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Volume 36 Issue 2
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An Atomic Magnetometer with Spin-Projection Noise Proportional to $\sqrt{{T_2}}$
Hai-Feng Dong, Xiao-Fei Wang, Ji-Min Li, Jing-Ling Chen, Yuan Ren
Chin. Phys. Lett. 2019, 36 (2): 020701 .   DOI: 10.1088/0256-307X/36/2/020701
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There is a common sense view for atomic magnetometers that their spin-projection-noises (SPNs) are inversely proportional to $\sqrt{{T_2}}$, where $T_2$ is the transverse relaxation time. We analyze the current atomic magnetometer types and give a counter-example of this common sense, which is the all-optical spin precession modulated three-axis atomic magnetometer proposed by our group in 2015. Unlike the other atomic magnetometers, the SPN of this kind of atomic magnetometers is proportional to $\sqrt{{T_2}}$ due to the fact that the scale factor between $P_x$ and $B$ can be unrelated to the transverse relaxation time $T_2$. We demonstrate this irrelevance experimentally and analyze the SPN theoretically. Using short-pulse ultra-high power laser to fully polarize the atoms, the phenomenon that SPN decreases with $T_2$ may also be demonstrated experimentally and a new tool for researching SPN in atomic magnetometers may be realized.
Development of Preparation Systems with K$_{2}$CsSb Photocathodes and Study on the Preparation Process
Fan Zhang, Xiao-Ping Li, Xiao-Shen Li
Chin. Phys. Lett. 2019, 36 (2): 022901 .   DOI: 10.1088/0256-307X/36/2/022901
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The next generation of advanced light sources requires photons with large average flux and high brightness, which needs advanced electron gun matched with excellent photocathode materials. K$_{2}$CsSb photocathode has the advantages of high quantum efficiency, long lifetime and instantaneous response. This study introduces the design of a set of K$_{2}$CsSb photocathode preparation systems and detailed preparation process of K$_{2}$CsSb photocathodes, including sequential deposition process and co-deposition process, and finally develops a K$_{2}$CsSb photocathode. The influence of laser power on the quantum efficiency is also investigated.
A Stable Wavelength Operation Ho:YAG Laser with Orthogonally Polarized Pump
Jing-Liang Liu, Xin-Yu Chen, Rui-Ming Wang, Chun-Ting Wu, Guang-Yong Jin
Chin. Phys. Lett. 2019, 36 (2): 024201 .   DOI: 10.1088/0256-307X/36/2/024201
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A stable wavelength operation Ho:YAG laser dual-pumped by two orthogonally polarized Tm:YLF lasers is reported. Under the cw operation mode, a laser output power of 24 W is measured. The corresponding optical-optical conversion efficiency is 44.75% and the slope efficiency is 50.12%. Under the Q-switched operation mode, the output maximum average power is 22.8 W at the re-frequency of 6 kHz. The corresponding optical-optical conversion efficiency and slope efficiency are 42.64% and 48.01%, respectively. The output central wavelength is 2090.73 nm, the linewidth is 0.40 nm, and the beam quality is $M^{2} < 1.6$. Moreover, the shift of the output central wavelength is less than 0.01 nm, and the linewidth shift is also less than 0.01 nm.
Physically Realizable Broadband Acoustic Metamaterials with Anisotropic Density
Zhi-Miao Lu, Li Cai, Ji-Hong Wen, Xing Chen
Chin. Phys. Lett. 2019, 36 (2): 024301 .   DOI: 10.1088/0256-307X/36/2/024301
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Transformation acoustics are concentrated for the purpose of designing novel acoustic devices to tailor acoustic waves to achieve desirable characteristics. However, these devices require fluid or fluid-like materials with an anisotropic density that generally does not exist in nature. Therefore, we introduce pentamode metamaterials into an alternating multilayer isotropic medium model to build fluid-like metamaterials with an anisotropic density. A 2D acoustic bending based on transformation acoustics is established and investigated to verify our method. This idea provides a method to design broadband and physically realizable acoustic metamaterials with an anisotropic density and is meaningful for the design of acoustic metamaterials.
Pitch Shift in Exsomatized Cochlea Observed by Laser Interferometry
Zhang-Cai Long, Tao Shen, Yan-Ping Zhang, Lin Luo
Chin. Phys. Lett. 2019, 36 (2): 024302 .   DOI: 10.1088/0256-307X/36/2/024302
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Pitch is one of the most important auditory perception characteristics of sound; however, the mechanism underlying the pitch perception of sound is unclear. Although theoretical researches have suggested that perception of virtual pitch is connected with physics in cochlea of inner ear, there is no direct experimental observation of virtual pitch processing in the cochlea. By laser interferometry, we observe shift phenomena of virtual pitch in basilar membrane vibration of exsomatized cochlea, which is consistent with perceptual pitch shift observed in psychoacoustic experiments. This means that the complex mechanical vibration of basilar membrane in cochlea plays an important role in pitch information processing during hearing.
Dynamical Study of Granular Flow through a Two-Dimensional Hopper
Lina Yang, Yu-Qi Chen
Chin. Phys. Lett. 2019, 36 (2): 024501 .   DOI: 10.1088/0256-307X/36/2/024501
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The mass flow rate of a granular flow through an aperture under gravity is a long-standing challenge issue in physical science. We show that for steady flow field close to laminar flow, the dynamical equations together with the continue equation and Mohr-circle description of the stress are closed, and hence solvable. In a case of streamline guided by the two-dimensional hopper, we obtain a consistent condition and use it to determine the stress and the velocity distribution. Our result indicates that 3/2 power scaling behavior is recovered with a coefficient $C(\mu,\alpha)$ being a function of frictional coefficient and the hopper angle. It is found that the predicted coefficient $C(\mu,\alpha)$ is compatible with previous studies.
Successive Picket Drive for Mitigating the Ablative Richtmyer–Meshkov Instability
Meng Li, Wen-Hua Ye
Chin. Phys. Lett. 2019, 36 (2): 025201 .   DOI: 10.1088/0256-307X/36/2/025201
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The ablative Richtmyer–Meshkov instability (ARMI) is crucial to the successful ignition implosion of the inertial confinement fusion (ICF) because of its action as the seed of the Rayleigh–Taylor instability. In usual ICF implosions, the first shock driven by various foots of the pulses plays a central role in the ARMI growth. We propose a new scheme for refraining from ARMI with a pulse of successive pickets. With the successive-picket pulse design, a rippled capsule surface is compressed by three successive shocks with sequentially strengthening intensities and ablated stabilization, and the ablative Richtmyer–Meshkov growth is mitigated quite effectively. Our numerical simulations and theoretical analyses identify the validity of this scheme.
Dynamic Spallation in Uranium under Laser Shock Loading
Da-Wu Xiao, Hua Shu, Dong-Li Zou, Chao Lu, Li-Feng He
Chin. Phys. Lett. 2019, 36 (2): 026201 .   DOI: 10.1088/0256-307X/36/2/026201
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The spall behavior of uranium is investigated using direct laser ablation loading experiments. The uranium targets are cut and ground to 0.05 mm, 0.1 mm, and 0.15 mm in thickness. Laser energies are varied to yield a constant peak pressure. This results in different strain rates and varying degrees of damage to the uranium targets. The spall strength is calculated and analyzed from the free surface velocity histories recorded using a line velocity interferometer for any reflections system. The spall strength increases from 4.3 GPa to 9.4 GPa with strain rates ranging from $4.0\times10^{6}$ s$^{-1}$ to $1.7\times10^{7}$ s$^{-1}$. Post-mortem analysis is performed on the recovered samples, revealing the twin-matrix interfaces together with the inclusions to be the primary factor governing the spall fracture of uranium.
CH$_{3}$NH$_{3}$ Formed by Electron Injection at Heterojunction Inducing Peculiar Properties of CH$_{3}$NH$_{3}$PbI$_{3}$ Material
Ao Zhang, Yun-Lin Chen, Chun-Xiu Zhang, Jun Yan
Chin. Phys. Lett. 2019, 36 (2): 026701 .   DOI: 10.1088/0256-307X/36/2/026701
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The effect of formed CH$_{3}$NH$_{3}$ at the heterojunction on properties of CH$_{3}$NH$_{3}$PbI$_{3}$ material is investigated based on experiment and theoretical calculation. Our calculation results show that the giant dielectric constant, anomalous hysteresis and long-lasting polarization for CH$_{3}$NH$_{3}$PbI$_{3}$ originate from the formed CH$_{3}$NH$_{3}$ at the heterojunction. It is found that the induced weak EPS by the reorientation of CH$_{3}$NH$_{3}$ sub-group along the built-in electric field enables us to effectively increase the ordering of entire lead-halide framework. In addition, the heterojunction has an advantage of channel separation between carrier transport and electron diffusion. These properties of the heterojunction are the main origin of the high efficiency of CH$_{3}$NH$_{3}$PbI$_{3}$ solar cells.
Probing Lattice Vibrations at SiO$_{2}$/Si Surface and Interface with Nanometer Resolution
Yue-Hui Li, Mei Wu, Rui-Shi Qi, Ning Li, Yuan-Wei Sun, Cheng-Long Shi, Xue-Tao Zhu, Jian-Dong Guo, Da-Peng Yu, Peng Gao
Chin. Phys. Lett. 2019, 36 (2): 026801 .   DOI: 10.1088/0256-307X/36/2/026801
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Recent advances in monochromatic aberration corrected electron microscopy make it possible to detect the lattice vibrations with both high-energy resolution and high spatial resolution. Here, we use sub-10 meV electron energy loss spectroscopy to investigate the local vibrational properties of the SiO$_{2}$/Si surface and interface. The energy of the surface mode is thickness dependent, showing a blue shift as $z$-thickness (parallel to the fast electron beam) of SiO$_{2}$ film increases, while the energy of the bulk mode and the interface mode keeps constant. The intensity of the surface mode is well-described by a Bessel function of the second kind. The mechanism of the observed spatially dependent vibrational behavior is discussed and compared with dielectric response theory analysis. Our nanometer scale measurements provide useful information on the bonding conditions at the surface and interface.
Eigenstate Distribution Fluctuation of a Quenched Disordered Bose–Hubbard System in Thermal-to-Localized Transitions
Junjun Xu, Yanxing Li
Chin. Phys. Lett. 2019, 36 (2): 027201 .   DOI: 10.1088/0256-307X/36/2/027201
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We study the thermalization of a quenched disordered Bose–Hubbard system. By considering the eigenstate distribution fluctuation, we show that the thermal to many-body localized transition is always connected to a minimum of this distribution fluctuation. We also observe a Mott-localized regime, where the system fails to thermalize due to the strong on-site repulsion. Lastly, we show how to detect this eigenstate distribution fluctuation in a cold atom system, which is equivalent to measure the Loschmidt echo of the system. Our work suggests a way to measure the thermal-to-localized transitions in experiments, especially for a large system.
Phonon Limited Electron Mobility in Germanium FinFETs: Fin Direction Dependence
Ying Jing, Gen-Quan Han, Yan Liu, Jin-Cheng Zhang, Yue Hao
Chin. Phys. Lett. 2019, 36 (2): 027301 .   DOI: 10.1088/0256-307X/36/2/027301
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We investigate the phonon limited electron mobility in germanium (Ge) fin field-effect transistors (FinFETs) with fin rotating within (001), (110), and (111)-oriented wafers. The coupled Schrödinger–Poisson equations are solved self-consistently to calculate the electronic structures for the two-dimensional electron gas, and Fermi's golden rule is used to calculate the phonon scattering rate. It is concluded that the intra-valley acoustic phonon scattering is the dominant mechanism limiting the electron mobility in Ge FinFETs. The phonon limited electron motilities are influenced by wafer orientation, channel direction, fin thickness $W_{\rm fin}$, and inversion charge density $N_{\rm inv}$. With the fixed $W_{\rm fin}$, fin directions of $\langle 110\rangle$, $\langle 1\bar{1}2\rangle$ and $\langle \bar{1}10\rangle$ within (001), (110), and (111)-oriented wafers provide the maximum values of electron mobility. The optimized $W_{\rm fin}$ for mobility is also dependent on wafer orientation and channel direction. As $N_{\rm inv}$ increases, phonon limited mobility degrades, which is attributed to electron repopulation from a higher mobility valley to a lower mobility valley as $N_{\rm inv}$ increases.
Influence of Precursor Powder Fabrication Methods on the Superconducting Properties of Bi-2223 Tapes
Li-Jun Cui, Ping-Xiang Zhang, Guo Yan, Yong Feng, Xiang-Hong Liu, Jian-Feng Li, Xi-Feng Pan, Sheng-Nan Zhang, Xiao-Bo Ma, Jin-Shan Li
Chin. Phys. Lett. 2019, 36 (2): 027401 .   DOI: 10.1088/0256-307X/36/2/027401
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Bi-2223 precursor powders are prepared by both oxalate co-precipitation (CP) and spray pyrolysis (SP) methods. The influence of fabrication methods on the superconducting properties of Bi-2223 tapes are systematically studied. Compared to the CP method, SP powder exhibits spherical particle before calcination and smaller particle size after calcinations with more uniform chemical composition, which leads to a lower reaction temperature during calcination process for Bi-2223 tapes. Meanwhile, the non-superconducting phases in SP powder are more uniformly distributed with smaller particle sizes. These features result in finer homogeneity of critical current in large-length of Bi-2223 tape, higher density of filaments and better texture after heat treatment. Therefore, the SP method could be considered as a better route to prepare precursor powder for large-length Bi-2223 tape fabrication.
Absorptive Fabry–Pérot Interference in a Metallic Nanostructure
Rui Wang, Yan-Ling Wu, B. H. Yu, Li-Li Hu, C. Z. Gu, J. J. Li, Jimin Zhao
Chin. Phys. Lett. 2019, 36 (2): 027801 .   DOI: 10.1088/0256-307X/36/2/027801
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In conventional optics, the Fabry–Pérot (FP) effect is only considered for transparent materials at a macroscopic dimension. Down to the nanometer scale, for absorptive metallic structures, the FP effect has not been directly observed so far. It is unclear whether such a macroscopic effect still holds for a subwavelength metallic nanostructure. Here, we demonstrate the probing of FP interference in a series of nanometer-thick Au films with subwavelength hole arrays. The evidence from both linear and second harmonic generation signals, together with angle-resolved investigations, exhibit features of a FP effect. We also derive an absorptive FP interference equation, which well explains our experimental results. Our results for the first time experimentally confirm the long-persisting hypothesis that the FP effect holds ubiquitously in a metallic nanostructure.
Effect of Nanorod Diameters on Optical Properties of GaN-Based Dual-Color Nanorod Arrays
Liang-Sen Feng, Zhe Liu, Ning Zhang, Bin Xue, Jun-Xi Wang, Jin-Min Li
Chin. Phys. Lett. 2019, 36 (2): 027802 .   DOI: 10.1088/0256-307X/36/2/027802
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Dual-color (blue and green) InGaN/GaN nanorod light-emitting diodes (LEDs) with three different nanorod diameters are fabricated. Enhancement of luminescence intensity per area is observed in blue and green wells, to varying degrees. When the diameter is 40 nm, it sharply decreases, which could be explained by the sidewall nonradiative recombination. Time-resolved photoluminescence is conducted to study the carrier lifetime. High recombination rate is observed in nanorod arrays, and is an order of magnitude less than that of the planar LED. When the diameter is 40 nm, the nonradiative lifetime decreases, and this explains the decrease of intensity. The 3D-FDTD simulations show the enhancement of light extraction out of geometry structure by calculating the transmittance of the nanorod arrays.
Structural Variation and Its Influence on the $1/f$ Noise of a-Si$_{1-x}$Ru$_{x}$ Thin Films Embedded with Nanocrystals
Chong Wang, Hao Zhong, Eddy Simoen, Xiang-Dong Jiang, Ya-Dong Jiang, Wei Li
Chin. Phys. Lett. 2019, 36 (2): 028101 .   DOI: 10.1088/0256-307X/36/2/028101
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The structural variation and its influence on the $1/f$ noise of a-Si$_{1-x}$Ru$_{x}$ thin films are investigated by Raman spectroscopy, transmission electron microscopy, and low frequency noise measurement. The Ru atoms are introduced into the amorphous silicon thin films by rf magnetron co-sputtering. Ru$_{2}$Si nanocrystals are found in the as-deposited samples. It is shown that the $1/f$ noise of the films can be reduced by a slight doping with Ru atoms. Moreover, both the microstructure and the $1/f$ noise performance of a-Si$_{1-x}$Ru$_{x}$ thin films could be improved through a high-temperature annealing treatment.
Formation of Two-Dimensional AgTe Monolayer Atomic Crystal on Ag(111) Substrate
Li Dong, Aiwei Wang, En Li, Qin Wang, Geng Li, Qing Huan, Hong-Jun Gao
Chin. Phys. Lett. 2019, 36 (2): 028102 .   DOI: 10.1088/0256-307X/36/2/028102
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We report on the formation of two-dimensional monolayer AgTe crystal on Ag(111) substrates. The samples are prepared in ultrahigh vacuum by deposition of Te on Ag(111) followed by annealing. Using a scanning tunneling microscope (STM) and low electron energy diffraction (LEED), we investigate the atomic structure of the samples. The STM images and the LEED pattern show that monolayer AgTe crystal is formed on Ag(111). Four kinds of atomic structures of AgTe and Ag(111) are observed: (i) flat honeycomb structure, (ii) bulked honeycomb, (iii) stripe structure, (iv) hexagonal structure. The structural analysis indicates that the formation of the different atomic structures is due to the lattice mismatch and relief of the intrinsic strain in the AgTe layer. Our results provide a simple and convenient method to produce monolayer AgTe atomic crystal on Ag(111) and a template for study of novel physical properties and for future quantum devices.
Ultrafast Carrier Dynamics and Terahertz Photoconductivity of Mixed-Cation and Lead Mixed-Halide Hybrid Perovskites
Wan-Ying Zhao, Zhi-Liang Ku, Li-Ping Lv, Xian Lin, Yong Peng, Zuan-Ming Jin, Guo-Hong Ma, Jian-Quan Yao
Chin. Phys. Lett. 2019, 36 (2): 028401 .   DOI: 10.1088/0256-307X/36/2/028401
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Using time-dependent terahertz spectroscopy, we investigate the role of mixed-cation and mixed-halide on the ultrafast photoconductivity dynamics of two different methylammonium (MA) lead-iodide perovskite thin films. It is found that the dynamics of conductivity after photoexcitation reveals significant correlation on the microscopy crystalline features of the samples. Our results show that mixed-cation and lead mixed-halide affect the charge carrier dynamics of the lead-iodide perovskites. In the (5-AVA)$_{0.05}$(MA)$_{0.95}$PbI$_{2.95}$Cl$_{0.05}$/spiro thin film, we observe a much weaker saturation trend of the initial photoconductivity with high excitation fluence, which is attributed to the combined effect of sequential charge carrier generation, transfer, cooling and polaron formation.
Carrier Dynamics Determined by Carrier-Phonon Coupling in InGaN/GaN Multiple Quantum Well Blue Light Emitting Diodes
Sheng Cao, Xiao-Ming Wu, Jun-Lin Liu, Feng-Yi Jiang
Chin. Phys. Lett. 2019, 36 (2): 028501 .   DOI: 10.1088/0256-307X/36/2/028501
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Phonon sidebands in the electrolumiescence (EL) spectra of InGaN/GaN multiple quantum well blue light emitting diodes are investigated. S-shaped injection current dependence of the energy spacing (ES) between the zero-phonon and first-order phonon-assisted luminescence lines is observed in a temperature range of 100–150 K. The S-shape is suppressed with increasing temperature from 100 to 150 K, and vanishes at temperature above 200 K. The S-shaped injection dependence of ES at low temperatures could be explained by the three stages of carrier dynamics related to localization states: (i) carrier relaxation from shallow into deep localization states, (ii) band filling of shallow and deep localization states, and (iii) carrier overflow from deep to shallow localization states and to higher energy states. The three stages show strong temperature dependence. It is proposed that the fast change of the carrier lifetime with temperature is responsible for the suppression of S-shaped feature. The proposed mechanisms reveal carrier recombination dynamics in the EL of InGaN/GaN MQWs at various injection current densities and temperatures.
19 articles