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Generation of valley pump currents in silicene John Tombe Jada Marcellino, Mei-Juan Wang(王美娟), Sa-Ke Wang(汪萨克) Chin. Phys. B, 2019, 28 (1): 017204.   DOI: 10.1088/1674-1056/28/1/017204 Abstract （348066）   HTML    PDF （433KB）（344777）       Knowledge map    We propose a workable scheme for generating a bulk valley pump current in a silicene-based device which consists of two pumping regions characterized by time-dependent strain and staggered potentials, respectively. In a one-dimension model, we show that a pure valley current can be generated, in which the two valley currents have the same magnitude but flow in opposite directions. Besides, the pumped valley current is quantized and maximized when the Fermi energy of the system locates in the bandgap opened by the two pumping potentials. Furthermore, the valley current can be finely controlled by tuning the device parameters. Our results are useful for the development of valleytronic devices based on two-dimensional materials.

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Spin and valley filter in strain engineered silicene Wang Sa-Ke (汪萨克), Wang Jun (汪军) Chin. Phys. B, 2015, 24 (3): 037202.   DOI: 10.1088/1674-1056/24/3/037202 Abstract （321028）   HTML    PDF （643KB）（318676）       Knowledge map    The realization of a perfect spin or valley filtering effect in two-dimensional graphene-like materials is one of the fundamental objectives in spintronics and valleytronics. For this purpose, we study spin- and valley-dependent transport in a silicene system with spatially alternative strains. It is found that due to the valley-opposite gauge field induced by the strain, the strained silicene with a superlattice structure exhibits an angle-resolved valley and spin filtering effect when the spin-orbit interaction is considered. When the interaction that breaks the time reversal symmetry is introduced, such as the spin or valley dependent staggered magnetization, the system is shown to be a perfect spin and valley half metal in which only one spin and valley species is allowed to transport. Our findings are helpful to design both spintronic and valleytronic devices based on silicene.

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Spin and valley half metal induced by staggered potential and magnetization in silicene Wang Sa-Ke (汪萨克), Tian Hong-Yu (田宏玉), Yang Yong-Hong (杨永宏), Wang Jun (汪军) Chin. Phys. B, 2014, 23 (1): 017203.   DOI: 10.1088/1674-1056/23/1/017203 Abstract （300430）      PDF （639KB）（302725）       Knowledge map    We investigate the electron transport in silicene with both staggered electric potential and magnetization; the latter comes from the magnetic proximity effect by depositing silicene on a magnetic insulator. It is shown that the silicene could be a spin and valley half metal under appropriate parameters when the spin–orbit interaction is considered; further, the filtered spin and valley could be controlled by modulating the staggered potential or magnetization. It is also found that in the spin-valve structure of silicene, not only can the antiparallel magnetization configuration significantly reduce the valve-structure conductance, but the reversing staggered electric potential can cause a high-performance magnetoresistance due to the spin and valley blocking effects. Our findings show that the silicene might be an ideal basis for the spin and valley filter analyzer devices.

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Topological phase in one-dimensional Rashba wire Sa-Ke Wang(汪萨克), Jun Wang(汪军), Jun-Feng Liu(刘军丰) Chin. Phys. B, 2016, 25 (7): 077305.   DOI: 10.1088/1674-1056/25/7/077305 Abstract （202991）   HTML    PDF （397KB）（198507）       Knowledge map    We study the possible topological phase in a one-dimensional (1D) quantum wire with an oscillating Rashba spin-orbital coupling in real space. It is shown that there are a pair of particle-hole symmetric gaps forming in the bulk energy band and fractional boundary states residing in the gap when the system has an inversion symmetry. These states are topologically nontrivial and can be characterized by a quantized Berry phase ±π or nonzero Chern number through dimensional extension. When the Rashba spin-orbital coupling varies slowly with time, the system can pump out 2 charges in a pumping cycle because of the spin flip effect. This quantized pumping is protected by topology and is robust against moderate disorders as long as the disorder strength does not exceed the opened energy gap.

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Efficient collinear frequency tripling of femtosecond laser with compensation of group velocity delay Wang Yan-Ling(王燕玲), Zhou Xu-Gui(周绪桂), Wu Hong(吴洪), and Ding Liang-En(丁良恩) Chin. Phys. B, 2009, 18 (10): 4308-4313.   DOI: 10.1088/1674-1056/18/10/036 Abstract （2161）      PDF （708KB）（98637）       Knowledge map    This paper demonstrates an approach that negative uniaxial crystal has a relative anomalous dispersion effect which can compensate group velocity delay, and applies this approach to nonlinear frequency conversion of an ultrafast laser field. High efficiency of the third harmonic generation is experimentally fulfilled by adopting a collinear configuration of doubing-compensation-tripling system. Through finely adjusting the incident angle and optical axis direction of the compensation plate, it obtains ultraviolet (UV) output energy of 0.32 mJ centered at 270 nm with spectral bandwidth of 2 nm when input beam at 800 nm was 70 fs pulse duration and 6 mJ pulse energy which was extracted from Ti:sapphire laser system by a diaphragm, corresponding to an 800-to-270 nm conversion efficiency of 5.3% and a factor-of-1.6 improvement in the third harmonic generation of UV band in comparison with a general conventional configuration. Furthermore, when the full energy of 18 mJ from a Ti:sapphire laser system was used and optimized, the UV emission could reach 0.83 mJ.

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Compression of the self-Q-switching in semiconductor disk lasers with single-layer graphene saturable absorbers Yu Zhen-Hua (于振华), Tian Jin-Rong (田金荣), Song Yan-Rong (宋晏蓉) Chin. Phys. B, 2014, 23 (9): 094206.   DOI: 10.1088/1674-1056/23/9/094206 Abstract （5065）      PDF （2034KB）（83601）       Knowledge map    We demonstrate the first use of single layer graphene for compressing self-Q-switching pulses in semiconductor disk lasers. The gain region of the semiconductor disk laser used InGaAs quantum wells with a central wavelength of 1030 nm. Due to self saturable absorption of the quantum wells, the disk laser emitted at the self-Q-switching state with a pulse width of 13 μs. By introducing the single layer graphene as a saturable absorber into the V-shaped laser cavity, the pulse width of the self-pulse was compressed to 2 μs with a lower pump power of 300 mW. As the pump power was increased, multiple pulses with the pulse width of 1.8 μs appeared. The compression factor was about 7.2.

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High performance pentacene organic field-effect transistors consisting of biocompatible PMMA/silk fibroin bilayer dielectric Li Hai-Qiang (李海强), Yu Jun-Sheng (于军胜), Huang Wei (黄伟), Shi Wei (施薇), Huang Jiang (黄江) Chin. Phys. B, 2014, 23 (3): 038505.   DOI: 10.1088/1674-1056/23/3/038505 Abstract （1032）      PDF （492KB）（62458）       Knowledge map    Pentacene organic field-effect transistors (OFETs) based on single-or double-layer biocompatible dielectrics of poly(methyl methacrylate) (PMMA) and/or silk fibroin (SF) are fabricated. Compared with those devices based on single PMMA or SF dielectric or SF/PMMA bilayer dielectric, the OFETs with biocompatible PMMA/SF bilayer dielectric exhibit optimal performance with a high field-effect mobility of 0.21 cm2/Vs and a current on/off ratio of 1.5×104. By investigating the surface morphology of the pentacene active layer through atom force microscopy and analyzing the electrical properties, the performance enhancement is mainly attributed to the crystallization improvement of the pentacene and the smaller interface trap density at the dielectric/organic interface. Meanwhile, a low contact resistance also indicates that a good electrode/organic contact is formed, thereby assisting the performance improvement of the OFET.

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Coherence transfer from 1064 nm to 578 nm using an optically referenced frequency comb Fang Su (方苏), Jiang Yan-Yi (蒋燕义), Chen Hai-Qin (陈海琴), Yao Yuan (姚远), Bi Zhi-Yi (毕志毅), Ma Long-Sheng (马龙生) Chin. Phys. B, 2015, 24 (7): 074202.   DOI: 10.1088/1674-1056/24/7/074202 Abstract （1165）   HTML    PDF （487KB）（62254）       Knowledge map    A laser at 578 nm is phase-locked to an optical frequency comb (OFC) which is optically referenced to a subhertz-linewidth laser at 1064 nm. Coherence is transferred from 1064 nm to 578 nm via the OFC. By comparing with a cavity-stabilized laser at 578 nm, the absolute linewidth of 1.1 Hz and the fractional frequency instability of 1.3× 10-15 at an averaging time of 1 s for each laser at 578 nm have been determined, which is limited by the performance of the reference laser for the OFC.

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A population-level model from the microscopic dynamics in Escherichia coli chemotaxis via Langevin approximation He Zhuo-Ran (贺卓然), Wu Tai-Lin (吴泰霖), Ouyang Qi (欧阳颀), Tu Yu-Hai (涂豫海) Chin. Phys. B, 2012, 21 (9): 098701.   DOI: 10.1088/1674-1056/21/9/098701 Abstract （1437）      PDF （7039KB）（48756）       Knowledge map    Recent extensive studies of Escherichia coli (E. coli) chemotaxis have achieved a deep understanding of its microscopic control dynamics. As a result, various quantitatively predictive models have been developed to describe the chemotactic behavior of E. coli motion. However, a population-level partial differential equation (PDE) that rationally incorporates such microscopic dynamics is still insufficient. Apart from the traditional Keller-Segel (K-S) equation, many existing population-level models developed from the microscopic dynamics are integro-PDEs. The difficulty comes mainly from cell tumbles which yield a velocity jumping process. Here, we propose a Langevin approximation method that avoids such a difficulty without appreciable loss of precision. The resulting model not only quantitatively reproduces the results of pathway-based single-cell simulators, but also provides new inside information on the mechanism of E. coli chemotaxis. Our study demonstrates a possible alternative in establishing a simple population-level model that allows for the complex microscopic mechanisms in bacterial chemotaxis.

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Effect of following strength on pedestrian counter flow Kuang Hua (邝华), Li Xing-Li (李兴莉), Wei Yan-Fang (韦艳芳), Song Tao (宋涛), Dai Shi-Qiang (戴世强) Chin. Phys. B, 2010, 19 (7): 070517.   DOI: 10.1088/1674-1056/19/7/070517 Abstract （1825）      PDF （2420KB）（42272）       Knowledge map    This paper proposes a modified lattice gas model to simulate pedestrian counter flow by considering the effect of following strength which can lead to appropriate responses to some complicated situations. Periodic and open boundary conditions are adopted respectively. The simulation results show that the presented model can reproduce some essential features of pedestrian counter flows, e.g., the lane formation and segregation effect. The fundamental diagrams show that the complete jamming density is independent of the system size only when the width W and the length L are larger than some critical values respectively, and the larger asymmetrical conditions can better avoid the occurrence of deadlock phenomena. For the mixed pedestrian flow, it can be found that the jamming cluster is mainly caused by those walkers breaking the traffic rules, and the underlying mechanism is analysed. Furthermore, the comparison of simulation results and the experimental data is performed, it is shown that this modified model is reasonable and more realistic to simulate and analyse pedestrian counter flow.

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Nanoscale guiding for cold atoms based on surface plasmons alongtips of metallic wedges Wang Zheng-Ling (王正岭), Tang Wei-Min (唐伟民), Zhou Ming (周明), Gao Chuan-Yu (高传玉) Chin. Phys. B, 2013, 22 (7): 073701.   DOI: 10.1088/1674-1056/22/7/073701 Abstract （758）      PDF （2707KB）（41342）       Knowledge map    We propose a novel scheme to guide neutral cold atoms in a nanoscale region based on surface plasmons (SPs) of one pair and two pairs of tips of metallic wedges with locally enhanced light intensity and sub-optical wavelength resolution. We analyze the near-field intensity distribution of the tip of the metallic wedge by the FDTD method, and study the total intensity as well as the total potential of optical potentials and van der Waals potentials for 87Rb atoms in the light field of one pair and two pairs of tips of metallic wedges. It shows that the total potentials of one pair and two pairs of tips of metallic wedges can generate a gravito-optical trap and a dark closed trap for nanoscale guiding of neutral cold atoms. Guided atoms can be cooled with efficient intensity-gradient Sisyphus cooling by blue-detuned light field. This provides an important step towards the generation of hybrid systems consisting of isolated atoms and solid devices.

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Kink effect in current–voltage characteristics of a GaN-based high electron mobility transistor with an AlGaN back barrier Ma Xiao-Hua (马晓华), Lü Min (吕敏), Pang Lei (庞磊), Jiang Yuan-Qi (姜元祺), Yang Jing-Zhi (杨靖治), Chen Wei-Wei (陈伟伟), Liu Xin-Yu (刘新宇) Chin. Phys. B, 2014, 23 (2): 027302.   DOI: 10.1088/1674-1056/23/2/027302 Abstract （892）      PDF （409KB）（33831）       Knowledge map    The kink effect in current–voltage (IV) characteristic s seriously deteriorates the performance of a GaN-based HEMT. Based on a series of direct current (DC) IV measurements in a GaN-based HEMT with an AlGaN back barrier, a possible mechanism with electron-trapping and detrapping processes is proposed. Kink-related deep levels are activated by a high drain source voltage (Vds) and located in a GaN channel layer. Both electron trapping and detrapping processes are accomplished with the help of hot electrons from the channel by impact ionization. Moreover, the mechanism is verified by two other DC IV measurements and a model with an expression of the kink current.

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Conservation laws of the generalized short pulse equation Zhang Zhi-Yong (张智勇), Chen Yu-Fu (陈玉福) Chin. Phys. B, 2015, 24 (2): 020201.   DOI: 10.1088/1674-1056/24/2/020201 Abstract （1165）   HTML    PDF （192KB）（28385）       Knowledge map    We show that the generalized short pulse equation is nonlinearly self-adjoint with differential substitution. Moreover, any adjoint symmetry is a differential substitution of nonlinear self-adjointness, and vice versa. Consequently, the general conservation law formula is constructed and new conservation laws for some special cases are found.

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The consistent Riccati expansion and new interaction solution for a Boussinesq-type coupled system Ruan Shao-Qing (阮少卿), Yu Wei-Feng (余炜沣), Yu Jun (俞军), Yu Guo-Xiang (余国祥) Chin. Phys. B, 2015, 24 (6): 060201.   DOI: 10.1088/1674-1056/24/6/060201 Abstract （1001）   HTML    PDF （271KB）（26080）       Knowledge map    Starting from the Davey–Stewartson equation, a Boussinesq-type coupled equation system is obtained by using a variable separation approach. For the Boussinesq-type coupled equation system, its consistent Riccati expansion (CRE) solvability is studied with the help of a Riccati equation. It is significant that the soliton–cnoidal wave interaction solution, expressed explicitly by Jacobi elliptic functions and the third type of incomplete elliptic integral, of the system is also given.

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Analysis of the breakdown mechanism for an ultra high voltage high-side thin layer silicon-on-insulator p-channel lateral double-diffused metal oxide semiconductor Zhuang Xiang(庄翔), Qiao Ming(乔明), Zhang Bo(张波), and Li Zhao-Ji(李肇基) Chin. Phys. B, 2012, 21 (3): 037305.   DOI: 10.1088/1674-1056/21/3/037305 Abstract （1246）      PDF （1679KB）（24149）       Knowledge map    This paper discusses the breakdown mechanism and proposes a new simulation and test method of breakdown voltage (BV) for an ultra-high-voltage (UHV) high-side thin layer silicon-on-insulator (SOI) p-channel lateral double-di?used metal oxide semiconductor (LDMOS). Compared with the conventional simulation method, the new one is more accordant with the actual conditions of a device that can be used in the high voltage circuit. The BV of the SOI p-channel LDMOS can be properly represented and the effect of reduced bulk field can be revealed by employing the new simulation method. Simulation results show that the off-state (on-state) BV of the SOI p-channel LDMOS can reach 741 (620) V in the 3-μm-thick buried oxide layer, 50-μm-length drift region, and at -400 V back-gate voltage, enabling the device to be used in a 400 V UHV integrated circuit.

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Adsorption of sodium ions and hydrated sodium ions on a hydrophobic graphite surface via cation-$\pi$ interactions Shi Guo-Sheng(石国升), Wang Zhi-Gang(王志刚), Zhao Ji-Jun(赵纪军), Hu Jun(胡钧), and Fang Hai-Ping(方海平) Chin. Phys. B, 2011, 20 (6): 068101.   DOI: 10.1088/1674-1056/20/6/068101 Abstract （1840）      PDF （3011KB）（22810）       Knowledge map    Using density functional theory computation, we show that sodium ions and hydrated sodium ions can be strongly adsorbed onto a hydrophobic graphite surface via cation-$\pi$ interactions. The key to this cation-π interaction is the coupling of the delocalized $\pi$ states of graphite and the empty orbitals of sodium ions. This finding implies that the property of the graphite surface is extremely dependent on the existence of the ions on the surface, suggesting that the hydrophobic property of the graphite surface may be affected by the existence of the sodium ions.

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Transfer function modeling and analysis of the open-loop Buck converter using the fractional calculus Wang Fa-Qiang (王发强), Ma Xi-Kui (马西奎) Chin. Phys. B, 2013, 22 (3): 030506.   DOI: 10.1088/1674-1056/22/3/030506 Abstract （1347）      PDF （457KB）（21912）       Knowledge map    Based on the fact that the real inductor and the real capacitor are fractional order in nature and the fractional calculus, the transfer function modeling and analysis of the open-loop Buck converter in continuous conduction mode (CCM) operation are carried out in this paper. The fractional order small signal model and the corresponding equivalent circuit of the open-loop Buck converter in CCM operation are presented. The transfer functions from the input voltage to the output voltage, from the input voltage to the inductor current, from the duty cycle to the output voltage, from the duty cycle to the inductor current, and the output impedance of the open-loop Buck converter in CCM operation are derived, and their bode diagrams and step responses are calculated, respectively. It is found that all the derived fractional order transfer functions of the system are influenced by the fractional orders of the inductor and the capacitor. Finally, the realization of the fractional order inductor and the fractional order capacitor is designed, and the corresponding PSIM circuit simulation results of the open-loop Buck converter in CCM operation are given to confirm the correctness of the derivations and the theoretical analysis.

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Adaptive backstepping control of the uncertain Lü system Yu Yong-Guang (于永光), Zhang Suo-Chun (张锁春) Chinese Physics, 2002, 11 (12): 1249-1253.   DOI: 10.1088/1009-1963/11/12/306 Abstract （1180）      PDF （232KB）（17587）       Knowledge map    In this paper we investigate further the method for controlling the uncertain Lü system via adaptive backstepping. The Lü system is transformed into the so-called general strict-feedback form. Then a novel control method is designed for controlling the uncertain Lü system. Especially, this method can overcome the singularity problem. Numerical simulations show the effectiveness and feasibility of this approach.

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Silicon nanoparticles：Preparation, properties, and applications Chang Huan (常欢), Sun Shu-Qing (孙树清) Chin. Phys. B, 2014, 23 (8): 088102.   DOI: 10.1088/1674-1056/23/8/088102 Abstract （793）      PDF （2101KB）（15671）       Knowledge map    Silicon nanoparticles have attracted great attention in the past decades because of their intriguing physical properties, active surface state, distinctive photoluminescence and biocompatibility. In this review, we present some of the recent progress in preparation methodologies and surface functionalization approaches of silicon nanoparticles. Further, their promising applications in the fields of energy and electronic engineering are introduced.

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Magnetic iron oxide nanoparticles：Synthesis and surface coating techniques for biomedical applications Sun Sheng-Nan (孙圣男), Wei Chao (魏超), Zhu Zan-Zan (朱赞赞), Hou Yang-Long (侯仰龙), Subbu S Venkatraman, Xu Zhi-Chuan (徐梽川) Chin. Phys. B, 2014, 23 (3): 037503.   DOI: 10.1088/1674-1056/23/3/037503 Abstract （2033）      PDF （4676KB）（15310）       Knowledge map    Iron oxide nanoparticles are the most popular magnetic nanoparticles used in biomedical applications due to their low cost, low toxicity, and unique magnetic property. Magnetic iron oxide nanoparticles, including magnetite (Fe3O4) and maghemite (γ-Fe2O3), usually exhibit a superparamagnetic property as their size goes smaller than 20 nm, which are often denoted as superparamagnetic iron oxide nanoparticles (SPIONs) and utilized for drug delivery, diagnosis, therapy, and etc. This review article gives a brief introduction on magnetic iron oxide nanoparticles in terms of their fundamentals of magnetism, magnetic resonance imaging (MRI), and drug delivery, as well as the synthesis approaches, surface coating, and application examples from recent key literatures. Because the quality and surface chemistry play important roles in biomedical applications, our review focuses on the synthesis approaches and surface modifications of iron oxide nanoparticles. We aim to provide a detailed introduction to readers who are new to this field, helping them to choose suitable synthesis methods and to optimize the surface chemistry of iron oxide nanoparticles for their interests. Cited: Web of science (68)