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Chin. Phys. Lett.  
  Chin. Phys. Lett.--2015, 32 (1)   Published: 23 December 2014
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GENERAL

Determining Separability with Entanglement of Formation and Entanglement Sudden Death

CHEN Xiao-Yu
Chin. Phys. Lett. 2015, 32 (1): 010301 doi: 10.1088/0256-307X/32/1/010301
Full Text: [PDF 445 KB] (205)
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An algorithm is developed to calculate the entanglement of formation for bipartite quantum states to determine numerically the sufficient condition of separability. The algorithm is applied to two 3×3 positive partial transpose states mixed with white noise. For these two noisy states, our numerical sufficient conditions of separability are not far from the best necessary conditions of separability.

Subdiffusion of Dipolar Gas in One-Dimensional Quasiperiodic Potentials

BAI Xiao-Dong, XUE Ju-Kui
Chin. Phys. Lett. 2015, 32 (1): 010302 doi: 10.1088/0256-307X/32/1/010302
Full Text: [PDF 1151 KB] (106)
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Considering the discrete nonlinear Schrödinger model with dipole-dipole interactions (DDIs), we comparatively and numerically study the effects of contact interaction, DDI and disorder on the properties of diffusion of dipolar condensate in one-dimensional quasi-periodic potentials. Due to the coupled effects of the contact interaction and the DDI, some new and interesting mechanisms are found: both the DDI and the contact interaction can destroy localization and lead to a subdiffusive growth of the second moment of the wave packet. However, compared with the contact interaction, the effect of DDI on the subdiffusion is stronger. Furthermore and interestingly, we find that when the contact interaction (λ1) and DDI (λ2) satisfy λ1≳2λ2, the property of the subdiffusion depends only on contact interaction; when λ1≲2λ2, the property of the subdiffusion is completely determined by DDI. Remarkably, we numerically give the critical value of disorder strength v* for different values of contact interaction and DDI. When the disorder strength v≥v*, the wave packet is localized. On the contrary, when the disorder strength v≤v*, the wave packet is subdiffusive.

Effect of the Minimal Length on Bose–Einstein Condensation in the Relativistic Ideal Bose Gas

ZHANG Xiu-Ming, TIAN Chi
Chin. Phys. Lett. 2015, 32 (1): 010303 doi: 10.1088/0256-307X/32/1/010303
Full Text: [PDF 490 KB] (57)
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Based on the generalized uncertainty principle (GUP), the critical temperature and the Helmholtz free energy of Bose–Einstein condensation (BEC) in the relativistic ideal Bose gas are investigated. At the non-relativistic limit and the ultra-relativistic limit, we calculate the analytical form of the shifts of the critical temperature and the Helmholtz free energy caused by weak quantum gravitational effects. The exact numerical results of these shifts are obtained. Quantum gravity effects lift the critical temperature of BEC. By measuring the shift of the critical temperature, we can constrain the deformation parameter β0. Furthermore, at lower densities, omitting quantum gravitational effects may lead to a metastable state while at sufficiently high densities, quantum gravitational effects tend to make BEC unstable. Using the numerical methods, the stable-unstable transition temperature is found.

Is the High-Frequency Signal Necessary for the Resonance in the Delayed System?

LV Mei-Lei, SHEN Gang, WANG Hai-Lun, YANG Jian-Hua
Chin. Phys. Lett. 2015, 32 (1): 010501 doi: 10.1088/0256-307X/32/1/010501
Full Text: [PDF 2379 KB] (65)
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In a delayed system excited by low-frequency and high-frequency signals, the necessity of the high-frequency signal on the resonance is discussed. By adjusting the delay time, the resonance occurs in a wide scope of frequencies, including the primary, subharmonic and superharmonic frequencies. Only for very few cases does the high-frequency signal have a positive effect on the resonance. It is the traditional vibrational resonance phenomenon. In most situations, the high-frequency excitation is unnecessary for the resonance. An appropriate delay, rather than the high-frequency signal, is the key factor in improving the weak low-frequency signal.

Change of State of a Dynamical Unit in the Transition of Coherence

YANG Yan-Jin, DU Ru-Hai, WANG Sheng-Jun, JIN Tao, QU Shi-Xian
Chin. Phys. Lett. 2015, 32 (1): 010502 doi: 10.1088/0256-307X/32/1/010502
Full Text: [PDF 576 KB] (62)
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The change of state of one map in the network of nonlocal coupled logistic maps at the transition of coherence is studied. With the increase of coupling strength, the network dynamics transits from the incoherent state into the coherent state. In the process, the iteration of the map first changes from chaos to period state, then from periodic to chaotic state again. For the periodic doubling bifurcations, similar to an isolated map, the largest Lyapunov exponent tends to zero from a negative value. However, the states of coupled maps exhibit complex behavior rather than converge to a few fixed values. The behavior brings a new chimera state of coupled logistic maps. The bifurcation diagram is identical to the phase order of maps iterations. For the bifurcation between 1-band and multi-band chaos, the symmetry of chaotic bands emerges and the transition of the order of iteration direction occurs.

An Analytical Study on the Synchronization of Murali–Lakshmanan–Chua Circuits

G. Sivaganesh
Chin. Phys. Lett. 2015, 32 (1): 010503 doi: 10.1088/0256-307X/32/1/010503
Full Text: [PDF 696 KB] (60)
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An explicit analytical solution is presented for unidirectionally coupled two Murali–Lakshmanan–Chua circuits exhibiting chaos synchronization in their dynamics. The transition of the system from an unsynchronized state to a state of complete synchronization under the influence of the coupling parameter is observed through phase portraits obtained from the analytical solutions of the circuit equations characterizing the system.

Dick Effect in a Microwave Frequency Standard Based on Laser-Cooled 113Cd+ Ions

ZHANG Jian-Wei, MIAO Kai, WANG Li-Jun
Chin. Phys. Lett. 2015, 32 (1): 010601 doi: 10.1088/0256-307X/32/1/010601
Full Text: [PDF 547 KB] (51)
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The Dick effect is one of the main limits to the frequency stability of a passive frequency standard, especially for the fountain clock and ion clock operated in pulsed mode which require unavoidable dead time during interrogation. Here we measure the phase noise of the interrogation oscillator applied in the microwave frequency standard based on laser-cooled 113Cd+ ions, and analyze the Allan deviation limited by the Dick effect. The results indicate that the Dick effect is one of the key issues for the cadmium ion clock to reach expected frequency stability. This problem can be resolved by interrogating the local oscillator continuously with two ion traps.
NUCLEAR PHYSICS

Experimental Study of Beta-Delayed Proton Emission of 36,37Ca

SUN Li-Jie, LIN Cheng-Jian, XU Xin-Xing, WANG Jian-Song, JIA Hui-Ming, YANG Feng, YANG Yan-Yun, YANG Lei, BAO Peng-Fei, ZHANG Huan-Qiao, JIN Shi-Lun, WU Zhen-Dong, ZHANG Ning-Tao, CHEN Si-Ze, MA Jun-Bing, MA Peng, MA Nan-Ru, LIU Zu-Hua
Chin. Phys. Lett. 2015, 32 (1): 012301 doi: 10.1088/0256-307X/32/1/012301
Full Text: [PDF 732 KB] (52)
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The investigation of beta-delayed proton decay mode has become a powerful probe to study the proton-rich nuclei and their nuclear structure. To study exotic nuclei with extremely low purity produced by the Radioactive Ion Beam Line in Lanzhou, we perform an experiment of beta-delayed proton emission of 36,37Ca under a high-intensity continuous-beam mode. Ions are implanted into a double-sided silicon strip detector, where the subsequent decays are correlated to the preceding implantations in time sequence. The energy spectra of delayed protons from 36,37Caβ decay, half-lives and decay branching ratios are measured. The experimental results confirm the previous literature data and some improved results are obtained as well, demonstrating the feasibility of our detection approach and the reliability of our data analysis procedure. This allows for the development of more powerful detection arrays and further research on nuclei closer to proton-drip line on the basis of present work.
ATOMIC AND MOLECULAR PHYSICS

A New Reaction Path for the C+NO→CN+O Reaction: Effect of Reagent Rotation on the Stereodynamics on the 4A" Potential-Energy Surface

WEI Qiang
Chin. Phys. Lett. 2015, 32 (1): 013101 doi: 10.1088/0256-307X/32/1/013101
Full Text: [PDF 589 KB] (25)
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The stereodynamics of the C+NO reaction is investigated at 0.06 eV by means of the quasi-classical trajectory method on a recent ab initio 4A" potential energy surface (PES). The influences of rotation excitation (j=0–3) on stereodynamics are discussed. The obtained stereodynamical information is compared with the previously reported results on the 2A' and 2A" PESs to give a full insight into the chemical stereodynamics of the title reaction.

Spectra of 42S1/2→32D5/2 Transitions of a Single Trapped 40Ca+ Ion

GONG Shi-Jie, ZHOU Fei, WU Hao-Yu, WAN Wei, CHEN Liang, FENG Mang
Chin. Phys. Lett. 2015, 32 (1): 013201 doi: 10.1088/0256-307X/32/1/013201
Full Text: [PDF 583 KB] (36)
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We investigate the spectra of the electric quadrupole 42S1/2→32D5/2 transitions in a single 40Ca+ ion confined in a home-built linear trap. We probe the transitions with an ultra-narrow bandwidth laser at 729 nm. In a weak magnetic field, the quadrupole transition splits into ten components with the maximal line strength proportional to their squared Clebsch–Gordan factors. In a magnetic field of the order of Gauss, the observed equidistant sideband reflects the Zeeman substructure modulated by the quantized oscillation due to the secular motion in the trap. The temperature of the trapped ion can be determined by the envelope of the sideband spectrum. We also demonstrate the Rabi oscillation in a carrier transition after the ion has been Doppler cooled, which can be fitted by the model with the thermal state of motion.

Quantum Path Selection and Isolated-Attosecond-Pulse Generation of H2+ with an Intense Laser Pulse and a Static Field

MIAO Xiang-Yang, LIU Sha-Sha
Chin. Phys. Lett. 2015, 32 (1): 013301 doi: 10.1088/0256-307X/32/1/013301
Full Text: [PDF 1474 KB] (41)
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We theoretically investigate the high-order-harmonic generation from the H2+ molecular ion exposed to the combination of an intense trapezoidal laser and a static field. The results show that the harmonic spectrum is obviously extended and the short quantum path is selected to contribute to the spectrum, because the corresponding long path is seriously suppressed. Then the combined Coulomb and laser field potentials and the time-dependent electron wave packet distributions are applied to illustrate the physical mechanism of high-order harmonic generation. Finally, by adjusting the intensity of the static field and superposing a properly selected range of the HHG spectrum, a 90-as isolated attosecond pulse is straightforwardly obtained.
FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)

Exact Evolution of Ultrashort Hollow-Airy Pulses in the Spatiotemporal Domain

ZHANG Jing-Fang, WANG Zhao-Ying, LIN Qiang
Chin. Phys. Lett. 2015, 32 (1): 014201 doi: 10.1088/0256-307X/32/1/014201
Full Text: [PDF 1809 KB] (55)
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An exact analytic expression for an ultrashort hollow-Airy wave packet is presented beyond the slowly varying envelope approximation. The hollow-Airy wave packet combines the hollow-Gaussian beam in the spatial domain and the Airy pulse in the temporal domain. The spatiotemporal propagation dynamics of the ultrashort hollow-Airy pulse are analyzed by the numerical simulations. During the propagation in free space, the spatial intensity profile evolves from hollow-Gaussian to Gaussian shape; the temporal intensity profile retains Airy shape over several Rayleigh ranges. The acceleration property of the ultrashort Airy pulse is also demonstrated.

Experimental Detection of Depth of Field for a Thermal Light Lensless Ghost Imaging System

GAO Lu, TIAN Jia, LIN Hai-Long
Chin. Phys. Lett. 2015, 32 (1): 014202 doi: 10.1088/0256-307X/32/1/014202
Full Text: [PDF 6220 KB] (56)
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We propose optical experiments to study the depth of field for a thermal light lensless ghost imaging system. It is proved that the diaphragm is an important factor to influence the depth of field, and the ghost images of two detected objects with longitudinal distance less than the depth of field can be achieved simultaneously. The longitudinal coherence scale of the thermal light lensless ghost imaging determines the depth of field. Theoretical analysis can well explain the experimental results.

Efficient Diode-Pumped Actively Q-Switched Ceramic Nd:YAG/YVO4 Raman Laser Operating at 1657 nm

ZHANG Hua-Nian, CHEN Xiao-Han, WANG Qing-Pu, LI Ping
Chin. Phys. Lett. 2015, 32 (1): 014203 doi: 10.1088/0256-307X/32/1/014203
Full Text: [PDF 555 KB] (28)
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A diode-pumped actively Q-switched Raman laser is demonstrated, with YVO4 employed as Raman active medium, based on a ceramic Nd:YAG laser operating at 1444 nm. The first-stokes Raman generation at 1657 nm is achieved. A maximum output power of as high as 612 mW is obtained under a pump power of 20.7 W and at a pulse repetition frequency rate of 20 kHz, corresponding to an optical-to-optical conversion efficiency of 3%.

Mode-Locked Thulium Ytterbium Co-Doped Fiber Laser with Graphene Oxide Paper Saturable Absorber

S. M. Azooz, S. W. Harun, H. Ahmad, A. Halder, M. C. Paul, M.Pal, S. K. Bhadra
Chin. Phys. Lett. 2015, 32 (1): 014204 doi: 10.1088/0256-307X/32/1/014204
Full Text: [PDF 496 KB] (81)
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A mode-locked thulium ytterbium co-doped fiber laser (TYDFL) is proposed and demonstrated by using a commercial graphene oxide (GO) paper as saturable absorber (SA). The GO paper is sandwiched between two fiber ferrules and incorporates a ring laser cavity to generate soliton pulse train operating at 1942.0 nm at a threshold multimode pump power as low as 1.8 W. The mode-locked TYDFL has a repetition rate of 22.32 MHz and the calculated pulse width of 1.1 ns. Even though the SA has a low damage threshold, the easy fabrication of GO paper should promote its potential application in ultrafast photonics.

Accelerating Generalized Polygon Beams and Their Propagation

ZHANG Yun-Tian, ZHANG Zhi-Gang, CHENG Teng, ZHANG Qing-Chuan, WU Xiao-Ping
Chin. Phys. Lett. 2015, 32 (1): 014205 doi: 10.1088/0256-307X/32/1/014205
Full Text: [PDF 10021 KB] (23)
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Accelerating beams with intensity cusps and exotic topological properties are drawing increasing attention as they have extensive uses in many intriguing fields. We investigate the structural features of accelerating polygon beams, show their generalized mathematical form theoretically, and discuss the even-numbered polygon beams. Furthermore, we also carry out the experiment and observe the intensity evolution during their propagation.

Observation of Self-Frequency Doubling in Diode-Pumped Mode-Locked Nd-Doped La3Ga5SiO14 Laser

LIU Jia-Xing, WANG Zhao-Hua, TIAN Wen-Long, WANG Qing, ZHANG Zhi-Guo, WEI Zhi-Yi, YU Hao-Hai, ZHANG Huai-Jin, WANG Ji-Yang
Chin. Phys. Lett. 2015, 32 (1): 014206 doi: 10.1088/0256-307X/32/1/014206
Full Text: [PDF 574 KB] (23)
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A diode-pumped passively mode-locked Nd-doped La3Ga5SiO14 (Nd:LGS) laser is realized by using a semiconductor saturable absorber mirror. With the pump power of 2 W, we obtain a 532 nm self-frequency doubling (SFD) laser together with a 10.9 ps fundamental laser at the repetition rate of 173.7 MHz. To the best of our knowledge, it is the first time for self-frequency doubling in the diode-pumped mode-locked Nd:LGS laser. Benefited from the diode lasers and its self-frequency doubling property, Nd:LGS could be a potential candidate for compact, stable and cheap ultrafast green laser sources.

Visibility and Resolution Enhancement of Fourth-Order Ghost Interference with Thermal Light

WEN Feng, ZHANG Xun, YUAN Chen-Zhi, LI Chang-Biao, WANG Jing-Da, ZHANG Yan-Peng
Chin. Phys. Lett. 2015, 32 (1): 014207 doi: 10.1088/0256-307X/32/1/014207
Full Text: [PDF 546 KB] (42)
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A scheme for fourth-order double-slit ghost interference with a pseudo-thermal light source is proposed. It is shown that not only can the visibility be dramatically enhanced compared to the third-order case, but also higher resolution is demonstrated if we scan two of three reference detectors in opposite directions with the same speed, meanwhile another two in identical directions where the speed of one reference detector is twice the other. The results show that the visibility and resolution improvement of the fourth-order ghost interference fringe can be applied to the Nth-order ghost imaging.

Junction-Temperature Measurement in InAs/InP(100) Quantum-Dot Lasers

LI Shi-Guo, GONG Qian, CAO Chun-Fang, WANG Xin-Zhong, YAN Jin-Yi, WANG Hai-Long
Chin. Phys. Lett. 2015, 32 (1): 014208 doi: 10.1088/0256-307X/32/1/014208
Full Text: [PDF 697 KB] (33)
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We report on the measurement of junction temperature of the InAs/InP(100) quantum dot lasers working in the 1.55 μm wavelength region. The measurement is based on analyzing the temperature induced mode shift of the Fabry–Perot cavity. Under pulsed operation mode, more than 20°C junction temperature rise is measured for the quantum-dot (QD) laser when the duty cycle is increased from 1% to 95%. For a reference quantum well laser, the junction temperature rise is obtained as only around 3°C. The large junction temperature rise might be a crucial factor to improve the performance of QD lasers.

Thermal Analysis of Implant-Defined Vertical Cavity Surface Emitting Laser Array

XUN Meng, XU Chen, XIE Yi-Yang, DENG Jun, XU Kun, CHEN Hong-Da
Chin. Phys. Lett. 2015, 32 (1): 014209 doi: 10.1088/0256-307X/32/1/014209
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A three-dimensional electrical-thermal coupling model based on the finite element method is applied to study thermal properties of implant-defined vertical cavity surface emitting laser (VCSEL) arrays. Several parameters including inter-element spacing, scales, injected current density and substrate temperature are considered. The actual temperatures obtained through experiment are in excellent agreement with the calculated results, which proves the accuracy of the model. Due to the serious thermal problem, it is essential to design arrays of low self-heating. The analysis can provide a foundation for designing VCSEL arrays in the future.

Synthesis of Multi-Color Long Laser Pulses for Strong Attosecond Pulse Generation

LI Fei, WANG Guo-Li, ZHAO Song-Feng, ZHOU Xiao-Xin
Chin. Phys. Lett. 2015, 32 (1): 014210 doi: 10.1088/0256-307X/32/1/014210
Full Text: [PDF 800 KB] (47)
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We theoretically investigate the high-order harmonics and attosecond pulses generated in a single mid-infrared and synthesized two- and three-color fields. We demonstrate that one can obtain a sub-cycle field by combining two or more long pulses at incommensurate frequencies, if the phases and amplitudes of each field are properly optimized. Compared with the one-color field, the harmonic yields in synthesized fields can be enhanced more than two orders with the same total laser power. The technique of waveform synthesizing shows the possibility of generating intense single attosecond pulses by using longer driving laser pulses without the need of gating techniques with experiment.

Design and Optimization of Omnidirectional Band Gap for One-Dimensional Periodic and Quasiperiodic Phononic Heterostructures

CHEN Zhao-Jiang
Chin. Phys. Lett. 2015, 32 (1): 014301 doi: 10.1088/0256-307X/32/1/014301
Full Text: [PDF 608 KB] (39)
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A new kind of one-dimensional multilayer phononic heterostructure is constructed to obtain a broad acoustic omnidirectional reflection (ODR) band. The heterostructure is formed by combining finite periodic phononic crystals (PnCs) and Fibonacci (or Thue–Morse) quasiperiodic PnCs. From the numerical results performed by the transfer matrix method, it is found that the ODR bands can be enlarged obviously by using the combination of periodic and quasi-periodic PnCs. Moreover, an application of particle swarm optimization in designing and optimizing acoustic ODR bands is reported. With regards to different thickness ratios and periodic numbers in the heterostructure, we give some optimization examples and finally achieve phononic heterostructure with a very broad ODR bandwidth. The result provides a new approach to achieve broad acoustic ODR bandwidth, and will be applied in design of omnidirectional acoustic mirrors.

Sound Absorption Enhancement by Thin Multi-Slit Hybrid Structures

REN Shu-Wei, MENG Han, XIN Feng-Xian, LU Tian-Jian
Chin. Phys. Lett. 2015, 32 (1): 014302 doi: 10.1088/0256-307X/32/1/014302
Full Text: [PDF 1014 KB] (29)
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We report an extraordinary sound absorption enhancement in low and intermediate frequencies achieved by a thin multi-slit hybrid structure formed by incorporating micrometer scale micro-slits into a sub-millimeter scale meso-slit matrix. Theoretical and numerical results reveal that this exotic phenomenon is attributed to the noticeable velocity and temperature gradients induced at the junctures of the micro- and meso-slits, which cause significant loss of sound energy as a result of viscous and thermal effects. It is demonstrated that the proposed thin multi-slit hybrid structure with micro-scale configuration is capable of controling low frequency noise with large wavelength, which is attractive for applications where the size and weight of a sound absorber are restricted.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Ion-Acoustic Shock Waves in Nonextensive Electron-Positron-Ion Plasma

M. Ferdousi, S. Yasmin, S. Ashraf, A. A. Mamun
Chin. Phys. Lett. 2015, 32 (1): 015201 doi: 10.1088/0256-307X/32/1/015201
Full Text: [PDF 655 KB] (39)
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A rigorous theoretical investigation is made of ion-acoustic shock structures in an unmagnetized three-component plasma whose constituents are nonextensive electrons, nonextensive positrons, and inertial ions. The Burgers equation is derived by employing the reductive perturbation method. The effects of electron and positron nonextensivity and ion kinematic viscosity on the properties of these ion-acoustic shock waves are briefly discussed. It is found that shock waves with positive and negative potentials are obtained to depend on the plasma parameters. The entailment of our results may be useful to understand some astrophysical and cosmological scenarios including stellar polytropes, hadronic matter and quark-gluon plasma, protoneutron stars, dark-matter halos, etc., where effects of nonextensivity can play significant roles.
CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES

High-Pressure Phase Transitions of PbTe Using the First-Principles Calculations

LI Yan-Chun, LI Gong, LIN Chuan-Long, LI Xiao-Dong, LIU Jing
Chin. Phys. Lett. 2015, 32 (1): 016101 doi: 10.1088/0256-307X/32/1/016101
Full Text: [PDF 564 KB] (48)
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High-pressure structural phase transitions in PbTe are investigated by means of the first principles total energy calculations within the generalized gradient approximation (GGA) and local density approximation (LDA) by using the density functional theory. First principle calculation shows that PbTe is stable with the NaCl-type (B1) structure under ambient conditions and transforms to the CsCl-type (B2) structure under high pressure via an intermediate phase. Two candidate structures of the intermediate phase, namely Pnma and Cmcm, are chosen for total energy calculations and discussed. It indicates that the intermediate phase adopts the Pnma structure rather than the Cmcm structure, and lattice parameters of the Pnma phase calculated by using GGA and LDA are in consistent with experimental results.

Impact of Arsenic Related Defects on Electronic Performance of ZrO2/GaAs: Density Functional Theory Calculations

WANG Yu-Peng, WANG Yong-Ping, SHI Li-Bin
Chin. Phys. Lett. 2015, 32 (1): 016102 doi: 10.1088/0256-307X/32/1/016102
Full Text: [PDF 620 KB] (24)
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Arsenic can diffuse into high-κ dielectrics during GaAs-based metal oxide semiconductor transistor process, which causes the degradation of gate dielectrics. To explore the origins of the degradation, we employ nonlocal B3LYP hybrid functional to study arsenic related defects in ZrO2. Via band alignments between the GaAs and ZrO2, we are able to determine the defect formation energy in the GaAs relative to the ZrO2 band gap and assess how they will affect the device performance. Arsenic at the interstitial site serves as a source of positive fixed charge while at the oxygen or zirconium substitutional site changes its charge state within the band gap of GaAs. Moreover, it is found that arsenic related defects produce conduction band offset reduction and gap states, which will increase the gate leakage current.

Elastic and Optoelectronic Properties of KCdF3: ab initio Calculations through LDA/GGA/TB-mBJ within FP-LAPW Method

K. Ephraim Babu, N. Murali, K. Vijaya Babu, B. Kishore Babu, V. Veeraiah
Chin. Phys. Lett. 2015, 32 (1): 016201 doi: 10.1088/0256-307X/32/1/016201
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Ab initio calculations are performed on the electronic, structural, elastic and optical properties of the cubic perovskite KCdF3. The Kohn–Sham equations are solved by applying the full potential linearized augmented plane wave (FP-LAPW) method. The exchange correlation effects are included through the local density approximation (LDA), generalized gradient approximation (GGA) and modified Becke-Johnson (mBJ) exchange potential. The calculated lattice constant is in good agreement with the experimental result. The elastic properties such as elastic constants, anisotropy factor, shear modulus, Young's modulus and Poisson's ratio are calculated. KCdF3 is ductile and elastically anisotropic. The calculations of the electronic band structure, density of states (DOS) and charge density show that this compound has an indirect energy band gap (M–Γ) with a mixed ionic and covalent bonding. The contribution of the different bands is analyzed from the total and partial density of states curves. Optical response of the dielectric functions, optical reflectivity, absorption coefficient, real part of optical conductivity, refractive index, extinction coefficient and electron energy loss, are presented for the energy range of 0–40 eV. The compound KCdF3 can be used for high-frequency optical and optoelectronic devices.

A New Method for Determining the Equation of State of Aluminized Explosive

ZHOU Zheng-Qing, NIE Jian-Xin, GUO Xue-Yong, WANG Qiu-Shi, OU Zhuo-Cheng, JIAO Qing-Jie
Chin. Phys. Lett. 2015, 32 (1): 016401 doi: 10.1088/0256-307X/32/1/016401
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The time-dependent Jones–Wilkins–Lee equation of state (JWL-EOS) is applied to describe detonation state products for aluminized explosives. To obtain the time-dependent JWL-EOS parameters, cylinder tests and underwater explosion experiments are performed. According to the result of the wall radial velocity in cylinder tests and the shock wave pressures in underwater explosion experiments, the time-dependent JWL-EOS parameters are determined by iterating these variables in AUTODYN hydrocode simulations until the experimental values are reproduced. In addition, to verify the reliability of the derived JWL-EOS parameters, the aluminized explosive experiment is conducted in concrete. The shock wave pressures in the affected concrete bodies are measured by using manganin pressure sensors, and the rod velocity is obtained by using a high-speed camera. Simultaneously, the shock wave pressure and the rod velocity are calculated by using the derived time-dependent JWL equation of state. The calculated results are in good agreement with the experimental data.

In Situ Electrical Resistivity and Hall Effect Measurement of β-HgS under High Pressure

HU Ting-Jing, CUI Xiao-Yan, LI Xue-Fei, WANG Jing-Shu, YANG Jing-Hai, GAO Chun-Xiao
Chin. Phys. Lett. 2015, 32 (1): 016402 doi: 10.1088/0256-307X/32/1/016402
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With in situ electrical resistivity and Hall effect measurement, the transport properties and carrier behavior of β-HgS under high pressure are investigated up to 32.9 GPa. The electrical resistivity changes discontinuously at 5.4, 14.6, and 25.0 GPa. These discontinuities correspond to the phase transitions of β-HgS from zinc blende to cinnabar, then to rock salt structure. For the zinc blende structure, the decrease of carrier concentration and the increase of mobility indicate that the originally overlapped valence band and conduction band separate with pressure. For the rock salt phase, the increase of ionized impurity concentration leads to the decrease of mobility with pressure.

Percolation Transitions of Random Networks under a Weight Probability Function

JIA Xiao, HONG Jin-Song, YANG Hong-Chun, YANG Chun, FU Chuan-Ji, HU Jian-Quan, SHI Xiao-Hong
Chin. Phys. Lett. 2015, 32 (1): 016403 doi: 10.1088/0256-307X/32/1/016403
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Based on the clusters growth mechanisms, we study a percolation model where the clusters are assigned to a weight probability function and the intracluster edges are excluded. The weight probability function includes a tunable parameter α. The model can realize the phase transition from continuous to multiple discontinuous and discontinuous as the value of α is tuned. According to the properties of the weight probability function, three typical cases which correspond to different clusters growth mechanisms are analyzed. When the system size N is equal to 1/α, probability modulation effect indicates that the percolation process generates a continuous phase transition which is similar to the classical Erdös–Rényi (ER) network model. At α=1, it is shown that the lower pseudotransition point is converging to 1 in the thermodynamic limit and the cluster size distribution at the lower pseudotransition point does not obey the power-law behavior, indicating a first-order phase transition. For α=N−1/2, the order parameter exhibits multiple jumps and the magnitude of the jumps are randomly distributed. The numerical simulations find that the relative variance of the order parameter is nonzero on an extended interval. It indicates that the order parameter is non-self-averaging. The cluster size heterogeneity decreases oscillatorily from some moment, which also implies the phenomenon.

Effects of Film Thickness and Ar/O2 Ratio on Resistive Switching Characteristics of HfOx-Based Resistive-Switching Random Access Memories

GUO Ting-Ting, TAN Ting-Ting, LIU Zheng-Tang
Chin. Phys. Lett. 2015, 32 (1): 016801 doi: 10.1088/0256-307X/32/1/016801
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Cu/HfOx/n+Si devices are fabricated to investigate the influence of technological parameters including film thickness and Ar/O2 ratio on the resistive switching (RS) characteristics of HfOx films, in terms of switch ratio, endurance properties, retention time and multilevel storage. It is revealed that the RS characteristics show strong dependence on technological parameters mainly by altering the defects (oxygen vacancies) in the film. The sample with thickness of 20 nm and Ar/O2 ratio of 12:3 exhibits the best RS behavior with the potential of multilevel storage. The conduction mechanism of all the films is interpreted based on the filamentary model.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Quasi-Particle Properties in Copper Using the GW Approximation

YI Zhi-Jun
Chin. Phys. Lett. 2015, 32 (1): 017101 doi: 10.1088/0256-307X/32/1/017101
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The electronic structures, absorption spectra and colors of Cu are calculated. Calculations are performed in the GW approximation (GWA) approximation, where G refers to Green's function and W is the dynamically screened Coulomb interaction. The calculated absorption spectra and color of Cu based on the density functional theory and the GWA are presented, and the calculated results within the GWA agree well with measurements. The calculated results indicate that many-body effects play an important role for the quasi-particle property calculations of Cu.

Structural, Electrical, and Lithium Ion Dynamics of Li2MnO3 from Density Functional Theory

CHEN Yong-Chang, HUO Miao, LIU Yang, CHEN Tong, LENG Cheng-Cai, LI Qiang, SUN Zhao-Lin, SONG Li-Juan
Chin. Phys. Lett. 2015, 32 (1): 017102 doi: 10.1088/0256-307X/32/1/017102
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The layered Li2MnO3 is investigated by using the first-principles calculations within the GGA and GGA+U scheme, respectively. Within the GGA+U approach, the calculated intercalation voltage (ranges from 4.5 V to 4.9 V) is found to be in good agreement with experiments. From the analysis of electronic structure, the pure phase Li2MnO3 is insulating, which is indicative of poor electronic-conduction properties. However, further studies of lithium ion diffusion in bulk Li2MnO3 show that unlike the two-dimensional diffusion pathways in rock salt structure layered cathode materials, lithium can diffuse in a three-dimensional pathway in Li2MnO3, with moderate lithium migration energy barrier ranges from 0.57 to 0.63 eV.

Characterization of Interface Charge in NbAlO/AlGaN/GaN MOSHEMT with Different NbAlO Thicknesses

FENG Qian, DU Kai, DAI Bo, DONG Liang, FENG Qing
Chin. Phys. Lett. 2015, 32 (1): 017301 doi: 10.1088/0256-307X/32/1/017301
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We investigate the influence of interface charge on electrical performance of NbAlO/AlGaN/GaN metal-oxide-semiconductor high electron mobility transistors (MOSHEMTs). Through CV measurements and simulations, we find that the donor-type interface fixed charge density Qit of 2.2×1013 cm−2 exists at the NbAlO/AlGaN interface, which induces the shift of the threshold voltage much more negative. Furthermore, a trap density of approximately 0.43×1013–1.14×1013 cm−2eV−1 is obtained at the NaAlO/AlGaN interface, which is consistent with the frequency-dependent capacitance and conductance measurement results.

Experimental Measurements of the Sensitivity of Fiber-optic Bragg Grating Sensors with a Soft Polymeric Coating under Mechanical Loading, Thermal and Magnetic under Cryogenic Conditions

GUAN Ming-Zhi, WANG Xing-Zhe, XIN Can-Jie, ZHOU You-He, MA Li-Zhen
Chin. Phys. Lett. 2015, 32 (1): 017401 doi: 10.1088/0256-307X/32/1/017401
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The strain and temperature sensing performance of fiber-optic Bragg gratings (FBGs) with soft polymeric coating, which can be used to sense internal strain in superconducting coils, are evaluated under variable cryogenic field and magnetic field. The response to a temperature and strain change of coated-soft polymeric FBGs is tested by comparing with those of coated-metal FBGs. The results indicate that the coated-soft polymeric FBGs can freely detect temperature and thermal strain, their accuracy and repeatability are also discussed in detail. At variable magnetic field, the tested results indicate that the cross-coupling effects of FBGs with different matrixes are not negligible to measure electromagnetic strain during fast excitation. The present results are expected to be able to provide basis measurements on the strain of pulsed superconducting magnet/cable (cable-around-conduit conductors, cable-in-conduit conductors), independently or utilized together with other strain measurement methods.

Effects of Doping on the Magnetic Properties and Frustration of Hexagonal YMn0.9A0.1O3 (A=Al, Fe, and Cu)

XIAO Li-Xia, JIN Zhao, XIA Zheng-Cai, SHI Li-Ran, HUANG Jun-Wei, CHEN Bo-Rong, SHANG Cui, WEI Meng, LONG Zhuo
Chin. Phys. Lett. 2015, 32 (1): 017501 doi: 10.1088/0256-307X/32/1/017501
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The doping effects on the frustration and the magnetic properties in hexagonal compounds of YMn0.9A0.1O3 (A=Al, Fe and Cu) are investigated. Experimental results indicate that both the non-magnetic and magnetic ion dopants lead to the increase of magnetic moments and the decrease of the absolute value of Curie–Weiss temperature (|θCW|). Compared with pure YMnO3, the geometrical frustration of YMn0.9A0.1O3 is greatly suppressed and the magnetic coupling in that exhibits dopant-dependent. In addition, for the doped YMn0.9A0.1O3, the antiferromagnetic transition temperature (TN) is also suppressed slightly, which shows an abnormal dilution effect and it may be ascribed to the reduction of frustration due to the chemical substitution.

Preparation and Magnetic Properties of SrFe12O19 Ferrites Suitable for Use in Self-Biased LTCC Circulators

PENG Long, HU Yue-Bin, GUO Cheng, LI Le-Zhong, WANG Rui, HU Yun, TU Xiao-Qiang
Chin. Phys. Lett. 2015, 32 (1): 017502 doi: 10.1088/0256-307X/32/1/017502
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Strontium ferrites with different Bi2O3 content are prepared by the solid phase method, and their magnetic properties are investigated primarily. The Bi2O3 additive and sintering temperature separately exhibit a strong effect on the sintering density, crystal structure, and magnetic properties of the ferrites. As to the ferrites with 3 wt% Bi2O3, the relatively high sintering density ρs, saturation magnetization Ms, and intrinsic coercivity Hci can be obtained at a low sintering temperature of 900°C even much lower. Furthermore, the effective magnetic anisotropy constant Keff and magnetic anisotropy field Ha of the ferrites are calculated from the magnetization curve by the law of approach to saturation. It is suggested that the low-temperature sintered SrFe12O19 ferrites with Ms of 285.6 kA/m and Ha of 1564.6 kA/m possess a significant potentiality for applying in the self-biased low-temperature co-fired ceramics circulators from 34 to 40 GHz.

Interface Effects on the Magnetoelectric Properties of Magnetoelectric Multilayer Composites

CHENG Ji-Hua, WANG Yin-Gang, XIE Dan
Chin. Phys. Lett. 2015, 32 (1): 017503 doi: 10.1088/0256-307X/32/1/017503
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The magnetoelectric (ME) effect is studied in the terfenol-D/Pb(Zr, Ti)O3 (PZT) multilayer composites prepared by silver epoxy. A theoretical model reveals that the ME voltage coefficient αE,31 is a constant when the total thickness of the multilayer composites is the same. However, the interface defects exist in multilayer composites in experiments and the interface energy loss increases with increasing the stacking periodicity, which leads to the gradual decrease of the ME voltage coefficient αE, 31. The resonant frequency of terfenol-D/PZT multilayer composites is independent of the stacking periodicity and agrees well with the predicted one. One can achieve a strong ME coupling by improving the interface conditions to meet the needs for practical applications.

Structures and Magnetic Properties of Europium-Transition Metal-Gallium Ternary Intermetallic Compounds with 1:3 Type

HE Qiang, GUO Yong-Quan
Chin. Phys. Lett. 2015, 32 (1): 017504 doi: 10.1088/0256-307X/32/1/017504
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The crystal structures and magnetic properties of novel EuTrGa3−r (T=Pd, Ir, Rh) intermetallic compounds are investigated by using powder x-ray diffraction and magnetic measurements. EuTrGa3−r crystallizes in orthorhombic structure with space group of Cmcm and Z=4. There are four kinds of nonequivalent 4c crystal positions in EuTrGa3−r unit cell, which are occupied by 4Eu, 4GaI, 4(GaII, T) and 4GaIII, respectively. EuTrGa3−r exhibits the complex magnetic states in low-temperature regime, with the three-, two- and one-antiferromagnetic transitions occurring for T=Ir, T=Rh and T=Pd, respectively. It might be due to the Kondo effect: a localized antiferromagnetic interaction of the isolated impurity spins with the surrounding conduction electrons at low-temperature regime.

Layered Compounds AFBiS2: Superior Birefringent Crystals

WANG Hai
Chin. Phys. Lett. 2015, 32 (1): 017801 doi: 10.1088/0256-307X/32/1/017801
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First-principles calculations predict that SrFBiS2 has a superior birefringence of 1.28, which is larger than the giant birefringence of LaOBiS2 [Wang H, Chin. Phys. Lett. 31 2013 047802]. An AF layer (i.e., SrF) is shown to be important by the further investigations on AFBiS2 (A=Mg, Ca, Ba). Here MgFBiS2 exhibits the largest inherent birefringence (∼1.66) among single-crystal compounds. The origin of SBF is also discussed based on the electronic structure and refractive index.
CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

Protein Based Localized Surface Plasmon Resonance Gas Sensing

Meisam Omidi, Gh. Amoabediny, F. Yazdian, M. Habibi-Rezaei
Chin. Phys. Lett. 2015, 32 (1): 018701 doi: 10.1088/0256-307X/32/1/018701
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We apply the localized surface plasmon resonance (LSPR) of gold nanoparticles (GNPs) covalently coupled with cytochrome c (cyt c) to create a nanobiosensor for detecting hydrogen sulfide (H2S) in the range of 15–100 ppb. Monolayer formation of GNPs on glass surface functionalized with 3-aminopropyltrimethoxysilane (APTMS) is performed for fabricating a chip-based format of the optical transducer. By chemical introduction of short-chain thiol derivatives on cyt c protein shell via its lysine residues, a very fast self-assembled monolayer (SAM) of cyt c is formed on the GNPs. Significant shifts in the LSPR peak (ΔλLSPR) are observed by reacting H2S with cyt c. Results show a linear relationship between ΔλLSPR and H2S concentration. Furthermore, shifts in the LSPR peak are reversible and the peak positions return to their pre-exposure values once the H2S is removed. The experimental results strongly indicate that the protein based LSPR chip can be successfully used as a simple, fast, sensitive and quantitative sensor for H2S detection.

Error Threshold of Fully Random Eigen Model

LI Duo-Fang, CAO Tian-Guang, GENG Jin-Peng, QIAO Li-Hua, GU Jian-Zhong, ZHAN Yong
Chin. Phys. Lett. 2015, 32 (1): 018702 doi: 10.1088/0256-307X/32/1/018702
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Species evolution is essentially a random process of interaction between biological populations and their environments. As a result, some physical parameters in evolution models are subject to statistical fluctuations. In this work, two important parameters in the Eigen model, the fitness and mutation rate, are treated as Gaussian distributed random variables simultaneously to examine the property of the error threshold. Numerical simulation results show that the error threshold in the fully random model appears as a crossover region instead of a phase transition point, and as the fluctuation strength increases the crossover region becomes smoother and smoother. Furthermore, it is shown that the randomization of the mutation rate plays a dominant role in changing the error threshold in the fully random model, which is consistent with the existing experimental data. The implication of the threshold change due to the randomization for antiviral strategies is discussed.
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