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Volume 37 Issue 2
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GENERAL
Phase Diagram of a Spin-Orbit Coupled Dipolar Fermi Gas at T=0K
Xue-Jing Feng, Lan Yin
Chin. Phys. Lett. 2020, 37 (2): 020301 .   DOI: 10.1088/0256-307X/37/2/020301
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We study a homogeneous two-component dipolar Fermi gas with 1D spin-orbit coupling (SOC) at zero temperature and find that the system undergoes a transition from the paramagnetic phase to the ferromagnetic phase under suitable dipolar interaction constant $\lambda_{\rm d}$, SOC constant $\lambda_{\rm SOC}$ and contact interaction constant $\lambda_{\rm s}$. This phase transition can be of either 1st order or 2nd order, depending on the parameters. Near the 2nd-order phase transition, the system is partially magnetized in the ferromagnetic phase. With SOC, the ferromagnetic phase can even exist in the absence of the contact interaction. The increase in dipolar interaction, SOC strength, and contact interaction are all helpful to stabilize the ferromagnetic state. The critical dipolar interaction strength at the phase transition can be reduced by the increase in SOC strength or contact interaction. Phase diagrams of these systems are obtained.
Measurement of Spin Singlet-Triplet Qubit in Quantum Dots Using Superconducting Resonator
Xing-Yu Zhu, Tao Tu, Ao-Lin Guo, Zong-Quan Zhou, Guang-Can Guo
Chin. Phys. Lett. 2020, 37 (2): 020302 .   DOI: 10.1088/0256-307X/37/2/020302
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The spin qubit in quantum dots is one of the leading platforms for quantum computation. A crucial requirement for scalable quantum information processing is the high efficient measurement. Here we analyze the measurement process of a quantum-dot spin qubit coupled to a superconducting transmission line resonator. Especially, the phase shift of the resonator is sensitive to the spin states and the gate operations. The response of the resonator can be used to measure the spin qubit efficiently, which can be extend to read out the multiple spin qubits in a scalable solid-state quantum processor.
ATOMIC AND MOLECULAR PHYSICS
Generation of 88as Isolated Attosecond Pulses with Double Optical Gating
Xiaowei Wang, Li Wang, Fan Xiao, Dongwen Zhang, Zhihui Lü, Jianmin Yuan, Zengxiu Zhao
Chin. Phys. Lett. 2020, 37 (2): 023201 .   DOI: 10.1088/0256-307X/37/2/023201
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Isolated attosecond pulses with a duration of 88 as are generated in the spectral range of 29–72 eV using double optical gating technique. The gate width is set to be shorter than half the optical cycle to avoid carrier envelop phase stabilization of the 4.2 fs driving laser pulses centered at 800 nm. The attosecond pulse duration is measured with the technique of frequency resolved optical gating for complete reconstruction of attosecond bursts.
Single- and Double-Electron Capture Processes in Low-Energy Collisions of N$^{4+}$ Ions with He
Kun Wang, Xiao-Xia Wang, Yi-Zhi Qu, Chun-Hua Liu, Ling Liu, Yong Wu, Robert J. Buenker
Chin. Phys. Lett. 2020, 37 (2): 023401 .   DOI: 10.1088/0256-307X/37/2/023401
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We investigate the electron capture processes of N$^{4+}$(1$s^{2}2s$) colliding with He(1$s^{2}$) in the energy range of 10–1700 eV/amu using the quantum-mechanical molecular-orbital close-coupling (QMOCC) method. Total and state-selective single-electron capture and double-electron capture (SEC and DEC) cross sections are obtained and compared with other available studies. The results agree better with the experimental data in both trend and magnitude when the electron translation factor (ETF) effects are included. Our results indicate that both the SEC and DEC processes play important roles in the considered energy region. For the SEC processes, the N$^{3+}$(1$s^{2}2p^{2}$) + He$^{+}$(1$s$) states are the dominant capture states, and the N$^{2+}$(1$s^{2}2s2p^{2}$) + He$^{2+}$ states are the main DEC states.
FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)
Spider Structure of Photoelectron Momentum Distributions of Ionized Electrons from Hydrogen Atoms for Extraction of Carrier Envelope Phase of Few-Cycle Pulses
Jiu Tang, Guizhong Zhang, Yufei He, Meng Li, Xin Ding, Jianquan Yao
Chin. Phys. Lett. 2020, 37 (2): 024201 .   DOI: 10.1088/0256-307X/37/2/024201
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The spider structure in the photoelectron momentum distributions (PMDs) of ionized electrons from the hydrogen atom is simulated by solving the time-dependent Schrödinger equation (TDSE). We find that the spider structure exhibits sensitive dependence on carrier envelope phase (CEP) of the few-cycle pulses. To elucidate the striking CEP dependence of the spider structure, we select three physical parameters $I_{\rm L}$, $I_{\rm R}$, and $I_{\rm R}/I_{\rm L}$ to quantitatively characterize the variations of the spider structure induced by altering the CEPs. $I_{\rm L}$ is the sum of the left half panel of the transverse cut curves (i.e., the sum of all the negative momenta along the laser polarization direction), $I_{\rm R}$ is the sum of the right half panel of the transverse cut curves (i.e., the sum of all the positive momenta along the laser polarization direction), and $I_{\rm R}/I_{\rm L}$ is the ratio between the two sums. These parameters are shown to have monotonic relation with the CEP value, which is exploited to extract the CEPs. We anticipate that our method will be useful for obtaining CEPs encoded in the spider structure of PMDs.
Wavefront Shaping for Fast Focusing Light through Scattering Media Based on Parallel Wavefront Optimization and Superpixel Method
Yingchun Ding, Xinjing Lv, Youquan Jia, Bin Zhang, Zhaoyang Chen, Qiang Liu
Chin. Phys. Lett. 2020, 37 (2): 024202 .   DOI: 10.1088/0256-307X/37/2/024202
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When light travels in biological tissues, it undergoes multiple scattering and forms speckles, which seriously restricts the penetration depth of optical imaging in biological tissues. With wavefront shaping method, by modulating the wavefront of incident light to compensate for the wavefront aberration, light focusing and scanning imaging through scattering media can be achieved. However, wavefront shaping must be accomplished within the speckle decorrelation time. Considering the short speckle decorrelation time of living tissues, the speed of wavefront shaping is rather essential. We propose a new iterative optimization wavefront shaping method to improve the speed of wavefront shaping in which the existing parallel optimization wavefront shaping method is improved and is combined with the superpixel method. Compared with the traditional multi-frequency parallel optimization method, the modulation rate of our method is doubled. Moreover, we combine the high frame rate amplitude modulator, i.e., the digital micromirror device (DMD), with the superpixel method to replace the traditional phase modulator (i.e., spatial light modulator), which further increases the optimization speed. In our experiment, when the number of the optical modes is 400, light focusing is achieved with only 1000 DMD superpixel masks and the enhancement factor reaches 223. Our approach provides a new path for fast light focusing through wavefront shaping.
A CMOS Compatible Si Template with (111) Facets for Direct Epitaxial Growth of III–V Materials
Wen-Qi Wei, Jian-Huan Wang, Jie-Yin Zhang, Qi Feng, Zihao Wang, Hong-Xing Xu, Ting Wang, Jian-Jun Zhang
Chin. Phys. Lett. 2020, 37 (2): 024203 .   DOI: 10.1088/0256-307X/37/2/024203
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III–V quantum dot (QD) lasers monolithically grown on CMOS-compatible Si substrates are considered as essential components for integrated silicon photonic circuits. However, epitaxial growth of III–V materials on Si substrates encounters three obstacles: mismatch defects, antiphase boundaries (APBs), and thermal cracks. We study the evolution of the structures on U-shaped trench-patterned Si (001) substrates with various trench orientations by homoepitaxy and the subsequent heteroepitaxial growth of GaAs film. The results show that the formation of (111)-faceted hollow structures on patterned Si (001) substrates with trenches oriented along [110] direction can effectively reduce the defect density and thermal stress in the GaAs/Si epilayers. The (111)-faceted silicon hollow structure can act as a promising platform for the direct growth of III–V materials for silicon based optoelectronic applications.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
Phase Effects of Long-Wavelength Rayleigh–Taylor Instability on the Thin Shell
Zhi-Yuan Li, Li-Feng Wang, Jun-Feng Wu, Wen-Hua Ye
Chin. Phys. Lett. 2020, 37 (2): 025201 .   DOI: 10.1088/0256-307X/37/2/025201
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Taking the long-wavelength Rayleigh–Taylor instability (RTI) on the thin shell of inertial confinement fusion as the research object, a linear analytical model is presented to study the phase effects that are caused by the phase difference of single-mode perturbations on the two interfaces. Its accuracy is tested by numerical simulations. By analyzing the characteristic of this model, it is found that the phase difference does not change the basic RTI structure (only one spike and one bubble in a period). However, the symmetry of the spike and bubble is destroyed, which has non-expected influences on the convergent motion of ICF targets. Meanwhile, the phenomenon that the distance between spikes and bubbles along the vertical direction of acceleration differs by $\pi$ is demonstrated. It is also shown that when the phase difference is large, the temporal evolution of the RTI is more serious and the thin target is easier to tend to break.
CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES
Stable Compositions, Structures and Electronic Properties in K–Ga Systems Under Pressure
Chao Wang, Yun-Xian Liu, Xin Chen, Pin Lv, Hai-Rui Sun, Xiao-Bing Liu
Chin. Phys. Lett. 2020, 37 (2): 026201 .   DOI: 10.1088/0256-307X/37/2/026201
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New stable stoichiometries in K–Ga systems are firstly investigated up to 100 GPa by the unbiased structure searching techniques. Six novel compositions as K$_{4}$Ga, K$_{3}$Ga, K$_{2}$Ga, KGa, KGa$_{2}$ and KGa$_{4}$ are found to be thermodynamically stable under pressure. Most of the predicted stable phases exhibit metallic character, while the $Fd\bar{3}m$ KGa phase behaves as a semiconductor with a bandgap $\sim $1.62 eV. Notably, the gallium atoms exhibit different interesting morphologies; e.g., Ga$_{2}$ units, zigzag chains, six rings and cage. We further investigate the bonding nature of K–Ga systems with help of electron localization function and Bader charge analyses. Strong covalent bonding characteristics are found between the Ga and Ga atoms, and ionic bonding patterns are observed between the K and Ga atoms. Meanwhile, we notice charge transferring from the K atom to the Ga atom in the K–Ga systems. The present results can be helpful for understanding the diverse structures and properties of K–Ga binary compounds at high pressures.
Effect of Zr Content on Formation and Optical Properties of the Layered PbZr$_{x}$Ti$_{1-x}$O$_{3}$ Films
Yang-Yang Xu, Yu Wang, Ai-Yun Liu, Wang-Zhou Shi, Gu-Jin Hu, Shi-Min Li, Hui-Yong Deng, Ning Dai
Chin. Phys. Lett. 2020, 37 (2): 026801 .   DOI: 10.1088/0256-307X/37/2/026801
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PbZr$_{x}$Ti$_{1-x}$O$_{3}$ (PZT) films are fabricated on F-doped tin oxide (FTO) substrates using chemical solutions containing PVP polymer and rapid thermal annealing processing. The dependence of the layered PZT multilayer formation and their optical properties on the Zr content $x$ are examined. It is found that all the PZT films are crystallized and exhibit 110-preferred orientation. When $x$ varies in the region of 0–0.8, the PZT films display lamellar structures, and a high reflection band occurs in each optical reflectance spectrum curve. Especially, those PZT films with Zr/Ti atomic ratio of 35/65–65/35 show clearly layered cross-sectional morphologies arranged alternatively by porous and dense PZT layers, and have a peak optical reflectivity of $>$70% and a band width of $>$45 nm. To obtain the optimal Bragg reflection performance of the PZT multilayers, the Zr content should be selected in the range of 0.35–0.65.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
Adsorption of Perylene on Si(111)($7 \times 7$)
Dandan Guan, Xinwei Wang, Hongying Mao, Shining Bao, Jin-Feng Jia
Chin. Phys. Lett. 2020, 37 (2): 027101 .   DOI: 10.1088/0256-307X/37/2/027101
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We investigate the adsorption of organic molecular semiconductor perylene on ($7 \times 7$) reconstructed Si(111) surface by ultraviolet photoemission spectroscopy. It is observed that seven features that derive from the organic material are located at 0.71, 2.24, 4.0, 5.9, 7.46, 8.65 and 9.95 eV in binding energy. The theoretical calculation results reveal the most stable adsorption geometry of organic molecule perylene on Si(111) ($7 \times 7$) substrates is at the beginning of deposition.
Effects of Low-Damage Plasma Treatment on the Channel 2DEG and Device Characteristics of AlGaN/GaN HEMTs
SiQin-GaoWa Bao, Jie-Jie Zhu, Xiao-Hua Ma, Bin Hou, Ling Yang, Li-Xiang Chen, Qing Zhu, Yue Hao
Chin. Phys. Lett. 2020, 37 (2): 027301 .   DOI: 10.1088/0256-307X/37/2/027301
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We investigate the effects of remote nitride-based plasma treatment on the channel carrier and device characteristics of AlGaN/GaN high electron mobility transistors (HEMTs). A 200 W NH$_{3}$/N$_{2}$ remote plasma causes little degeneration of carrier mobility and an increase in electron density due to surface alteration, which results in a decrease in sheet resistance and an increase in output current by 20–30%. Improved current slump, suppressed gate leakage current, and improved Schottky contact properties are also achieved by using low-damage nitride-based plasma treatment. It is found that NH$_{3}$/N$_{2}$ remote plasma treatment is a promising technique for GaN-based HEMTs to modulate the surface conditions and channel properties.
Reduction of Electron Leakage of AlGaN-Based Deep Ultraviolet Laser Diodes Using an Inverse-Trapezoidal Electron Blocking Layer
Zhong-Qiu Xing, Yong-Jie Zhou, Yu-Huai Liu, Fang Wang
Chin. Phys. Lett. 2020, 37 (2): 027302 .   DOI: 10.1088/0256-307X/37/2/027302
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To improve the optical and electrical properties of AlGaN-based deep ultraviolet lasers, an inverse-trapezoidal electron blocking layer is designed. Lasers with three different structural electron blocking layers of rectangular, trapezoidal and inverse-trapezoidal structures are established. The energy band, electron concentration, electron current density, $P$–$I$ and $V$–$I$ characteristics, and the photoelectric conversion efficiency of different structural devices are investigated by simulation. The results show that the optical and electrical properties of the inverse-trapezoidal electron blocking layer laser are better than those of rectangular and trapezoidal structures, owing to the effectively suppressed electron leakage.
Stable Intrinsic Long Range Antiferromagnetic Coupling in Dilutely V Doped Chalcopyrite
Weiyi Gong, Ching-Him Leung, Chuen-Keung Sin, Jingzhao Zhang, Xiaodong Zhang, Bin Xi, Junyi Zhu
Chin. Phys. Lett. 2020, 37 (2): 027501 .   DOI: 10.1088/0256-307X/37/2/027501
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A stable and long-range antiferromagnetic (AFM) coupling without charge carrier mediators has been searched for a long time, but the existence of this kind of coupling is still lacking. Based on first principle calculations, we systematically study carrier free long-range AFM coupling in four transition metal chalcopyrite systems: ABTe$_2$ (A = Cu or Ag, B = Ga or In) in the dilute doping case. The AFM coupling is mainly due to the $p$–$d$ coupling and electron redistribution along the interacting chains. The relatively small energy difference between $p$ and $d$ orbitals, as well as between dopants and atoms in the middle of the chain can enhance the stability of long-range AFM configurations. A multi-band Hubbard model is proposed to provide fundamental understanding of long-range AFM coupling.
Physical Properties of Half-Heusler Antiferromagnet MnPtSn Single Crystal
Qi Wang, Qianheng Du, Cedomir Petrovic, Hechang Lei
Chin. Phys. Lett. 2020, 37 (2): 027502 .   DOI: 10.1088/0256-307X/37/2/027502
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We report the growth of ternary half-Heusler MnPtSn single crystals and detailed study on its structural and physical properties. MnPtSn single crystal has a larger lattice parameter than that in polycrystal and it exhibits antiferromagnetism with transition temperature $T_{\rm N}$ at about 215 K, distinctly different from the ferromagnetism of MnPtSn polycrystal. Hall resistivity measurement indicates that the dominant carriers are hole-type and the nearly temperature-independent carrier concentration reaches about $2.86\times10^{22}$ cm$^{-3}$ at 5 K. Moreover, the carrier mobility is also rather low (4.7 cm$^{2}$$\cdot$V$^{-1}$s$^{-1}$ at 5 K). The above results strongly suggest that the significant Mn/Sn anti-site defects, i.e., the content of Mn in MnPtSn single crystal, play a vital role on structural, magnetic and transport properties.
CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
Near-Field Optical Identification of Metallic and Semiconducting Single-Walled Carbon Nanotubes
Lele Wang, Bosai Lyu, Qiang Gao, Jiajun Chen, Zhe Ying, Aolin Deng, Zhiwen Shi
Chin. Phys. Lett. 2020, 37 (2): 028101 .   DOI: 10.1088/0256-307X/37/2/028101
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Single-walled carbon nanotubes (SWCNTs), due to their outstanding electrical and optical properties, are expected to have extensive applications, such as in transparent conductive films and ultra-small field-effect transistors (FETs). However, those applications can only be best realized with pure metallic or pure semiconducting SWCNTs. Hence, identifying and separating metallic from semiconducting SWCNTs in as-grown samples are crucial. In addition, knowledge of the type of an SWCNT is also important for further exploring its new properties in fundamental science. Here we report employing scanning near-field optical microscopy (SNOM) as a direct and simple method to identify metallic and semiconducting SWCNTs on SiO$_2$/Si substrates. Metallic and semiconducting SWCNTs show distinct near-field optical responses because the metallic tubes support plasmons whereas the semiconducting tubes do not. The reliability of this method is verified using FET testing and Rayleigh scattering spectroscopy. Our result demonstrates that the SNOM technique provides a reliable, simple, noninvasive and in situ method to distinguish between metallic and semiconducting SWCNTs.
Nucleation, Growth, and Aggregation of Au Nanocrystals on Liquid Surfaces
Lu Li, Zhi-Long Bao, Xun-Heng Ye, Jia-Wei Shen, Bo Yang, Gao-Xiang Ye, Xiang-Ming Tao
Chin. Phys. Lett. 2020, 37 (2): 028102 .   DOI: 10.1088/0256-307X/37/2/028102
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We report the formation of gold ramified aggregates after deposition of Au on an ionic liquid surface by thermal evaporation method at room temperature. It is observed that the aggregates are composed of both granules and nanocrystals with hexagonal or triangular appearances. The most probable size of the nanocrystals is much larger than that of the granules and it increases with the nominal deposition thickness. The formation mechanism of the granules, nanocrystals and aggregates is presented.
Controlling the Coffee Ring Effect on Graphene and Polymer by Cations
Haijun Yang, Yizhou Yang, Shiqi Sheng, Binghai Wen, Nan Sheng, Xing Liu, Rongzheng Wan, Long Yan, Zhengchi Hou, Xiaoling Lei, Guosheng Shi, Haiping Fang
Chin. Phys. Lett. 2020, 37 (2): 028103 .   DOI: 10.1088/0256-307X/37/2/028103
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Recently, there are great efforts that have been taken to suppressing/controlling the coffee ring effect, but it is of challenge to achieve inexpensive and efficient control with less disturbance, suitable for scalable production and highly enhancing the printing/dyeing color fastness. By only adding trace amounts of salt into the suspensions, here we experimentally achieve the facile and highly efficient control of the coffee ring effect of suspended matter on substrates of graphene, natural graphite, and polyethylene terephthalate surfaces. Notably, friction force measurements show that ion-controlled uniform patterns also greatly enhance color fastness. Molecular dynamics simulations reveal that, due to strong hydrated cation-$\pi$ interactions between hydrated cations and aromatic rings in the substrate surface, the suspended matters are adsorbed on the surfaces mediated by cations so that the suspended matters are uniformly distributed. These findings will open new avenues for fabricating functional patterns on graphene substrates and will benefit practical applications including printing, coating, and dyeing.
18 articles