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Chin. Phys. Lett.  
  Chin. Phys. Lett.--2016, 33 (12)   Published: 28 November 2016
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Wigner-Matrix-Based Normality Test and Application to Weak Signal Detection in SISO/SIMO Systems

Jun Chen, Fei Wang, Jian-Jiang Zhou
Chin. Phys. Lett. 2016, 33 (12): 120201 doi: 10.1088/0256-307X/33/12/120201
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Based on the asymptotic spectral distribution of Wigner matrices, a new normality test method is proposed via reforming the white noise sequence. In this work, the asymptotic cumulative distribution function (CDF) of eigenvalues of the Wigner matrix is deduced. A numerical Kullback–Leibler divergence of the empirical spectral CDF based on test samples from the deduced asymptotic CDF is established, which is treated as the test statistic. For validating the superiority of our proposed normality test, we apply the method to weak 8PSK signal detection in the single-input single-output (SISO) system and the single-input multiple-output (SIMO) system. By comparing with other common normality tests and the existing signal detection methods, simulation results show that the proposed method is superior and robust.

Time-Bin Phase-Encoding Measurement-Device-Independent Quantum Key Distribution with Four Single-Photon Detectors

Guang-Zhao Tang, Shi-Hai Sun, Huan Chen, Chun-Yan Li, Lin-Mei Liang
Chin. Phys. Lett. 2016, 33 (12): 120301 doi: 10.1088/0256-307X/33/12/120301
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Measurement-device-independent quantum key distribution (MDI-QKD) eliminates all loopholes on detection. Previous experiments of time-bin phase-encoding MDI-QKD allow a factor of $\frac{3}{4}$ loss in the final key for the incapability of identifying two successive detection events by a single photon detector. Here we propose a new scheme to realize the time-bin phase-encoding MDI-QKD. The polarization states are used to generate the time bins and the phase-encoding states. The factor of loss in the final key is eliminated by using four single photon detectors at the measurement site. We show the feasibility of our scheme with a proof-of-principle experimental demonstration. The phase reference frame is rotated extremely slowly with only passive stabilization measures. The quantum bit error rate can reach 0.8% in the $Z$-basis and 26.2% in the $X$-basis.

Decoy State Quantum Key Distribution via Beam-Wandering Modeled Atmosphere Channel

Sheng-Li Zhang, Chen-Hui Jin, Jian-Sheng Guo, Jian-Hong Shi, Xu-Bo Zou, Guang-Can Guo
Chin. Phys. Lett. 2016, 33 (12): 120302 doi: 10.1088/0256-307X/33/12/120302
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We investigate the decoy state quantum key distribution via the atmosphere channels. We consider the efficient decoy state method with one-signal state and two-decoy states. Our results show that the decoy state method works even in the channels with fluctuating transmittance. Nevertheless, the key generation rate will be dramatically decreased by atmosphere turbulence, which sheds more light on the characterization of atmosphere turbulence in realistic free-space based quantum key distributions.

Effect of Network Size on Collective Motion of Mean Field for a Globally Coupled Map with Disorder

Jing-Hui Li
Chin. Phys. Lett. 2016, 33 (12): 120501 doi: 10.1088/0256-307X/33/12/120501
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We investigate the effect of the network size (or the elements number) on the collective motion of the mean field for a globally coupled map with disorder. It is shown that, with the increasing network size, the collective motion of the mean field of the globally coupled map can be shrunk periodically. In the absence of disorder or in the presence of disorder while without the coupling, this phenomenon is absent. Our result means that disorder can make the globally coupled map tame itself for certain numbers of network size. In addition, we discuss the possible application of our result to the network for action potential wave block at-a-distance in the heart.

Interaction of Double Sine-Gordon Solitons with External Potentials: an Analytical Model

S. Nazifkar, K. Javidan, M. Sarbishaei
Chin. Phys. Lett. 2016, 33 (12): 120502 doi: 10.1088/0256-307X/33/12/120502
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Interaction of double sine-Gordon solitons with a space dependent potential wall as well as a potential well is investigated by employing an analytical model based on the collective coordinate approach. The potential is added to the model through a suitable nontrivial metric for the background spacetime. The model is able to predict most of the features of the soliton-potential interaction. It is shown that a soliton can pass through a potential barrier if its velocity is larger than a critical velocity which is a function of the initial soliton conditions and also characters of the potential. It is interesting that the solitons of the double sine-Gordon model can be trapped by a potential barrier and oscillate there. This situation is very important in applied physics. The soliton-well system is investigated by using the presented model. Analytical results are also compared with the results of the direct numerical solutions.

Optical-Electrical Characteristics and Carrier Dynamics of Semi-Insulation GaAs by Terahertz Spectroscopic Technique

Xiao-Wei Han, Lei Hou, Lei Yang, Zhi-Quan Wang, Meng-Meng Zhao, Wei Shi
Chin. Phys. Lett. 2016, 33 (12): 120701 doi: 10.1088/0256-307X/33/12/120701
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GaAs has been widely used to fabricate a variety of optoelectronic devices by virtue of its superior performance, and it is very important to accurately measure its electrical and optical properties. In this study, a semi-insulation (SI) GaAs wafer is investigated by the terahertz (THz) non-destructive testing technology. Using an air biased coherent generation and detection THz time domain spectroscopy system, the THz time domain waveform and spectrum of SI-GaAs are obtained by the time domain spectroscopy module, and its optical-electrical characteristics including complex refractive index, permittivity and dielectric loss angle are calculated. Its carrier lifetime is measured by the optical-pump THz-probe module, and the THz pulse induced intervalley scattering in photo-excited SI-GaAs is discussed.

Nuclear Stopping and Pauli Blocking in Heavy-Ion Reactions near Fermi Energy

Yong-Zhong Xing, Xiao-Bin Liu, Ying-Long Shi, Hong-Fei Zhang, Yu-Ming Zheng
Chin. Phys. Lett. 2016, 33 (12): 122501 doi: 10.1088/0256-307X/33/12/122501
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The dissipation phenomenon in the heavy-ion reaction at incident energy near the Fermi energy is studied by simulating the reaction $^{129}$Xe+$^{129}$Sn with the isospin-dependent quantum molecular dynamics model. The calculations involving a proper prescription of implementing the Pauli exclusion principle show that the isotropy ratio measured by free protons emitted in the reaction at energy slightly higher than the Fermi energy is in agreement with the experimental data recently released by the INDRA collaboration. A feasible value of the Pauli-blocking factor is estimated by comparing the theoretical results with the experimental data for the energy range considered here.

Electromagnetically Induced Transparency in a Cold Gas with Strong Atomic Interactions

Yue-Chun Jiao, Xiao-Xuan Han, Zhi-Wei Yang, Jian-Ming Zhao, Suo-Tang Jia
Chin. Phys. Lett. 2016, 33 (12): 123201 doi: 10.1088/0256-307X/33/12/123201
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Electromagnetically induced transparency (EIT) is investigated in a system of cold, interacting cesium Rydberg atoms. The utilized cesium levels $6S_{1/2}$, $6P_{3/2}$ and $nD_{5/2}$ constitute a cascade three-level system, in which a coupling laser drives the Rydberg transition, and a probe laser detects the EIT signal on the $6S_{1/2}$ to $6P_{3/2}$ transition. Rydberg EIT spectra are found to depend on the strong interaction between the Rydberg atoms. Diminished EIT transparency is obtained when the Rabi frequency of the probe laser is increased, whereas the corresponding linewidth remains unchanged. To model the system with a three-level Lindblad equation, we introduce a Rydberg-level dephasing rate $\gamma_{3}=\kappa \times (\rho_{33}/{\it \Omega}_{\rm p})^2$, with a value $\kappa$ that depends on the ground-state atom density and the Rydberg level. The simulation results are largely consistent with the measurements. The experiments, in which the principal quantum number is varied between 30 and 43, demonstrate that the EIT reduction observed at large ${\it \Omega}_{\rm p}$ is due to the strong interactions between the Rydberg atoms.

Dynamic Interference Photoelectron Spectra in Double Ionization: Numerical Simulation of 1D Helium

Fu Sun, Dong Wei, Gui-Zhong Zhang, Xin Ding, Jian-Quan Yao
Chin. Phys. Lett. 2016, 33 (12): 123202 doi: 10.1088/0256-307X/33/12/123202
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We report our numerical simulation on the dynamic interference photoelectron spectra for a one-dimensional (1D) He model exposed to intense ultrashort extreme ultraviolet (XUV) laser pulses. The results demonstrate an unambiguous interference feature in the photoelectron spectra, and the interference is unveiled to originate from the dynamic Stark effect. The interference photoelectron spectra are prompted for intense sub-femtosecond XUV laser pulses in double ionization. The stationary phase picture is corroborated qualitatively in the two-electron system. The ability of probing the dynamic Stark effect by the photoelectron spectra in a pragmatic experiment of single-photon double ionization of He may shed light on further investigation on multi-electron atoms and molecules.

Generalized Hellmann–Feynman Theorem and Its Applications

Xin Sun
Chin. Phys. Lett. 2016, 33 (12): 123601 doi: 10.1088/0256-307X/33/12/123601
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The Hellmann–Feynman (H-F) theorem is generalized from stationary state to dynamical state. The generalized H-F theorem promotes molecular dynamics to go beyond adiabatic approximation and clears confusion in the Ehrenfest dynamics.

Coupling of Cutoff Modes in a Chain of Nonlinear Metallic Nanorods

Wei-Na Cui, Hong-Xia Li, Min Sun, Yong-Yuan Zhu
Chin. Phys. Lett. 2016, 33 (12): 124101 doi: 10.1088/0256-307X/33/12/124101
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We study the coupling of cutoff modes in a chain of metallic nanorods embedded in a Kerr nonlinear optical medium with strong near-field interactions analytically. Based on a quasidiscreteness approach, we derive a system of two coupled nonlinear Schrödinger equations governing the evolution of the envelopes of these modes. It is shown that this system supports a variety of subwavelength plasmonic lattice vector solitons of the bright-bright, bright-dark, dark-bright, and dark-dark type through a cross-phase modulation. It is also shown that the existence of different solitons depends strongly on the gap width scaled for the rod radius and the type of nonlinearity of the embedded medium.

Low Power Consumption Distributed-Feedback Quantum Cascade Lasers Operating in Continuous-Wave Mode above 90$^{\circ}\!$C at $\lambda \sim7.2$µm

Yue Zhao, Jin-Chuan Zhang, Zhi-Wei Jia, Ying-Hui Liu, Ning Zhuo, Shen-Qiang Zhai, Feng-Qi Liu, Zhan-Guo Wang
Chin. Phys. Lett. 2016, 33 (12): 124201 doi: 10.1088/0256-307X/33/12/124201
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We report on the design and fabrication of $\lambda\sim 7.2$ µm distributed feedback quantum cascade lasers for very high temperature cw operation and low electrical power consumption. The cw operation is reported above 90$^{\circ}\!$C. For a 2-mm-long and 10-µm-wide laser coated with high-reflectivity on the rear facet, more than 170 mW of output power is obtained at 20$^{\circ}\!$C with a threshold power consumption of 2.4 W, corresponding to 30 mW with a threshold power consumption of 3.9 W at 90$^{\circ}\!$C. Robust single-mode emission with a side-mode suppression ratio above 25 dB is continuously tunable by the heat sink temperature or injection current.

An Efficient Single-Frequency Yb-Doped All-Fiber MOPA Laser at 1064.3nm

Jin Kang, Bao-Le Lu, Xin-Yuan Qi, Xiao-Qiang Feng, Hao-Wei Chen, Man Jiang, Yang Wang, Pan Fu, Jin-Tao Bai
Chin. Phys. Lett. 2016, 33 (12): 124202 doi: 10.1088/0256-307X/33/12/124202
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An efficient narrow-linewidth single-frequency (SF) Yb-doped all-fiber master oscillator power amplifier (MOPA) laser operating at 1064.3 nm is demonstrated experimentally. A ring cavity SF fiber laser is used as the seed source for the MOPA system and the Yb-doped fibers are employed as the gain medium or the saturable absorber. The SF operation is observed to be stable without mode hopping. The highest output power of 266 mW is obtained under the 400 mW pump power with the corresponding slope efficiency of 66.2%. The linewidth of the amplified output laser is approximately 1 kHz and its optical signal-to-noise ratio is over 45 dB.

The Image Property in an EIT Information Transfer System

Li-Yun Zhang, Hua-Jie Hu, Xin Yang, Ming-Tao Cao, Dong Wei, Pei Zhang, Hong Gao, Fu-Li Li
Chin. Phys. Lett. 2016, 33 (12): 124203 doi: 10.1088/0256-307X/33/12/124203
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We focus on the study of the transferred image property in an electromagnetically induced transparency (EIT) system. In our experiment, a triple-peak image is effectively transferred from a coupling beam to a signal beam based on the EIT effect. It is found that the transferred image intensity profile of the signal beam is the same as that of the coupling beam while not in phase. Furthermore, the propagation property of the transferred image is studied. Due to the narrowing effect, the transferred image keeps narrowing and maintains the shape well within a certain distance outside of the medium. Our experimental results are in excellent agreement with the theoretical analysis.

Large Signal Modulation Characteristics in the Transition Regime for Two-State Lasing Quantum Dot Lasers

Zun-Ren Lv, Hai-Ming Ji, Xiao-Guang Yang, Shuai Luo, Feng Gao, Feng Xu, Tao Yang
Chin. Phys. Lett. 2016, 33 (12): 124204 doi: 10.1088/0256-307X/33/12/124204
Full Text: [PDF 1921 KB] (Downloads:23)
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Large-signal modulation capability, as an important performance indicator, is directly related to the high-speed optical communication technology involved. We experimentally and theoretically investigate the large-signal modulation characteristics of the simultaneous ground-state (GS) and the excited-state (ES) lasing in InAs/GaAs quantum dot laser diodes. The large-signal modulation capability of total light intensity in the transition regime from GS lasing to two-state lasing is unchanged as the bias-current increases. However, GS and ES large-signal eye diagrams show obvious variations during the transition. Relaxation oscillations and large-signal eye diagrams for GS, ES, and total light intensities are numerically simulated and analyzed in detail by using a rate-equation model. The findings show that a complementary relationship between the light intensities for GS and ES lasing exists in both the transition regime and the two-state lasing regime, leading to a much smaller overshooting power and a shorter settling time for the total light intensity. Therefore, the eye diagrams of GS or ES lasing are diffuse whereas those of total light intensity are constant as the bias-current increases in the transition regime.

Spectral Beam Combining of Fiber Lasers by Using Reflecting Volume Bragg Gratings

Tai-Dou Zhou, Xiao-Bao Liang, Chao Li, Lei Zhao, Jian-Jun Wang, Feng Jing
Chin. Phys. Lett. 2016, 33 (12): 124205 doi: 10.1088/0256-307X/33/12/124205
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By employing three reflecting volume Bragg gratings, a near-infrared 4-channel spectral-beam-combining system is demonstrated to present 720 W combined power with a combining efficiency of 94.7%. The combined laser beam is near-diffraction-limited with a beam factor $M^{2}\sim1.54$. During this 4-channel beam-combining process, no special active cooling measures are used to evaluate the volume Bragg gratings as combining elements are under the higher power laser operation. Thermal expansion and period distortion are verified in a 2 kW 2-channel beam-combining process, and the heat issue in the transmission case is found to be more remarkable than that in the diffraction case. Transmitted and diffracted beams experience wave-front aberrations with different degrees, thus leading to distinct beam deterioration.

Tight Focusing Properties of Radially Polarized Gaussian Beams with Pair of Vortices

C. A. P. Janet, K. B. Rajesh, M. Udhayakumar, Z. Jaroszewicz, T. V. S. Pillai
Chin. Phys. Lett. 2016, 33 (12): 124206 doi: 10.1088/0256-307X/33/12/124206
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The tight focusing properties of a radially polarized Gaussian beam with a nested pair of vortices having a radial wave front distribution are investigated theoretically by the vector diffraction theory. The results show that the optical intensity in the focal region can be altered considerably by changing the location of the vortices nested in a radially polarized Gaussian beam. It is noted that focal evolution from one annular focal pattern to a highly confined focal spot in the transverse direction is observed corresponding to the change in the location of the optical vortices in the input plane. It is also observed that the generated focal hole or spot lead to a focal shift along the optical axis remarkably under proper radial phase modulation. Hence the proposed system may be applied to construct tunable optical traps for both high and low refractive index particles.

A Single Mode Hybrid III–V/Silicon On-Chip Laser Based on Flip-Chip Bonding Technology for Optical Interconnection

Hai-Ling Wang, Wan-Hua Zheng
Chin. Phys. Lett. 2016, 33 (12): 124207 doi: 10.1088/0256-307X/33/12/124207
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A single mode hybrid III–V/silicon on-chip laser based on the flip-chip bonding technology for on-chip optical interconnection is demonstrated. A single mode Fabry–Pérot laser structure with micro-structures on an InP ridge waveguide is designed and fabricated on an InP/AlGaInAs multiple quantum well epitaxial layer structure wafer by using i-line lithography. Then, a silicon waveguide platform including a laser mounting stage is designed and fabricated on a silicon-on-insulator substrate. The single mode laser is flip-chip bonded on the laser mounting stage. The lasing light is butt-coupling to the silicon waveguide. The laser power output from a silicon waveguide is 1.3 mW, and the threshold is 37 mA at room temperature and continuous wave operation.

Numerical Perspective of Second-Harmonic Generation of Circumferential Guided Wave Propagation in a Circular Tube

Ming-Liang Li, Ming-Xi Deng, Wu-Jun Zhu, Guang-Jian Gao, Yan-Xun Xiang
Chin. Phys. Lett. 2016, 33 (12): 124301 doi: 10.1088/0256-307X/33/12/124301
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The effect of second-harmonic generation (SHG) by primary (fundamental) circumferential guided wave (CGW) propagation is investigated from a numerical standpoint. To enable that the second harmonic of the primary CGW mode can accumulate along the circumferential direction, an appropriate mode pair of primary and double frequency CGWs is chosen. Finite element simulations and evaluations of nonlinear CGW propagation are analyzed for the selected CGW mode pair. The numerical simulations performed directly demonstrate that the response of SHG is completely generated by the desired primary CGW mode that satisfies the condition of phase velocity matching at a specific driving frequency, and that the second harmonic of the primary CGW mode does have a cumulative effect with circumferential angles. The numerical perspective obtained yields an insight into the complicated physical process of SHG of primary CGW propagation unavailable previously.

A Simple Method for Source Depth Estimation with Multi-path Time Delay in Deep Ocean

Kun-De Yang, Qiu-Long Yang, Xiao-Le Guo, Ran Cao
Chin. Phys. Lett. 2016, 33 (12): 124302 doi: 10.1088/0256-307X/33/12/124302
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A method of source depth estimation based on the multi-path time delay difference is proposed. When the minimum time arrivals in all receiver depths are snapped to a certain time on time delay-depth plane, time delay arrivals of surface-bottom reflection and bottom-surface reflection intersect at the source depth. Two hydrophones deployed vertically with a certain interval are required at least. If the receiver depths are known, the pair of time delays can be used to estimate the source depth. With the proposed method the source depth can be estimated successfully in a moderate range in the deep ocean without complicated matched-field calculations in the simulations and experiments.

A Videographic Study of Dynamic Phase Separation for Immiscible Solutions under Acoustic Levitation Condition

Wei-Li Wang, Yu-Hao Wu, Xiao-Yu Lu, Bing-Bo Wei
Chin. Phys. Lett. 2016, 33 (12): 124303 doi: 10.1088/0256-307X/33/12/124303
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The transparent aqueous solutions of succinonitrile (SCN) provide an effective model system to simulate the phase separation process of various advanced materials. Here we report a real-time and in-situ study of phase separation dynamics for the SCN-15%H$_{2}$O, SCN-48%H$_{2}$O and SCN-70%H$_{2}$O solutions implemented by high-speed CCD videography together with acoustic levitation technique. It is found that liquid phase separation induces an unsteady state of drop rotation under levitated conditions. The resultant centrifugal force plays the dominant role in the migration of secondary liquid globules. The most desirable homogeneously dispersive structures can only be derived from the earlier stage of phase separation, whereas three kinds of macrosegregation are always the finally stable structure patterns. The migration velocity of minor liquid phase displays the nonlinear feature owing to the variations of globule location and centrifugal force. The surface tensions and volume fractions of immiscible phases also show a conspicuous influence upon the evolution dynamics of separation morphology.

Measurement of the Elasticity of Biological Soft Tissue of Finite Thickness

Hong-Sheng Zhou, Tong-Yu Wang, Zheng Xu, Qian Cheng, Meng-Lu Qian, Xiao-Yi Liu
Chin. Phys. Lett. 2016, 33 (12): 124601 doi: 10.1088/0256-307X/33/12/124601
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Elasticity is of profound significance to evaluating the function of a biological soft tissue. When the elasticity of a tissue is macroscopically changed, it means that the biological function of the tissue is abnormal and some disease or injury may occur. In the present work, an elastometer is developed to measure the elasticity of biological soft tissues. The measurement is based on the indentation method and the force is measured by the bending of the cantilever. The force-indentation data of the soft tissue is experimentally measured by this elastometer and Young's modulus of the tissue is calculated using the Hertz–Sneddon model. For comparison, a numerical model for the indentation method is established using the finite element method. The difference between the actual modulus and the measured modulus is discussed. The effect of the thickness of the specimen on the measurement is investigated. Young's moduli of beef, porcine liver and porcine kidney are experimentally measured. The results indicate that our elastometer is effective in measuring Young's modulus of a soft tissue quantitatively.

Outstanding Magneto-Caloric Effect of a Gd$_{60}$Ni$_{37}$Co$_{3}$ Amorphous Alloy

Yan-Fei Ma, Ben-Zhen Tang, Lei Xia, Ding Ding
Chin. Phys. Lett. 2016, 33 (12): 126101 doi: 10.1088/0256-307X/33/12/126101
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Outstanding magneto-caloric properties of a Gd$_{60}$Ni$_{37}$Co$_{3}$ amorphous alloy are reported. The magnetic entropy change peak ($-\Delta S_{\rm m}^{\rm peak}$) near the Curie temperature ($T_{\rm c}=135$ K) of the amorphous alloy under 5 T is about 10.42 J$\cdot$kg$^{-1}$K$^{-1}$ and the refrigeration capacity (RC) under 5 T is about 860 J$\cdot$kg$^{-1}$, both of which are almost the highest among the amorphous alloys with $T_{\rm c}$ above 100 K. The magneto-caloric behaviors and the mechanism for the rather high magneto-caloric effect of the Gd$_{60}$Ni$_{37}$Co$_{3}$ metallic glass are investigated.

Temperature-Dependent Debye Temperature and Specific Capacity of Graphene

Xiao-Xia Ren, Wei Kang, Zheng-Fu Cheng, Rui-Lun Zheng
Chin. Phys. Lett. 2016, 33 (12): 126501 doi: 10.1088/0256-307X/33/12/126501
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The shot-range interaction and the atomic anharmonic vibration are both considered, and then the analytic functions of the Debye temperature, the specific capacity and the thermal conductivity of graphene with the temperature are obtained. The influence of anharmonic vibration on these thermal physical properties is also investigated. Some theoretical results are given. If only the harmonic approximation is considered, the Debye temperature of the graphene is unrelated to the temperature. If the anharmonic terms are considered, it increases slowly with the increasing temperature. The molar heat capacity of the graphene increases nonlinearly with the increasing temperature. The mean free path of phonons and the thermal conductivity of the graphene decrease nonlinearly with the increasing temperature. The relative changes of the Debye temperature, the specific heat capacity and the thermal conductivity caused by the anharmonic terms increase with the increasing temperature. The anharmonic effect of atomic vibration becomes more significant under higher temperature.

Micro-Mechanism of Silicon-Based Waveguide Surface Smoothing in Hydrogen Annealing

Qian-Qian Duan, Xin-Yu Ren, Ao-Qun Jian, Hui Zhang, Jian-Long Ji, Qiang Zhang, Wen-Dong Zhang, Sheng-Bo Sang
Chin. Phys. Lett. 2016, 33 (12): 126801 doi: 10.1088/0256-307X/33/12/126801
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The micro-mechanism of the silicon-based waveguide surface smoothing is investigated systematically to explore the effects of silicon-hydrogen bonds on high-temperature hydrogen annealing waveguides. The effect of silicon-hydrogen bonds on the surface migration movement of silicon atoms and the waveguide surface topography are revealed. The micro-migration from an upper state to a lower state of silicon atoms is driven by silicon-hydrogen bonding, which is the key to ameliorate the rough surface morphology of the silicon-based waveguide. The process of hydrogen annealing is experimentally validated based on the simulated parameters. The surface roughness declines from 1.523 nm to 0.461 nm.

Topological Phase in Non-centrosymmetric Material NaSnBi Hot!

Xia Dai, Cong-Cong Le, Xian-Xin Wu, Sheng-Shan Qin, Zhi-Ping Lin, Jiang-Ping Hu
Chin. Phys. Lett. 2016, 33 (12): 127301 doi: 10.1088/0256-307X/33/12/127301
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We predict that a non-centrosymmetric material NaSnBi locates in a three-dimensional non-trivial topological phase under ambient pressure based on first-principle calculations. By deriving the effective model around the ${\it \Gamma}$ point, we find that the topological phase transition is driven by a Rashba spin-orbital coupling through an odd number of pairs of band touch due to a small anisotropic gap caused by quintic dispersion terms. In contrast to conventional topological insulators, the spin texture of the surface Dirac cone is right-handed and the surface states are strikingly different for different surface terminations.

Experimental Investigation of Electronic Structure of La(O,F)BiSe$_{2}$

Jun Ma, Bin-Bin Fu, Jun-Zhang Ma, Ling-Yuan Kong, Di Chen, Ji-Feng Shao, Chang-Jin Zhang, Tian Qian, Yu-Heng Zhang, Hong Ding
Chin. Phys. Lett. 2016, 33 (12): 127401 doi: 10.1088/0256-307X/33/12/127401
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La(O,F)BiSe$_{2}$ is a layered superconductor and has the same crystal structure with La(O,F)BiS$_{2}$. We investigate the electronic structure of La(O,F)BiSe$_{2}$ using the angle-resolved photoemission spectroscopy. Two electron-like Fermi surfaces around $X(\pi,0)$ are observed, corresponding to the electron doping of 0.23 per Bi site. We clearly resolve anisotropic band splitting along both ${\it \Gamma}$–$X$ and $M$–$X$ due to the cooperative effects of large spin-orbit coupling and interlayer coupling. Moreover, we observe an almost non-dispersive electronic state around $-$0.2 eV between the electron-like bands. This state vanishes after in-situ K evaporation, indicating that it could be the localized surface state caused by defects on the cleaved surface.

Possible Nodeless Superconducting Gaps in Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ and YBa$_2$Cu$_3$O$_{7-x}$ Revealed by Cross-Sectional Scanning Tunneling Spectroscopy Hot!

Ming-Qiang Ren, Ya-Jun Yan, Tong Zhang, Dong-Lai Feng
Chin. Phys. Lett. 2016, 33 (12): 127402 doi: 10.1088/0256-307X/33/12/127402
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Pairing in the cuprate high-temperature superconductors and its origin remain among the most enduring mysteries in condensed matter physics. With cross-sectional scanning tunneling microscopy/spectroscopy, we clearly reveal the spatial-dependence or inhomogeneity of the superconducting gap structure of Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ (Bi2212) and YBa$_2$Cu$_3$O$_{7-x}$ (YBCO) along their $c$-axes on a scale shorter than the interlayer spacing. By tunneling into the (100) plane of a Bi2212 single crystal and a YBCO film, we observe both U-shaped tunneling spectra with extended flat zero-conductance bottoms, and V-shaped gap structures, in different regions of each sample. On the YBCO film, tunneling into a (110) surface only reveals a U-shaped gap without any zero-bias peak. Our analysis suggests that the U-shaped gap is likely a nodeless superconducting gap. The V-shaped gap has a very small amplitude, and is likely proximity-induced by regions having the larger U-shaped gap.

The Complex Magnetism in the Breathing Pyrochlore LiIn(Cr$_{1-x}$Rh$_x$)$_4$O$_8$

Dong-Yi Wang, Cheng Tan, Kevin Huang, Lei Shu
Chin. Phys. Lett. 2016, 33 (12): 127501 doi: 10.1088/0256-307X/33/12/127501
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We perform a detailed investigation of the new 'breathing' pyrochlore compound LiInCr$_4$O$_8$ through Rh substitution with measurements of magnetic susceptibility, specific heat, and x-ray powder diffraction. The antiferromagnetic phase of LiInCr$_4$O$_8$ is found to be slowly suppressed with increasing Rh, up to the critical concentration of $x=0.1$ where the antiferromagnetic phase is still observed with the peak in specific heat $T_{\rm p}=12.5$ K, slightly lower than $T_{\rm p}=14.3$ K for the $x=0$ compound. From the measurements of magnetization we also uncover evidence that substitution increases the amount of frustration. Comparisons are made with the LiGa$_y$In$_{1-y}$Cr$_4$O$_8$ system as well as other frustrated pyrochlore-related materials and comparable amounts of frustration are found. The results of this work show that the engineered breathing pyrochlores present an important method to further understand the complex magnetism in frustrated systems.

High Lattice Match Growth of InAsSb Based Materials by Molecular Beam Epitaxy

Yang Ren, Rui-Ting Hao, Si-Jia Liu, Jie Guo, Guo-Wei Wang, Ying-Qiang Xu, Zhi-Chuan Niu
Chin. Phys. Lett. 2016, 33 (12): 128101 doi: 10.1088/0256-307X/33/12/128101
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High lattice match growth of InAsSb based materials on GaSb substrates is demonstrated. The present results indicate that a stable substrate temperature and the optimal flux ratios are of critical importance in achieving a homogeneous InAsSb based material composition throughout the growth period. The quality of these epilayers is assessed using a high-resolution x-ray diffraction and atomic force microscope. The mismatch between the GaSb substrate and InAsSb alloy achieves almost zero, and the rms surface roughness of InAsSb alloy achieves around 1.7 Å over an area of 28 µm $\times$ 28 µm. At the same time, the mismatches between GaSb and InAs/InAs$_{0.73}$Sb$_{0.27}$ superlattices (SLs) achieve approximately 100 arcsec (75 periods) and zero (300 periods), with the surface rms roughnesses of InAs/InAs$_{0.73}$Sb$_{0.27}$ SLs around 1.8 Å (75 periods) and 2.1 Å (300 periods) over an area of 20 µm$\times$20 µm, respectively. After fabrication and characterization of the devices, the dynamic resistance of the n-barrier-n InAsSb photodetector near zero bias is of the order of 10$^{6}$ $\Omega\cdot$cm$^{2}$. At 77 K, the positive-intrinsic-negative photodetectors are demonstrated in InAsSb and InAs/InAsSb SL (75 periods) materials, exhibiting fifty-percent cutoff wavelengths of 3.8 µm and 5.1 µm, respectively.

C-Implanted N-Polar GaN Films Grown by Metal Organic Chemical Vapor Deposition

Ying Zhao, Sheng-Rui Xu, Zhi-Yu Lin, Jin-Cheng Zhang, Teng Jiang, Meng-Di Fu, Jia-Duo Zhu, Qin Lu, Yue Hao
Chin. Phys. Lett. 2016, 33 (12): 128102 doi: 10.1088/0256-307X/33/12/128102
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C-implantation N-polar GaN films are grown on $c$-plane sapphire substrates by metal organic chemical vapor deposition. C-implantation induces a large number of defects and causes disorder of the lattice structure in the N-polar GaN film. Raman measurements performed on the N-polar GaN film before C-implantation after C-implantation and subsequent annealing at 1050$^{\circ}\!$C for 5 min indicate that after annealing the disordered GaN lattice is almost recovered. High resolution x-ray diffraction shows that after implantation there is an obvious increase of screw-dislocation densities, and the densities of edge dislocation show slight change. Carbon implantation can induce deep acceptors in GaN, thus the background carriers induced by the high oxygen incorporation in the N-polar GaN film will be partially compensated for, resulting in 25 times the resistivity, which is demonstrated by the temperature-dependent Hall-effect measurement.

Molecular Beam Epitaxy of Zero Lattice-Mismatch InAs/GaSb Type-II Superlattice

Hai-Long Yu, Hao-Yue Wu, Hai-Jun Zhu, Guo-Feng Song, Yun Xu
Chin. Phys. Lett. 2016, 33 (12): 128103 doi: 10.1088/0256-307X/33/12/128103
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Type-II InAs/GaSb superlattices made of 13 InAs monolayers (MLs) and 7 GaSb MLs are grown on GaSb substrates by solid source molecular beam epitaxy. To obtain lattice-matched structures, thin InSb layers are inserted between InAs and GaSb layers. We complete a series of experiments to investigate the influence of the InSb deposition time, V/III beam-equivalent pressure ratio and interruption time between each layer, and then characterize the superlattice (SL) structures with high-resolution x-ray diffraction and atomic force microscopy. The optimized growth parameters are applied to grow the 100-period SL structure, resulting in the full-width half-maximum of 29.55 arcsec for the first SL satellite peak and zero lattice-mismatch between the zero-order SL peak and the GaSb substrate peak.

Hopf Amplification Originated from the Force-Gating Channels of Auditory Hair Cells

Lin Tian, Yan-Ping Zhang, Zhang-Cai Long
Chin. Phys. Lett. 2016, 33 (12): 128701 doi: 10.1088/0256-307X/33/12/128701
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The sense of mammalian hearing exhibits nonlinear phenomena which are most significant to hearing function, such as nonlinear dynamic compression, nonlinear tuning and combination tones. These nonlinear phenomena are suggested to originate from the Hopf amplification within the cochlea, while the mechanism underlying the Hopf amplification remains elusive. According to the experimental results of force-gating channel operation in hair cells, through a theoretic model, this work reveals a velocity-dependent open probability of force-gating channels in auditory hair cells, and a velocity-dependent active force produced by the force-gating channel operating, which makes sensors hear typical Hopf vibrators with nonlinear hearing phenomena.
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