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Chin. Phys. Lett.  
  Chin. Phys. Lett.--2015, 32 (10)   Published: 14 September 2015
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An Efficient Multiparty Quantum-State Sharing Scheme

QIN Hua-Wang, DAI Yue-Wei
Chin. Phys. Lett. 2015, 32 (10): 100301 doi: 10.1088/0256-307X/32/10/100301
Full Text: [PDF 384 KB] (16)
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An efficient multiparty quantum secret sharing scheme is proposed, in which the secret is a quantum state, and the dealer encodes the secret by performing the operations of quantum-controlled-not and Hadamard gate. The participants perform the single-particle measurements on their particles, and then can cooperate to recover the original quantum state. In our scheme, both the dealer and the participants do not need to perform the entanglement measurement. Compared with the existing schemes, our scheme is simpler and more efficient.

Motion of a Nonrelativistic Quantum Particle in Non-commutative Phase Space

FATEME Hoseini, MA Kai, HASSAN Hassanabadi
Chin. Phys. Lett. 2015, 32 (10): 100302 doi: 10.1088/0256-307X/32/10/100302
Full Text: [PDF 396 KB] (8)
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The equation governing the motion of a quantum particle is considered in nonrelativistic non-commutative phase space. For this aim, we first study new Poisson brackets in non-commutative phase space and obtain the modified equations of motion. Next, using novel transformations, we solve the equation of motion and report the exact analytical solutions.

Quantum Correlations in Ising-XYZ Diamond Chain Structure under an External Magnetic Field

Faizi E., Eftekhari H.
Chin. Phys. Lett. 2015, 32 (10): 100303 doi: 10.1088/0256-307X/32/10/100303
Full Text: [PDF 10378 KB] (6)
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We consider an entangled Ising-XYZ diamond chain structure. Quantum correlations for this model are investigated by using quantum discord and trace distance discord. Quantum correlations are obtained for different values of the anisotropy parameter, magnetic field and temperature. By comparison between quantum correlations, we show that the trace distance discord is always larger than quantum discord. Finally, some novel effects such as increasing the quantum correlations with temperature and constructive role of anisotropy parameter, which may play to the quantum correlations, are observed.

On Hawking Radiation of 3D Rotating Hairy Black Holes

Belhaj A., Chabab M., El Moumni H., Masmar K., Sedra M. B.
Chin. Phys. Lett. 2015, 32 (10): 100401 doi: 10.1088/0256-307X/32/10/100401
Full Text: [PDF 398 KB] (12)
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We study the Hawking radiation of 3D rotating hairy black holes. Specifically, we compute the transition probability of bosonic and fermionic particles in such backgrounds. Then, we show that the transition probability is independent of the nature of the particle. It is observed that the charge of the scalar hairy B and the rotation parameter a control such a probability.

Optimal Performance Analysis of a Three-Terminal Thermoelectric Refrigerator with Ideal Tunneling Quantum Dots

SU Hao, SHI Zhi-Cheng, HE Ji-Zhou
Chin. Phys. Lett. 2015, 32 (10): 100501 doi: 10.1088/0256-307X/32/10/100501
Full Text: [PDF 2597 KB] (7)
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The model of a three-terminal thermoelectric refrigerator with ideal tunneling quantum dots is established. It consists of a cavity connected to two quantum dots embedded between two electron reservoirs at different temperatures and chemical potentials. According to the Landauer formula the expressions for the heat current, the cooling rate and the coefficient of performance (COP) are derived analytically. The performance characteristic curves of the cooling rate versus the coefficient of performance are plotted with numerical calculation. The optimal regions of the cooling rate and the COP are determined. Moreover, we optimize the cooling rate and the COP with respect to the position of energy level of the right quantum dot, respectively. The influence of the width of energy level and the temperature ratio on performance of the three-terminal thermoelectric refrigerator is analyzed. Lastly, when the width of energy level is small enough, the optimal performance of the refrigerator is discussed in detail.

A Longitudinal Zeeman Slower Based on Ring-Shaped Permanent Magnets for a Strontium Optical Lattice Clock

WANG Qiang, LIN Yi-Ge, GAO Fang-Lin, LI Ye, LIN Bai-Ke, MENG Fei, ZANG Er-Jun, LI Tian-Chu, FANG Zhan-Jun
Chin. Phys. Lett. 2015, 32 (10): 100701 doi: 10.1088/0256-307X/32/10/100701
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We report a longitudinal Zeeman slower based on ring-shaped permanent magnetic dipoles used for the strontium optical lattice clock. The Zeeman slower is composed of 40 permanent magnets with the same outer diameter but different inner diameters. The maximum variation of the axial field from its target values is less than 2%. In most parts of the Zeeman slower, the intensity variations of the field in radial spatial distribution are less than 0.1 mT. With this Zeeman slower, the strontium atoms are slowed down to 95 m/s, and approximately 2% of the total atoms are slowed down to less than 50 m/s.

Tunneling of Relativistic Bosons Induced by Magnetic Fields in the Magnetar's Crust

Marina-Aura Dariescu, Ciprian Dariescu, Denisa-Andreea Mihu
Chin. Phys. Lett. 2015, 32 (10): 101101 doi: 10.1088/0256-307X/32/10/101101
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The present work is devoted to the study of bosons evolving in the frozen magnetar's crust endowed with an ultra-strong magnetic field orthogonal to an electric field, both described by periodic functions. We discuss the quantum tunneling process through the one-dimensional potential barrier along Oz. The solutions to the Klein–Gordon equation are expressed in terms of Mathieu's functions which, for computable particle's energy range, are turning from oscillatory to exponentially growing modes along Oz. Within the Jeffreys–Wentzel–Kramers–Brillouin framework, the transmission coefficient is computed for the particle momentum in the middle of the instability range.

Identification of Y(4008), Y(4140), Y(4260), and Y(4360) as Tetraquark States

ZHOU Ping, DENG Cheng-Rong, PING Jia-Lun
Chin. Phys. Lett. 2015, 32 (10): 101201 doi: 10.1088/0256-307X/32/10/101201
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Within the framework of a color flux-tube model with a four-body confinement potential, the tetraquark states [cq][cq] (q=u or d) with IJPC=01 are systematically investigated. The numerical results indicate that states Y(4008), Y(4140), Y(4260), and Y(4360) can be uniformly described as tetraquark states [cq][cq] with n2S+1LJ of 11P1, 15P1, 25P1 and 15F1, respectively, in the color flux-tube model. They are compact three-dimensional spatial configurations similar to a rugby ball, higher orbital angular momentum L, more prolate. The four-body confinement interaction based on a color flux-tube picture should be responsible for the formation of those compact tetraquark states.

High-Power Dual-End-Pumped Actively Q-Switched Ho:YAG Ceramic Laser

DUAN Xiao-Ming, YUAN Jin-He, YAO Bao-Quan, DAI Tong-Yu, LI Jiang, PAN Yu-Bai
Chin. Phys. Lett. 2015, 32 (10): 104201 doi: 10.1088/0256-307X/32/10/104201
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We present a high-power Ho:YAG ceramic laser pumped at 1908 nm. Using a dual-end-pumped structure, the maximum continuous-wave output power of 48 W is obtained, corresponding to a slope efficiency of 70.4% with respect to the absorbed pump power. At actively Q-switched mode, the maximum average output power of 46 W and the minimum pulse width of 21 ns are achieved at a pulse repetition frequency of 20 kHz, corresponding to a peak power of approximately 109.5 kW. In addition, the beam-quality M2 factor is found to be 1.4 at the maximum output power.

Light Focusing through Scattering Media by Particle Swarm Optimization

HUANG Hui-Ling, CHEN Zi-Yang, SUN Cun-Zhi, LIU Ji-Lin, PU Ji-Xiong
Chin. Phys. Lett. 2015, 32 (10): 104202 doi: 10.1088/0256-307X/32/10/104202
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We demonstrate light focusing through scattering media by introducing particle swarm optimization for modulating the phase wavefront. Light refocusing is simulated numerically based on the angular spectrum method and the circular Gaussian distribution model of the scattering media. Experimentally, a spatial light modulator is used to control the phase of incident light, so as to make the scattered light converge to a focus. The influence of divided segments of input light and the effect of the number of iterations on light intensity enhancement are investigated. Simulation results are found to be in good agreement with the theoretical analysis for light refocusing.

High-Power and High-Efficiency Operation of Terahertz Quantum Cascade Lasers at 3.3 THz

LI Yuan-Yuan, LIU Jun-Qi, WANG Tao, LIU Feng-Qi, ZHAI Shen-Qiang, ZHANG Jin-Chuan, ZHUO Ning, WANG Li-Jun, LIU Shu-Man, WANG Zhan-Guo
Chin. Phys. Lett. 2015, 32 (10): 104203 doi: 10.1088/0256-307X/32/10/104203
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A high-power and high-efficiency GaAs/AlGaAs-based terahertz (THz) quantum cascade laser structure emitting at 3.3 THz is presented. The structure is based on a hybrid bound-to-continuum transition and resonant-phonon extraction active region combined with a semi-insulating surface-plasmon waveguide. By optimizing material structure and device processing, the peak optical output power of 758 mW with a threshold current density of 120 A/cm2 and a wall-plug efficiency of 0.92% at 10 K and 404 mW at 77 K are obtained in pulsed operation. The maximum operating temperature is as high as 115 K. In the cw mode, a record optical output power of 160 mW with a threshold current density of 178 A/cm2 and a wall-plug efficiency of 1.32% is achieved at 10 K.

Polarization Stable Vertical Cavity Surface Emitting Laser Array Based on Proton Implantation

XUN Meng, XU Chen, XIE Yi-Yang, DENG Jun, XU Kun, JIANG Guo-Qing, PAN Guan-Zhong, CHEN Hong-Da
Chin. Phys. Lett. 2015, 32 (10): 104204 doi: 10.1088/0256-307X/32/10/104204
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Polarization stable characteristic of vertical cavity surface emitting laser array with rectangular element structure based on proton implantation is achieved. Arrays with different aperture sizes and different array scales are investigated. The maximum orthogonal polarization suppression ratio of a 6×6 array with 6 μm × 4 μm elements is as high as 16.1 dB at 51 mA. The x-polarization dominates y-polarization in the operation current range from the threshold to the saturated current. The full widths at half maximum in far-field profiles for x-polarization and y-polarization are 8.8° and 10.7°, respectively. These results suggest that stable polarization is available in the implant-defined VCSEL array.

Efficient Passively Q-Switched Nd:YAG/Cr4+:YAG/LBO Microchip Laser

FU Sheng-Gui, OUYANG Xue-Ying, LIU Xiao-Juan
Chin. Phys. Lett. 2015, 32 (10): 104205 doi: 10.1088/0256-307X/32/10/104205
Full Text: [PDF 584 KB] (1)
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Performance of an LD-end-pumped passively Q-switched Nd:YAG/Cr4+:YAG microchip laser operating at 1123 nm is studied. A maximum average output power of 517 mW with an optical-to-optical conversion efficiency of 12.6% and a slope efficiency of 25.8% is obtained under a pump power of 4.1 W. A minimum pulse width of 1.1 ns with a pulse repetition rate of 20.2 kHz is obtained, and the corresponding pulse energy and peak power are 25.6 μJ and 23.3 kW, respectively. To our knowledge, the 23.3 kW peak power is the highest among 1123 nm lasers. Additionally, based on the 1123 nm laser, with LBO as the frequency doubler, a 288-mW green-yellow laser at 561 nm is successfully achieved.

Surface Plasmon Interference Lithography Assisted by a Fabry–Perot Cavity Composed of Subwavelength Metal Grating and Thin Metal Film

LIANG Hui-Min, WANG Jing-Quan, WANG Xue, WANG Gui-Mei
Chin. Phys. Lett. 2015, 32 (10): 104206 doi: 10.1088/0256-307X/32/10/104206
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A surface plasmon interference lithography assisted by a Fabry–Perot (F-P) cavity composed of subwavelength metal gratings and a thin metal film is proposed to fabricate high-quality nanopatterns. The calculated results indicate that uniform straight interference fringes with high contrast and high electric-field intensity are formed in the resist under the F-P cavity. The analyses of spatial frequency spectra illuminate the physical mechanism of the formation for the interference fringes. The influence of the F-P cavity spacing is discussed in detail. Moreover, the error analyses reveal that all parameters except the metal grating period in this scheme can bear large tolerances for the device fabrication.

Attosecond-Resolution Er:Fiber-Based Optical Frequency Comb

YAN Lu-Lu, ZHANG Yan-Yan, ZHANG Long, FAN Song-Tao, ZHANG Xiao-Fei, GUO Wen-Ge, ZHANG Shou-Gang, JIANG Hai-Feng
Chin. Phys. Lett. 2015, 32 (10): 104207 doi: 10.1088/0256-307X/32/10/104207
Full Text: [PDF 856 KB] (3)
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Highly stable frequency-controlled optical frequency combs are key elements of many applications in time-frequency and optical-metrology domains. In this work, we demonstrate a highly stable frequency-controlled erbium-fiber-based optical frequency comb system. Its repetition rate is phase-stabilized to a continuous-wave laser with both an intra-cavity electro-optic modulator and a piezo-transducer; while the carrier-envelope-offset frequency is phase-locked to a radio-frequency signal generator by controlling the pump power. In-loop relative frequency stabilities of the comb are below 1 ×10−16 at 1 s, and integrate down to low 10−20 level at 104 s. The corresponding timing uncertainties are 100–200 as over the full measurement range.

Cr2+:ZnS Saturable Absorber Passively Q-Switched Ho:LuVO4 Laser

CUI Zheng, YAO Bao-Quan, DUAN Xiao-Ming, BAI Shuang, LI Jiang, YUAN Jin-He, DAI Tong-Yu, LI Chao-Yu, PAN Yu-Bai
Chin. Phys. Lett. 2015, 32 (10): 104208 doi: 10.1088/0256-307X/32/10/104208
Full Text: [PDF 701 KB] (2)
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We report a cw Tm:YAP laser resonantly pumped Ho:LuVO4 laser in passively Q-switched (PQS) mode with Cr2+:ZnS as a saturable absorber (SA). The influence of different transmittances of the output coupler on laser output performance is analyzed. With T=50%, the maximum PQS average output power of 2.3 W is obtained, corresponding to the slope efficiency and the optical–optical conversion efficiency are 35.1% and 19.8%, respectively. Also, the minimum pulse width of 100 ns is achieved at the maximum pulse repetition frequency of 34.2 kHz. When the maximum cw output power is 2.7 W, the beam quality factor of the horizontal direction M2x=1.04 and the vertical direction M2y=1.10 are obtained. In addition, the central wavelength of the laser output remains to be 2057.5 nm with the output coupler transmittances of 50% and 60% in both cw and PQS operations. The results show that the Cr2+:ZnS can be used as an SA in a Ho:LuVO4 laser around 2-μm wavelength.

Heptad Phase Vortex Array in Extremely Deep Fresnel Diffraction Region Generated by Asymmetrical Metal Subwavelength Holes Film

JIANG Shu-Na, LI Xing, MA Li, GAO Ya-Ru, GUI Wei-Ling, CHENG Chuan-Fu
Chin. Phys. Lett. 2015, 32 (10): 104209 doi: 10.1088/0256-307X/32/10/104209
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We report a heptad vortex array structure in the wave fields in an extremely deep Fresnel diffraction region by asymmetrical subwavelength holes in a metal film illuminated with linearly polarized light. A Mach–Zehnder interferometer with a microscopic objective is used to record the wave fields at different distances, and the phase maps are extracted by Fourier transform of the interference intensities. We study the evolutions of the heptad vortex array with distance from the sample to the object plane. To explain the formations and the evolutions of the vortex array, we calculate the diffracted wave fields with Kirchhoff's diffraction theory. The calculations are basically consistent with the experimental results, and the properties of the heptad vortex array structure are reasonably explained.

Trapping and Cooling of Single Atoms in an Optical Microcavity by a Magic-Wavelength Dipole Trap

LI Wen-Fang, DU Jin-Jin, WEN Rui-Juan, LI Gang, ZHANG Tian-Cai
Chin. Phys. Lett. 2015, 32 (10): 104210 doi: 10.1088/0256-307X/32/10/104210
Full Text: [PDF 828 KB] (6)
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We present trapping and cooling of single cesium atoms inside a microcavity by means of an intracavity far-off-resonance trap (FORT). By the 'magic' wavelength FORT, we achieve state-insensitive single-atom trapping and cooling in a microcavity. The cavity transmission of the probe beam strongly coupled to single atoms enables us to continuously observe the intracavity atom trapping. The average atomic localization time inside the bright FORT is about 7 ms by introducing cavity cooling with appropriate detuning. This experiment presents great potential in coherent state manipulation for strongly coupled atom–photon systems in the context of cavity quantum electrodynamics.

Thermal Transport in Methane Hydrate by Molecular Dynamics and Phonon Inelastic Scattering

WANG Zhao-Liang, YUAN Kun-Peng, TANG Da-Wei
Chin. Phys. Lett. 2015, 32 (10): 104401 doi: 10.1088/0256-307X/32/10/104401
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The heat conduction and thermal conductivity for methane hydrate are simulated from equilibrium molecular dynamics. The thermal conductivity and temperature dependence trend agree well with the experimental results. The nonmonotonic temperature dependence is attributed to the phonon inelastic scattering at higher temperature and to the confinement of the optic phonon modes and low frequency phonons at low temperature. The thermal conductivity scales proportionally with the van der Waals interaction strength. The conversion of a crystal-like nature into an amorphous one occurs at higher strength. Both the temperature dependence and interaction strength dependence are explained by phonon inelastic scattering.

MF-DFA Analysis of Turbulent Transport Measured by a Multipurpose Probe

Lafouti M., Ghoranneviss M.
Chin. Phys. Lett. 2015, 32 (10): 105201 doi: 10.1088/0256-307X/32/10/105201
Full Text: [PDF 615 KB] (3)
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The effect of time of applied bias on the edge turbulent transport is analyzed by the multi-fractal detrend fluctuation analysis (MF-DFA) method in the IR-T1 tokamak. The generalized Hurst exponents and the multifractal spectrum are computed by this method. The MF-DFA method is applied to the fluctuation of gradient of floating potential time series collected by a multipurpose probe. The monofractality or multifractality of the time series can be detected by generalized exponent. The multifractal spectrum describes the singularity content of the process. The results show that with applying bias to the plasma at different times (t=15 ms, 18 ms and 22 ms), the degree of multifractality changes. It reaches the minimum when the bias is applied at t=18 ms. The multifractality source of data is investigated by the surrogate method (phase randomization techniques). The surrogate method can destroy the different types of correlations in all the sizes of fluctuations. The results show that the long-range correlation contributes more to multifractality than the fat tail distribution.

Magneto-Caloric Response of a Gd55Co25Al18Sn2 Bulk Metallic Glass

DING Ding, ZHANG Yi-Qing, XIA Lei
Chin. Phys. Lett. 2015, 32 (10): 106101 doi: 10.1088/0256-307X/32/10/106101
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The magneto-caloric effect (MCE) of a Gd55Co25Al18Sn2 bulk metallic glass (BMG) is investigated. The Gd55Co25Al18Sn2 as-cast rod prepared by a water-cooled copper mold suction casting method exhibits typical amorphous characteristics. The maximum magnetic entropy change (−ΔSmpeak) and the magnetic refrigerant capacity (RC) of the BMG under a field of 5 T are about 9.32 J⋅kg−1⋅K−1 and 832 J⋅kg−1, respectively, both of which are larger than the values of the Gd55Co25Al20 BMG. The mechanism for the improved MCE by minor Sn addition is studied and the field dependence of −ΔSmpeak is investigated for a better understanding on the magneto-caloric behaviors of Gd55Co25Al18Sn2 BMG.

External-Strain-Induced Raman Scattering Modification in g-C3N4 Structures

LI Ting-Hui, LI Hai-Tao, PAN Jiang-Hong, GUO Jun-Hong, HU Fang-Ren
Chin. Phys. Lett. 2015, 32 (10): 106201 doi: 10.1088/0256-307X/32/10/106201
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Regulation of optical properties and electronic structure of graphitic carbon nitride (g-C3N4) via external strain has attracted much attention due to its potential in photocatalyst and electronic devices. However, the identification of g-C3N4 structure transformation induced by strain is greatly lacking. In this work, the Raman spectra of g-C3N4 with external strain are determined theoretically based on the density function theory. Deformation induced by external strain not only regulates the Raman mode positions but also leads to a Raman mode splitting, which can be ascribed to crystal symmetry destruction by strain engineering. Our results suggest the use of Raman scattering in structural identification in deformed g-C3N4 structure.

Growth and Characterization of InAs1−xSbx with Different Sb Compositions on GaAs Substrates

SUN Qing-Ling, WANG Lu, WANG Wen-Qi, SUN Ling, LI Mei-Cheng, WANG Wen-Xin, JIA Hai-Qiang, ZHOU Jun-Ming, CHEN Hong
Chin. Phys. Lett. 2015, 32 (10): 106801 doi: 10.1088/0256-307X/32/10/106801
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InAs1−xSbx with different compositions is grown by molecular beam epitaxy on (100)-oriented semi-insulating GaAs substrates. The increase of Sb content in the epilayer results in the deterioration of crystal quality and surface morphology. Hall measurements show that the carrier concentration increases with the composition of Sb. The electron mobility decreases initially, when Sb composition exceeds a certain value, and the mobility increases slightly. In this work, we emphasize the comparison of crystal quality, surface morphology and electrical properties of epilayers with different Sb compositions.

Observation of Fermi Arcs in Non-Centrosymmetric Weyl Semi-Metal Candidate NbP Hot!

XU Di-Fei, DU Yong-Ping, WANG Zhen, LI Yu-Peng, NIU Xiao-Hai, YAO Qi, Dudin Pavel, XU Zhu-An, WAN Xian-Gang, FENG Dong-Lai
Chin. Phys. Lett. 2015, 32 (10): 107101 doi: 10.1088/0256-307X/32/10/107101
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We report the surface electronic structure of niobium phosphide NbP single crystal on (001) surface by vacuum ultraviolet angle-resolved photoemission spectroscopy. Combining with our first principle calculations, we identify the existence of the Fermi arcs originated from topological surface states. Furthermore, the surface states exhibit circular dichroism pattern, which may correlate with its non-trivial spin texture. Our results provide critical evidence for the existence of the Weyl Fermions in NbP, which lays the foundation for further research.

Transport through a Single Barrier on Monolayer MoS2

CHENG Fang, REN Yi, SUN Jin-Fang
Chin. Phys. Lett. 2015, 32 (10): 107301 doi: 10.1088/0256-307X/32/10/107301
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We investigate theoretically quantum transport through a single barrier on monolayer MoS2. It is found that the transmission properties of spin-up (down) electrons in the K valley are the same as spin-down (up) electrons in the K' valley due to the time-reversal symmetry. Generally, the transmission probability for transport through an n–n–n (or p–p–p) junction is an oscillating function of incident angle, barrier height, as well as the incident energy of electrons. The present transmission shows a directional-dependent tunneling depending sensitively on the spin orientation for transport through a p–p–p junction. While for transport through an n–p-n junction, monolayers of MoS2 become opaque for almost all angles of incident θ0 except for θ0∼θ0m (the resonant angles). The positions and numbers of resonant peaks in the transmission are determined by the distance between the two barriers and the spin orientation. The conductance in such systems can be tuned significantly by changing the height of the electric potential.

Wet Chemical Etching of Antimonide-Based Infrared Materials

HAO Hong-Yue, XIANG Wei, WANG Guo-Wei, XU Ying-Qiang, REN Zheng-Wei, HAN Xi, HE Zhen-Hong, LIAO Yong-Ping, WEI Si-Hang, NIU Zhi-Chuan
Chin. Phys. Lett. 2015, 32 (10): 107302 doi: 10.1088/0256-307X/32/10/107302
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The roughness and the crystallographic orientation selectivity of etched antimonide-based infrared materials are examined and are used to optimize the chemical mesa etching process of the InAs/GaSb superlattice photodiode with the goal of reducing the dark current. The etchant used is based on phosphoric acid (H3PO4), citric acid (C6H8O7) and hydrogen peroxide (H2O2). The roughness of the mesa sidewalls and etching rates are compared and used to find an optimized etchant, with which we obtain optimized mid-wavelength infrared photodiodes possessing an R0A value of 466 Ω⋅cm2 and a detectivity of 1.43×1011 cm⋅Hz1/2W−1. Crystallographic orientation selectivity is seen in InAs etching, and also is seen in the InAs/GaSb superlattice wet chemical etching process.

Effect of Thermal Annealing on Light-Induced Minority Carrier Lifetime Enhancement in Boron-Doped Czochralski Silicon

WANG Hong-Zhe, ZHENG Song-Sheng, CHEN Chao
Chin. Phys. Lett. 2015, 32 (10): 107303 doi: 10.1088/0256-307X/32/10/107303
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The effect of thermal annealing on the light-induced effective minority carrier lifetime enhancement (LIE) phenomenon is investigated on the p-type Czochralski silicon (Cz-Si) wafer passivated by a phosphorus-doped silicon nitride (P-doped SiNx) thin film. The experimental results show that low temperature annealing (below 300°C) can not only increase the effective minority carrier lifetime of P-doped SiNx passivated boron-doped Cz-Si, but also improve the LIE phenomenon. The optimum annealing temperature is 180°C, and its corresponding effective minority carrier lifetime can be increased from initial 7.5 μs to maximum 57.7 μs by light soaking within 15 min after annealing. The analysis results of high-frequency dark capacitance-voltage characteristics reveal that the mechanism of the increase of effective minority carrier lifetime after low temperature annealing is due to the sharp enhancement of field effect passivation induced by the negative fixed charge density, while the mechanism of the LIE phenomenon after low temperature annealing is attributed to the enhancement of both field effect passivation and chemical passivation.

Contact-Size-Dependent Cutoff Frequency of Bottom-Contact Organic Thin Film Transistors

SUN Jing, WANG Hong, WANG Zhan, WU Shi-Wei, MA Xiao-Hua
Chin. Phys. Lett. 2015, 32 (10): 107304 doi: 10.1088/0256-307X/32/10/107304
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The contact-size-dependent characteristic of cutoff frequency fT in bottom-contact organic thin film transistors (OTFTs) is studied. The effects of electrode thickness, field-effect mobility, channel length and gate-source voltage on the contact length (source and drain electrodes' length) related contact resistance of bottom-contact OTFTs are performed with a modified transmission line model. It is found that the contact resistance increases dramatically when the contact length is scaled down to 200 nm. With the help of the contact length related contact resistance, contact-size-dependent fT of bottom-contact OTFTs is studied and it is found that fT increases with the decrease of the contact length in bottom-contact OTFTs.

Waveguide Mode Splitter Based on Multi-mode Dielectric-Loaded Surface Plasmon Polariton Waveguide

CAI Yong-Jing, LI Ming, XIONG Xiao, YU Le, REN Xi-Feng, GUO Guo-Ping, GUO Guang-Can
Chin. Phys. Lett. 2015, 32 (10): 107305 doi: 10.1088/0256-307X/32/10/107305
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In photonic integrated circuits, information is usually encoded in the optical path. In this work, based on the multi-mode dielectric-loaded surface plasmon polariton waveguide, we numerically design a directional coupler, which can divide the different waveguide eigenmodes into different optical paths. The results show a possibility to encode information onto different waveguide modes. We also experimentally demonstrate that the splitting ratio of this directional coupler structure can be tuned without changing its size.

New Superconductivity Dome in LaFeAsO1−xFx Accompanied by Structural Transition Hot!

YANG Jie, ZHOU Rui, WEI Lin-Lin, YANG Huai-Xin, LI Jian-Qi, ZHAO Zhong-Xian, ZHENG Guo-Qing
Chin. Phys. Lett. 2015, 32 (10): 107401 doi: 10.1088/0256-307X/32/10/107401
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High-temperature superconductivity is often found in the vicinity of antiferromagnetism. This is also true in LaFeAsO1−xFx (x≤0.2) and many other iron-based superconductors, which leads to proposals that superconductivity is mediated by fluctuations associated with the nearby magnetism. Here we report the discovery of a new superconductivity dome without low-energy magnetic fluctuations in LaFeAsO1−xFx with 0.25≤x≤0.75, where the maximal critical temperature Tc at xopt=0.5–0.55 is even higher than that at x ≤0.2. By nuclear magnetic resonance and transmission electron microscopy, we show that a C4 rotation symmetry-breaking structural transition takes place for x>0.5 above Tc. Our results point to a new paradigm of high temperature superconductivity.

Polarization Insensitivity in Double-Split Ring and Triple-Split Ring Terahertz Resonators

WU Qian-Nan, LAN Feng, TANG Xiao-Pin, YANG Zi-Qiang
Chin. Phys. Lett. 2015, 32 (10): 107801 doi: 10.1088/0256-307X/32/10/107801
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A modified double-split ring resonator and a modified triple-split ring resonator, which offer polarization-insensitive performance, are investigated, designed and fabricated. By displacing the two gaps of the conventional double-split ring resonator away from the center, the second resonant frequency for the 0° polarized wave and the resonant frequency for the 90° polarized wave become increasingly close to each other until they are finally identical. Theoretical and experimental results show that the modified double-split ring resonator and the modified triple-split ring resonator are insensitive to different polarized waves and show strong resonant frequency dips near 433 and 444 GHz, respectively. The results of this work suggest new opportunities for the investigation and design of polarization-dependent terahertz devices based on split ring resonators.

Synthesis, Structure and Optical Properties of CdO Nanocrystals Directly Grown on Cd Foil

LI Yong, LING Hong, GAO Lei, SONG Yue-Li, TIAN Ming-Li, ZHOU Feng-Qun
Chin. Phys. Lett. 2015, 32 (10): 107802 doi: 10.1088/0256-307X/32/10/107802
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Semiconductor nanocrystals directly grown on the conducting metal can lower the contact resistance and can benefit the electron transfer between the semiconductor and the metal. In the present work, CdO nanocrystals are directly synthesized on the conducting Cd foil through a simple solvothermal method. Cd foil is used as the Cd2+ source and the substrate. The average size of CdO nanocrystals is ∼23.1 nm by analyzing the XRD data. Moreover the growth mechanism is discussed. A hierarchic structure characterized by the nano rods and nano particles in the top and bottom layers, respectively, can be observed. From the UV-vis absorption analyzed by Tauc's relation, the two different optical band gaps are obtained. The photoluminescence spectrum is obtained and studied.

Ab Initio Study of the Dynamical Si–O Bond Breaking Event in α-Quartz

SU Rui, ZHANG Hong, HAN Wei, CHEN Jun
Chin. Phys. Lett. 2015, 32 (10): 107803 doi: 10.1088/0256-307X/32/10/107803
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The Si–O bond breaking event in the -quartz at the first triplet (T1) excitation state is studied by using ab initio molecular dynamics (AIMD) and nudged elastic band calculations. A meta-stable non-bridging oxygen hole center and center (NBOHC-E') is observed in the AIMD which consists of a broken Si–O bond with a Si–O distance of 2.54Å. By disallowing the re-bonding of the Si and O atoms, another defect configuration (III-Si/V-Si) is obtained and validated to be stable at both ground and excitation states. The NBOHC-E' is found to present on the minimal energy pathway of the initial to III-Si/V-Si transition, showing that the generating of the NBOHC-E' is an important step of the excitation induced structure defect. The energy barriers to produce the NBOHC-E' and III-Si/V-Si defects are calculated to be 1.19 and 1.28 eV, respectively. The electronic structures of the two defects are calculated by the self-consistent GW calculations and the results show a clear electron transition from the bonding orbital to the non-bonding orbital.

Au Microdisk-Size Dependence of Quantum Dot Emission from the Hybrid Metal-Distributed Bragg Reflector Structures Employed for Single Photon Sources

WANG Hai-Yan, SU Dan, YANG Shuang, DOU Xiu-Ming, ZHU Hai-Jun, JIANG De-Sheng, NI Hai-Qiao, NIU Zhi-Chuan, ZHAO Cui-Lan, SUN Bao-Quan
Chin. Phys. Lett. 2015, 32 (10): 107804 doi: 10.1088/0256-307X/32/10/107804
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We investigate metallic microdisk-size dependence of quantum dot (QD) spontaneous emission rate and micro-antenna directional emission effect for the hybrid metal-distributed Bragg reflector structures based on a particular single QD emission. It is found that the measured photoluminescence (PL) intensity is very sensitive to the size of metallic disk, showing an enhancement factor of 11 when the optimal disk diameter is 2 μm and the numerical aperture of microscope objective NA=0.5. It is found that for large metal disks, the Purcell effect is dominant for enhanced PL intensity, whereas for small size disks the main contribution comes from plasmon scattering at the disk edge within the light cone collected by the microscope objective.

High-Performance Hybrid White Organic Light-Emitting Diodes Utilizing a Mixed Interlayer as the Universal Carrier Switch

DING Lei, LI Huai-Kun, ZHANG Mai-Li, CHENG Jun, ZHANG Fang-Hui
Chin. Phys. Lett. 2015, 32 (10): 107805 doi: 10.1088/0256-307X/32/10/107805
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A new interlayer is successfully used to be a universal carrier switch, developing high-performance hybrid white organic light-emitting diodes (WOLEDs). By dint of this interlayer, the two-color hybrid WOLED shows a maximum total current efficiency (CE) and power efficiency (PE) of 48.1 cd/A and 37.6 lm/W, respectively, while the three-color hybrid WOLED shows a maximum total CE and PE of 33.8 cd/A and 25.7 lm/W, respectively. The color rendering index of the three-color hybrid WOLEDs are ≥75, which is already a sufficient level for many commercial lighting applications. In addition, both the two-color and three-color hybrid WOLEDs show low efficiency roll-off and stable color. Furthermore, devices with the new interlayer show much higher performance than devices with the most commonly used 4,4-N,N-dicarbazolebiphenyl and N,N'-di(naphthalene-1-yl)-N,N'-diphenyl-benzidine interlayers.

Fabrication of Through Micro-hole Arrays in Silicon Using Femtosecond Laser Irradiation and Selective Chemical Etching

GAO Bo, CHEN Tao, CHEN Ying, SI Jin-Hai, HOU Xun
Chin. Phys. Lett. 2015, 32 (10): 107901 doi: 10.1088/0256-307X/32/10/107901
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We demonstrate a method of fabricating through micro-holes and micro-hole arrays in silicon using femtosecond laser irradiation and selective chemical etching. The micro-hole formation mechanism is identified as the chemical reaction of the femtosecond laser-induced structure change zone and hydrofluoric acid solution. The morphologies of the through micro-holes and micro-hole arrays are characterized by using scanning electronic microscopy. The effects of the pulse number on the depth and diameter of the holes are investigated. Honeycomb arrays of through micro-holes fabricated at different laser powers and pulse numbers are demonstrated.

Simple Method to Fabricate Au Nanoparticle-Decorated TiO2 Nanotube Arrays for Enhanced Visible Light Photocurrent

LU Yu-Hua, WANG Wen-Gui, WENG Yu-Yan, DONG Wen
Chin. Phys. Lett. 2015, 32 (10): 108101 doi: 10.1088/0256-307X/32/10/108101
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Au nanoparticle-decorated TiO2 nanotube arrays are prepared by a simple method, which is a thermal annealing thin gold film deposited on anodic oxidized TiO2 nanotube arrays. These electron microscope images present that Au nanoparticles are well dispersed within the wall and on the surface of the TiO2 nanotubes. Meanwhile, the morphologies of Au nanoparticles can be controlled by changing the thickness of the deposited gold film. Associated with the excitation of localized surface plasmon resonances, the prepared Au nanoparticle-decorated TiO2 nanotube arrays could work as visible light responsive photocatalysts to produce a greatly enhanced photocurrent density. By varying the initial gold film thickness, such Au nanoparticle-decorated TiO2 nanotube arrays could be optimized to obtain the highest photocurrent generation efficiency in the visible and UV light regions.

Fabrication and Piezoelectric Characterization of Single Crystalline GaN Nanobelts

WU Dong-Xu, CHENG Hong-Bin, ZHENG Xue-Jun, WANG Xian-Ying, WANG Ding, LI Jia
Chin. Phys. Lett. 2015, 32 (10): 108102 doi: 10.1088/0256-307X/32/10/108102
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GaN nanobelts are synthesized using the chemical vapor deposition method with the catalyst of Ni. The microstructure, composition and photoluminescence property are characterized by x-ray diffraction, field emission scanning electron microscopy, high-resolution transmission electron microscopy and photoluminescence spectra. The results demonstrate that the single crystalline GaN nanobelts are grown with a hexagonal wurtzite structure, in width ranging from 500 nm to 2 μm and length up to 10–20 μm. Moreover, a large piezoelectric coefficient d33 of 20 pm/V is obtained from GaN nanobelts by an atomic force microscopy and the high piezoelectric property implies that the perfect single crystallinity and the freedom of dislocation for the GaN nanobelt have significant impact on the electromechanical response.

High-Efficiency Bottom-Emitting Organic Light-Emitting Diodes with Double Aluminum as Electrodes

ZHANG Hong-Mei, WANG Dan-Bei, WU Yuan-Wu, FANG Da, HUANG Wei
Chin. Phys. Lett. 2015, 32 (10): 108501 doi: 10.1088/0256-307X/32/10/108501
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Bottom-emitting organic light-emitting diodes (BOLEDs), using Al/MoO3 as the semitransparent anode and LiF/Al as the reflective cathode and Alq3 as the emitter, are fabricated. At the same time, the performance improvement of the BOLEDs having a capping layer inserted between the semitransparent anode and the glass substrate is studied. The optimized microcavity BOLED shows a current efficiency (5.49 cd/A) enhancement of 10% compared with a conventional BOLED based on ITO (5.0 cd/A). Slight color variation is observed in 120° forward viewing angle with 50 nm BCP as the capping layer. Strong dependence of efficiency on Al anode thickness and the thickness and refractor index of the capping layer is explained. The results indicate that the BOLEDs with the double-aluminum electrode have potential practical applications.

Statistical Modeling of Gate Capacitance Variations Induced by Random Dopants in Nanometer MOSFETs Reserving Correlations

LÜ Wei-Feng, WANG Guang-Yi, LIN Mi, SUN Ling-Ling
Chin. Phys. Lett. 2015, 32 (10): 108502 doi: 10.1088/0256-307X/32/10/108502
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We consider intrinsic gate capacitance variations due to random dopants in the nanometer metal oxide semiconductor field effect transistor (MOSFET) channel. The variations of total gate capacitance and gate trans−capacitances are investigated and the strong correlations between the trans−capacitance variations are discovered. A simple statistical model is proposed for accurately capturing total gate capacitance variability based on the correlations. The model fits very well with the Monte Carlo simulations and the average errors are -0.033% for n-type metal-oxide semiconductor and -0.012% for p-type metal-oxide semiconductor, respectively. Our simulation studies also indicate that, owing to these correlations, the total gate capacitance variability will not dominate in gate capacitance variations.

Quantum Coupling Effect between Quantum Dot and Quantum Well in a Resonant Tunneling Photon-Number-Resolving Detector

WENG Qian-Chun, AN Zheng-Hua, XIONG Da-Yuan, ZHU Zi-Qiang
Chin. Phys. Lett. 2015, 32 (10): 108503 doi: 10.1088/0256-307X/32/10/108503
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Excited states of InAs quantum dots (QDs) can be energetically coupled with the confined level of GaAs quantum wells (QWs) in a thin-barrier resonant tunneling diode (RTD). Single charge variation in the coupled QD can effectively switch on/off the resonant tunneling current passing through RTD, not only for efficient single-photon detection but also for photon-number-resolving detection. We present the study of the QD–QW coupling effect in the quantum dot coupled resonant tunneling diode (QD-cRTD) and figure out important factors for further improving the detector performance.

Temperature Effects on Information Capacity and Energy Efficiency of Hodgkin–Huxley Neuron

WANG Long-Fei, JIA Fei, LIU Xiao-Zhi, SONG Ya-Lei, YU Lian-Chun
Chin. Phys. Lett. 2015, 32 (10): 108701 doi: 10.1088/0256-307X/32/10/108701
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Recent experimental and theoretical studies show that energy efficiency, which measures the amount of information processed by a neuron with per unit of energy consumption, plays an important role in the evolution of neural systems. Here we calculate the information rates and energy efficiencies of the Hodgkin–Huxley (HH) neuron model at different temperatures in a noisy environment. It is found that both the information rate and energy efficiency are maximized by certain temperatures. Though the information rate and energy efficiency cannot be maximized simultaneously, the neuron holds a high information processing capacity at the temperature corresponding to the maximal energy efficiency. Our results support the idea that the energy efficiency is a selective pressure that influences the evolution of nervous systems.

Improvements for Manipulating DNA with Optical Tweezers

ZHU Chun-Li, LI Jing
Chin. Phys. Lett. 2015, 32 (10): 108702 doi: 10.1088/0256-307X/32/10/108702
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Recently, numerous biological macromolecular experiments have been conducted with optical tweezers. For the single molecular stretching experiment with optical tweezers, three ways to determine the initial adhesion point of DNA on the coverslip are described in this work. In addition, a new method through analyzing the displacement variance of the trapped particle to obtain the trap height is introduced. Using our proposed methods, the obtained force-extension curve for the operated dsDNA agrees well with the worm-like chain model. These improved methods are also applicable to other related biological macromolecular experiments requiring high precision.

Quintessence Cosmology with an Effective Λ-Term in Lyra Manifold

Khurshudyan M., Pasqua A., Sadeghi J., Farahani H.
Chin. Phys. Lett. 2015, 32 (10): 109501 doi: 10.1088/0256-307X/32/10/109501
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We study quintessence cosmology with an effective Λ-term in Lyra manifold. We consider three different models by choosing variable Λ depending on time, the Hubble parameter and the energy density of dark matter and dark energy. Dark energy is assumed as quintessence which interacts with the dark matter. Using numerical analysis we investigate the behavior of cosmological parameters in three different models and compare our results with observational data. State-finder diagnostic is also performed for all models.
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