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Chiral State Conversion in a Levitated Micromechanical Oscillator with ${\boldsymbol In~Situ}$ Control of Parameter Loops
Peiran Yin, Xiaohui Luo, Liang Zhang, Shaochun Lin, Tian Tian, Rui Li, Zizhe Wang, Changkui Duan, Pu Huang, and Jiangfeng Du
Chin. Phys. Lett. 2020, 37 (10):
100301
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DOI: 10.1088/0256-307X/37/10/100301
Physical systems with gain and loss can be described by a non-Hermitian Hamiltonian, which is degenerated at the exceptional points (EPs). Many new and unexpected features have been explored in the non-Hermitian systems with a great deal of recent interest. One of the most fascinating features is that chiral state conversion appears when one EP is encircled dynamically. Here, we propose an easy-controllable levitated microparticle system that carries a pair of EPs and realize slow evolution of the Hamiltonian along loops in the parameter plane. Utilizing the controllable rotation angle, gain and loss coefficients, we can control the structure, size and location of the loops in situ. We demonstrate that, under the joint action of topological structure of energy surfaces and nonadiabatic transitions, the chiral behavior emerges both along a loop encircling an EP and even along a straight path away from the EP. This work broadens the range of parameter space for the chiral state conversion, and proposes a useful platform to explore the interesting properties of exceptional points physics.
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Abundant Traveling Wave Structures of (1+1)-Dimensional Sawada–Kotera Equation: Few Cycle Solitons and Soliton Molecules
Wei Wang, Ruoxia Yao, and Senyue Lou
Chin. Phys. Lett. 2020, 37 (10):
100501
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DOI: 10.1088/0256-307X/37/10/100501
Traveling wave solutions have been well studied for various nonlinear systems. However, for high order nonlinear physical models, there still exist various open problems. Here, travelling wave solutions to the well-known fifth-order nonlinear physical model, the Sawada–Kotera equation, are revisited. Abundant travelling wave structures including soliton molecules, soliton lattice, kink-antikink molecules, peak-plateau soliton molecules, few-cycle-pulse solitons, double-peaked and triple-peaked solitons are unearthed.
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Tunable Optical Bandpass Filter via a Microtip-Touched Tapered Optical Fiber
Peng-Fei Zhang, Li-Jun Song, Chang-Lin Zou, Xin Wang, Chen-Xi Wang, Gang Li, and Tian-Cai Zhang
Chin. Phys. Lett. 2020, 37 (10):
104201
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DOI: 10.1088/0256-307X/37/10/104201
We demonstrate a tunable bandpass optical filter based on a tapered optical fiber (TOF) touched by a hemispherical microfiber tip (MFT). Other than the interference and selective material absorption effects, the filter relies on the controllable and wavelength-dependent mode–mode interactions in TOF. Experimentally, a large range of tunability is realized by controlling the position of the MFT in contact with the TOF for various TOF radii, and two distinct bandpass filter mechanisms are demonstrated. The center wavelength of the bandpass filter can be tuned from 890 nm to 1000 nm, while the FWHM bandwidth can be tuned from 110 nm to 240 nm when the MFT touches the TOF in the radius range from 160 nm to 390 nm. The distinction ratio can reach $28 \pm 3$ dB experimentally. The combined TOF-MFT is an in-line tunable bandpass optical filter that has great application potential in optical networks and spectroscopy, and the principle could also be generalized to other integrated photonic devices.
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A Ubiquitous Thermal Conductivity Formula for Liquids, Polymer Glass, and Amorphous Solids
Qing Xi, Jinxin Zhong, Jixiong He, Xiangfan Xu, Tsuneyoshi Nakayama, Yuanyuan Wang, Jun Liu, Jun Zhou, and Baowen Li
Chin. Phys. Lett. 2020, 37 (10):
104401
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DOI: 10.1088/0256-307X/37/10/104401
The microscopic mechanism of thermal transport in liquids and amorphous solids has been an outstanding problem for a long time. There have been several approaches to explain the thermal conductivities in these systems, for example, Bridgman's formula for simple liquids, the concept of the minimum thermal conductivity for amorphous solids, and the thermal resistance network model for amorphous polymers. Here, we present a ubiquitous formula to calculate the thermal conductivities of liquids and amorphous solids in a unified way, and compare it with previous ones. The calculated thermal conductivities using this formula without fitting parameters are in excellent agreement with the experimental data. Our formula not only provides a detailed microscopic mechanism of heat transfer in these systems, but also resolves the discrepancies between existing formulae and experimental data.
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Molecular Dynamics Simulations of the Interface between Porous and Fused Silica
Ye Tian, Xiaodong Yuan , Dongxia Hu , Wanguo Zheng , and Wei Han
Chin. Phys. Lett. 2020, 37 (10):
106101
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DOI: 10.1088/0256-307X/37/10/106101
Molecular dynamics simulations are performed to gain insights into the structural and vibrational properties of interface between porous and fused silica. The Si–O bonds formed in the interface exhibit the same lengths as the bulk material, whereas the coordination defects in the interface are at an intermediate level as compared with the dense and porous structures. Clustered bonds are identified from the interface, which are associated with the reorganization of the silica surface. The bond angle distributions show that the O–Si–O bond angles keep the average value of 109$^{\circ}$, whereas the Si–O–Si angles of the interface present in a similar manner to those in porous silica. Despite the slight structural differences, similarities in the vibrations are observed, which could further demonstrate the stability of porous silica films coated on the fused silica.
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Structural Domain Imaging and Direct Determination of Crystallographic Orientation in Noncentrosymmetric Ca$_{3}$Ru$_{2}$O$_{7}$ Using Polarized Light Reflectance
Guoxiong Tang, Libin Wen, Hui Xing, Wenjie Liu, Jin Peng, Yu Wang, Yupeng Li, Baijiang Lv, Yusen Yang, Chao Yao, Yueshen Wu, Hong Sun, Zhu-An Xu, Zhiqiang Mao, and Ying Liu
Chin. Phys. Lett. 2020, 37 (10):
106102
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DOI: 10.1088/0256-307X/37/10/106102
The noncentrosymmetricity of a prototypical correlated electron system Ca$_{3}$Ru$_{2}$O$_{7}$ renders extensive interest in the possible polar metallic state, along with multiple other closely competing interactions. However, the structural domain formation in this material often complicates the study of intrinsic material properties. It is crucial to fully characterize the structural domains for unrevealing underlying physics. Here, we report the domain imaging on Ca$_{3}$Ru$_{2}$O$_{7}$ crystal using the reflection of polarized light at normal incidence. The reflection anisotropy measurement utilizes the relative orientation between electric field component of the incident polarized light and the principal axis of the crystal, and gives rise to a peculiar contrast. The domain walls are found to be the interfaces between 90$^{\circ}$ rotated twin crystals by complementary magnetization measurements. A distinct contrast in reflectance is also found in the opposite cleavage surfaces, owing to the polar mode of the RuO$_{6}$ octahedra. More importantly, the analysis of the contrast between all inequivalent cleavage surfaces enables a direct determination of the crystallographic orientation of each domain. Such an approach provides an efficient yet feasible method for structural domain characterization, which can also find applications in noncentrosymmetric crystals in general.
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Effect of B-Site Ordering on the Magnetic Order in Multifunctional La$_{2}$NiMnO$_{6}$ Double Perovskite
Dexin Yang, Rui Jiang, Yaohua Zhang, Hui Zhang, Senlin Lei, Tao Yang, Xiaoshi Hu, Shuai Huang, Jingyuan Ge, Kunpeng Su, Haiou Wang, and Dexuan Huo
Chin. Phys. Lett. 2020, 37 (10):
106201
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DOI: 10.1088/0256-307X/37/10/106201
To obtain various Ni/Mn orderings, we use a low-temperature synthesized method to modulate the Ni/Mn ordering of the ferromagnetic-ferroelastic La$_{2}$NiMnO$_{6}$ compound, and the Ni/Mn ordering is estimated by the low-temperature saturation magnetism. The microstructures, crystal structures and magnetic properties are investigated, and the Landau theory are used to describe the form and magnitude of the coupling effects between Ni/Mn ordering and magnetic order parameters. It is predicted that the Ni/Mn ordering would be a strong coupling effect with the Curie transition temperatures if the La$_{2}$NiMnO$_{6}$ sample stoichiometry is close.
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Diffraction-Limited Imaging with a Graphene Metalens
Xueyan Li, Han Lin, Yuejin Zhao, and Baohua Jia
Chin. Phys. Lett. 2020, 37 (10):
106801
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DOI: 10.1088/0256-307X/37/10/106801
Planar graphene metalens has demonstrated advantages of ultrathin thickness (200 nm), high focusing resolution (343 nm) and efficiency ($>$32%) and robust mechanical strength and flexibility. However, diffraction-limited imaging with such a graphene metalens has not been realized, which holds the key to designing practical integrated imaging systems. In this work, the imaging rule for graphene metalenses is first derived and theoretically verified by using the Rayleigh-Sommerfeld diffraction theory to simulate the imaging performance of the 200 nm ultrathin graphene metalens. The imaging rule is applicable to graphene metalenses in different immersion media, including water or oil. Based on the theoretical prediction, high-resolution imaging using the graphene metalens with diffraction-limited resolution (500 nm) is demonstrated for the first time. This work opens the possibility for graphene metalenses to be applied in particle tracking, microfluidic chips and biomedical devices.
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Coupling Stacking Orders with Interlayer Magnetism in Bilayer H-VSe$_{2}$
Aolin Li, Wenzhe Zhou, Jiangling Pan, Qinglin Xia, Mengqiu Long, and Fangping Ouyang
Chin. Phys. Lett. 2020, 37 (10):
107101
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DOI: 10.1088/0256-307X/37/10/107101
Stacking-dependent magnetism in van der Waals materials has caught intense interests. Based on the first principle calculations, we investigate the coupling between stacking orders and interlayer magnetic orders in bilayer H-VSe$_{2}$. It is found that there are two stable stacking orders in bilayer H-VSe$_{2}$, named AB-stacking and A$^{\prime}$B-stacking. Under standard DFT framework, the A$^{\prime}$B-stacking prefers the interlayer AFM order and is semiconductive, whereas the AB-stacking prefers the FM order and is metallic. However, under the DFT+$U$ framework both the stacking orders prefer the interlayer AFM order and are semiconductive. By detailedly analyzing this difference, we find that the interlayer magnetism originates from the competition between antiferromagnetic interlayer super-superexchange and ferromagnetic interlayer double exchange, in which both the interlayer Se-4$p_{z}$ orbitals play a crucial role. In the DFT+$U$ calculations, the double exchange is suppressed due to the opened bandgap, such that the interlayer magnetic orders are decoupled with the stacking orders. Based on this competition mechanism, we propose that a moderate hole doping can significantly enhance the interlayer double exchange, and can be used to switch the interlayer magnetic orders in bilayer VSe$_{2}$. This method is also applicable to a wide range of semiconductive van der Waals magnets.
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Superconductivity of Lanthanum Superhydride Investigated Using the Standard Four-Probe Configuration under High Pressures
Fang Hong, Liuxiang Yang, Pengfei Shan, Pengtao Yang, Ziyi Liu, Jianping Sun, Yunyu Yin, Xiaohui Yu, Jinguang Cheng, and Zhongxian Zhao
Chin. Phys. Lett. 2020, 37 (10):
107401
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DOI: 10.1088/0256-307X/37/10/107401
Recently, the theoretically predicted lanthanum superhydride, LaH$_{10 \pm \delta}$, with a clathrate-like structure was successfully synthesized and found to exhibit a record high superconducting transition temperature $T_{\rm c} \approx 250$ K at $\sim $170 GPa, opening a new route for room-temperature superconductivity. However, since in situ experiments at megabar pressures are very challenging, few groups have reported the $\sim $250 K superconducting transition in LaH$_{10 \pm \delta}$. Here, we establish a simpler sample-loading procedure that allows a relatively large sample size for synthesis and a standard four-probe configuration for resistance measurements. Following this procedure, we successfully synthesized LaH$_{10 \pm \delta}$ with dimensions up to $10 \times 20$ μm$^{2}$ by laser heating a thin La flake and ammonia borane at $\sim $1700 K in a symmetric diamond anvil cell under the pressure of 165 GPa. The superconducting transition at $T_{\rm c} \approx 250$ K was confirmed through resistance measurements under various magnetic fields. Our method will facilitate explorations of near-room-temperature superconductors among metal superhydrides.
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Field-Induced Metal–Insulator Transition in $\beta$-EuP$_3$
Guangqiang Wang, Guoqing Chang, Huibin Zhou, Wenlong Ma, Hsin Lin, M. Zahid Hasan, Su-Yang Xu, and Shuang Jia
Chin. Phys. Lett. 2020, 37 (10):
107501
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DOI: 10.1088/0256-307X/37/10/107501
Metal–insulator transition (MIT) is one of the most conspicuous phenomena in correlated electron systems. However such a transition has rarely been induced by an external magnetic field as the field scale is normally too small compared with the charge gap. We present the observation of a magnetic-field-driven MIT in a magnetic semiconductor $\beta $-EuP$_3$. Concomitantly, we find a colossal magnetoresistance in an extreme way: the resistance drops billionfold at 2 K in a magnetic field less than 3 T. We ascribe this striking MIT as a field-driven transition from an antiferromagnetic and paramagnetic insulator to a spin-polarized topological semimetal, in which the spin configuration of Eu$^{2+}$ cations and spin-orbital coupling play a crucial role. As a phosphorene-bearing compound whose electrical properties can be controlled by the application of field, $\beta $-EuP$_3$ may serve as a tantalizing material in the basic research and even future electronics.
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Tuning of the Magnetic Damping Parameter by Varying Cr Composition in Fe$_{1-x}$Cr$_x$ Alloy
Mao Yang, Xianyang Lu, Bo Liu, Xuezhong Ruan, Junran Zhang, Xiaoqian Zhang, Dawei Huang, Jing Wu, Jun Du, Bo Liu, Hao Meng, Liang He, and Yongbing Xu
Chin. Phys. Lett. 2020, 37 (10):
107502
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DOI: 10.1088/0256-307X/37/10/107502
We investigate the magnetic damping parameter of Fe$_{1-x}$Cr$_x$ thin films using the time-resolved magneto-optical Kerr effect technique. It is demonstrated that the overall effective damping parameter is enhanced with the increasing Cr concentration. The effective damping at high field $\alpha_{0}$ is found to be significantly enhanced when increasing the Cr concentration with the $\alpha_{0}=0.159$ in the Fe$_{45}$Cr$_{55}$ enhanced by 562% compared with that of $\alpha_{0}=0.024$ in the pure Fe film. This study provides a new approach of controlling the effective damping parameter with a desired magnitude via varying Cr composition.
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Magnetic Phase Diagram of Cu$_{4-x}$Zn$_x$(OH)$_6$FBr Studied by Neutron-Diffraction and $\mu$SR Techniques
Yuan Wei, Xiaoyan Ma, Zili Feng, Devashibhai Adroja, Adrian Hillier, Pabitra Biswas, Anatoliy Senyshyn, Andreas Hoser, Jia-Wei Mei, Zi Yang Meng, Huiqian Luo, Youguo Shi, and Shiliang Li
Chin. Phys. Lett. 2020, 37 (10):
107503
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DOI: 10.1088/0256-307X/37/10/107503
We systematically investigate the magnetic properties of Cu$_{4-x}$Zn$_x$(OH)$_6$FBr using the neutron diffraction and muon spin rotation and relaxation (μSR) techniques. Neutron-diffraction measurements suggest that the long-range magnetic order and the orthorhombic nuclear structure in the $x = 0$ sample can persist up to $x = 0.23$ and 0.43, respectively. The temperature dependence of the zero-field μSR spectra provides two characteristic temperatures, $T_{A_0}$ and $T_{\lambda}$, which are associated with the initial drop close to zero time and the long-time exponential decay of the muon relaxation, respectively. Comparison between $T_{A_0}$ and $T_{\rm M}$ from previously reported magnetic-susceptibility measurements suggest that the former comes from the short-range interlayer-spin clusters that persist up to $x = 0.82$. On the other hand, the doping level where $T_{\lambda}$ becomes zero is about 0.66, which is much higher than threshold of the long-range order, i.e., $\sim$0.4. Our results suggest that the change in the nuclear structure may alter the spin dynamics of the kagome layers and a gapped quantum-spin-liquid state may exist above $x = 0.66$ with the perfect kagome planes.
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Quantum Oscillations and Electronic Structure in the Large-Chern-Number Topological Chiral Semimetal PtGa
Sheng Xu, Liqin Zhou, Xiao-Yan Wang, Huan Wang, Jun-Fa Lin, Xiang-Yu Zeng, Peng Cheng, Hongming Weng, and Tian-Long Xia
Chin. Phys. Lett. 2020, 37 (10):
107504
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DOI: 10.1088/0256-307X/37/10/107504
We report the magnetoresistance (MR), de Haas-van Alphen (dHvA) oscillations and the electronic structures of single-crystal PtGa. The large unsaturated MR is observed with the magnetic field $B \parallel [111]$. Evident dHvA oscillations with the $B \parallel [001]$ configuration are observed, from which twelve fundamental frequencies are extracted and the spin-orbit coupling (SOC) induced band splitting is revealed. The light cyclotron effective masses are extracted from the fitting by the thermal damping term of the Lifshitz–Kosevich formula. Combining with the calculated frequencies from the first-principles calculations, the dHvA frequencies $F_1/F_3$ and $F_{11}/F_{12}$ are confirmed to originate from the electron pockets at $\mit\Gamma$ and $R$, respectively. The first-principles calculations also reveal the existence of spin-3/2 Rarita–Schwinger–Weyl fermions and time-reversal doubling of the spin-1 excitation at $\mit\Gamma$ and $R$ with large Chern numbers of $\pm4$ when SOC is included.
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Scrolled Production of Large-Scale Continuous Graphene on Copper Foils
Zhibin Zhang, Jiajie Qi, Mengze Zhao, Nianze Shang, Yang Cheng, Ruixi Qiao, Zhihong Zhang, Mingchao Ding, Xingguang Li, Kehai Liu, Xiaozhi Xu, Kaihui Liu, Can Liu, and Muhong Wu
Chin. Phys. Lett. 2020, 37 (10):
108101
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DOI: 10.1088/0256-307X/37/10/108101
We report an efficient and economical way for mass production of large-scale graphene films with high quality and uniformity. By using the designed scrolled copper-graphite structure, a continuous graphene film with typical area of $200 \times 39$ cm$^{2}$ could be obtained in 15 min, and the production rate of the graphene film and space utilization rate of the CVD reactor can reach 520 cm$^{2}$$\cdot$min$^{-1}$ and 0.38 cm$^{-1}$$\cdot$min$^{-1}$, respectively. Our method provides a guidance for the industrial production of graphene films, and may also accelerate its large-scale applications.
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Antimony Selenide Thin Film Solar Cells with an Electron Transport Layer of Alq$_{3}$
Wen-Jian Shi, Ze-Ming Kan, Chuan-Hui Cheng, Wen-Hui Li, Hang-Qi Song, Meng Li, Dong-Qi Yu, Xiu-Yun Du, Wei-Feng Liu, Sheng-Ye Jin, and Shu-Lin Cong
Chin. Phys. Lett. 2020, 37 (10):
108401
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DOI: 10.1088/0256-307X/37/10/108401
We fabricated Sb$_{2}$Se$_{3}$ thin film solar cells using tris(8-hydroxy-quinolinato) aluminum (Alq$_{3}$) as an electron transport layer by vacuum thermal evaporation. Another small organic molecule of N,N'-bis(naphthalen-1-yl)-N,N'-bis(phenyl)benzidine (NPB) was used as a hole transport layer. We took ITO/NPB/Sb$_{2}$Se$_{3}$/Alq$_{3}$/Al as the device architecture. An open circuit voltage ($V_{\rm oc}$) of 0.37 V, a short circuit current density ($J_{\rm sc}$) of 21.2 mA/cm$^{2}$, and a power conversion efficiency (PCE) of 3.79% were obtained on an optimized device. A maximum external quantum efficiency of 73% was achieved at 600 nm. The $J_{\rm sc}$, $V_{\rm oc}$, and PCE were dramatically enhanced after introducing an electron transport layer of Alq$_{3}$. The results suggest that the interface state density at Sb$_{2}$Se$_{3}$/Al interface is decreased by inserting an Alq$_{3}$ layer, and the charge recombination loss in the device is suppressed. This work provides a new electron transport material for Sb$_{2}$Se$_{3}$ thin film solar cells.
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23 articles
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