪峰), Yun Wang(王允), Yun-Long He(何云龙), Ye Tian(田野), Qing He(何晴), Ji Wu(吴忌), Wei Mao(毛维), Xiao-Hua Ma(马晓华), Jin-Cheng Zhang(张进成), Yue Hao(郝跃)
Chin. Phys. B, 2018, 27 (9): 097308 doi: 10.1088/1674-1056/27/9/097308
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In this work, AlGaN/GaN FinFETs with different fin widths have been successfully fabricated, and the recessed-gate FinFETs are fabricated for comparison. The recessed-gate FinFETs exhibit higher transconductance value and positive shift of threshold voltage. Moreover, with the fin width of the recessed-gate FinFETs increasing, the variations of both threshold voltage and the transconductance increase. Next, transfer characteristics of the recessed-gate FinFETs with different fin widths and recessed-gate depths are simulated by Silvaco software. The relationship between the threshold voltage and the AlGaN layer thickness has been investigated. The simulation results indicate that the slope of threshold voltage variation reduces with the fin width decreasing. Finally, a simplified threshold voltage model for recessed-gate FinFET is established, which agrees with both the experimental results and simulation results.

Effect of SiN: Hx passivation layer on the reverse gate leakage current in GaN HEMTs

Sheng Zhang(张昇), Ke Wei(魏珂), Yang Xiao(肖洋), Xiao-Hua Ma(马晓华), Yi-Chuan Zhang(张一川), Guo-Guo Liu(刘果果), Tian-Min Lei(雷天民), Ying-Kui Zheng(郑英奎), Sen Huang(黄森), Ning Wang(汪宁), Muhammad Asif, Xin-Yu Liu(刘新宇)
Chin. Phys. B, 2018, 27 (9): 097309 doi: 10.1088/1674-1056/27/9/097309
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This paper concentrates on the impact of SiN passivation layer deposited by plasma-enhanced chemical vapor deposition (PECVD) on the Schottky characteristics in GaN high electron mobility transistors (HEMTs). Three types of SiN layers with different deposition conditions were deposited on GaN HEMTs. Atomic force microscope (AFM), capacitance-voltage (C-V), and Fourier transform infrared (FTIR) measurement were used to analyze the surface morphology, the electrical characterization, and the chemical bonding of SiN thin films, respectively. The better surface morphology was achieved from the device with lower gate leakage current. The fixed positive charge Qf was extracted from C-V curves of Al/SiN/Si structures and quite different density of trap states (in the order of magnitude of 1011-1012 cm-2) was observed. It was found that the least trap states were in accordance with the lowest gate leakage current. Furthermore, the chemical bonds and the %H in Si-H and N-H were figured from FTIR measurement, demonstrating an increase in the density of Qf with the increasing %H in N-H. It reveals that the effect of SiN passivation can be improved in GaN-based HEMTs by modulating %H in Si-H and N-H, thus achieving a better Schottky characteristics.

Transport spectroscopy through dopant atom array in silicon junctionless nanowire transistors

Xiao-Song Zhao(赵晓松), Wei-Hua Han(韩伟华), Yang-Yan Guo(郭仰岩), Ya-Mei Dou(窦亚梅), Fu-Hua Yang(杨富华)
Chin. Phys. B, 2018, 27 (9): 097310 doi: 10.1088/1674-1056/27/9/097310
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We demonstrate electron transport spectroscopy through a dopant atom array in n-doped silicon junctionless nanowire transistors within a temperature range from 6 K to 250 K. Several current steps are observed at the initial stage of the transfer curves below 75 K, which result from the electron transport from Hubbard bands to one-dimensional conduction band. The current-off voltages in the transfer curves have a strikingly positive shift below 20 K and a negative shift above 20 K due to the electrostatic screening induced by the ionized dopant atoms. There exists the minimum electron mobility at a critical temperature of 20 K, resulting from the interplay between thermal activation and impurity scattering. Furthermore, electron transport behaviors change from hopping conductance to thermal activation conductance at the temperature of 30 K.

Adsorptions of metal adatoms on graphene-like BC3 and their rich electronic properties: A first-principles study

Pengfei Sui(隋鹏飞), Jiaqi Dai(戴佳琦), Yinchang Zhao(赵银昌), Zhenhong Dai(戴振宏)
Chin. Phys. B, 2018, 27 (9): 097311 doi: 10.1088/1674-1056/27/9/097311
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Density functional calculations have been performed to investigate the adsorption of twenty two different kinds of metal adatoms on graphene-like BC3. In contrast to the graphene adsorbed with adatoms, the BC3 with adatoms shows many interesting properties. (1) The interaction between the metal adatoms and the BC3 sheet is remarkably strong. The Li, Na, K, and Ca possess the binding energies larger than the cohesive energies of their corresponding bulk metals. (2) The Li, Na, and K adatoms form approximately ideal ionic bonds with BC3, while the Be, Mg, and Ca adatoms form ionic bonds with BC3 with slight hybridization of covalent bonds. The Al, Ga, In, Sn, and all transition metal adatoms form covalent bonds with BC3. (3) For all the structures studied, there exhibit metal, half-metal, semiconducting, and spin-semiconducting behaviors. Especially, the BC3 with Co adatom shows a quantum anomalous Hall (QAH) phase with a Chern number of -1 based on local density approximation calculations. (4) For Li, Na, K, Ca, Ga, In, Sn, Ti, V, Cr, Ni, Pd, and Pt, there exists a trend that the adatom species with lower ionization potential have lower work function. Our results indicate the potential applications of functionalization of BC3 with metal adatoms.

0-π transition induced by the barrier strength in spin superconductor Josephson junctions Hot!

Wen Zeng(曾文), Rui Shen(沈瑞)
Chin. Phys. B, 2018, 27 (9): 097401 doi: 10.1088/1674-1056/27/9/097401
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The Andreev-like levels and the free energy of the spin superconductor/insulator/spin superconductor junction are obtained by using the Bogoliubov-de Gennes equation. The phase dependence of the spin supercurrents exhibits a 0-π transition by changing the barrier strength. The dependences of the critical current on the barrier strength and the temperature are also presented.

Modulational instability, quantum breathers and two-breathers in a frustrated ferromagnetic spin lattice under an external magnetic field

Wanhan Su(苏琬涵), Jiayu Xie(谢家玉), Tianle Wu(吴天乐), Bing Tang(唐炳)
Chin. Phys. B, 2018, 27 (9): 097501 doi: 10.1088/1674-1056/27/9/097501
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The modulational instability, quantum breathers and two-breathers in a frustrated easy-axis ferromagnetic zig-zag chain under an external magnetic field are investigated within the Hartree approximation. By means of a linear stability analysis, we analytically study the discrete modulational instability and analyze the effect of the frustration strength on the discrete modulational instability region. Using the results from the discrete modulational instability analysis, the presence conditions of those stationary bright type localized solutions are presented. On the other hand, we obtain the analytical expressions for the stationary bright localized solutions and analyze the effect of the frustration on their emergence conditions. By taking advantage of these bright type single-magnon bound wave functions obtained, quantum breather states in the present frustrated ferromagnetic zig-zag lattice are constructed. What is more, the analytical forms for quantum two-breather states are also obtained. In particular, the energy level formulas of quantum breathers and two-breathers are derived.

Effect of particle size distribution on magnetic behavior of nanoparticles with uniaxial anisotropy

S Rizwan Ali, Farah Naz, Humaira Akber, M Naeem, S Imran Ali, S Abdul Basit, M Sarim, Sadaf Qaseem
Chin. Phys. B, 2018, 27 (9): 097503 doi: 10.1088/1674-1056/27/9/097503
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The effect of particle size distribution on the field and temperature dependence of the hysteresis loop features like coercivity (HC), remanence (MR), and blocking temperature (TB) is simulated for an ensemble of single domain ferromagnetic nanoparticles with uniaxial anisotropy. Our simulations are based on the two-state model for T<TB and the metropolis Monte-Carlo method for T>TB. It is found that the increase in the grain size significantly enhances HC and TB. The presence of interparticle exchange interaction in the system suppresses HC but causes MR to significantly increase. Our results show that the parameters associated with the particle size distribution (Dd,δ) such as the mean particle size d and standard-deviation δ play key roles in the magnetic behavior of the system.

Thickness dependent manipulation of uniaxial magnetic anisotropy in Fe-thin films by oblique deposition

Qeemat Gul, Wei He(何为), Yan Li(李岩), Rui Sun(孙瑞), Na Li(李娜), Xu Yang(杨旭), Yang Li(李阳), Zi-Zhao Gong(弓子召), ZongKai Xie(谢宗凯), Xiang-Qun Zhang(张向群), Zhao-Hua Cheng(成昭华)
Chin. Phys. B, 2018, 27 (9): 097504 doi: 10.1088/1674-1056/27/9/097504
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The uniaxial magnetic anisotropy of obliquely deposited Fe(001)/Pd film on MgO(001) substrate is investigated as a function of deposition angle and film thickness. The values of incidence angle of Fe flux relative to surface normal of the substrate are 0°, 45°, 55°, and 70°, respectively. In-situ low energy electron diffraction is employed to investigate the surface structures of the samples. The Fe film thicknesses are determined to be 50 ML, 45 ML, 32 ML, and 24 ML (1 ML=0.14 nm) by performing x-ray reflectivity on the grown samples, respectively. The normalized remanent magnetic saturation ratio and coercivity are obtained by the longitudinal surface magneto-optical Kerr effect. Here, the magnetic anisotropy constants are quantitatively determined by fitting the anisotropic magnetoresistance curves under different fields. These measurements show four-fold cubic anisotropy in a large Fe film thickness (50 ML) sample, but highly in-plane uniaxial magnetic anisotropies in thin films (24 ML and 32 ML) samples. In the obliquely deposited Fe films, the coercive fields and the uniaxial magnetic anisotropies (UMAs) increase as the deposition angle becomes more and more tilted. In addition, the UMA decreases with the increase of the Fe film thickness. Our work provides the possibility of manipulating uniaxial magnetic anisotropy, and paves the way to inducing UMA by oblique deposition with smaller film thickness.

Enhanced magneto-electric effect in manganite tricolor superlattice with artificially broken symmetry

Huanyu Pei(裴环宇), Shujin Guo(郭蜀晋), Hong Yan(闫虹), Changle Chen(陈长乐), Bingcheng Luo(罗炳成), Kexin Jin(金克新)
Chin. Phys. B, 2018, 27 (9): 097701 doi: 10.1088/1674-1056/27/9/097701
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The magneto-electric effect in magnetic materials has been widely investigated, but obtaining an enhanced magneto-electric effect is challenging. In this study, tricolor superlattices composed of manganese oxides–Pr0.9Ca0.1MnO3, La0.9Sr0.1MnO3, and La0.9Sb0.1MnO3–on (001)-oriented Nb:SrTiO3 substrates with broken space-inversion and time-reversal symmetries are designed. Regarding the electric polarization in the hysteresis loops of the superlattices at different external magnetic fields, both coercive electric field Ec and remnant polarization intensity Pr clearly show strong magnetic-field dependences. At low temperatures (<120 K), a considerable magneto-electric effect in the well-defined tricolor superlattice is observed that is absent in the single compounds. Both maxima of the magneto-electric coupling coefficients ΔEc and ΔPr appear at 30 K. The magnetic dependence of the dielectric constant further supports the magneto-electric effect. Moreover, a dependence of the magneto-electric effect on the periodicity of the superlattices with various structures is observed, which indicates the importance of interfaces. Our experimental results verify previous theoretical results regarding magneto-electric interactions, thereby paving the way for the design and development of novel magneto-electric devices based on manganite ferromagnets.

Crystal growth and spectral properties of Tb: Lu2O3

Jiaojiao Shi(施佼佼), Bin Liu(刘斌), Qingguo Wang(王庆国), Huili Tang(唐慧丽), Feng Wu(吴锋), Dongzhen Li(李东振), Hengyu Zhao(赵衡煜), Zhanshan Wang(王占山), Wen Deng(邓文), Xu Zian(徐子安), Xu Jiayue(徐家跃), Xiaodong Xu(徐晓东), Jun Xu(徐军)
Chin. Phys. B, 2018, 27 (9): 097801 doi: 10.1088/1674-1056/27/9/097801
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The crystal growth, x-ray diffraction pattern, absorption spectrum, emission spectrum, and fluorescence lifetime of a Tb:Lu2O3 single crystal were studied. Excited at 483 nm, the peak absorption cross-section was calculated to be 3.5×10-22 cm2, and the full width at half maximum was found to be 2.85 nm. The Judd-Ofelt (J-O) intensity parameters Ω2, Ω4, and Ω6 were computed to be 3.79×10-20 cm2, 1.30×10-20 cm2, and 1.08×10-20 cm2, with a spectroscopic quality factor Ω4/Ω6 being 1.20. The emission cross-sections of green emission around 543 nm and yellow emission around 584 nm were calculated to be 9.43×10-22 cm2 and 1.32×10-22 cm2, respectively. The fluorescence lifetime τexp of 5D4 was fitted to be 1.13 ms. The data suggest that the Tb:Lu2O3 crystal could be a potential candidate for green and yellow laser operation.

Quantum frequency down-conversion of single photons at 1552 nm from single InAs quantum dot

Ben Ma(马奔), Si-Hang Wei(魏思航), Ze-Sheng Chen(陈泽升), Xiang-Jun Shang(尚向军), Hai-Qiao Ni(倪海桥), Zhi-Chuan Niu(牛智川)
Chin. Phys. B, 2018, 27 (9): 097802 doi: 10.1088/1674-1056/27/9/097802
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Near-infrared single photon sources in telecommunication bands, especially at 1550 nm, are required for long-distance quantum communication. Here a down-conversion quantum interface is implemented, where the single photons emitted from single InAs quantum dot at 864 nm is down converted to 1552 nm by using a fiber-coupled periodically poled lithium niobate (PPLN) waveguide and a 1.95 μm pump laser, and the frequency conversion efficiency is~40%. The single-photon purity of quantum dot emission is preserved during the down-conversion process, i.e., g(2)(0), only 0.22 at 1552 nm. This present technique advances the Ⅲ-V semiconductor quantum dots as a promising platform for long-distance quantum communication.


Dynamically tunable terahertz passband filter based on metamaterials integrated with a graphene middle layer

MaoSheng Yang(杨茂生), LanJu Liang(梁兰菊), DeQuan Wei(韦德泉), Zhang Zhang(张璋), Xin Yan(闫昕), Meng Wang(王猛), JianQuan Yao(姚建铨)
Chin. Phys. B, 2018, 27 (9): 098101 doi: 10.1088/1674-1056/27/9/098101
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The dynamic tunability of a terahertz (THz) passband filter was realized by changing the Fermi energy (EF) of graphene based on the sandwiched structure of metal-graphene-metal metamaterials (MGMs). By using plane wave simulation, we demonstrated that the central frequency (f0) of the proposed filter can shift from 5.04 THz to 5.71 THz; this shift is accompanied by a 3 dB bandwidth (Δf) decrease from 1.82 THz to 0.01 THz as the EF increases from 0 to 0.75 eV. Additionally, in order to select a suitable control equation for the proposed filter, the curves of Δf and f0 under different graphene EF were fitted using five different mathematical models. The fitting results demonstrate that the DoseResp model offers accurate predictions of the change in the 3 dB bandwidth, and the Quartic model can successfully describe the variation in the center frequency of the proposed filter. Moreover, the electric field and current density analyses show that the dynamic tuning property of the proposed filter is mainly caused by the competition of two coupling effects at different graphene EF, i.e., graphene-polyimide coupling and graphene-metal coupling. This study shows that the proposed structures are promising for realizing dynamically tunable filters in innovative THz communication systems.

Effect of intramolecular and intermolecular hydrogen bonding on the ESIPT process in DEAHB molecule

Hui Li(李慧), Lina Ma(马丽娜), Hang Yin(尹航), Ying Shi(石英)
Chin. Phys. B, 2018, 27 (9): 098201 doi: 10.1088/1674-1056/27/9/098201
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Density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods are used to investigate the influences of intramolecular and intermolecular hydrogen bonding on excited-state intramolecular proton transfer (ESIPT) for the 4-N,N'-(diethylamino)-2-hydroxybenzaldehyde (DEAHB). The structures of DEAHB and its hydrogen-bonded complex in the ground-state and the excited-state are optimized. In addition, the detailed descriptions of frontier molecular orbitals of the DEAHB monomer and DEAHB-DMSO complex are presented. Moreover, the transition density matrix is worked out to gain deeper insight into the orbitals change. It is hoped that the present work not only elaborates different influence mechanisms between intramolecular and intermolecular hydrogen bonding interactions on the ESIPT process for DEAHB, but also may be helpful to design and develop new materials and applications involved DEAHB systems in the future.

Heavy ion induced upset errors in 90-nm 64 Mb NOR-type floating-gate Flash memory

Jin-Shun Bi(毕津顺), Kai Xi(习凯), Bo Li(李博), Hai-Bin Wang(王海滨), Lan-Long Ji(季兰龙), Jin Li(李金), Ming Liu(刘明)
Chin. Phys. B, 2018, 27 (9): 098501 doi: 10.1088/1674-1056/27/9/098501
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Upset errors in 90-nm 64 Mb NOR-type floating-gate Flash memory induced by accelerated 129Xe and 209Bi ions are investigated in detail. The linear energy transfer covers the range from 50 to 99.8 MeV/(mg/cm2). When the memory chips are powered off during heavy ions irradiation, single-event-latch-up and single-event-function-interruption are excluded, and only 0->1 upset errors in the memory array are observed. These error bit rates seem very difficult to achieve and cannot be simply recovered based on the power cycle. The number of error bits shows a strong dependence on the linear energy transfer (LET). Under room-temperature annealing conditions, the upset errors can be reduced by about two orders of magnitude using rewrite/reprogram operations, but they subsequently increase once again in a few minutes after the power cycle. High-temperature annealing can diminish almost all error bits, which are affected by the lower LET 129Xe ions. The percolation path between the floating-gate (FG) and the substrate contributes to the radiation-induced leakage current, and has been identified as the root cause of the upset errors of the Flash memory array in this work.

Efficiency-enhanced AlGaInP light-emitting diodes using transparent plasmonic silver nanowires

Xia Guo(郭霞), Qiao-Li Liu(刘巧莉), Hui-Jun Tian(田慧军), Chun-Wei Guo(郭春威), Chong Li(李冲), An-Qi Hu(胡安琪), Xiao-Ying He(何晓颖), Hua Wu(武华)
Chin. Phys. B, 2018, 27 (9): 098502 doi: 10.1088/1674-1056/27/9/098502
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Silver nanowire (AgNW) networks have been demonstrated to exhibit superior transparent and conductive performance over that of indium-doped tin oxide (ITO) and have been proposed to replace ITO, which is currently widely used in optoelectronic devices despite the scarcity of indium on Earth. In this paper, the current spreading and enhanced transmittance induced by AgNWs, which are two important factors influencing the light output power, were analyzed. The enhanced transmittance was studied by finite-difference time-domain simulation and verified by cathodoluminescence measurements. The enhancement ratio of the light output power decreased as the GaP layer thickness increased, with enhancement ratio values of 79%, 52%, and 15% for GaP layer thicknesses of 0.5 μ, 1 μ, and 8 μ, respectively, when an AgNW network was included in AlGaInP light-emitting diodes. This was because of the decreased current distribution tunability of the AgNW network with the increase of the GaP layer thickness. The large enhancement of the light output power was caused by the AgNWs increasing carrier spread out of the electrode and the enhanced transmittance induced by the plasmonic AgNWs. Further decreasing the sheet resistance of AgNW networks could raise their light output power enhancement ratio.

Modeling and identification of magnetostrictive hysteresis with a modified rate-independent Prandtl-Ishlinskii model

Wei Wang(王伟), Jun-en Yao(姚骏恩)
Chin. Phys. B, 2018, 27 (9): 098503 doi: 10.1088/1674-1056/27/9/098503
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This paper presents a modified rate-independent Prandtl-Ishlinskii (MRIPI) model based on the Fermi-Dirac distribution for the asymmetric hysteresis description of magnetostrictive actuators. Generally, the classical Prandtl-Ishlinskii (CPI) model can hardly describe the asymmetric hysteresis. To overcome this limitation, various complex operators have been developed to replace the classical operator. In this study, the proposed MRIPI model maintains the classical operator while a modified input function based on the Fermi-Dirac distribution is presented to replace the classical input function. With this method, the MRIPI model can describe the asymmetric hysteresis of magnetostrictive actuators in a relatively simple mathematic format and has fewer parameters to be identified. A velocity-based sine cosine algorithm (VSCA) is also proposed for the parameter identification of the MRIPI model. To verify the validity of the MRIPI model, experiments are performed and the results are compared with those of the existing modeling methods.

Dependence of switching process on the perpendicular magnetic anisotropy constant in P-MTJ

Mao-Sen Yang(杨茂森), Liang Fang(方粮), Ya-Qing Chi(池雅庆)
Chin. Phys. B, 2018, 27 (9): 098504 doi: 10.1088/1674-1056/27/9/098504
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We investigate the dependence of the switching process on the perpendicular magnetic anisotropy (PMA) constant in perpendicular spin transfer torque magnetic tunnel junctions (P-MTJs) using micromagnetic simulations. It is found that the final stable states of the magnetization distribution of the free layer after switching can be divided into three different states based on different PMA constants:vortex, uniform, and steady. Different magnetic states can be attributed to a trade-off among demagnetization, exchange, and PMA energies. The generation of the vortex state is also related to the non-uniform stray field from the polarizer, and the final stable magnetization is sensitive to the PMA constant. The vortex and uniform states have different switching processes, and the switching time of the vortex state is longer than that of the uniform state due to hindrance by the vortex.

Potentials of classical force fields for interactions between Na+ and carbon nanotubes Hot!

De-Yuan Li(李德远), Guo-Sheng Shi(石国升), Feng Hong(洪峰), Hai-Ping Fang(方海平)
Chin. Phys. B, 2018, 27 (9): 098801 doi: 10.1088/1674-1056/27/9/098801
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Carbon nanotubes (CNTs) have long been expected to be excellent nanochannels for use in desalination membranes and other bio-inspired human-made channels owing to their experimentally confirmed ultrafast water flow and theoretically predicted ion rejection. The correct classical force field potential for the interactions between cations and CNTs plays a crucial role in understanding the transport behaviors of ions near and inside the CNT, which is key to these expectations. Here, using density functional theory calculations, we provide classical force field potentials for the interactions of Na+/hydrated Na+ with (7,7), (8,8), (9,9), and (10,10)-type CNTs. These potentials can be directly used in current popular classical software such as nanoscale molecular dynamics (NAMD) by employing the tclBC interface. By incorporating the potential of hydrated cation-π interactions to classical all-atom force fields, we show that the ions will move inside the CNT and accumulate, which will block the water flow in wide CNTs. This blockage of water flow in wide CNTs is consistent with recent experimental observations. These results will be helpful for the understanding and design of desalination membranes, new types of nanofluidic channels, nanosensors, and nanoreactors based on CNT platforms.

Cascading failure in multilayer networks with dynamic dependency groups

Lei Jin(金磊), Xiaojuan Wang(王小娟), Yong Zhang(张勇), Jingwen You(由婧文)
Chin. Phys. B, 2018, 27 (9): 098901 doi: 10.1088/1674-1056/27/9/098901
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The cascading failure often occurs in real networks. It is significant to analyze the cascading failure in the complex network research. The dependency relation can change over time. Therefore, in this study, we investigate the cascading failure in multilayer networks with dynamic dependency groups. We construct a model considering the recovery mechanism. In our model, two effects between layers are defined. Under Effect 1, the dependent nodes in other layers will be disabled as long as one node does not belong to the largest connected component in one layer. Under Effect 2, the dependent nodes in other layers will recover when one node belongs to the largest connected component. The theoretical solution of the largest component is deduced and the simulation results verify our theoretical solution. In the simulation, we analyze the influence factors of the network robustness, including the fraction of dependent nodes and the group size, in our model. It shows that increasing the fraction of dependent nodes and the group size will enhance the network robustness under Effect 1. On the contrary, these will reduce the network robustness under Effect 2. Meanwhile, we find that the tightness of the network connection will affect the robustness of networks. Furthermore, setting the average degree of network as 8 is enough to keep the network robust.


Retraction: Detection of finger interruptions in silicon solar cells using photoluminescence imaging(Chinese Physics B, 2018, Vol. 27, No. 6, 068801)

Lei Zhang(张磊), Peng Liang(梁鹏), Hui-Shi Zhu(朱慧时), Pei-De Han(韩培德)
Chin. Phys. B, 2018, 27 (9): 099901 doi: 10.1088/1674-1056/27/9/099901
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Since publication, it has been brought to the attention of the Editorial Office of Chinese Physics B that parts of this paper showed strong similarities to the following article (including one equation, some analyses, the motivation and the conclusion) without citation:“Detection of Finger Interruptions in Silicon Solar Cells Using Line Scan Photoluminescence Imaging,” IEEE Journal of Photovoltaics, 2017, vol. 7, No. 6, pp. 1496-1502.
Following our investigation, this article has been retracted by the Editorial Office of Chinese Physics B.
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