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Revisiting Laser-Intensity-Dependent Ionization and Fragmentation of C$_{60}$
D. P. Dong, B. H. Yang, D. B. Qian, W. C. Zhou, S. F. Zhang, and X. Ma
Chin. Phys. Lett. 2021, 38 (8 ):
083301
.
DOI: 10.1088/0256-307X/38/8/083301
We revisit the laser-intensity-dependent ionization and fragmentation yields of C$_{60}$ molecules irradiated by 25-fs, 798-nm laser pulses based on the approach in which photoions are measured via a velocity map imaging spectrometer working in a time-sliced mode. This approach dramatically improves the signal-to-background ratio compared to those using a simple (traditional) time-of-flight mode (spectrometer), and thus allows us to measure the laser-intensity dependences down to a previously untouched region, which is expected to provide new insights into the intense-field ionization and fragmentation of C$_{60}$. Indeed, we find that the saturation intensities for C$_{60}$ ionizations and the onset intensity for C$_{60}$ fragmentation are much lower than those reported in previous experiments. Furthermore, the derived saturation-intensity dependence on charge distribution demonstrates the validity of the over-the-barrier ionization using a conducting sphere model.
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PT Symmetry Induced Rings of Lasing Threshold Modes Embedded with Discrete Bound States in the Continuum
Qianju Song, Shiwei Dai, Dezhuan Han, Z. Q. Zhang, C. T. Chan, and Jian Zi
Chin. Phys. Lett. 2021, 38 (8 ):
084203
.
DOI: 10.1088/0256-307X/38/8/084203
It is well known that spatial symmetry in a photonic crystal (PhC) slab is capable of creating bound states in the continuum (BICs), which can be characterized by topological charges of polarization vortices. Here, we show that when a PT-symmetric perturbation is introduced into the PhC slab, a new type of BICs ($pt$-BICs) will arise from each ordinary BIC together with the creation of rings of lasing threshold modes with $pt$-BICs embedded in these rings. Different from ordinary BICs, the $Q$-factor divergence rate of a $pt$-BIC is reduced and anisotropic in momentum space. Also, $pt$-BICs can even appear at off-high symmetry lines of the Brillouin zone. The $pt$-BICs also carry topological charges and can be created or annihilated with the total charge conserved. A unified picture on $pt$-BICs and the associated lasing threshold modes is given based on the temporal coupled mode theory. Our findings reveal the new physics arising from the interplay between PT symmetry and BIC in PhC slabs.
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Excitation of RSAEs during Sawteeth-Like Oscillation in EAST
Ming Xu, Guoqiang Zhong, Baolong Hao, Wei Shen, Liqun Hu, Wei Chen, Zhiyong Qiu, Xuexi Zhang, Youjun Hu, Yingying Li, Hailin Zhao, Haiqing Liu, Bo Lyu, and the EAST Team
Chin. Phys. Lett. 2021, 38 (8 ):
085201
.
DOI: 10.1088/0256-307X/38/8/085201
The excitation condition of reversed shear Alfvén eigenmodes (RSAEs) has been investigated during sawtooth-like oscillation in the EAST tokamak. The sawtooth-like phenomena can be reproduced in the configuration of reversed magnetic shear, and the threshold gradient of electron temperature is formed accordingly, together with the increasing of the confinement of thermal particles. The distribution function of energetic ions density is altered dramatically when the neutral beam is switched from NBI1L (tangent) to NBI1R (perpendicular), which can be captured by the measurement of radial neutron camera. The RSAEs are excited easily in the vicinity of $q_{\min}$ (1.99 m $\leq R \leq 2.06$ m) for the injection of neutral beam with perpendicular direction, which should be excited by the steep gradient of energetic ions density. Furthermore, the excitation of RSAEs and the formation of threshold gradient of electron temperature can take place concurrently, which means that the neutral beam with perpendicular injection is beneficial for the establishment of internal transport barrier.
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Synergistic Influences of Kinetic Effects from Thermal Particles and Fast Ions on Internal Kink Mode
Yutian Miao, G. Z. Hao, Yue Liu, H. D. He, W. Chen, Y. Q. Wang, A. K. Wang, and M. Xu
Chin. Phys. Lett. 2021, 38 (8 ):
085202
.
DOI: 10.1088/0256-307X/38/8/085202
The kinetic effects of thermal particles and fast ions on internal kink (IK) mode are numerically investigated by the MHD-kinetic hybrid code MARS-K. It is shown that either thermal particles or fast ions have stabilizing influence on IK. However, the former can not fully stabilize IK, and the later can suppress the IK. In addition, the synergistic effect from thermal particles and fast ions induces more stronger damping on IK. The kinetic effects from particles significantly raise the critical value of poloidal beta ($\beta_{\rm p}^{\rm crit}$) for driving IK in the toroidal plasma. This implies a method of controlling IK or sawtooth in the high-$\beta_{\rm p}$ discharge scenario of tokamak. It is noted that, at the $q=1$ rational surface, mode structure becomes more sharp due to the self-consistent modification by particles' kinetic effect.
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Superconductivity in Shear Strained Semiconductors
Chang Liu, Xianqi Song, Quan Li, Yanming Ma, and Changfeng Chen
Chin. Phys. Lett. 2021, 38 (8 ):
086301
.
DOI: 10.1088/0256-307X/38/8/086301
Semiconductivity and superconductivity are remarkable quantum phenomena that have immense impact on science and technology, and materials that can be tuned, usually by pressure or doping, to host both types of quantum states are of great fundamental and practical significance. Here we show by first-principles calculations a distinct route for tuning semiconductors into superconductors by diverse large-range elastic shear strains, as demonstrated in exemplary cases of silicon and silicon carbide. Analysis of strain driven evolution of bonding structure, electronic states, lattice vibration, and electron-phonon coupling unveils robust pervading deformation induced mechanisms auspicious for modulating semiconducting and superconducting states under versatile material conditions. This finding opens vast untapped structural configurations for rational exploration of tunable emergence and transition of these intricate quantum phenomena in a broad range of materials.
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Ce-Site Dilution in the Ferromagnetic Kondo Lattice CeRh$_6$Ge$_4$
Jia-Cheng Xu, Hang Su, Rohit Kumar, Shuai-Shuai Luo, Zhi-Yong Nie, An Wang, Feng Du, Rui Li, Michael Smidman, and Hui-Qiu Yuan
Chin. Phys. Lett. 2021, 38 (8 ):
087101
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DOI: 10.1088/0256-307X/38/8/087101
The heavy fermion ferromagnet CeRh$_6$Ge$_4$ is the first example of a clean stoichiometric system where the ferromagnetic transition can be continuously suppressed by hydrostatic pressure to a quantum critical point. In order to reveal the outcome when the magnetic lattice of CeRh$_6$Ge$_4$ is diluted with non-magnetic atoms, this study reports comprehensive measurements of the physical properties of both single crystal and polycrystalline samples of La$_x$Ce$_{1-x}$Rh$_6$Ge$_4$. With increasing $x$, the Curie temperature decreases, and no transition is observed for $x > 0.25$, while the system evolves from exhibiting coherent Kondo lattice behaviors at low $x$ to the Kondo impurity scenario at large $x$. Moreover, non-Fermi liquid behavior is observed over a wide doping range, which agrees well with the disordered Kondo model for $0.52 \leq x \leq 0.66$, while strange metal behavior is revealed in the vicinity of $x_{\rm c} = 0.26$.
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Coexistence of Charge Order and Antiferromagnetic Order in an Extended Periodic Anderson Model
Yanting Li , Bixia Gao , Qiyu Wang , Juan Zhang , and Qiaoni Chen
Chin. Phys. Lett. 2021, 38 (8 ):
087102
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DOI: 10.1088/0256-307X/38/8/087102
The competition between the RKKY interaction and the Kondo effect leads to a magnetic phase transition, which occurs ubiquitously in heavy fermion materials. However, there are more and more experimental evidences indicating that the valence fluctuation plays an essential role in the Ce- and Y-based compounds. We study an extended periodic Anderson model (EPAM) which includes the onsite Coulomb repulsion $U_{cf}$ between the localized electrons and conduction electrons. By employing the density matrix embedding theory, we investigate the EPAM in the symmetric case at half filling. By fixing the onsite Coulomb repulsion $U$ of the localized electrons to an intermediate value, the interplay between the RKKY interaction, the Kondo effect and the Coulomb repulsion $U_{cf}$ brings rich physics. We find three different phases, the antiferromagnetic phase, the charge order phase and paramagnetic phase. When the hybridization strength $V$ between the localized orbital and the conduction orbital is small, the Kondo effect is weak so that the AF phase and the CO phase are present. The phase transition between the two long-range ordered phase is of first order. We also find a coexistence region between the two phases. As $V$ increases, the Kondo effect becomes stronger, and the paramagnetic phase appears between the other two phases.
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Universal Theory and Basic Rules of Strain-Dependent Doping Behaviors in Semiconductors
Xiaolan Yan, Pei Li, Su-Huai Wei, and Bing Huang
Chin. Phys. Lett. 2021, 38 (8 ):
087103
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DOI: 10.1088/0256-307X/38/8/087103
Enhancing the dopability of semiconductors via strain engineering is critical to improving their functionalities, which is, however, largely hindered by the lack of basic rules. In this study, for the first time, we develop a universal theory to understand the total energy changes of point defects (or dopants) with different charge states under strains, which can exhibit either parabolic or superlinear behaviors, determined by the size of defect-induced local volume change ($\Delta V$). In general, $\Delta V$ increases (decreases) when an electron is added (removed) to (from) the defect site. Consequently, in terms of this universal theory, three basic rules can be obtained to further understand or predict the diverse strain-dependent doping behaviors, i.e., defect formation energies, charge-state transition levels, and Fermi pinning levels, in semiconductors. These three basic rules could be generally applied to improve the doping performance or overcome the doping bottlenecks in various semiconductors.
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Proximity Effect of Epitaxial Iron Phthalocyanine Molecules on High-Quality Graphene Devices
Haiyang Pan, Xiaobo Wang, Qiaoming Wang, Xiaohua Wu, Chang Liu, Nian Lin, and Yue Zhao
Chin. Phys. Lett. 2021, 38 (8 ):
087201
.
DOI: 10.1088/0256-307X/38/8/087201
Depositing magnetic insulators on graphene has been a promising route to introduce magnetism via exchange proximity interaction in graphene for future spintronics applications. Molecule-based magnets may offer unique opportunities because of their synthesis versatility. Here, we investigate the magnetic proximity effect of epitaxial iron phthalocyanine (FePc) molecules on high-quality monolayer and bilayer graphene devices on hexagonal boron nitride substrates by probing the local and nonlocal transport. Although the FePc molecules introduce large hole doping effects combined with mobility degradation, the magnetic proximity gives rise to a canted antiferromagnetic state under a magnetic field in the monolayer graphene. On bilayer graphene and FePc heterostructure devices, the nonlocal transport reveals a pronounced Zeeman spin-Hall effect. Further analysis of the scattering mechanism in the bilayer shows a dominated long-range scattering. Our findings in graphene/organic magnetic insulator heterostructure provide a new insight for use of molecule-based magnets in two-dimensional spintronic devices.
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Magnetic-Field-Induced Spin Nematicity in FeSe$_{1-x}$S$_{x}$ and FeSe$_{1-y}$Te$_{y}$ Superconductor Systems
Shaobo Liu, Jie Yuan, Sheng Ma, Zouyouwei Lu, Yuhang Zhang, Mingwei Ma, Hua Zhang, Kui Jin, Li Yu, Fang Zhou, Xiaoli Dong, and Zhongxian Zhao
Chin. Phys. Lett. 2021, 38 (8 ):
087401
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DOI: 10.1088/0256-307X/38/8/087401
The angular-dependent magnetoresistance (AMR) of the $ab$ plane is measured on the single crystals of iron-chalcogenide FeSe$_{1-x}$S$_{x}$ ($x = 0$, 0.07, 0.13 and 1) and FeSe$_{1-y}$Te$_{y}$ ($y = 0.06$, 0.61 and 1) at various temperatures under fields up to 9 T. A pronounced twofold-anisotropic carrier-scattering effect is identified by AMR, and attributed to a magnetic-field-induced spin nematicity that emerges from the tetragonal normal-state regime below a characteristic temperature $T_{\rm sn}$. This magnetically polarized spin nematicity is found to be ubiquitous in the isoelectronic FeSe$_{1-x}$S$_{x}$ and FeSe$_{1-y}$Te$_{y}$ systems, no matter whether the sample shows an electronic nematic order at $T_{\rm s} \lesssim T_{\rm sn}$, or an antiferromagnetic order at $T_{\rm N} < T_{\rm sn}$, or neither order. Importantly, we find that the induced spin nematicity shows a very different response to sulfur substitution from the spontaneous electronic nematicity: The spin-nematic $T_{\rm sn}$ is not suppressed but even enhanced by the substitution, whereas the electronic-nematic $T_{\rm s}$ is rapidly suppressed, in the FeSe$_{1-x}$S$_{x}$ system. Furthermore, we find that the superconductivity is significantly suppressed with the enhancement of the induced spin nematicity in both FeSe$_{1-x}$S$_{x}$ and FeSe$_{1-y}$Te$_{y}$ samples.
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Large Magnetoresistance and Nontrivial Berry Phase in Nb$_3$Sb Crystals with A15 Structure
Qin Chen, Yuxing Zhou, Binjie Xu, Zhefeng Lou, Huancheng Chen, Shuijin Chen, Chunxiang Wu, Jianhua Du, Hangdong Wang, Jinhu Yang, and Minghu Fang
Chin. Phys. Lett. 2021, 38 (8 ):
087501
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DOI: 10.1088/0256-307X/38/8/087501
Compounds with the A15 structure have attracted extensive attention due to their superconductivity and nontrivial topological band structures. We have successfully grown Nb$_3$Sb single crystals with the A15 structure and systematically measured the longitudinal resistivity, Hall resistivity and quantum oscillations in magnetization. Similar to other topological trivial/nontrivial semimetals, Nb$_3$Sb exhibits large magnetoresistance (MR) at low temperatures (717$\%$, 2 K and 9 T), unsaturating quadratic field dependence of MR and up-turn behavior in $\rho_{xx}(T)$ curves under magnetic field, which is considered to result from a perfect hole-electron compensation, as evidenced by the Hall resistivity measurements. The nonzero Berry phase obtained from the de-Hass van Alphen (dHvA) oscillations demonstrates that Nb$_3$Sb is topologically nontrivial. These results indicate that Nb$_{3}$Sb superconductor is also a semimetal with large MR and nontrivial Berry phase. This indicates that Nb$_{3}$Sb may be another platform to search for the Majorana zero-energy mode.
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Magnetic Anisotropy Induced by Orbital Occupation States in La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ Films
Huaixiang Wang, Jinghua Song, Weipeng Wang, Yuansha Chen, Xi Shen, Yuan Yao, Junjie Li, Jirong Sun, and Richeng Yu
Chin. Phys. Lett. 2021, 38 (8 ):
087502
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DOI: 10.1088/0256-307X/38/8/087502
Interface engineering is an effective and feasible method to regulate the magnetic anisotropy of films by altering interfacial states between films. Using the technique of pulsed laser deposition, we prepared La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ (LSMO) and La$_{0.67}$Sr$_{0.33}$MnO$_{3}$/SrCoO$_{2.5}$ (LSMO/SCO) films on (110)-oriented La$_{0.3}$Sr$_{0.7}$Al$_{0.65}$Ta$_{0.35}$O$_{3}$ substrates. By covering the SCO film above the LSMO film, we transformed the easy magnetization axis of LSMO from the [001] axis to the [1$\bar{1}$0] axis in the film plane. Based on statistical analyses, we find that the corresponding Mn–Mn ionic distances are different in the two types of LSMO films, causing different distortions of Mn–O octahedron in LSMO. In addition, it also induces diverse electronic occupation states in Mn$^{3+}$ ions. The $e_{\rm g}$ electron of Mn$^{3+}$ occupies 3$z^{2}-r^{2}$ and $x^{2}-y^{2}$ orbitals in the LSMO and LSMO/SCO, respectively. We conclude that the electronic spin reorientation leads to the transformation of the easy magnetization axis in the LSMO films.
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Narrow Waveguide Based on Ferroelectric Domain Wall
Gongzheng Chen, Jin Lan, Tai Min, and Jiang Xiao
Chin. Phys. Lett. 2021, 38 (8 ):
087701
.
DOI: 10.1088/0256-307X/38/8/087701
Ferroelectric materials are spontaneous symmetry breaking systems that are characterized by ordered electric polarizations. Similar to its ferromagnetic counterpart, a ferroelectric domain wall can be regarded as a soft interface separating two different ferroelectric domains. Here we show that two bound state excitations of electric polarization (polar wave), or the vibration and breathing modes, can be hosted and propagate within the ferroelectric domain wall. In particular, the vibration polar wave has zero frequency gap, thus is constricted deeply inside ferroelectric domain wall, and can even propagate in the presence of local pinnings. The ferroelectric domain wall waveguide as demonstrated here offers a new paradigm in developing ferroelectric information processing units.
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Improvement of Photoluminescence of Perovskite CH$_{3}$NH$_{3}$PbI$_{3}$ by Adding Additional CH$_{3}$NH$_{3}$I during Grinding
Dou-Dou Qian, Lei Liu, Zhi-Xue Xing, Rui Dong, Li Wu, Hong-Kun Cai, Yong-Fa Kong, Yi Zhang, and Jing-Jun Xu
Chin. Phys. Lett. 2021, 38 (8 ):
087801
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DOI: 10.1088/0256-307X/38/8/087801
The organic-inorganic hybrid perovskite CH$_{3}$NH$_{3}$PbI$_{3}$ has been a good candidate for many optoelectronic applications such as light-emitting diodes due to its unique properties. Optimizing the optical properties of the CH$_{3}$NH$_{3}$PbI$_{3}$ material to improve the device performance is a hot topic. Herein, a new strategy is proposed to enhance the light emission of CH$_{3}$NH$_{3}$PbI$_{3}$ phosphor effectively. By adding the reactant CH$_{3}$NH$_{3}$I powder in an appropriate proportion and simply grinding, the emission intensity of CH$_{3}$NH$_{3}$PbI$_{3}$ is greatly improved. The advantages of the proposed method are swiftness, simplicity and reproducibility, and no requirement for a complex organic ligand. The mechanism of this phenomenon is revealed by x-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, photoluminescence, and temperature-dependent photoluminescence. This study offers a unique insight for optimizing the optical properties of halide perovskite materials.
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Effect of Fluorine Substitution on the Electrochemical Property and Structural Stability of a Lithium-Excess Cation Disordered Rock-Salt Cathode
Panpan Li , Zhijie Feng , Tao Cheng , Yingchun Lyu, and Bingkun Guo
Chin. Phys. Lett. 2021, 38 (8 ):
088201
.
DOI: 10.1088/0256-307X/38/8/088201
Lithium-excess cation disordered rock-salt materials have received much attention because of their high-capacity as a candidate for cathodes for lithium-ion batteries. The ultra-high specific capacity comes from the coordinated charge compensation of both transition metal and lattice oxygen. However, the oxygen redox at high voltage usually leads to irreversible oxygen release, thereby degrading the structure stability and electrochemical performance. Lithium-excess Li$_{1.14}$Ni$_{0.57+0.5 x}$Ti$_{0.19-0.5 x}$Mo$_{0.10}$O$_{2-x}$F$_{x}$ ($x=0$, 0.05, 0.10, 0.15, and 0.20) with different amounts of fluorine substitution were synthesized. Among them, Li$_{1.14}$Ni$_{0.620}$Ti$_{0.140}$Mo$_{0.10}$O$_{1.85}$F$_{0.15}$ exhibits a lower capacity decline, better rate performance, and lower structure damage. The effects of fluorine substitution on the electrochemical property and structural stability were systematic studied by x-ray photoelectron spectroscopy and in situ XRD etc. Results show that fluorine substitution reduces the average valence of the anion, allowing a larger proportion of low-valent redox active transition metals, increasing the transition metal redox capacity, inhibiting irreversible oxygen release and side reaction. Fluorine substitution further improves the structural stability and suppresses lattice deformation of the material.
26 articles