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Momentum Spectroscopy for Multiple Ionization of Cold Rubidium in the Elliptically Polarized Laser Field
Junyang Yuan, Yixuan Ma, Renyuan Li, Huanyu Ma, Yizhu Zhang, Difa Ye, Zhenjie Shen, Tianmin Yan, Xincheng Wang, Matthias Weidemüller, Yuhai Jiang
Chin. Phys. Lett. 2020, 37 (5):
053201
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DOI: 10.1088/0256-307X/37/5/053201
Employing recently developed magneto-optical trap recoil ion momentum spectroscopy (MOTRIMS) combined with cold atoms, strong laser pulse, and ultrafast technologies, we study momentum distributions of the multiply ionized cold rubidium (Rb) induced by the elliptically polarized laser pulses (35 fs, $1.3\times 10^{15}$ W/cm$^{2}$). The complete vector momenta of Rb$^{n+}$ ions up to charge state $n = 4$ are recorded with extremely high resolution (0.12 a.u. for Rb$^{+}$). Variations of characteristic multi-bands are displayed in momentum distributions because the ellipticity varies from the linear to circular polarization, are interpreted qualitatively with the classical over-barrier ionization model. Present momentum spectroscopy of cold heavy alkali atoms presents novel strong-field phenomena beyond the noble gases.
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Unusual Destruction and Enhancement of Superfluidity of Atomic Fermi Gases by Population Imbalance in a One-Dimensional Optical Lattice
Qijin Chen, Jibiao Wang, Lin Sun, Yi Yu
Chin. Phys. Lett. 2020, 37 (5):
053702
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DOI: 10.1088/0256-307X/37/5/053702
We study the superfluid behavior of a population imbalanced ultracold atomic Fermi gases with a short range attractive interaction in a one-dimensional (1D) optical lattice, using a pairing fluctuation theory. We show that, besides widespread pseudogap phenomena and intermediate temperature superfluidity, the superfluid phase is readily destroyed except in a limited region of the parameter space. We find a new mechanism for pair hopping, assisted by the excessive majority fermions, in the presence of continuum-lattice mixing, which leads to an unusual constant Bose-Einstein condensate (BEC) asymptote for $T_{\rm c}$ that is independent of pairing strength. In result, on the BEC side of unitarity, superfluidity, when it exists, may be strongly enhanced by population imbalance.
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Indium Tin Oxide Coated D-Shape Fiber as a Saturable Absorber for Generating a Dark Pulse Mode-Locked Laser
B. Nizamani, S. Salam, A. A. A. Jafry, N. M. Zahir, N. Jurami, M. I. M. Abdul Khudus, A. Shuhaimi, E. Hanafi, S. W. Harun
Chin. Phys. Lett. 2020, 37 (5):
054202
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DOI: 10.1088/0256-307X/37/5/054202
A dark pulse mode-locked laser is experimentally demonstrated using the indium tin oxide (ITO) coated D-shape fiber as a saturable absorber (SA). Using the polishing wheel technique, a D-shape single mode fiber was fabricated. A 60-nm-thick layer of ITO was deposited over the D-shape fiber using the electron beam deposition method. The SA has a saturation intensity of 40.32 MW/cm$^{2}$ and a modulation depth of 3.5%. A stable dark pulse mode-locked laser was observed at a central wavelength of 1559.4 nm with repetition rate 0.98 MHz, pulse width 370 ns and signal-to-noise ratio 61 dB.
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High-Efficiency Spectral-Beam-Combined 930nm Diode Laser Source
Yi-Chen Xu, Zhi-Min Wang, Feng-Feng Zhang, Rui-Nan Yang, Xu-Chao Liu, Yue Song, Yong Bo, Qin-Jun Peng, Zu-Yan Xu
Chin. Phys. Lett. 2020, 37 (5):
054203
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DOI: 10.1088/0256-307X/37/5/054203
Spectral beam combining is an effective way to achieve high-brightness direct diode laser output. We present an experimental study on spectral beam combining with external cavity based on transmission grating. Using a series of cylindrical transform lenses with different focal lengths, spectral beaming combining efficiency is greatly improved, and the results of wavelength intervals are consistent with the theoretical calculations. With the injection current of 90 A, a 75.1 W cw 930 nm output power with wavelength span of 18.6 nm and spectral beam combining efficiency of 92.7% is achieved, the beam parameter product is 5.77 mm$\cdot$mrad.
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Approach to Single-Mode Dominated Resonant Emission in GaN-Based Square Microdisks on Si
Meng-Han Liu, Peng Chen, Zi-Li Xie, Xiang-Qian Xiu, Dun-Jun Chen, Bin Liu, Ping Han, Yi Shi, Rong Zhang, You-Dou Zheng, Kai Cheng, Li-Yang Zhang
Chin. Phys. Lett. 2020, 37 (5):
054204
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DOI: 10.1088/0256-307X/37/5/054204
Square microdisks with round corners are fabricated using a standard GaN-based blue LED on Si substrates. Whispering gallery-like modes in the square microdisks are investigated by finite-difference time-domain simulation. The simulation results reveal that the round corners in square microdisks can substantially suppress the number of light propagation paths and further reduce the number of optical modes. A confocal micro-photoluminescence is performed to analyze the optical properties of the square microdisks at room temperature. The single-mode dominant resonant emission is obtained in the square microdisk with corner radius of 1.5 μm.
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Tunable Double-Band Perfect Absorbers via Acoustic Metasurfaces with Nesting Helical Tracks
Shu-Huan Xie, Xinsheng Fang, Peng-Qi Li, Sibo Huang, Yu-Gui Peng, Ya-Xi Shen, Yong Li, Xue-Feng Zhu
Chin. Phys. Lett. 2020, 37 (5):
054301
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DOI: 10.1088/0256-307X/37/5/054301
We propose a design of tunable double-band perfect absorbers based on the resonance absorption in acoustic metasurfaces with nesting helical tracks and deep-subwavelength thicknesses ($ < \lambda /30$ with $\lambda$ being the operation wavelength). By rotating the cover cap with an open aperture on the nesting helical tracks, we can tailor the effective lengths of resonant tubular cavities in the absorber at will, while the absorption peak frequency is flexibly shifted in spectrum and the acoustic impedance is roughly matched with air. The simulated particle velocity fields at different configurations reveal that sound absorption mainly occurs at the open aperture. Our experiment measurements agree well with the theoretical analysis and simulation, demonstrating the wide-spectrum and tunable absorption performance of the designed flat acoustic device.
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Simulation of the Weakly Nonlinear Rayleigh–Taylor Instability in Spherical Geometry
Yun-Peng Yang, Jing Zhang, Zhi-Yuan Li, Li-Feng Wang, Jun-Feng Wu, Wen-Hua Ye, Xian-Tu He
Chin. Phys. Lett. 2020, 37 (5):
055201
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DOI: 10.1088/0256-307X/37/5/055201
The Rayleigh–Taylor instability at the weakly nonlinear (WN) stage in spherical geometry is studied by numerical simulation. The mode coupling processes are revealed. The results are consistent with the WN model based on parameter expansion, while higher order effects are found to be non-negligible. For Legendre mode perturbation $P_n(\cos\theta)$, the nonlinear saturation amplitude (NSA) of the fundamental mode decreases with the mode number $n$. When $n$ is large, the spherical NSA is lower than the corresponding planar one. However, for large $n$, the planar NSA can be recovered by applying Fourier transformation to the bubble/spike near the equator and calculating the NSA of the converted trigonometric harmonic.
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Bubble Formation in Apatite Structures by He-Ion Irradiation at High Temperature
Cai-Yu Wu, Ting-Ting Gao, Zhi-Wei Lin, Yue Zhang, Huan-Huan He, Jian Zhang
Chin. Phys. Lett. 2020, 37 (5):
056101
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DOI: 10.1088/0256-307X/37/5/056101
Apatite ceramics Ca$_{10}$(PO$_{4})_{6}$$X_{2}$ ($X=$F, OH) were prepared by the standard solid state sintering method and irradiated with He ions under a fluence of $5\times 10^{16}$ ions/cm$^{2}$ at 450 $^{\circ}\!$C. Irradiation induced formation and growth of the He bubbles were observed by a transmission electron microscope. Hydroxyapatite Ca$_{10}$(PO$_{4})_{6}$(OH)$_{2}$ and fluoroapatite Ca$_{10}$(PO$_{4})_{6}$F$_{2}$ with different He bubble morphologies indicate the influence of OH$^{-}$/F$^{-}$ substitution on the He-ion annealing efficiency, as well as the structure itself, which affects the process of He bubble evolution and formation. The grain boundaries also act as sinks to accumulate He bubbles. No obvious irradiation damage but slight intensity reduction and left shift of diffraction peaks were observed according to the grazing incidence x-ray diffraction and Raman spectra characterizations, indicating that defects of interstitials and vacancies were generated.
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Electrically Tunable Wafer-Sized Three-Dimensional Topological Insulator Thin Films Grown by Magnetron Sputtering
Qixun Guo, Yu Wu, Longxiang Xu, Yan Gong, Yunbo Ou, Yang Liu, Leilei Li, Yu Yan, Gang Han, Dongwei Wang, Lihua Wang, Shibing Long, Bowei Zhang, Xun Cao, Shanwu Yang, Xuemin Wang, Yizhong Huang, Tao Liu, Guanghua Yu, Ke He, Jiao Teng
Chin. Phys. Lett. 2020, 37 (5):
057301
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DOI: 10.1088/0256-307X/37/5/057301
Three-dimensional (3D) topological insulators (TIs) are candidate materials for various electronic and spintronic devices due to their strong spin-orbit coupling and unique surface electronic structure. Rapid, low-cost preparation of large-area TI thin films compatible with conventional semiconductor technology is the key to the practical applications of TIs. Here we show that wafer-sized Bi$_{2}$Te$_{3}$ family TI and magnetic TI films with decent quality and well-controlled composition and properties can be prepared on amorphous SiO$_{2}$/Si substrates by magnetron cosputtering. The SiO$_{2}$/Si substrates enable us to electrically tune (Bi$_{1-x}$Sb$_{x})_{2}$Te$_{3}$ and Cr-doped (Bi$_{1-x}$Sb$_{x})_{2}$Te$_{3}$ TI films between p-type and n-type behavior and thus study the phenomena associated with topological surface states, such as the quantum anomalous Hall effect (QAHE). This work significantly facilitates the fabrication of TI-based devices for electronic and spintronic applications.
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Origin of Anisotropy in Gadolinium Crystal Using a New Spin Hamiltonian
Dan Wei, Zhibin Chen, Hui Yang, Yongjun Cao, Chuan Liu
Chin. Phys. Lett. 2020, 37 (5):
057501
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DOI: 10.1088/0256-307X/37/5/057501
Single crystal rare-earth magnets, such as hexagonal-close-packed gadolinium, usually have a large second order anisotropy $K_2$ and a negative first order anisotropy $K_1$ at low temperatures, which are difficult to explain using microscopic theories. An atomic scale effective spin Hamiltonian ${\mathcal F}[\{{\boldsymbol S}_i\}]$ is proposed, which, apart from the usual isotropic nearest neighbor coupling $J$, consists of two new terms that are different for in-plane and out-of-plane neighbors and which are characterized by two new couplings $C_1$ and $C_2$, respectively. The hybrid Monte–Carlo method is utilized to sample this system to the desired Boltzmann-like distribution $\exp(-{\mathcal F}/k_{_{\rm B}}T)$. It is found that $K_2$ and $K_1$ are compatible with the experimental values and arise naturally from the exchange anisotropy $C_1$ and $C_2$, which are less than 0.01$\%$ in magnitude of the isotropic exchange energy $J$. This new model spin Hamiltonian can also be applied to study other magnetic properties.
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GaP-Based High-Efficiency Elliptical Cylinder Metasurface in Visible Light
Shuai-Meng Wang, Xiao-Hong Sun, De-Li Chen, Fan Wu
Chin. Phys. Lett. 2020, 37 (5):
057801
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DOI: 10.1088/0256-307X/37/5/057801
Compared with the metal antenna metasurface, the dielectric metasurface has better optical characteristics and smaller ohmic loss in the optical band, which makes it superior. An elliptical cylindrical nanostructured antenna is designed using GaP with excellent transmission characteristics in the visible band. This structure has a transmission efficiency of up to 0.96 in the visible light band. Based on the Pancharatnam–Berry (PB) phase control principle, the metasurface structure composed of the antennas is studied, and its abnormal refraction metasurface and focusing meta-lens are analyzed. It is a highly efficient sub-wavelength structure, and promises great potential for the applications of circular polarization optics, nanolithography, dense storage and biophotonics.
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Ultrafine Mo-Doped Co$_{2}$P Nanorods Anchored on Reduced Graphene Oxide as Efficient Electrocatalyst for the Hydrogen Evolution Reaction
Yi-Xuan Wang, Qing Yang, Chuang Liu, Guang-Xia Wang, Min Wu, Hao Liu, Yong-Ming Sui, Xin-Yi Yang
Chin. Phys. Lett. 2020, 37 (5):
058201
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DOI: 10.1088/0256-307X/37/5/058201
One-dimensional (1D) transition metal phosphides (TMPs) with large specific surface areas, high charge transfer efficiency and excellent electrical conductivity have attracted significant attention in hydrogen evolution reaction (HER) as versatile and active catalysts. Herein, the sub-4 nm Mo-Co$_{2}$P ultrafine nanorods (NRs) anchored on reduced graphene oxide (rGO) were successfully synthesized by a colloidal mesostructured strategy. Electrochemical test results reveal that the Mo-Co$_{2}$P@rGO electrode exhibits superior activity with overpotentials of 204 mV and Tafel slope of 88 mV/dec for HER at 10 mA/cm$^{2}$, relative to the Co$_{2}$P@rGO electrode in 0.5 M H$_{2}$SO$_{4}$ solution. This improvement could be ascribed to the Mo doping, which results in more active sites, higher electrical conductivity and faster electron-transfer rates. This versatile strategy will provide a promising pathway for transition metal-doped compounds as an efficient catalyst.
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Rapid Structure-Based Screening Informs Potential Agents for Coronavirus Disease (COVID-19) Outbreak
Zhi-Wei Yang, Yi-Zhen Zhao, Yong-Jian Zang, He Wang, Xun Zhu, Ling-Jie Meng, Xiao-Hui Yuan, Lei Zhang, Sheng-Li Zhang
Chin. Phys. Lett. 2020, 37 (5):
058701
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DOI: 10.1088/0256-307X/37/5/058701
Coronavirus Disease 2019 (COVID-19), caused by the novel coronavirus, has spread rapidly across China. Consequently, there is an urgent need to sort and develop novel agents for the prevention and treatment of viral infections. A rapid structure-based virtual screening is used for the evaluation of current commercial drugs, with structures of human angiotensin converting enzyme II (ACE2), and viral main protease, spike, envelope, membrane and nucleocapsid proteins. Our results reveal that the reported drugs Arbidol, Chloroquine and Remdesivir may hinder the entry and release of virions through the bindings with ACE2, spike and envelope proteins. Due to the similar binding patterns, NHC ($\beta$-d-N4-hydroxycytidine) and Triazavirin are also in prospects for clinical use. Main protease (3CLpro) is likely to be a feasible target of drug design. The screening results to target 3CLpro reveal that Mitoguazone, Metformin, Biguanide Hydrochloride, Gallic acid, Caffeic acid, Sulfaguanidine and Acetylcysteine seem be possible inhibitors and have potential application in the clinical therapy of COVID-19.
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27 articles
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