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Chin. Phys. Lett.  
  Chin. Phys. Lett.--2014, 31 (7)   Published: 30 June 2014
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GENERAL

Dressed Dark Solitons of the Defocusing Nonlinear Schrödinger Equation

LOU Sen-Yue, CHENG Xue-Ping, TANG Xiao-Yan
Chin. Phys. Lett. 2014, 31 (7): 070201 doi: 10.1088/0256-307X/31/7/070201
Full Text: [PDF 2040 KB] (370)
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The nonlinear Schrödinger equation is proved to be consistent-tanh-expansion (CTE) solvable. Some types of dark soliton solutions dressed by cnoidal periodic waves are obtained by means of the CTE method.

A Hierarchy of New Nonlinear Evolution Equations and Their Bi-Hamiltonian Structures

GENG Xian-Guo, WANG Hui
Chin. Phys. Lett. 2014, 31 (7): 070202 doi: 10.1088/0256-307X/31/7/070202
Full Text: [PDF 386 KB] (149)
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A hierarchy of new nonlinear evolution equations associated with a 3×3 matrix spectral problem with four potentials is proposed, in which two typical members are a new coupled Burgers equation and a new coupled KdV equation. The bi-Hamiltonian structures for the hierarchy of nonlinear evolution equations are established by using the trace identity.

Interactions between Solitons and Cnoidal Periodic Waves of the Gardner Equation

YU Wei-Feng, LOU Sen-Yue, YU Jun, HU Han-Wei
Chin. Phys. Lett. 2014, 31 (7): 070203 doi: 10.1088/0256-307X/31/7/070203
Full Text: [PDF 539 KB] (138)
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The Gardner equation is one of the most important prototypic models in nonlinear physics. Many scholars pay much attention to the Gardner equation and various nonlinear excitations of the Gardner equation have been found by many methods. However, it is very difficult to find interaction solutions among different types of nonlinear excitations. In this work, with the help of the Riccati equation, the Gardner equation is solved by the consistent Riccati expansion. Furthermore, we obtain the soliton-cnoidal wave interaction solutions of the Gardner equation.

Single-Photon Transport Properties in Coupled-Resonator Waveguide with Nonlocal Coupling to a Whispering-Gallery Resonator Interacting with Two Separated Atoms

ZHOU Tao, ZANG Xiao-Fei, CHEN Jing
Chin. Phys. Lett. 2014, 31 (7): 070301 doi: 10.1088/0256-307X/31/7/070301
Full Text: [PDF 579 KB] (84)
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We investigate the single-photon transport properties in a one-dimensional coupled-resonator waveguide non-locally coupled to a whispering-gallery resonator embedded with two separated two-level atoms based on the real-space approach. The control of single-photon transport is realized by modulating the detuning between two separated atoms, phase differences, and the symmetric/asymmetric nonlocal couplings. The multi-frequency photon-filter is obtained, and the influences of dissipation effects on single-photon transmission spectra and the phase shift are also discussed.

A Security Proof of Measurement Device Independent Quantum Key Distribution: From the View of Information Theory

LI Fang-Yi, YIN Zhen-Qiang, LI Hong-Wei, CHEN Wei, WANG Shuang, WEN Hao, ZHAO Yi-Bo, HAN Zheng-Fu
Chin. Phys. Lett. 2014, 31 (7): 070302 doi: 10.1088/0256-307X/31/7/070302
Full Text: [PDF 432 KB] (71)
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Although some ideal quantum key distribution protocols have been proved to be secure, there have been some demonstrations that practical quantum key distribution implementations were hacked due to some real-life imperfections. Among these attacks, detector side channel attacks may be the most serious. Recently, a measurement device independent quantum key distribution protocol [Phys. Rev. Lett. 108 (2012) 130503] was proposed and all detector side channel attacks are removed in this scheme. Here a new security proof based on quantum information theory is given. The eavesdropper's information of the sifted key bits is bounded. Then with this bound, the final secure key bit rate can be obtained.

Damping in a Squeezed Bath and Its Time Evolution through the Complete Class of Gaussian Quasi-Distributions

Mohammad Reza Bazrafkan, Seyed Mahmoud Ashrafi, Fahimeh Naghdi
Chin. Phys. Lett. 2014, 31 (7): 070303 doi: 10.1088/0256-307X/31/7/070303
Full Text: [PDF 440 KB] (28)
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By virtue of the thermo-entangled states representation of the density operator and using the dissipative interaction picture, we solve the master equation of a driven damped harmonic oscillator in a squeezed bath. We show that the essential part of the dynamics can be expressed by the convolution of the initial Wigner function with a special kind of normalized Gaussian in the phase space and relate the dynamics with the change of Gaussian ordering of the density operator.

Adiabatic Deutsch–Jozsa Problem Solved by Modifying the Initial Hamiltonian

SUN Jie, LU Song-Feng, LIU Fang, ZHOU Qing, ZHANG Zhi-Gang
Chin. Phys. Lett. 2014, 31 (7): 070304 doi: 10.1088/0256-307X/31/7/070304
Full Text: [PDF 433 KB] (40)
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We present an alternate adiabatic evolution for the Deutsch–Jozsa problem. The biggest difference of our adiabatic evolution constructed here with those appearing before is that an alternate initial Hamiltonian is used for the adiabatic evolution, with which the evolution task can be finished in O(1) time complexity. Our construction mostly resembles the one discussed by Das et al. [Phys. Rev. A 65 (2002) 062310], except for the initial system Hamiltonian of the adiabatic algorithm.

Bianchi Type-II Inflationary Models with Stiff Matter and Decaying Cosmological Term

Shri Ram, Priyanka
Chin. Phys. Lett. 2014, 31 (7): 070401 doi: 10.1088/0256-307X/31/7/070401
Full Text: [PDF 514 KB] (31)
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We deal with Einstein's field equations with a time-decaying cosmological term of the forms (i) Λ = β(ä/a) + α/a2 and (ii) Λ = α/a2, where a is the average scale factor of the universe, α and β are constants for a spatially homogeneous and anisotropic LRS Bianchi type-II spacetime. Exact solutions of the field equations for stiff matter are obtained by applying a special law of variation for the Hubble parameter. Anisotropic cosmological models are presented with a constant negative deceleration parameter which corresponds to the accelerated phase of the present universe. The cosmological constant Λ is obtained as a decreasing function of time that is approaching a small positive value at the present epoch, which is corroborated by the consequences from recent supernovae Ia observations. The physical and kinematical behaviors of the models are also discussed.

Effects of Spike Frequency Adaptation on Synchronization Transitions in Electrically Coupled Neuronal Networks with Scale-Free Connectivity

WANG Lei, ZHANG Pu-Ming, LIANG Pei-Ji, QIU Yi-Hong
Chin. Phys. Lett. 2014, 31 (7): 070501 doi: 10.1088/0256-307X/31/7/070501
Full Text: [PDF 1158 KB] (55)
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Effects of spike frequency adaptation (SFA) on the synchronous behavior of population neurons are investigated in electrically coupled networks with a scale-free property. By a computational approach, we corroborate that pairwise correlations between neurons would decrease if neurons exhibit the feature of SFA, which is similar to previous experimental observations. However, unlike the case of pairwise correlations, population activities of neurons show a rather complex variation mode: compared with those of non-adapted neurons, neurons in the networks having weak-degrees of SFA will impair population synchronizations; while neurons exhibiting strong-degrees of SFA will enhance population synchronizations. Moreover, a variation of coupling strength between neurons will not alter this phenomenon significantly, unless the coupling strength is too weak. Our results suggest that synchronous activity of electrically coupled population neurons is adaptation-dependent, and this adaptive feature may imply some coding strategies of neuronal populations.

The Fermion Representation of Quantum Toroidal Algebra on 3D Young Diagrams

CAI Li-Qiang, WANG Li-Fang, WU Ke, YANG Jie
Chin. Phys. Lett. 2014, 31 (7): 070502 doi: 10.1088/0256-307X/31/7/070502
Full Text: [PDF 469 KB] (31)
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We develop an equivalence between the diagonal slices and the perpendicular slices of 3D Young diagrams via Maya diagrams. Furthermore, we construct the fermion representation of quantum toroidal algebra on the 3D Young diagrams perpendicularly sliced.

Phase Transitions of Ferromagnetic Potts Models on the Simple Cubic Lattice

WANG Shun, XIE Zhi-Yuan, CHEN Jing, Bruce Normand, XIANG Tao
Chin. Phys. Lett. 2014, 31 (7): 070503 doi: 10.1088/0256-307X/31/7/070503
Full Text: [PDF 628 KB] (24)
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We investigate the 2- and 3-state ferromagnetic Potts models on the simple cubic lattice using the tensor renormalization group method with higher-order singular value decomposition (HOTRG). HOTRG works in the thermodynamic limit, where we use the Zq symmetry of the model, combined with a new measure for detecting the transition, to improve the accuracy of the critical point for the 2-state model by two orders of magnitude, obtaining Tc=4.51152469(1). The 3-state model is far more complex, and we improve the overall understanding of this case by calculating its thermodynamic quantities with high accuracy. Our results verify that the first-order nature of the phase transition and the HOTRG transition temperature benchmarks the most recent Monte Carlo result.

Nano-Traceability Study of a Cr Standard Grating Fabricated by Laser-Focused Atomic Deposition

LEI Li-Hua, LI Yuan, FAN Guo-Fang, WENG Jun-Jing, DENG Xiao, CAI Xiao-Yu, LI Tong-Bao
Chin. Phys. Lett. 2014, 31 (7): 070601 doi: 10.1088/0256-307X/31/7/070601
Full Text: [PDF 4407 KB] (22)
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A dimensional artifact is developed, which is a chromium (Cr) deposition grating fabricated by a laser-focused atomic deposition technique. The mean pitch of the grating is measured by using a metrological atomic force microscope with a large range, where a series of reference signs have been performed to locate the deposition area. Cosine error of the measurement result is analyzed and eliminated by the iterative angle calibration. The measurement result shows that the mean pitch of the grating is 212.66 ± 0.02 nm, which is very close to half of the standing laser wavelength (λ=425.55 nm). This means that the grating has traceability with high accuracy and can substitute the laser interference technology for instrument calibration. Moreover, using the Cr deposition grating as a nano standard can shorten the traceability chain and improve the practical application.
NUCLEAR PHYSICS

Description of the Structural Properties of Low-Lying States in 102Ru with IBM2

ZHANG Da-Li, YUAN Shu-Qing, DING Bin-Gang,
Chin. Phys. Lett. 2014, 31 (7): 072101 doi: 10.1088/0256-307X/31/7/072101
Full Text: [PDF 494 KB] (27)
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We describe the properties of low-lying states of 102Ru within the framework of the proton-neutron interacting model IBM2. The theoretical predictions of the ground state, quasi-γ and quasi-β bands, and the ratios of the B(E2) transition strengths are reproduced very well. The structural properties of 102Ru are identified in the parameters space of the interacting boson model (IBM2). The characteristic feature of the energy spectrum structure exhibits that 102Ru is very close to the critical point of Uπν(5)–Oπν(6) transition and towards Uπν(5) symmetry. The key sensitive quantities of the B(E2) branching ratio clearly indicate that 102Ru is a primary Oπν(6) symmetry, while with a somewhat Uπν(5) symmetry. It is possible that the shape coexistence persists in 102Ru, whereas the evident fingerprint of the shape coexistence has not been observed.

New Parametrizations for a Model with Nonlinear Derivative Couplings

CHEN Yan-Jun
Chin. Phys. Lett. 2014, 31 (7): 072102 doi: 10.1088/0256-307X/31/7/072102
Full Text: [PDF 593 KB] (21)
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We propose three parameter sets for the Lagrangian with nonlinear derivative couplings in the relativistic mean field theory. The properties of finite nuclei and nuclear matter are explored. The study shows that a good description of binding energies, charge radii and neutron skin thickness of nuclei is achieved with this Lagrangian. It is also shown that this Lagrangian model leads to a softening of the equation of state and symmetry energy at high densities, and gives a much less repulsive optical potential at high nucleon energies compared to standard relativistic mean field models.

A Toy Model for Estimation of the Event Plane Non-Flat Effect on an Elliptic Flow in Heavy Ion Collision

ZHOU Feng-Chu, CAI Xu, ZHOU Dai-Cui
Chin. Phys. Lett. 2014, 31 (7): 072501 doi: 10.1088/0256-307X/31/7/072501
Full Text: [PDF 459 KB] (21)
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In heavy ion collision, the event plane is a key parameter defined as the plane composted by the impact parameter b and beam axis z. It is a crucial reference for various observables, which focus on the initial spatial anisotropy of the overlap region in heavy ion collision. We notice that in some recent heavy ion collision experiments, due to potentially inefficient or even the invalidity of experimental facilities, the reconstructed event plane, which is used in elliptic flow study, may be biased towards a non-flat distribution. In this study, we develop a toy model for fast estimation of the bias effect and its influence on the elliptic flow. The possible azimuthal bias of the detector is firstly studied by varying the part of its azimuthal information. We also study on the limit acceptance of the detector, which will be used to measure the particle of interest in an elliptic flow. The outcomes are presented by comparing the flow study results with or without the non-flat effect on the event plane.

Microstructure and Mechanical Properties of Ti3SiC2 Irradiated by Carbon Ions

WANG Kun, QI Qiang, CHENG Gui-Jun, SHI Li-Qun
Chin. Phys. Lett. 2014, 31 (7): 072801 doi: 10.1088/0256-307X/31/7/072801
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Thanks to its noteworthy mechanical properties, excellent damage tolerance and good thermal stability, the Ti3SiC2 ternary compound has attracted great concern and has been considered as a potential structural component material for the 4th generation of reactors (e.g., gas fast nuclear reactors) and future fusion reactors. The outstanding properties are due to the nanolamellar structure which imparts characteristics of both metals and ceramics to this material. In our work, Ti3SiC2 samples have been irradiated by C+ ions with a high fluence of 1.78×1017 ions/cm2 at a range of temperatures from 120°C–850°C. Subsequently, series of characterization techniques including synchrotron irradiation x-ray diffraction, scanning electron microscopy and nano-indentation are carried out to understand the changes of microstructure and mechanical properties. The composition exhibits high damage tolerant properties and a high recovery rate through the analysis, especially at high temperature. The minimum damage to an irradiated sample appears around 350°C in the temperature range 120°C–550°C. At a high irradiation temperature, a significant reduction in the damage can be achieved and an almost complete lack of damage compared with an un-irradiated sample is revealed at the temperature of 850°C.

Advantages of Artificial Neural Network in Neutron Spectra Unfolding

ZHU Qing-Jun, TIAN Li-Chao, YANG Xiao-Hu, GAN Long-Fei, ZHAO Na, MA Yan-Yun
Chin. Phys. Lett. 2014, 31 (7): 072901 doi: 10.1088/0256-307X/31/7/072901
Full Text: [PDF 846 KB] (27)
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Advantages of using the artificial neural network method in neutron spectra unfolding are investigated in comparison with the maximum entropy unfolding method. By introducing the information entropy theory, we find that for the spectrum with the information entropy over 3.5, the four-layer feed-forward neural network (11-35-55-60) and the maximum entropy method generally demonstrate the same unfolding performance, while the spectrum with the information entropy lower than 3.5, the artificial neural network unfolding model is recommend due to the fact that the artificial neural network method has a stronger negative correlation between the entropy of the spectra and the mean squares error of the spectra than the maximum entropy method.
ATOMIC AND MOLECULAR PHYSICS

Sr3Bi(PO4)3:Eu2+ Luminescence, Concentration Quenching and Crystallographic Sites

GAO Shao-Jie, LI Ting, ZHANG Zi-Cai, LI Pan-Lai, WANG Zhi-Jun, YANG Zhi-Ping
Chin. Phys. Lett. 2014, 31 (7): 073301 doi: 10.1088/0256-307X/31/7/073301
Full Text: [PDF 1020 KB] (28)
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A blue emitting phosphor Sr3Bi(PO4)3:Eu2+ is synthesized by a high-temperature solid state method, and its luminescent property is investigated. Sr3Bi(PO4)3:Eu2+ can create blue emission under the 332 radiation excitation, and the prominent luminescence in blue (423 nm) due to the 4f5d1→4f7 transition of the Eu2+ ion. The crystallographic sites of the Eu2+ ion in Sr3Bi(PO4)3 are analyzed, and the 420 and 440 nm emission peaks of the Eu2+ ion are assigned to the nine-coordination and eight-coordination, respectively. The emission intensity of Sr3Bi(PO4)3:Eu2+ is influenced by the Eu2+ doping content, and the concentration quenching effect is observed. The quenching mechanism is the dipole-dipole interaction, and the critical distance of energy transfer is calculated by the concentration quenching method to be approximately 1.72 nm.

Temperature of the Remaining Cold Atoms after Two-Step Photoionization in an 87Rb Vapor Cell Magneto-Optical Trap

RUAN Ya-Ping, JIA Feng-Dong, LIU Long-Wei, SUN Zhen, HUANG Wei, XUE Ping, XU Xiang-Yuan, DAI Xing-Can, ZHONG Zhi-Ping
Chin. Phys. Lett. 2014, 31 (7): 073401 doi: 10.1088/0256-307X/31/7/073401
Full Text: [PDF 636 KB] (18)
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The temperature of the remaining cold 87Rb atoms confined in a vapor cell magneto-optical trap after two-step photoionization has been measured. In the two-step photoionization process, the first excitation laser is served by the cooling laser and the second excitation laser is served by a continuous semiconductor laser with a wavelength of 450 nm. The results show that the temperature of the remaining cold atoms decreases as the intensity of the second excitation laser increases. Moreover, the relationship between the temperature T and number N of the remaining cold atoms generally follows a power law, while it deviates from the well-known T∝N1/3 and the power factor is smaller than 1/3. We propose that ion-atom collisions occurring during a photoionization process strongly influence the temperature scaling law in an optically dense magneto-optical trap in the presence of an ionization laser. In addition, the forced evaporative cooling due to the combined effect of the detuning of the first excitation laser and the two-step photoionization plays a role in cooling the remaining cold atoms and results in the dependence of the power factor on the detuning of the first excitation laser.

Observation of Faraday Rotation in Cold Atoms in an Integrating Sphere

ZHENG Ben-Chang, CHENG Hua-Dong, MENG Yan-Ling, XIAO Ling, WAN Jin-Yin, LIU Liang
Chin. Phys. Lett. 2014, 31 (7): 073701 doi: 10.1088/0256-307X/31/7/073701
Full Text: [PDF 893 KB] (15)
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The Faraday rotation of weak linearly polarized probe light is observed as it passes through a sample of cold 87Rb atoms prepared by diffused light in an integrating sphere. The rotation angle of the probe light-polarization as functions of laser intensity, detuning and biased magnetic field is measured. A Ramsey fringe with a linewidth of 35 Hz and contrast up to 92% is demonstrated. This method has potential applications in improving the performance of atomic clocks with cold atoms.
FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)

Non-Paraxial Propagation of Cylindrical Vector Vortex Beams in the Far-Field

GUO Li-Na, TANG Zhi-Lie, WANG Jie
Chin. Phys. Lett. 2014, 31 (7): 074101 doi: 10.1088/0256-307X/31/7/074101
Full Text: [PDF 794 KB] (32)
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On the basis of the vectorial Rayleigh diffraction integral, the analytical expressions for the electric fields of cylindrical vector vortex beams (CVVBs) with an arbitrary polarization order in the far-field are derived, which helps us investigate the far-field properties of the CVVBs in the non-paraxial and paraxial regimes. Some detailed comparisons of the non-paraxial results with the paraxial results are made, which show that the polarization order and the ratio of beam waist width to wavelength play an important role in determining the non-paraxiality of CVVBs. In addition, the polarization order and the ratio of beam waist width to wavelength have a great impact on the diffraction effect and the divergent behavior of CVVBs in the far-field.

Graphene Based Passively Q-Switched Nd:YAG Eye-Safe Laser

ZHANG Hua-Nian, LI Ming, CHEN Xiao-Han, WANG Qing-Pu, LI Ping
Chin. Phys. Lett. 2014, 31 (7): 074201 doi: 10.1088/0256-307X/31/7/074201
Full Text: [PDF 634 KB] (32)
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A passively Q-switched Nd YAG eye-safe laser operating at 1444 nm with graphene as a saturable absorber is reported. Under a pump power of 23.7 W, the maximum average output power, minimum pulse width, pulse repetition rate and single pulse energy are 411 mW, 560 ns, 85 kHz, and 4.83 μJ, respectively. This is the first demonstration of a Nd:YAG eye-safe laser passively Q-switched by graphene.

A Diode-Pumped 1617 nm Single Longitudinal Mode Er:YAG Laser with Intra-Cavity Etalons

DENG Yun, YAO Bao-Quan, JU You-Lun, DUAN Xiao-Ming, DAI Tong-Yu, WANG Yue-Zhu
Chin. Phys. Lett. 2014, 31 (7): 074202 doi: 10.1088/0256-307X/31/7/074202
Full Text: [PDF 586 KB] (25)
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We demonstrate the continuous wave p-polarized single longitudinal mode (SLM) operation of an Er:YAG laser at 1617.6 nm pumped by a diode-laser with three inserted Fabry–Perot (FP) etalons at room temperature. The Brewster angle inserted FP is applied to obtain the p-polarized laser. For free running, the maximum output power is 570 mW with a pump power of 12.5 W. An incident pump power of 12.5 W is used to generate the maximum p-polarized single longitudinal mode output power of 78.5 mW, corresponding to a slope efficiency of 1.6% and an optical-to-optical efficiency of 0.61%. The beam quality M2 is measured to be 1.15 at the highest SLM output power. This stable polarized SLM oscillation is encouraging due to its application for an injection-locked system used as a master laser.

A Stable Diffusion-Bonded Tm:YLF Bulk Laser with High Power Output at a Wavelength of 1889.5 nm

DUAN Xiao-Ming, DING Yu, YAO Bao-Quan, DAI Tong-Yu, LI Ying-Yi, JIA Fu-Li
Chin. Phys. Lett. 2014, 31 (7): 074203 doi: 10.1088/0256-307X/31/7/074203
Full Text: [PDF 580 KB] (20)
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A high power diode-pumped diffusion-bonded Tm:YLF laser operating at 1889.5 nm with a FWHM linewidth of less than 0.1 nm is reported. A Brewster plate and two Fabry–Perot etalons are inserted in the laser cavity for spectral narrowing and stabilization. Under an incident pump power of 136.8 W, 46.1 W of output power is achieved, corresponding to an optical-to-optical conversion efficiency of 33.7% and a slope efficiency of 42.8%. The laser wavelength shift of only 0.07 nm with the incident pump power from 20.1 W to 136.8 W is observed. The M2 factor at maximum output power is calculated to be 2.3 in the x-axis and 2.0 in the y-axis, respectively.

A Graphene-Based Passively Q-Switched Ho:YAG Laser

YAO Bao-Quan, CUI Zheng, DUAN Xiao-Ming, SHEN Ying-Jie, WANG Ji, DU Yan-Qiu
Chin. Phys. Lett. 2014, 31 (7): 074204 doi: 10.1088/0256-307X/31/7/074204
Full Text: [PDF 748 KB] (26)
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A 2.09-μm in-band pumped passively Q-switched Ho:YAG laser is demonstrated. Single layer graphene deposited on a quartz substrate is used as the saturable absorber for the Q-switched operation. The minimum pulse width of 2.11 μs is obtained at an average output power of 100 mW, corresponding to a pulse repetition frequency of 57.1 kHz and the pulse energy of 1.75 μJ. The beam quality factors M2 of the Q-switched laser are 1.18 and 1.22 in the horizontal and longitudinal direction, respectively. The optical-to-optical conversion efficiency of the passively Q-switched laser is 4.3%, which is the highest conversion efficiency in the 2 μm wavelength, to the best of our knowledge. It shows clearly that the Ho:YAG crystal is a potential gain medium in the 2 μm range for the graphene application.

A 16-Channel Distributed-Feedback Laser Array with a Monolithic Integrated Arrayed Waveguide Grating Multiplexer for a Wavelength Division Multiplex-Passive Optical Network System Network

ZHAO Jian-Yi, CHEN Xin, ZHOU Ning, HUANG Xiao-Dong, CAO Ming-De, LIU Wen
Chin. Phys. Lett. 2014, 31 (7): 074205 doi: 10.1088/0256-307X/31/7/074205
Full Text: [PDF 1749 KB] (17)
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A 16-channel distributed-feedback (DFB) laser array with a monolithic integrated arrayed waveguide grating multiplexer for a wavelength division multiplex-passive optical network system is fabricated by using the butt-joint metal organic chemical vapor deposition technology and nanoimpirnt technology. The results show that the threshold current is about 20–30 mA at 25°C. The DFB laser side output power is about 16 mW with a 150 mA injection current. The lasing wavelength is from 1550 nm to 1575 nm covering a more than 25 nm range with 200 GHz channel space. A more than 55 dB sidemode suppression ratio is obtained.

An 880-nm Laser-Diode End-Pumped Nd:YVO4 Slab Laser with a Hybrid Resonator

MAO Ye-Fei, ZHANG Heng-Li, XU Liu, DENG Bo, XING Ji-Chuan, XIN Jian-Guo, JIANG Yi
Chin. Phys. Lett. 2014, 31 (7): 074206 doi: 10.1088/0256-307X/31/7/074206
Full Text: [PDF 555 KB] (19)
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We present an experimental study of a continuous-wave Nd:YVO4 laser diode-pumped directly in band at 880 nm. By using a compact positive confocal unstable-stable hybrid resonator, a maximal laser output of 170 W at 1064 nm is realized. The slope efficiency and optical-to-optical efficiency are 56.7% and 51.3%, respectively. The M2 factors in the unstable direction and in the stable direction they are 1.9 and 1.3, respectively.

Laser-Induced Damage Threshold of TiO2 Films with Different Preparation Methods and Annealing Temperatures

XU Cheng, YANG Shuai, WANG Zhen, DENG Jian-Xin, ZHAO Yu-Long, FAN He-Liang, QIANG Ying-Huai, LI Da-Wei
Chin. Phys. Lett. 2014, 31 (7): 074207 doi: 10.1088/0256-307X/31/7/074207
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Sol-gel TiO2 films are prepared by the dip-coating method and the spin-coating method, and then annealing is performed at different temperatures. The structures, optical properties, surface morphologies, absorption and laser-induced damage threshold (LIDT) at 1064 nm and 12 ns of the films are investigated. The results show that the dip-coating method can be used to obtain a higher LIDT than the spin-coating method. When the annealing temperature increases from 80°C to 120°C, the dip-coated film obtains a higher LIDT, whereas the spin-coated film obtains a lower LIDT. In addition, the damage morphology is a spalling pit for the dip-coated film annealed at 80°C. When the annealing temperature increases to 120°C, it shows a melting area. For both the spin-coated films annealed at different temperatures, the damage morphologies are the combination of spalling and melting. The differences in LIDT and damage morphologies of the films are discussed.

High-Efficient Nd:YLF Q-Switched Laser Operating at 523.5 nm

LU Ting-Ting, MA Jian, HUANG Min-Jie, YANG Qi, ZHU Xiao-Lei, CHEN Wei-Biao
Chin. Phys. Lett. 2014, 31 (7): 074208 doi: 10.1088/0256-307X/31/7/074208
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An intracavity frequency doubling electro-optically Q-switched Nd:YLF 523.5 nm laser is developed. An appropriate cylindrical lens is employed in the oscillator to optimize the mode size and to improve the stability of the cavity. With an incident pump pulse energy of 58 mJ at a 500 Hz repetition rate, a green pulse energy of 16.8 mJ at 523.5 nm is obtained, corresponding to an optical-optical conversion efficiency of 29%. The pulse width is less than 8 ns, and the beam quality factor is M2≤2.5.

An 885-nm Direct Pumped Nd:CNGG 1061 nm Q-Switched Laser

LI Qi-Nan, ZHANG Tao, FENG Bao-Hua, ZHANG Zhi-Guo, ZHANG Huai-Jin, WANG Ji-Yang
Chin. Phys. Lett. 2014, 31 (7): 074209 doi: 10.1088/0256-307X/31/7/074209
Full Text: [PDF 585 KB] (14)
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The 885 nm direct pumping method, directly into the 4F3/2 emitting level of Nd3+ ion, is used to a Nd:CNGG crystal to product passive Q-switched 1061 nm laser pulses, for the first time to the best of our knowledge. A maximum average output power of 1.16 W for 1061 nm Q-switched pulses and a repetition rate of 12.54 kHz are obtained. The pulse width is measured to be 24 ns and the peak power is 3.843 kW. A high-quality fundamental transverse mode can be observed owing to the reduction of the thermal effect for Nd:CNGG crystal by 885 nm direct pumping.

Novel Dynamics of a Vortex in Three-Dimensional Dissipative Media with an Umbrella-Shaped Potential

LIU Yun-Feng, LIU Bin, HE Xing-Dao, LI Shu-Jing
Chin. Phys. Lett. 2014, 31 (7): 074210 doi: 10.1088/0256-307X/31/7/074210
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We report the novel dynamic of 3D dissipative vortices supported by an umbrella-shaped potential (USP) in the 3D complex Ginzburg–Landau (CGL) equation with the cubic-quintic nonlinearity. The stable solution of vortices with intrinsic vorticity S=1 and 2 are obtained in the 3D CGL equation. An appropriate USP forces the vortices continuously to throw out fundamental 3D solitons (light bullets) along the folding umbrella. The dynamic regions of the strength of the potential with the changing number of folding umbrella are analyzed, and the rate of throwing increases with the strength of the potential. A weak potential cannot provide vortices with enough force. Then, the vortices will be stretched into polygons. However, a strong potential will destroy the vortices.

Photoacoustic Imaging of Animals with an Annular Transducer Array

YANG Di-Wu, ZHOU Zhi-Bin, ZENG Lv-Ming, ZHOU Xin, CHEN Xing-Hui
Chin. Phys. Lett. 2014, 31 (7): 074301 doi: 10.1088/0256-307X/31/7/074301
Full Text: [PDF 526 KB] (14)
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A photoacoustic system with an annular transducer array is presented for rapid, high-resolution photoacoustic tomography of animals. An eight-channel data acquisition system is applied to capture the photoacoustic signals by using multiplexing and the total time of data acquisition and transferring is within 3 s. A limited-view filtered back projection algorithm is used to reconstruct the photoacoustic images. Experiments are performed on a mouse head and a rabbit head and clear photoacoustic images are obtained. The experimental results demonstrate that this imaging system holds the potential for imaging the human brain.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Influence of Forbidden Processes on Similarity Law in Argon Glow Discharge at Low Pressure

FU Yang-Yang, LUO Hai-Yun, ZOU Xiao-Bing, WANG Xin-Xin
Chin. Phys. Lett. 2014, 31 (7): 075201 doi: 10.1088/0256-307X/31/7/075201
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The similarity law of gas discharge is not always valid due to the occurrence of some elementary processes, such as the stepwise ionization process, which are defined as the forbidden processes. To research the influence of forbidden processes on the similarity law, physical parameters (i.e., the electric field, electron density, electron temperature) in similar gaps are investigated based on the fluid model of gas discharge. The products of gas pressure p and dimensions are kept to be constant in similar gaps and the discharge model is solved with and without the forbidden processes, respectively. Discharges in similar gaps are identified as glow discharges and the typical similarity relations all are investigated. The results show that the forbidden processes cause significant deviations of similarity relations from the theoretical ones and the deviations are enlarged as the scaled-down factor k increases. If the forbidden processes are excluded from the model, the similarity law will be valid in argon glow discharge at low pressure.

Quasi-Monoenergetic Electron Beam Generation from Nanothickness Solid Foils Irradiated by Circular-Polarization Laser Pulses

SU Heng-Yi, HUANG Yong-Sheng, WANG Nai-Yan, TANG Xiu-Zhang, LU Wei
Chin. Phys. Lett. 2014, 31 (7): 075202 doi: 10.1088/0256-307X/31/7/075202
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Ultrashort 1022–1024 W/cm2 laser pulses will offer the possibility of producing monoenergetic electron beams in the GeV–TeV level in the future. A laser-electron acceleration scheme is proposed by the interaction between a thin solid foil and an ultra-intense laser pulse for a0≥800σ0, where a0 is the normalized laser field and σ0 is the normalized plasma surface density. The energy of the electrons as a function of time can be described by a simple model which indicates that an exponential relationship exists between the energy and the normalized time τ. A quasi-monoenergetic high density electron beam with 1.3 GeV energy and a 2.2% energy spread has been predicted for a0=223.5 by particle-in-cell simulations. Characteristics of the ultra-high density electron layer formed in the early period of the acceleration are discussed.
CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES

Improved Photoluminescence in InGaN/GaN Strained Quantum Wells

DING Li-Zhen, CHEN Hong, HE Miao, JIANG Yang, LU Tai-Ping, DENG Zhen, CHEN Fang-Sheng, YANG Fan, YANG Qi, ZHANG Yu-Li
Chin. Phys. Lett. 2014, 31 (7): 076101 doi: 10.1088/0256-307X/31/7/076101
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The influence of strain accumulation on optical properties is investigated for InGaN/GaN-based blue light-emitting diodes grown by metal organic vapor-phase epitaxy. It is found that it is possible to reduce the strain relaxation and hence the nonradiative recombination centers in InGaN multi-quantum wells (MQWs) by adopting more InGaN/GaN MQWs pairs. The alleviation of strain relaxation in a superlattice layer results in the crystalline perfection and effective quality improvement of the epitaxial structures. With suitable control of the crystalline quality and reduced strain relaxation in the MQWs, there shows a 4-fold increase in light output luminous efficiency as compared to their conventional counterparts.

Interplay between External Strain and Oxygen Vacancies on Raman Spectra of SnO2

LI Ting-Hui, LI Hai-Tao, PAN Jiang-Hong
Chin. Phys. Lett. 2014, 31 (7): 076201 doi: 10.1088/0256-307X/31/7/076201
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Comprehensive first-principle calculations on strained SnO2 crystal structure indicate that the formation energy of different types of oxygen vacancies depends on the external strain. Many novel Raman modes can be observed, their intensities and positions are strongly dependent on applied stain, which can be ascribed to crystal symmetry destruction by oxygen vacancies. Applied strain can compress/stretch distances between Sn and O atoms; therefore, Sn–O band vibration frequencies can be adjusted accordingly. Our calculated results disclose that the Raman spectra of SnO2 crystal structure with different types of oxygen vacancies are obviously different, which can be used to identify the oxygen vacancy types in strained SnO2 crystal structures.

Majorization Relation in Quantum Critical Systems

HUAI Lin-Ping, ZHANG Yu-Ran, LIU Si-Yuan, YANG Wen-Li, QU Shi-Xian, FAN Heng
Chin. Phys. Lett. 2014, 31 (7): 076401 doi: 10.1088/0256-307X/31/7/076401
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The most basic local conversion is local operations and classical communications (LOCC), which is also the most natural restriction in quantum information processing. We investigate the conversions between the ground states in quantum critical systems via LOCC and propose a novel method to reveal the different convertibilities via majorization relation when a quantum phase transition occurs. The ground-state local convertibility in the one-dimensional transverse field Ising model is studied. It is shown that the LOCC convertibility changes nearly at the phase transition point. The relation between the order of quantum phase transitions and the LOCC convertibility is discussed. Our results are compared with the corresponding results by using the Rényi entropy and the LOCC convertibility with assisted entanglement.

High Solubility of Hetero-Valence Ion (Cu2+) for Reducing Phase Transition and Thermal Expansion of ZrV1.6P0.4O7

YUAN Bao-He, YUAN Huan-Li, SONG Wen-Bo, LIU Xian-Sheng, CHENG Yong-Guang, CHAO Ming-Ju, LIANG Er-Jun
Chin. Phys. Lett. 2014, 31 (7): 076501 doi: 10.1088/0256-307X/31/7/076501
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Large thermal expansion at room temperature and high phase transition temperature of ZrV2O7 limit its practical applications and are reduced by the high solubility of hetero-valence ion (Cu2+) on the basis of an equal-valence substitution of P5+ for V5+. The temperature-dependent Raman spectra show that Zr0.9Cu0.1V1.6P0.4O6.9 maintains a normal parent cubic structure till 173 K and transforms to a 3×3×3 cubic superstructure below 173 K. Temperature dependent x-ray diffraction patterns of Zr0.9Cu0.1V1.6P0.4O6.9 show near zero and negative thermal expansion. High solubility of lower valence Cu2+ relates to an equal-valence substitution of smaller P5+ for V5+, which extends the bond angle of V(P)–O–V in ZrV1.6P0.4O7 close to 180°. The change of microstructure is considered to be responsible for reduced phase transition temperature and thermal expansion.

Imaginary Part of the Surface Tension of Water

XIONG Xiao-Min, CHEN Lan, ZUO Wen-Long, LI Long-Fei, YANG Yue-Bin, PANG Zhi-Yong, ZHANG Jin-Xiu
Chin. Phys. Lett. 2014, 31 (7): 076801 doi: 10.1088/0256-307X/31/7/076801
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We report a direct measurement of the imaginary part of the surface tension of water through a dynamic scheme using a thin vertical glass fiber of diameter of 3 μm with one end glued onto a cantilever beam and the other end touching a water-air interface. The frequency dependence of the dissipation factor experienced by the glass fiber is exactly calculated through measuring the phase delay with various frequencies when the glass fiber is forced to oscillate vertically. We find the same intercept at the dissipation factor axis for different frequency dependences of the dissipation factor for different depths by which the glass fiber is dipped into water. This nonzero dissipation factor at zero frequency presents direct evidence of the existence of the imaginary part of surface tension of water and yields a complex surface tension of water σ=0.073 + i(0.017 ± 0.002) N/m at room temperature.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Current Induced Non-Volatile Resistive Switching Effect in Silicon Devices with Large Magnetoresistance

WANG Ji-Min, ZHANG Xiao-Zhong, PIAO Hong-Guang, LUO Zhao-Chu, XIONG Cheng-Yue
Chin. Phys. Lett. 2014, 31 (7): 077201 doi: 10.1088/0256-307X/31/7/077201
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We develop a non-volatile resistive switching device in a Si–SiO2–Mg structure with an on/off ratio of about 4.5 at a certain transition voltage after being stimulated by a large current. It is observed that the resistance transition voltage Vt shifts reproducibly under a reversed large current. By applying a reading voltage in the range of Vt, non-volatile resistive switching phenomena with an endurance of more than 80 cycles are observed. Moreover, it is also found that the magnetic field could shift Vt to higher values, yielding a voltage dependent room-temperature magnetoresistance in the range of 103% at 1 T. The multifunctional properties of the silicon device suggested by this work may be beneficial to the silicon based industry.

Growth of a-Plane InN Film and Its THz Emission

WANG Guang-Bing, ZHAO Guo-Zhong, ZHENG Xian-Tong, WANG Ping, CHEN Guang, RONG Xin, WANG Xin-Qiang
Chin. Phys. Lett. 2014, 31 (7): 077202 doi: 10.1088/0256-307X/31/7/077202
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We report the growth of a-plane InN on an r-plane sapphire substrate by plasma-assisted molecular-beam epitaxy. It is found that the a-plane InN is successfully grown by using a GaN buffer layer, which has been confirmed by reflection high-energy electron diffraction, x-ray diffraction and Raman scattering measurements. The Hall effect measurement shows that the electron mobility of the as-grown a-plane InN is about 406 cm2/V⋅s with a residual electron concentration of 5.7×1018 cm−3. THz emission from the a-plane InN film is also studied, where it is found that the emission amplitude is inversely proportional to the conductivity.

Transport and Capacitance Properties of Charge Density Wave in Few-Layer 2H–TaS2 Devices

CAO Yu-Fei, CAI Kai-Ming, LI Li-Jun, LU Wen-Jian, SUN Yu-Ping, WANG Kai-You
Chin. Phys. Lett. 2014, 31 (7): 077203 doi: 10.1088/0256-307X/31/7/077203
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We carefully investigate the transport and capacitance properties of few layer charge density wave (CDW) 2H–TaS2 devices. The CDW transition temperature and the threshold voltage vary from device to device, which is attributed to the interlayer interaction and inhomogeneous local defects of these micro-devices based on few layer 2H–TaS2 flakes. The nonlinear rather than linear current voltage characteristic of 2H–TaS2 devices is observed in our experiment at low temperature. The temperature dependence of the relative threshold voltage can be scaled to (1−T/Tr)0.5+δ with δ=0.08 for the different measured devices with the presence of the CDWs. The conductance-voltage and capacity-voltage measurements are performed simultaneously. At very low ac active voltage, we find that the hysteresis loops of these two measurements exactly match each other. Our results point out that the capacity-voltage measurements can also be used to define the threshold depinning voltage of the CDW, which gives us a new method to investigate the CDWs.

Two Superconducting Phases and Their Characteristics in Layered BaTi2(Sb1−xBix)2O with x=0.16

WU Yue, DONG Xiao-Li, MA Ming-Wei, YANG Huai-Xin, ZHANG Chao, ZHOU Fang, ZHOU Xing-Jiang, ZHAO Zhong-Xian
Chin. Phys. Lett. 2014, 31 (7): 077401 doi: 10.1088/0256-307X/31/7/077401
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Two correlated superconducting phases are identified in the layered superconductor BaTi2(Sb1−xBix)2O (x=0.16), with the superconducting transition temperatures of TC=6 K (the high TC phase) and 3.4 K (the low TC Phase), respectively. The 6 K superconducting phase appears first in the as-prepared sample and can decay into the low TC phase by exposure to an ambient atmosphere for a certain duration. Specially, the high TC phase can reappear from the decayed sample with the low TC phase by vacuum annealing. It is also found that the CDW/SDW order occurs only with the 6 K superconducting phase. These notable features and alteration of the superconductivity due to the post-processing and external pressure can be explained by the scenario of electronic phase separation.

Evolution from Diffuse Ferroelectric to Relaxor Ferroelectric in Pb1−xBax(Fe1/2Nb1/2)O3 Solid Solutions

LV Xin, WANG Nan, CHEN Xiang-Ming
Chin. Phys. Lett. 2014, 31 (7): 077701 doi: 10.1088/0256-307X/31/7/077701
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Dielectric and ferroelectric characteristics for Pb1−xBax(Fe1/2Nb1/2)O3 (x=0, 0.05, 0.1, 0.15, and 0.2) ceramics are determined together with their structures. X-ray diffraction (XRD) analysis confirms the solid solutions with the cubic structure. The dielectric nature changes from diffuse ferroelectric to relaxor ferroelectric with increasing x, while the phase transition temperature TC (or Tm) decreases monotonously. The diffuse ferroelectric phase transition is observed in the solid solutions with 0≤x≤0.05. For Pb1−xBax(Fe1/2Nb1/2)O3 with 0.1≤x≤0.2, relaxor ferroelectric behavior is determined, and the Vogel–Fulcher equation is used to describe the relaxor behavior. The 1/ϵ versus T plots reveal the diffusion dielectric characteristics in both diffuse and relaxor ferroelectrics.

Influence of Rapid Thermal Annealing on the Structure and Electrical Properties of Ce-Doped HfO2 Gate Dielectric

MENG Yong-Qiang, LIU Zheng-Tang, FENG Li-Ping, CHEN Shuai
Chin. Phys. Lett. 2014, 31 (7): 077702 doi: 10.1088/0256-307X/31/7/077702
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Ce-doped HfO2 (HfCeO) films are prepared by radio-frequency magnetron sputtering. The influences of rapid thermal annealing on the structure and electrical properties of HfCeO films are investigated. The results show that the incorporation of Ce into HfO2 increases the crystallization temperature of HfO2, and the cubic phase of HfO2 can be stabilized by incorporating Ce into HfO2. After high temperature annealing, Hf 4f core level spectra shift to a higher energy, whereas O 1s core level spectra shift to a lower energy. With increasing annealing temperatures, the effective permittivity increases, whereas the flat-band voltage shift and effective oxide charge density decrease. Moreover, the leakage current density of the HfCeO films decreases initially, and then increases as the annealing temperature increases.

Depolarization and Electrical Response of Porous PZT 95/5 Ferroelectric Ceramics under Shock Wave Compression

WANG Zhi-Zhu, JIANG Yi-Xuan, ZHANG Pan, WANG Xing-Zhe, HE Hong-Liang
Chin. Phys. Lett. 2014, 31 (7): 077703 doi: 10.1088/0256-307X/31/7/077703
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The release of bound charges by shock wave loading of poled lead zirconate titanate (PZT 95/5) ferroelectric ceramics can result in a high-power electrical energy output. In this study, a theoretical formulation describing the depolarization and electrical response of porous PZT 95/5 ceramics in the normal mode to shock wave compression loading perpendicular to the polarization direction is developed. The depoling process in porous poled PZT 95/5 ceramics is analyzed by using a parallel circuit consisting of a current source, capacitance, conductance and a circuit load. This modeling takes the effects of porosity on wave velocity and remanent polarization and dielectric constant into account, and the effects of variations in dielectric constant and conductivity in the shocked region are assessed. The output current characteristics of porous PZT 95/5 ceramics under short-circuit and resistive load conditions are analyzed and compared with the experiment, with the results showing that theoretical predictions taking into consideration the porosity of ferroelectric ceramics are in close agreement with the experimentally measured electrical response of porous PZT 95/5 under shock wave compression loading.

Planar Magnetic Metamaterial Slabs for Magnetic Resonance Imaging Applications

LI Chun-Lai, GUO Jie, ZHANG Peng, YU Quan-Qiang, MA Wei-Tao, MIAO Xi-Gen, ZHAO Zhi-Ya, LUAN Lin
Chin. Phys. Lett. 2014, 31 (7): 077801 doi: 10.1088/0256-307X/31/7/077801
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A type of planar magnetic metamaterial is proposed with a square winding microstructure as a superlens for magnetic resonance imaging (MRI) applications. A direct magnetic field mapping measurement demonstrates that the radio-frequency magnetic field passing through the superlens is increased by as high as 46.9% at the position of about 3 cm behind the superlens. The resonance frequency of the fabricated slabs is found to be in good agreement with the target frequency (63.6 MHz) for a 1.5 T MRI system. MRI experiments with the magnetic superlens show that the intensity of the image and the SNR (signal-to-noise ratio) are both enhanced, implying promising MRI applications of our planar magnetic superlens.

Paths for the Non-radiative Recombination Occurring in CdS:CdO/Si Multi-Interface Nanoheterostructure Array

LI Yong, WANG Xiao-Bo, ZHAO Jin-Chao, LI Xin-Jian
Chin. Phys. Lett. 2014, 31 (7): 077802 doi: 10.1088/0256-307X/31/7/077802
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A CdS:CdO/Si multi-interface nanoheterostructure array (CdS:CdO/Si-NPA) is prepared by a chemical bath deposition method, and three emission bands are observed in the as-grown CdS:CdO film. By measuring its temperature-dependent photoluminescence (PL) spectrum, the variation trends of the peak energies and intensities with temperature for the three bands are obtained. Based on the theoretical analyses and fitting results, the non-radiative recombination processes corresponding to the PL quenching for the three emission bands are attributed to the thermally activated transition between heavy-hole and light-hole levels (at low temperature) and the thermal escape due to the scattering from longitudinal optical phonons (at high temperature), the transition from acceptor levels to surface states, and the transition related to surface defect states, respectively. The clarification of the non-radiative recombination processes in CdS:CdO/Si-NPA might provide useful information for promoting the performance of optoelectronic devices based on CdS/Si nanoheterostructures.

Silver Nanoparticle Fabrication by Laser Ablation in Polyvinyl Alcohol Solutions

Halimah Mohamed. K, Mahmoud Goodarz Naseri, Amir Reza Sadrolhosseini, Arash Dehzangi, Ahmad Kamalianfar, Elias B Saion, Reza Zamiri, Hossein Abastabar Ahangar, Burhanuddin Y. Majlis
Chin. Phys. Lett. 2014, 31 (7): 077803 doi: 10.1088/0256-307X/31/7/077803
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A laser ablation technique is applied for synthesis of silver nanoparticles in different concentrations of polyvinyl alcohol (PVA) aqueous solution. The ablation of high pure silver plate in the solution is carried out by a nanosecond Q-switched Nd:YAG pulsed laser. X-ray diffraction and transmission electron microscopy are implemented to explore the particles sizes. The effects of PVA concentrations on the absorbance of the silver nanoparticles are studied as well, by using a UV-vis spectrophotometer. The preparation process is carried out for deionized water as a reference sample. The comparison of the obtained results with the reference sample shows that the formation efficiency of nanoparticles in PVA is much higher and the sizes of particles are also smaller.
CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

Resistive Switching Behavior in Amorphous Aluminum Oxide Film Grown by Chemical Vapor Deposition

QUAN Xiao-Tong, ZHU Hui-Chao, CAI Hai-Tao, ZHANG Jia-Qi, WANG Xiao-Jiao
Chin. Phys. Lett. 2014, 31 (7): 078101 doi: 10.1088/0256-307X/31/7/078101
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The repeatable bipolar resistive switching phenomenon is observed in amorphous Al2O3 prepared by metal-organic chemical vapor deposition on ITO glass, with ITO as the bottom electrode and Ag as the top electrode. The crystal structure, morphology, composition and optical properties of Al2O3 thin films are investigated by x-ray diffraction, x-ray photoelectron spectroscopy, atomic force microscopy and ultraviolet-visible-infrared spectroscopy, respectively. The electronic character of Ag/Al2O3/ITO structure is tested by an Agilent B1500A. The device shows a typical bipolar resistive switching behavior under the dc voltage sweep mode at room temperature. The variation ratio between HRS and LRS is larger than nearly three orders of magnitude, which indicates the good potential of this structure in future resistive random access memory (ReRAM) applications. Based on the conductive filament model, the high electric field is considered the main reason for the resistive switching according to our measurements.

Structural Evolution during the Oxidation Process of Graphite

FAN Bing-Bing, GUO Huan-Huan, ZHANG Rui, JIA Yu, SHI Chun-Yan
Chin. Phys. Lett. 2014, 31 (7): 078102 doi: 10.1088/0256-307X/31/7/078102
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The structural evolution during the oxidation process of graphite by a modified Hummers method is investigated. The graphite oxide (GO) composition, disorder parameter, and structures are confirmed by means of x-ray diffraction, Fourier transform infrared spectroscopy, Raman, and scanning electron microscope techniques. Results show that: Hydroxyl, carboxyl and ether groups are present in the low-temperature oxide (at 0°C); and the degree of oxidation is increased with a longer oxidation time. The middle-temperature oxidation (35°C) is a transitory stage with a slight change to the GO structures. While for the high-temperature oxidation (95°C), the hydroxyl, carboxyl and epoxide functional groups are largely originated on the GO flakes. Hydroxyl groups are transformed into more epoxide groups with longer oxidation time, and at the same time, ether groups are eliminated, leading to defects (such as holes) on the GO flakes.

Structure and Magnetic Properties of (In,Mn)As Based Core-Shell Nanowires Grown on Si(111) by Molecular-Beam Epitaxy

PAN Dong, WANG Si-Liang, WANG Hai-Long, YU Xue-Zhe, WANG Xiao-Lei, ZHAO Jian-Hua
Chin. Phys. Lett. 2014, 31 (7): 078103 doi: 10.1088/0256-307X/31/7/078103
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We report the structure and magnetic properties of (In,Mn)As based core-shell nanowires grown on Si (111) by molecular-beam epitaxy. Compared to the core InAs nanowire with a flat side facet and consistent diameter, the core-shell nanowire shows a rough sidewall and an inverse tapered geometry. X-ray diffraction, transmission electron microscopy and energy-dispersive x-ray spectroscopy show that (In,Mn)As is formed on the side facets of InAs nanowires with a mixture of wurtzite and zinc-blende structures. Two ferromagnetic transition temperatures of (In,Mn)As from magnetic measurement data are observed: one is less than 25 K, which could be attributed to the magnetic phase with diluted Mn atoms in the InAs matrix, and the other is at ∼300 K, which may originate from the undetectable secondary phases such as MnAs nanoclusters. The synthesis of (In,Mn)As based core-shell nanowires provides valuable information to exploit a new type of spintronic nano-materials.

Radio-Frequency Performance of Epitaxial Graphene Field-Effect Transistors on Sapphire Substrates

LIU Qing-Bin, YU Cui, LI Jia, SONG Xu-Bo, HE Ze-Zhao, LU Wei-Li, GU Guo-Dong, WANG Yuan-Gang, FENG Zhi-Hong
Chin. Phys. Lett. 2014, 31 (7): 078104 doi: 10.1088/0256-307X/31/7/078104
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We report dc and the first-ever measured small signal rf performance of epitaxial graphene field-effect transistors (GFETs), where the epitaxial graphene is grown by chemical vapor deposition (CVD) on a 2-inch c-plane sapphire substrate. Our epitaxial graphene material has a good flatness and uniformity due to the low carbon concentration during the graphene growth. With a gate length Lg=100 nm, the maximum drain source current Ids and peak transconductance gm reach 0.92 A/mm and 0.143 S/mm, respectively, which are the highest results reported for GFETs directly grown on sapphire. The extrinsic cutoff frequency (fT) and maximum oscillation frequency (fmax) of the device are 12 GHz and 9.5 GHz, and up to 32 GHz and 21.5 GHz after de-embedding, respectively. Our work proves that epitaxial graphene on sapphire substrates is a promising candidate for rf electronics.

Micrograting Displacement Sensor with Integrated Electrostatic Actuation

YAO Bao-Yin, FENG Li-Shuang, WANG Xiao, LIU Wei-Fang, LIU Mei-Hua
Chin. Phys. Lett. 2014, 31 (7): 078501 doi: 10.1088/0256-307X/31/7/078501
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A high-resolution micro-grating displacement sensor with diffraction-based and integrated electrostatic actuation is proposed and experimentally demonstrated. The Al reflecting membrane is fabricated at the bottom of a silicon moving part and the Au micro-gratings are patterned on a transparent substrate. This structure forms a phase sensitive diffraction grating, providing the displacement sensitivity of the micro-grating interferometer. It shows sensitivity adjustment and self-calibration capabilities with electrostatic actuation. Additional system components include a coherent light source, photodiodes, and required electronics. Experimental results show that the displacement sensor has a sensitivity of about 1.8 mV/nm and a resolution of less than 1 nm in the linear region. This displacement sensor is very promising in the fields requiring high sensitivity, broad dynamic range, and immunity to electromagnetic interference.

Ultralow-Voltage Electric-Double-Layer Oxide-Based Thin-Film Transistors with Faster Switching Response on Flexible Substrates

ZHANG Jin, WU Guo-Dong
Chin. Phys. Lett. 2014, 31 (7): 078502 doi: 10.1088/0256-307X/31/7/078502
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Phosphosilicate glass (PSG) electrolyte films are deposited by improving the content of phosphorus doping during plasma-enhanced chemical vapor deposition, and a fast electric-double-layer (EDL) polarization response of 100 kHz is measured. The mechanism of the fast polarization response and EDL formation are investigated in detail. By using PSG electrolyte films as gate dielectrics, indium-zinc-oxide (IZO) thin-film transistors (TFTs) are fabricated on flexible plastic substrates. Due to the huge EDL gate capacitance, such TFTs show only 0.8 V operation and excellent electrical performances with a large current on/off ratio of 107, low subthreshold swing of 72 mV/decade and high field-effect mobility of 16.76 cm2/V⋅s. More importantly, the devices exhibit a fast switching response above 100 Hz. Our results demonstrate that such PSG gated TFTs take a great step for low-power flexible oxide electronics application.

TixSb2Te Thin Films for Phase Change Memory Applications

TANG Shi-Yu, LI Run, OU Xin, XU Han-Ni, XIA Yi-Dong, YIN Jiang, LIU Zhi-Guo
Chin. Phys. Lett. 2014, 31 (7): 078503 doi: 10.1088/0256-307X/31/7/078503
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Sb2Te films with different Ti contents (TixSb2Te) are derived via the target-attachment method by using the magnetron sputtering technique. The effects of the Ti content on the phase change characteristics and the microstructures are investigated by x-ray diffraction, x-ray photoelectron spectroscopy, scanning electron microscopy and atom force microcopy. Resistance-temperature measurements are carried out to reveal the enhanced crystallization temperature of TixSb2Te films, indicating a better thermal stability in such films. Both the activation energy and the temperature for 10 y data retention increase with increasing the concentration of Ti. It indicates that the crystallization of the amorphous Sb2Te film could be suppressed by the introduction of Ti. The improvement of crystallization temperature and the thermal stability of the amorphous Sb2Te film results from the introduction of Ti in Sb-Te bond that decreases the binding energy of Sb 4d and Te 4d.

Two Typical Discontinuous Transitions Observed in a Generalized Achlioptas Percolation Process

HU Jian-Quan, YANG Hong-Chun, YANG Yu-Ming, FU Chuan-Ji, YANG Chun, SHI Xiao-Hong, JIA Xiao
Chin. Phys. Lett. 2014, 31 (7): 078901 doi: 10.1088/0256-307X/31/7/078901
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We extend the Achlioptas percolation (AP) process [Achlioptas et al. Science 323 (2009) 1453] to two generalized Achlioptas percolation processes named GAP1 and GAP2. GAP1 induces a weighted probability factor α in the node sampling process and excludes the intracluster links. Based on GAP1, GAP2 requires m pairs of nodes sampled to add m candidate links that should be residing in 2m different clusters at each step. In the evolution of GAP1, the phase transition can evolve from the continuous to the 'most explosive' percolation as the value of the factor α is decreasing to a certain negative number. It indicates that there might be a type of discontinuous transition induced by the probability modulation effect even in the thermodynamic limit, and the most explosive percolation is only one of its extreme cases. We analyze the characteristics of the evolving process of the two-nodes-clusters and the cluster-size distribution at the transformation point for different α; the numerical results suggest that there might be a critical value α0 and the phase transition should be discontinuous (αα0) or continuous (α>α0). In the evolution of GAP2, twice phase transitions are observed successively and the time duration between them becomes shorter till they amalgamate into the 'most explosive' percolation. The first transition is induced by the probability modulation effect analyzed in GAP1, the second transition, induced by the three coexisting giant clusters, is always discontinuous and the maximum jump of order parameter approaches N/3 while the value of the factor α is increasing to 1.4 approximately. In this work, two typical discontinuous transitions induced respectively by the probability modulation and the extended local competition are exhibited in GAP2, which might provide references to analyze the discontinuous phase transition in networks further.
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