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Volume 35 Issue 12
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Endoscopic Optical Doppler Tomography Based on Two-Axis Scanning MEMS Mirror
Dong-Lin Wang, Yun-Qi Hao, Feng-Xiao Zhai, Kun Yang, Hong-Qiong Liu, Qiao Chen, Huikai Xie
Chin. Phys. Lett. 2018, 35 (12): 120701 .   DOI: 10.1088/0256-307X/35/12/120701
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We study the feasibility of endoscopic optical Doppler tomography with a micro-electro-mechanical system (MEMS) mirror based probe. The additional phase shifts introduced by the probe are tracked and formulated. The suppression method of the probe phase shifts is proposed and validated by fluid flow detection experiments. In vivo blood flow detection is also implemented on a hairless mouse. The velocities of the blood flow in two directions are obtained to be $-$8.1 mm/s and 6.6 mm/s, respectively.
Sub-Doppler Laser Cooling of $^{23}$Na in Gray Molasses on the $D_{2}$ Line
Zhenlian Shi, Ziliang Li, Pengjun Wang, Zengming Meng, Lianghui Huang, Jing Zhang
Chin. Phys. Lett. 2018, 35 (12): 123701 .   DOI: 10.1088/0256-307X/35/12/123701
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We report on the efficient gray molasses cooling of sodium atoms using the $D_{2}$ optical transition at 589.1 nm. Thanks to the hyperfine split about 6${\it \Gamma}$ between $|F'=2\rangle$ and $|F'=3\rangle$ in the excited state 3$^{2}P_{3/2}$, this atomic transition is effective for the gray molasses cooling mechanism. Using this cooling technique, the atomic sample in $F=2$ ground manifold is cooled from 700 $\mu$K to 56 $\mu$K in 3.5 ms. We observe that the loading efficiency into magnetic trap is increased due to the lower temperature and high phase space density of atomic cloud after gray molasses. This technique offers a promising route for the fast cooling of the sodium atoms in the $F=2$ state.
Shaping the Wavefront of Incident Light with a Strong Robustness Particle Swarm Optimization Algorithm
Bi-Qi Li, Bin Zhang, Qi Feng, Xiao-Ming Cheng, Ying-Chun Ding, Qiang Liu
Chin. Phys. Lett. 2018, 35 (12): 124201 .   DOI: 10.1088/0256-307X/35/12/124201
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We demonstrate a modified particle swarm optimization (PSO) algorithm to effectively shape the incident light with strong robustness and short optimization time. The performance of the modified PSO algorithm and genetic algorithm (GA) is numerically simulated. Then, using a high speed digital micromirror device, we carry out light focusing experiments with the modified PSO algorithm and GA. The experimental results show that the modified PSO algorithm has greater robustness and faster convergence speed than GA. This modified PSO algorithm has great application prospects in optical focusing and imaging inside in vivo biological tissue, which possesses a complicated background.
High Ferroelectricities and High Curie Temperature of BiInO$_{3}$PbTiO$_{3}$ Thin Films Deposited by RF Magnetron Sputtering Method
Ke-xue Sun, Shu-yi Zhang, Kiyotaka Wasa
Chin. Phys. Lett. 2018, 35 (12): 124301 .   DOI: 10.1088/0256-307X/35/12/124301
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Properties of ferroelectric $x$BiInO$_{3}$-($1-x$)PbTiO$_{3}$ ($x$BI-($1-x$)PT) thin films deposited on (101) SrRuO$_{3}$/(200) Pt/(200) MgO substrates by rf magnetron sputtering method and effects of deposition conditions are investigated. The structures of the $x$BI-($1-x$)PT films are characterized by x-ray diffraction and scanning electron microscopy. The results indicate that the thin films are grown with mainly (001) orientation. The chemical compositions of the films are analyzed by scanning electron probe and the results indicate that the loss phenomena of Pb and Bi elements depend on the pressure and temperature during the sputtering process. The sputtering parameters including target composition, substrate temperature, and gas pressure are adjusted to obtain optimum sputtering conditions. To decrease leakage currents, 2 mol% La$_{2}$O$_{3}$ is doped in the targets. The $P$–$E$ hysteresis loops show that the optimized $x$BI-($1-x$)PT ($x=0.24$) film has high ferroelectricities with remnant polarization $2P_{\rm r}=80$ $\mu$C/cm$^{2}$ and coercive electric field $2E_{\rm c}=300$ kV/cm. The Curie temperature is about 640$^{\circ}\!$C. The results show that the films have optimum performance and will have wide applications.
Particle Growth in an Experimental Dusty Plasma System
Shou-Zhi Jiang, Xue-Ni Hou, Jie Kong, Lorin S. Matthews, Truell W. Hyde, Feng Huang, Min-Juan Wang
Chin. Phys. Lett. 2018, 35 (12): 125201 .   DOI: 10.1088/0256-307X/35/12/125201
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The coagulation and growth process of dust particles is investigated through laboratory experiment in a plasma system. A large number of dust particles with different sizes and shapes are formed. The growth process is characterized by the scattering laser intensity and fractal dimension. The comparisons of dust particles and scattering laser intensity obtained at different rf powers are presented. The three-dimensional distribution of dust particles is also given. These results provide an experimental basis for dust growth investigation.
Relativistic Spherical Plasma Waves in a Collisional and Warm Plasma
Zhong-Kui Kuang, Li-Hong Cheng, Pan-Fei Geng, Rong-An Tang, Ju-Kui Xue
Chin. Phys. Lett. 2018, 35 (12): 125202 .   DOI: 10.1088/0256-307X/35/12/125202
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Under Lagrange coordinates, the relativistic spherical plasma wave in a collisional and warm plasma is discussed theoretically. Within the Lagrange coordinates and using the Maxwell and hydrodynamics equations, a wave equation describing the relativistic spherical wave is derived. The damped oscillating spherical wave solution is obtained analytically using the perturbation theory. Because of the coupled effects of spherical geometry, thermal pressure, and collision effect, the electron damps the periodic oscillation. The oscillation frequency and the damping rate of the wave are related to not only the collision and thermal pressure effect but also the space coordinate. Near the center of the sphere, the thermal pressure significantly reduces the oscillation period and the damping rate of the wave, while the collision effect can strongly influence the damping rate. Far away from the spherical center, only the collision effect can reduce the oscillation period of the wave, while the collision effect and thermal pressure have weak influence on the damping rate.
Blistering and Helium Retention of Tungsten and 5% Chromium Doped Tungsten Exposed to 60keV Helium Ions Irradiation
Shu-qin Lv, Wen-jia Han, Jian-gang Yu, Hang Zhou, Mi Liu, Chang-an Chen, Kai-gui Zhu
Chin. Phys. Lett. 2018, 35 (12): 126101 .   DOI: 10.1088/0256-307X/35/12/126101
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Pure tungsten (W) and chromium doped W (W-5%Cr) are prepared by powder metallurgy. The microstructure, blistering and helium retention are investigated by x-ray diffraction, scanning electron microscopy, transmission electron microscopy and thermal desorption spectroscopy (TDS). These results show that the average size and density of helium blisters on the surface of pure W are much larger than those on the W-5%Cr alloy. Vacancy-impurity pairs can reduce the migration coefficients of vacancy and vacancy-helium complexes, and Cr may play a role of such an impurity. Moreover, the TDS result shows that the highest desorption peak moves to higher temperature, which is attributed to the He$_{m}$Cr$_{k}$V$_{n}$ complexes in the W-Cr alloy. In addition, the helium retention is found to be higher in W than in W-5%Cr.
A Calorimetric Study Assisted with First Principle Calculations of Specific Heat for Si-Ge Alloys within a Broad Temperature Range
Qing Wang, Hai-Peng Wang, De-Lu Geng, Ming-Xing Li, Bing-Bo Wei
Chin. Phys. Lett. 2018, 35 (12): 126501 .   DOI: 10.1088/0256-307X/35/12/126501
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Calorimetric measurements are performed to determine the specific heat of Si-$x$ at.% Ge (where $x=0$, 10, 30, 50, 70, 90 and 100) alloys within a broad temperature range from 123 to 823 K. The measured specific heat increases dramatically at low temperatures, and the composition dependence of specific heat is evaluated from the experimental results. Meanwhile, the specific heat at constant volume, the thermal expansion, and the bulk modulus of Si and Ge are investigated by the first principle calculations combined with the quasiharmonic approximation. The negative thermal expansion is observed for both Si and Ge. Furthermore, the isobaric specific heat of Si and Ge is calculated correspondingly from 0 K to their melting points, which is verified by the measured results and accounts for the temperature dependence in a still boarder range.
Structural Evolution and Phase Change Properties of C-Doped Ge$_{2}$Sb$_{2}$Te$_{5}$ Films During Heating in Air
Long Zheng, Xing-Ming Yang, Yi-Feng Hu, Liang-Jun Zhai, Jian-Zhong Xue, Xiao-Qin Zhu, Zhi-Tang Song
Chin. Phys. Lett. 2018, 35 (12): 126801 .   DOI: 10.1088/0256-307X/35/12/126801
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We elucidate the importance of a capping layer on the structural evolution and phase change properties of carbon-doped Ge$_{2}$Sb$_{2}$Te$_{5}$ (C-GST) films during heating in air. Both the C-GST films without and with a thin SiO$_{2}$ capping layer (C-GST and C-GST/SiO$_{2}$) are deposited for comparison. Large differences are observed between C-GST and C-GST/SiO$_{2}$ films in resistance-temperature, x-ray diffraction, x-ray photoelectron spectroscopy, Raman spectra, data retention capability and optical band gap measurements. In the C-GST film, resistance-temperature measurement reveals an unusual smooth decrease in resistance above 110$^{\circ}\!$C during heating. X-ray diffraction result has excluded the possibility of phase change in the C-GST film below 170$^{\circ}\!$C. The x-ray photoelectron spectroscopy experimental result reveals the evolution of Te chemical valence because of the carbon oxidation during heating. Raman spectra further demonstrate that phase changes from an amorphous state to the hexagonal state occur directly during heating in the C-GST film. The quite smooth decrease in resistance is believed to be related with the formation of Te-rich GeTe$_{4-n}$Ge$_{n}$ ($n=0$, 1) units above 110$^{\circ}\!$C in the C-GST film. The oxidation of carbon is harmful to the C-GST phase change properties.
Different Charging-Induced Modulations of Highest Occupied Molecular Orbital Energies in Fullerenes in Comparison with Carbon Nanotubes and Graphene Sheets
Hong-Ping Yang, Hai-Hong Bao, Li-Li Han, Wen-Juan Yuan, Jun Luo, Jing Zhu
Chin. Phys. Lett. 2018, 35 (12): 127301 .   DOI: 10.1088/0256-307X/35/12/127301
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The highest occupied molecular orbital (HOMO) energies of fullerenes are found by quantitative first-principles calculations to be raised by negative charging, and the rising rate rank of the fullerenes is C$_{60}>$C$_{70}>$C$_{80}>$C$_{90}$ $>$C$_{100}>$C$_{180}$. Then we compare fullerenes with carbon nanotubes (CNTs) and graphene sheets (GSs) and find that the increase of the HOMO energy of a fullerene is much faster than that of CNTs and graphene sheets with the same number of C atoms. The rising rate rank is fullerene$>$CNT$>$GS, which holds no matter what the number of C atoms is or which structure the fullerene isomer is. This work paves a new path for developing all-carbon devices with low-dimensional carbon nanomaterials as different functional elements.
Performance Improvement in Hydrogenated Few-Layer Black Phosphorus Field-Effect Transistors
He-Mei Zheng, Shun-Ming Sun, Hao Liu, Ya-Wei Huan, Jian-Guo Yang, Bao Zhu, Wen-Jun Liu, Shi-Jin Ding
Chin. Phys. Lett. 2018, 35 (12): 127302 .   DOI: 10.1088/0256-307X/35/12/127302
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A capping layer for black phosphorus (BP) field-effect transistors (FETs) can provide effective isolation from the ambient air; however, this also brings inconvenience to the post-treatment for optimizing devices. We perform low-temperature hydrogenation on Al$_{2}$O$_{3}$ capped BP FETs. The hydrogenated BP devices exhibit a pronounced improvement of mobility from 69.6 to 107.7 cm$^{2}$v$^{-1}$s$^{-1}$, and a dramatic decrease of subthreshold swing from 8.4 to 2.6 V/dec. Furthermore, high/low frequency capacitance–voltage measurements suggest reduced interface defects in hydrogenated BP FETs. This could be due to the passivation of interface traps at both Al$_{2}$O$_{3}$/BP and BP/SiO$_{2}$ interfaces with hydrogen revealed by secondary ion mass spectroscopy.
A Triplet Resonance in Superconducting Fe$_{1.03}$Se$_{0.4}$Te$_{0.6}$
Juanjuan Liu, A. T. Savici, G. E. Granroth, K. Habicht, Y. Qiu, Jin Hu, Z. Q. Mao, Wei Bao
Chin. Phys. Lett. 2018, 35 (12): 127401 .   DOI: 10.1088/0256-307X/35/12/127401
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From heavy fermion compounds and cuprates to iron pnictides and chalcogenides, a spin resonance at $\hbar{\it \Omega}_0\propto k_{\rm B}T_{\rm c}$ is a staple of nearly magnetic superconductors. Possible explanations include a two-particle bound state or loss of magnon damping in the superconducting state. While both scenarios suggest a central role for magnetic fluctuations, distinguishing them is important to identify the right theoretical framework to understand these types of unconventional superconductors. Using an inelastic neutron scattering technique, we show that the spin resonance in the optimally doped Fe$_{1.03}$Se$_{0.4}$Te$_{0.6}$ superconductor splits into three peaks in a high magnetic field, a signature of a two-particle $S=1$ triplet bound state.
Thermal conductivity in near-nodal superconductors
Hui Meng, Huan Zhang, Wan-Sheng Wang, Qiang-Hua Wang
Chin. Phys. Lett. 2018, 35 (12): 127402 .   DOI: 10.1088/0256-307X/35/12/127402
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The universal behavior of thermal conductivity at low temperatures is usually taken as the signature of gap nodes in superconductors. Here we show that in near-nodal superconductors the thermal conductivity obeys a two-parameter scaling law, and can develop super-universal behavior if the temperature is about half the gap minimum. However, when the temperature is fixed at about one quarter of the gap minimum, the thermal conductivity can develop a dip versus the scattering rate, which is in excellent agreement with the behavior of the experimental thermal conductivity in Sr$_2$RuO$_4$. Our theory is useful to correctly analyze the thermal conductivity in any near-nodal superconductor.
Magnetic and topological transitions in three-dimensional topological Kondo insulator
Huan Li, Zhi-Yong Wang, Xiao-Jun Zheng, Yu Liu, Yin Zhong
Chin. Phys. Lett. 2018, 35 (12): 127501 .   DOI: 10.1088/0256-307X/35/12/127501
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Using an extended slave-boson method, we draw a global phase diagram summarizing both magnetic phases and paramagnetic (PM) topological insulators (TIs) in a three-dimensional topological Kondo insulator (TKI). By including electron hopping (EH) up to the third neighbors, we identify four strong TI (STI) phases and two weak TI (WTI) phases. Then, the PM phase diagrams characterizing topological transitions between these TIs are depicted as functions of EH, $f$-electron energy level, and hybridization constant. We also find an insulator–metal transition from an STI phase that has surface Fermi rings and spin textures in qualitative agreement with the TKI candidate SmB$_6$. In the weak hybridization regime, antiferromagnetic (AF) order naturally arises in the phase diagrams. Depending on how the magnetic boundary crosses the PM topological transition lines, AF phases are classified into the AF topological insulator (AFTI) and the non-topological AF insulator, according to their $\mathcal{Z}_2$ indices. In two small regions of parameter space, two distinct topological transition processes between AF phases occur, leading to two types of AFTIs showing distinguishable surface dispersions around their Dirac points.
Surface-Induced Enhancement of Piezoelectricity in ZnO Nanowires
Gong Chen, Pan-Shuo Wang
Chin. Phys. Lett. 2018, 35 (12): 127701 .   DOI: 10.1088/0256-307X/35/12/127701
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Piezoelectric nanowires are promising building blocks in various micro-electromechanical systems. Using first-principles calculations, we systematically investigate the influence of surface and volume changes on piezoelectric coefficients in [001]-oriented ZnO nanowires and hollow nanowires. We find that the increased non-axial ion displacements under strain near the {100} surface cause a notable enhancement in piezoelectric coefficients for these nanowires. Furthermore, by introducing the obtained surface modifications, we break through the limitation of simulation size and obtain the piezoelectric coefficients at the experimental size. Our findings are of importance to expand simulations and guide experimental explorations.
Ultrafast charge transfer in dual graphene-WS$_{2}$ van der Waals quadrilayer heterostructures
Zong-Peng Song, Hai-Ou Zhu, Wen-Tao Shi, Da-Lin Sun, Shuang-Chen Ruan
Chin. Phys. Lett. 2018, 35 (12): 127801 .   DOI: 10.1088/0256-307X/35/12/127801
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Using dual graphene–WS$_{2}$ quadrilayer heterostructures as an example, we find that the ultrafast transfer of electrons from WS$_{2}$ to graphene takes place within 114 fs, and the Coulomb field of the charge can effectively affect the interlayer electron transfer. This effect illustrates that the charge transfer in such van der Waals heterostructures may be controlled by an externally applied electric field for promising applications in photoelectric devices.
Gravitational constant in f(R) theories of gravity with non-minimal coupling between matter and geometry
Jun Wang, Li-Jia Cao
Chin. Phys. Lett. 2018, 35 (12): 129801 .   DOI: 10.1088/0256-307X/35/12/129801
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We study the effect of the non-minimal coupling between matter and geometry on the gravitational constant in the context of $f(R)$ theories of gravity on cosmic scales. For a class of $f(R)$ models, the result shows that the value of the gravitational constant not only changes over time but also has the dampened oscillation behavior. Compared with the result of the standard ${\it \Lambda}$CDM model, the consequence suggests that the coupling between matter and geometry should be weak.
Erratum and Note: Measurement of Zeeman Shift of Cesium Atoms Using an Optical Nanofiber [Chin. Phys. Lett. 35(2018)083201]
Chuan-Biao Zhang, Dian-Qiang Su, Zhong-Hua Ji, Yan-Ting Zhao, Lian-Tuan Xiao, Suo-Tang Jia
Chin. Phys. Lett. 2018, 35 (12): 129901 .   DOI: 10.1088/0256-307X/35/12/129901
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18 articles