中国物理B

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Accelerator-mode islands and superdiffusion in double-kicked rotor

Fengdi Wang(王风涤) and Ping Fang(方萍)

2023 (6): 60504-060504. doi: 10.1088/1674-1056/accb4b

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This paper presents a theoretical investigation of the presence of acceleration islands in the phase space of double-kicked rotor (DKR) systems, which can lead to superdiffusive behavior. We establish the conditions for the existence of period-1 acceleration centers and subsequently calculate the stability conditions for both period-1 and period-2 accelerate mode islands. A detailed analysis of local and global diffusion in the vicinity of the islands and the stickiness regions is provided. It is demonstrated that the mean stickiness time decays exponentially when the phase point is located in the interior of the island. Moreover, the phase point undergoes a power-law decay with a power equal to approximately 5 when entering the sticky region. These findings offer a foundation for future exploration of quantum dynamics in the DKR system.

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Fragmentation dynamics of electron-impact double ionization of helium

Shiwei Liu(刘士炜), Difa Ye(叶地发), and Jie Liu(刘杰)

2023 (6): 63402-063402. doi: 10.1088/1674-1056/acbe33

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We study the double ionization dynamics of a helium atom impacted by electrons with full-dimensional classical trajectory Monte Carlo simulation. The excess energy is chosen to cover a wide range of values from 5 eV to 1 keV for comparative study. At the lowest excess energy, i.e., close to the double-ionization threshold, it is found that the projectile momentum is totally transferred to the recoil-ion while the residual energy is randomly partitioned among the three outgoing electrons, which are then most probably emitted with an equilateral triangle configuration. Our results agree well with experiments as compared with early quantum-mechanical calculation as well as classical simulation based on a two-dimensional Bohr's model. Furthermore, by mapping the final momentum vectors event by event into a Dalitz plot, we unambiguously demonstrate that the ergodicity has been reached and thus confirm a long-term scenario conceived by Wannier. The time scale for such few-body thermalization, from the initial nonequilibrium state to the final microcanonical distribution, is only about 100 attoseconds. Finally, we predict that, with the increase of the excess energy, the dominant emission configuration undergoes a transition from equilateral triangle to T-shape and finally to a co-linear mode. The associated signatures of such configuration transition in the electron-ion joint momentum spectrum and triple-electron angular distribution are also demonstrated.

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Broadband and wide-angle plane focal surface Luneburg lens

Jue Li(李珏), Yangyang Zhou(周杨阳), and Huanyang Chen(陈焕阳)

2023 (6): 64210-064210. doi: 10.1088/1674-1056/ac8e9e

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The energy crisis has aroused widespread concern, and the reform of energy structure is imminent. In the future, the energy structure will be dominated by the solar energy and other renewable energy sources. The solar concentrating technology as a promising method has been widely studied for collecting solar energy. However, the previous solar concentrating technologies suffer from some drawbacks, such as low focusing efficiency and large concentrating size. The Luneburg lens with highly efficient aberration-free focusing provides a new route for solar/energy concentrator. In this work, we designed a plane focal surface Luneburg lens (PFSLL) by transformation optics (TO). The PFSLL provides a relatively high focusing efficiency and concentration ratio of collection of energy. At the same time, it circumvents the disadvantage of curve surface of the classical Luneburg lens in device integration. Based on the reciprocity of electromagnetic waves, the PFSLL can also be applied to the antenna field to achieve broadband wide-angle scanning and highly directional radiation.

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Improving resolution of superlens based on solid immersion mechanism

Zhanlei Hao(郝占磊), Yangyang Zhou(周杨阳), Bei Wu(吴贝),Yineng Liu(刘益能), and Huanyang Chen(陈焕阳)

2023 (6): 64211-064211. doi: 10.1088/1674-1056/ac8726

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Super-resolution imaging with superlens has been one of the fundamental research topics. Unfortunately, the resolution of superlens is inevitably restrained by material loss. To address the problem, we introduce the solid immersion mechanism into the slab superlens and the cylindrical superlens. The proposed solid immersion slab superlens (SISSL) and the solid immersion cylindrical superlens (SICSL) can improve the resolution by converting evanescent wave to propagating wave using high refractive index materials. From the perspective of applications, the cylindrical superlens with finite cross section and the ability of magnification or demagnification has more advantages than the slab superlens. Therefore, we focus on demonstrating analytically the super-resolution imaging of SICSL. Due to the impedance mismatching caused by solid immersion mechanism, the whispering gallery modes (WGMs) are excited between SICSL and the air interface. We clarify the excitation conditions of WGMs and analyze their influence on the imaging quality of SICSL. The SISSL and SICSL may pave a way to apply in lithography technique and real-time biomolecular imaging in future.

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Two-photon absorption of FAPbBr₃ perovskite nanocrystals

Xuanyu Zhang(张轩宇), Shuyu Xiao(肖书宇), Xiongbin Wang(王雄彬), Tingchao He(贺廷超), and Rui Chen(陈锐)

2023 (6): 64212-064212. doi: 10.1088/1674-1056/acb203

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Perovskite nanocrystals (NCs) with high two-photon absorption (TPA) cross-section are of great interest due to their potential applications in three-dimensional optical data storage and multiphoton fluorescence microscopy. Among various perovskite materials, FAPbBr$_{3}$ NCs show a better development prospect due to their excellent stability. However, there are few reports on their nonlinear optical properties. In this work, the nonlinear optical behavior of FAPbBr$_{3}$ NCs is studied. The methods of multiphoton absorption photoluminescence saturation and open aperture $Z$-scan technique were applied to determine the TPA cross-section of FAPbBr$_{3}$ NCs, which was around $2.76 \times 10^{-45}$ cm$^{4}\cdot$s$\cdot $photon$^{-1}$ at 800 nm. In addition, temperature-dependent photoluminescence induced by TPA was investigated, and the small longitudinal optical phonon energy and electron-phonon coupling strength was obtained, which confirm the weak Pb-Br interaction. Meanwhile, it is found that the exciton binding energy in FAPbBr$_{3}$ NCs was 69.668 meV, which may be ascribed to the strong hydrogen bond interaction. It is expected that our findings will promote the application of FAPbBr$_{3}$ NCs in optoelectronic devices.

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Enhancement of thermal rectification by asymmetry engineering of thermal conductivity and geometric structure for multi-segment thermal rectifier

Fu-Ye Du(杜甫烨), Wang Zhang(张望), Hui-Qiong Wang(王惠琼), and Jin-Cheng Zheng(郑金成)

2023 (6): 64402-064402. doi: 10.1088/1674-1056/acc78c

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Thermal rectification is an exotic thermal transport phenomenon, an analog to electrical rectification, in which heat flux along one direction is larger than that in the other direction and is of significant interest in electronic device applications. However, achieving high thermal rectification efficiency or rectification ratio is still a scientific challenge. In this work, we performed a systematic simulation of thermal rectification by considering both efforts of thermal conductivity asymmetry and geometrical asymmetry in a multi-segment thermal rectifier. It is found that the high asymmetry of thermal conductivity and the asymmetry of the geometric structure of multi-segment thermal rectifiers can significantly enhance the thermal rectification, and the combination of both thermal conductivity asymmetry and geometrical asymmetry can further improve thermal rectification efficiency. This work suggests a possible way for improving thermal rectification devices by asymmetry engineering.

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Electronic and thermal properties of Ag-doped single crystal zinc oxide via laser-induced technique

Huan Xing(邢欢), Hui-Qiong Wang(王惠琼), Tinglu Song(宋廷鲁), Chunli Li(李纯莉), Yang Dai(戴扬), Gengming Fu(傅耿明), Junyong Kang(康俊勇), and Jin-Cheng Zheng(郑金成)

2023 (6): 66107-066107. doi: 10.1088/1674-1056/acae74

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The doping of ZnO has attracted lots of attention because it is an important way to tune the properties of ZnO. Post-doping after growth is one of the efficient strategies. Here, we report a unique approach to successfully dope the single crystalline ZnO with Ag by the laser-induced method, which can effectively further post-treat grown samples. Magnetron sputtering was used to coat the Ag film with a thickness of about 50 nm on the single crystalline ZnO. Neodymium-doped yttrium aluminum garnet (Nd:YAG) laser was chosen to irradiate the Ag-capped ZnO samples, followed by annealing at 700 ℃ for two hours to form ZnO:Ag. The three-dimensional (3D) information of the elemental distribution of Ag in ZnO was obtained through time-of-flight secondary ion mass spectrometry (TOF-SIMS). TOF-SIMS and core-level x-ray photoelectron spectroscopy (XPS) demonstrated that the Ag impurities could be effectively doped into single crystalline ZnO samples as deep as several hundred nanometers. Obvious broadening of core level XPS profiles of Ag from the surface to depths of hundred nms was observed, indicating the variance of chemical state changes in laser-induced Ag-doped ZnO. Interesting features of electronic mixing states were detected in the valence band XPS of ZnO:Ag, suggesting the strong coupling or interaction of Ag and ZnO in the sample rather than their simple mixture. The Ag-doped ZnO also showed a narrower bandgap and a decrease in thermal diffusion coefficient compared to the pure ZnO, which would be beneficial to thermoelectric performance.

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Hydrogen diffusion in C₁' phase clathrate hydrate

Zixuan Song(宋姿璇), Ziyue Zhou(周子岳), Yanwen Lin(林演文), Qiao Shi(石桥), Yongchao Hao(郝勇超),Yuequn Fu(付越群), Zhisen Zhang(张志森), and Jianyang Wu(吴建洋)

2023 (6): 66602-066602. doi: 10.1088/1674-1056/accd4b

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Recently, a new phase C$_{1}'$ H$_{2}$ hydrate was experimentally identified. In this work, the diffusive behaviors of H$_{2}$ in C$_{1}'$ phase clathrate hydrate are explored using classic molecular dynamics (MD) simulations. It reveals that the cage occupancy by H$_{2}$ molecule negligibly influences the C$_{1}'$ phase clathrate structure but greatly dictates the diffusion coefficient of H$_{2}$ molecule. Due to the small cage size and small windows connecting the neighboring cages in C$_{1}'$ phase clathrate, non-occupancy of the neighboring cages is demanded to enable the diffusion of H$_{2}$ molecule that is primarily dominated by hopping mechanism. Moreover, the analysis of diffusive free energy landscape reveals lower energy barrier of H$_{2}$ molecule in C$_{1}'$ phase clathrate hydrate than that of other gases in conventional clathrate hydrates, and that H$_{2}$ molecule travels through the windows between neighboring cages with preferential molecular orientation. This study provides critical physical insights into the diffusion behaviors of H$_{2}$ in the C$_{1}'$ phase clathrate hydrate, and implies that the C$_{1}'$ clathrate hydrate is a promising solid structure for the next-generation H$_{2}$ storage.

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Impacts of hydrogen annealing on the carrier lifetimes in p-type 4H-SiC after thermal oxidation

Ruijun Zhang(张锐军), Rongdun Hong(洪荣墩), Jingrui Han(韩景瑞), Hungkit Ting(丁雄杰), Xiguang Li(李锡光), Jiafa Cai(蔡加法), Xiaping Chen(陈厦平), Deyi Fu(傅德颐), Dingqu Lin(林鼎渠), Mingkun Zhang(张明昆), Shaoxiong Wu(吴少雄),Yuning Zhang(张宇宁), Zhengyun Wu(吴正云), and Feng Zhang(张峰)

2023 (6): 67205-067205. doi: 10.1088/1674-1056/ac89db

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Thermal oxidation and hydrogen annealing were applied on a 100 μm thick Al-doped p-type 4H-SiC epitaxial wafer to modulate the minority carrier lifetime, which was investigated by microwave photoconductive decay (μ-PCD). The minority carrier lifetime decreased after each thermal oxidation. On the contrary, with the hydrogen annealing time increasing to 3 hours, the minority carrier lifetime increased from 1.1 μs (as-grown) to 3.14 μs and then saturated after the annealing time reached 4 hours. The increase of surface roughness from 0.236 nm to 0.316 nm may also be one of the reasons for limiting the further improvement of the minority carrier lifetimes. Moreover, the whole wafer mappings of minority carrier lifetimes before and after hydrogen annealing were measured and discussed. The average minority carrier lifetime was up to 1.94 μs and non-uniformity of carrier lifetime reached 38% after 4-hour hydrogen annealing. The increasing minority carrier lifetimes could be attributed to the double mechanisms of excess carbon atoms diffusion caused by selective etching of Si atoms and passivation of deep-level defects by hydrogen atoms.

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Stability and multistability of synchronization in networks of coupled phase oscillators

Yun Zhai(翟云), Xuan Wang(王璇), Jinghua Xiao(肖井华), and Zhigang Zheng(郑志刚)

2023 (6): 60503-060503. doi: 10.1088/1674-1056/acc808

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Coupled phase oscillators usually achieve synchronization as the coupling strength among oscillators is increased beyond a critical value. The stability of synchronous state remains an open issue. In this paper, we study the stability of the synchronous state in coupled phase oscillators. It is found that numerical integration of differential equations of coupled phase oscillators with a finite time step may induce desynchronization at strong couplings. The mechanism behind this instability is that numerical accumulated errors in simulations may trigger the loss of stability of the synchronous state. Desynchronization critical couplings are found to increase and diverge as a power law with decreasing the integral time step. Theoretical analysis supports the local stability of the synchronized state. Globally the emergence of synchronous state depends on the initial conditions. Other metastable ordered states such as twisted states can coexist with the synchronous mode. These twisted states keep locally stable on a sparse network but lose their stability when the network becomes dense.

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Relaxation of Ne¹⁺ 1s⁰2s²2p⁶np produced by resonant excitation of an ultraintense ultrafast x-ray pulse

Jie Yan(闫杰), Yanpeng Liu(刘彦鹏), Yong Hou(侯永), Cheng Gao(高城), Jianhua Wu(吴建华), Jiaolong Zeng(曾交龙), and Jianmin Yuan(袁建民)

2023 (6): 63101-063101. doi: 10.1088/1674-1056/acc3fa

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The creation and relaxation of double $K$-hole states ${\rm 1s}^0{\rm 2s}^22{\rm p}^6n$p ($n\geq3$) of Ne$^{1+}$ in the interaction with ultraintense ultrafast x-ray pulses are theoretically investigated. The x-ray photon energies are selected so that x-rays first photoionize ${\rm 1s}^22{\rm s}^22{\rm p}^6$ of a neon atom to create a single $K$-hole state of ${\rm 1s}2{\rm s}^22{\rm p}^6$of Ne$^{1+}$, which is further excited resonantly to double $K$-hole states of $1{\rm s}^02{\rm s}^22{\rm p}^6n$p ($n\geq3$). A time-dependent rate equation is used to investigate the creation and relaxation processes of $1{\rm s}^02{\rm s}^22{\rm p}^6n$p, where the primary microscopic atomic processes including photoexcitation, spontaneous radiation, photoionization and Auger decay are considered. The calculated Auger electron energy spectra are compared with recent experimental results, which shows good agreement. The relative intensity of Auger electrons is very sensitive to the photon energy and bandwidth of x-ray pulses, which could be used as a diagnostic tool for x-ray free electron laser and atom experiments.

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Single-electron transport in H₂O@C₆₀ single-molecule transistors

Bowen Liu(刘博文), Jun Chen(陈俊), Yiping Ouyang(欧阳一平), Minhao Zhang(张敏昊), Yuan-Zhi Tan(谭元植), and Fengqi Song(宋凤麒)

2023 (6): 63601-063601. doi: 10.1088/1674-1056/acc801

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Single-molecule transistors (SMTs) based on fullerenes and their derivatives have been recognized as a long-sought platform for studying the single-electron transport properties. H₂O@C₆₀ is a combination of fullerene and H₂O, a typical light molecule. Here we use the ‘molecular surgery’ technique to synthesize the H₂O@C₆₀ molecule and then construct the H₂O@C₆₀ SMTs, together with the C₆₀ SMTs. Evidences for single-electron transport have been obtained in our measurements, including explicit Coulomb blockade and Coulomb oscillations. We then calculate the detailed parameters of the H₂O@C₆₀ and C₆₀ SMTs using a capacitance model derived from the Coulomb diamond feature, which gives a capacitance ratio of 1:5.05:8.52 for the H₂O@C₆₀ SMT and 1:29.5:74.8 for the C₆₀ SMT. Moreover, the gate efficiency factor α turns out to be 0.0686 in the H₂O@C₆₀ SMT, about ten times larger than that in the C₆₀ SMT. We propose that the enhanced gate efficiency in H₂O@C₆₀ SMT may be induced by the closer attachment of molecular orbital electron clouds to the gate substrate due to polarization effects of H₂O.

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Critical behavior in the epitaxial growth of two-dimensional tellurium films on SrTiO₃ (001) substrates

Haimin Zhang(张海民), Dezhi Song(宋德志), Fuyang Huang(黄扶旸), Jun Zhang(仉君), and Ye-Ping Jiang(蒋烨平)

2023 (6): 66802-066802. doi: 10.1088/1674-1056/acc80d

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Materials' properties may differ in the thin-film form, especially for epitaxial ultra-thin films, where the substrates play an important role in their deviation from the bulk quality. Here by molecular beam epitaxy (MBE) and scanning tunneling microscopy/spectroscopy, we investigate the growth kinetics of ultra-thin tellurium (Te) films on SrTiO₃ (STO) (001). The MBE growth of Te films usually exhibits Volmer-Weber (VW) island growth mode and no a-few-monolayer film with full coverage has been reported. The absence of wetting-layer formation in the VW growth mode of Te on STO (001) is resulted from its low diffusion barriers as well as its relatively higher surface energy compared with those of the substrate and the interface. Here we circumvent these limiting factors and achieve the growth of ultra-thin β-Te films with near-complete coverages by driving the growth kinetics to the extreme condition. There is a critical thickness (3 monolayer) above which the two-dimensional Te films can form on the STO (001) substrate. In addition, the scanning tunneling spectra on the ultra-thin Te film grown on STO exhibits an enormously large forbidden gap compared with that grown on the graphene substrate. Our work establishes the necessary conditions for the growth of ultra-thin materials with similar kinetics and thermodynamics.

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Flat band in hole-doped transition metal dichalcogenide observed by angle-resolved photoemission spectroscopy

Zilu Wang(王子禄), Haoyu Dong(董皓宇), Weichang Zhou(周伟昌), Zhihai Cheng(程志海), and Shancai Wang(王善才)

2023 (6): 67103-067103. doi: 10.1088/1674-1056/acc7f9

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Layered transition metal dichalcogenides (TMDCs) gained widespread attention because of their electron-correlation-related physics, such as charge density wave (CDW), superconductivity, etc. In this paper, we report the high-resolution angle-resolved photoemission spectroscopy (ARPES) studies on the electronic structure of Ti-doped $1T$-Ti$_x$Ta$_{1-x}$S$_2$ with different doping levels. We observe a flat band that originates from the formation of the star of David super-cell at the $x=5$% sample at the low temperature. With the increasing Ti doping levels, the flat band vanishes in the $x=8$% sample due to the extra hole carrier. We also find the band shift and variation of the CDW gap caused by the Ti-doping. Meanwhile, the band folding positions and the CDW vector $\bm q_{{\rm{CDW}}}$ are intact. Our ARPES results suggest that the localized flat band and the correlation effect in the $1T$-TMDCs could be tuned by changing the filling factor through the doping electron or hole carriers. The Ti-doped $1T$-Ti$_x$Ta$_{1-x}$S$_2$ provides a platform to fine-tune the electronic structure evolution and a new insight into the strongly correlated physics in the TMDC materials.

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Tunable correlation in twisted monolayer-trilayer graphene

Dongdong Ding(丁冬冬), Ruirui Niu(牛锐锐), Xiangyan Han(韩香岩), Zhuangzhuang Qu(曲壮壮), Zhiyu Wang(王知雨), Zhuoxian Li(李卓贤), Qianling Liu(刘倩伶), Chunrui Han(韩春蕊), and Jianming Lu(路建明)

2023 (6): 67204-067204. doi: 10.1088/1674-1056/acc8c3

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Flat-band physics of moiré superlattices, originally discovered in the celebrated twisted bilayer graphene, have recently been intensively explored in multilayer graphene systems that can be further controlled by electric field. In this work, we experimentally find the evidence of correlated insulators at half filling of the electron moiré band of twisted monolayer-trilayer graphene with a twist angle around 1.2°. Van Hove singularity (VHS), manifested as enhanced resistance and zero Hall voltage, is observed to be distinct in conduction and valence flat bands. It also depends on the direction and magnitude of the displacement fields, consistent with the asymmetric crystal structure. While the resistance ridges at VHS can be enhanced by magnetic fields, when they cross commensurate fillings of the moiré superlattice in the conduction band, the enhancement is so strong that signatures of correlated insulator appear, which may further develop into an energy gap depending on the correlation strength. At last, Fermi velocity derived from temperature coefficients of resistivity is compared between conduction and valence bands with different displacement fields. It is found that electronic correlation has a negative dependence on the Fermi velocity, which in turn could be used to quantify the correlation strength.

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Gate-controlled localization to delocalization transition of flat band wavefunction in twisted monolayer-bilayer graphene

Siyu Li(李思宇), Zhengwen Wang(王政文), Yucheng Xue(薛禹承), Lu Cao(曹路), Kenji Watanabe, Takashi Taniguchi, Hongjun Gao(高鸿钧), and Jinhai Mao(毛金海)

2023 (6): 67304-067304. doi: 10.1088/1674-1056/acc805

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Twisted graphene systems with flat bands have attracted much attention for they are excellent platforms to research novel quantum phases. Recently, transport measurements about twisted monolayer-bilayer graphene (tMBG) have shown the existence of correlated states and topological states in this system. However, the direct observations of the band structures and the corresponding spatial distributions are still not sufficient. Here we show that the distributions of flat bands in tMBG host two different modes by scanning tunneling microscopy and spectroscopy (STM/S). By tuning our tMBG device from the empty filling state to the full filling state through the back gate, we observe that the distributions of two flat bands develop from localized mode to delocalized mode. This gate-controlled flat band wavefunction polarization is unique to the tMBG system. Our work suggests that tMBG is promising to simulate both twisted bilayer graphene (TBG) and twisted double bilayer graphene (tDBG) and would be an ideal platform to explore novel moiré physics.

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Stochastic fluctuations in the rotation of the bacterial flagellar motor

Guanhua Yue(岳冠骅), Rongjing Zhang(张榕京), and Junhua Yuan(袁军华)

2023 (6): 68703-068703. doi: 10.1088/1674-1056/acc804

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The bacterial flagellar motor is a nanometer-sized rotary motor that generates the torque to drive the rotation of the flagellar filament. The output torque is an important property of the motor. The motor rotation was usually monitored by attaching a μm-sized bead to a shortened flagellar filament, and the torque was extracted by calculating the torque due to the viscous drag of the medium on the bead rotation. We sought for an independent extraction of the torque from thermal fluctuation in the motor rotation using the fluctuation theorem (FT). However, we identified an overwhelming fluctuation beyond the thermal noise that precluded the use of FT. We further characterized the timescale and the amplitude of this fluctuation, finding that it was probably due to the stepping of the motor. The amplitude of torque fluctuation we characterized here provided new information on the torque-generating interaction potential curve.

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Interaction solutions for the second extended (3+1)-dimensional Jimbo-Miwa equation

Hongcai Ma(马红彩), Xue Mao(毛雪), and Aiping Deng(邓爱平)

2023 (6): 60201-060201. doi: 10.1088/1674-1056/acb91c

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Based on the Hirota bilinear method, the second extended (3+1)-dimensional Jimbo-Miwa equation is established. By Maple symbolic calculation, lump and lump-kink soliton solutions are obtained. The interaction solutions between the lump and multi-kink soliton, and the interaction between the lump and triangular periodic soliton are derived by combining a multi-exponential function or trigonometric sine and cosine functions with quadratic functions. Furthermore, periodic-lump wave solution is derived via the ansatz including hyperbolic and trigonometric functions. Finally, 3D plots, 2D curves, density plots, and contour plots with particular choices of the suitable parameters are depicted to illustrate the dynamical features of these solutions.

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Complete hyperentangled Greenberger-Horne-Zeilinger state analysis for polarization and time-bin hyperentanglement

Zhi Zeng(曾志)

2023 (6): 60301-060301. doi: 10.1088/1674-1056/ac9044

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We present an efficient scheme for the complete analysis of hyperentangled Greenberger-Horne-Zeilinger (GHZ) state in polarization and time-bin degrees of freedom with two steps. Firstly, the polarization GHZ state is distinguished completely and nondestructively, resorting to the controlled phase flip (CPF) gate constructed by the cavity-assisted interaction. Subsequently, the time-bin GHZ state is analyzed by using the preserved polarization entanglement. With the help of CPF gate and self-assisted mechanism, our scheme can be directly generalized to the complete N-photon hyperentangled GHZ state analysis, and it may have potential applications in the hyperentanglement-based quantum communication.

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Entanglement properties of superconducting qubits coupled to a semi-infinite transmission line

Yang-Qing Guo(郭羊青), Ping-Xing Chen(陈平形), and Jian Li(李剑)

2023 (6): 60302-060302. doi: 10.1088/1674-1056/acc0fa

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Quantum entanglement, a key resource in quantum information processing, is reduced by interaction between the quantum system concerned and its unavoidable noisy environment. Therefore it is of particular importance to study the dynamical properties of entanglement in open quantum systems. In this work, we mainly focus on two qubits coupled to an adjustable environment, namely a semi-infinite transmission line. The two qubits' relaxations, through individual channels or collective channel or both, can be adjusted by the qubits' transition frequencies. We examine entanglement dynamics in this model system with initial Werner state, and show that the phenomena of entanglement sudden death and revival can be observed. Due to the hardness of preparing the Werner state experimentally, we introduce a new type of entangled state called pseudo-Werner state, which preserves as much entangling property as the Werner state, and more importantly, it is experiment friendly. Furthermore, we provide detailed procedures for generating pseudo-Werner state and studying entanglement dynamics with it, which can be straightforwardly implemented in a superconducting waveguide quantum electrodynamics system.

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Energy shift and subharmonics induced by nonlinearity in a quantum dot system

Yuan Zhou(周圆), Gang Cao(曹刚), Hai-Ou Li(李海欧), and Guo-Ping Guo(郭国平)

2023 (6): 60303-060303. doi: 10.1088/1674-1056/acc521

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The presence of anticrossings induced by coupling between two states causes curvature in energy levels, yielding a nonlinearity in the quantum system. When the system is driven back and forth along the bending energy levels, subharmonic transitions and energy shifts can be observed, which would cause a significant influence as the system is applied to quantum computing. In this paper, we study a longitudinally driven singlet-triplet (ST) system in a double quantum dot (DQD) system, and illustrate the consequences of nonlinearity by driving the system close to the anticrossings. We provide a straightforward theory to quantitatively describe the energy shift and subharmonics caused by nonlinearity, and find good agreement between our theoretical result and the numerical simulation. Our results reveal the existence of nonlinearity in the vicinity of anticrossings and provide a direct way of analytically assessing its impact, which can be applied to other quantum systems without excessive labor.

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Faithful and efficient hyperentanglement purification for spatial-polarization-time-bin photon system

Fang-Fang Du(杜芳芳), Gang Fan(樊钢), Yi-Ming Wu(吴一鸣), and Bao-Cang Ren(任宝藏)

2023 (6): 60304-060304. doi: 10.1088/1674-1056/aca395

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We present a faithful and efficient hyperentanglement purification protocol (hyper-EPP) for nonlocal two-photon systems in spatial-polarization-time-bin hyperentangled Bell states. As the single-photon detectors can detect and herald the undesirable properties caused by side leakage and finite coupling strength, the parity-check gates and swap gates of our hyper-EPP in the spatial, polarization and time-bin mode degrees of freedom (DoFs) work faithfully. The qubit-flip errors in photon systems in three DoFs can be corrected effectively with the faithful parity-check gates and the photon pairs can be reused to distill high-fidelity ones by introducing the faithful swap gates, which greatly increases the efficiency of our hyper-EPP. Further, the maximal hyperentanglement can be obtained in principle by operating multiple rounds of the hyper-EPP.

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A novel fractional-order hyperchaotic complex system and its synchronization

Mengxin Jin(金孟鑫), Kehui Sun(孙克辉), and Shaobo He(贺少波)

2023 (6): 60501-060501. doi: 10.1088/1674-1056/acc0f6

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A novel fractional-order hyperchaotic complex system is proposed by introducing the Caputo fractional-order derivative operator and a constant term to the complex simplified Lorenz system. The proposed system has different numbers of equilibria for different ranges of parameters. The dynamics of the proposed system is investigated by means of phase portraits, Lyapunov exponents, bifurcation diagrams, and basins of attraction. The results show abundant dynamical characteristics. Particularly, the phenomena of extreme multistability as well as hidden attractors are discovered. In addition, the complex generalized projective synchronization is implemented between two fractional-order hyperchaotic complex systems with different fractional orders. Based on the fractional Lyapunov stability theorem, the synchronization controllers are designed, and the theoretical results are verified and demonstrated by numerical simulations. It lays the foundation for practical applications of the proposed system.

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Synchronization of stochastic complex networks with time-delayed coupling

Duolan(朵兰), Linying Xiang(项林英), and Guanrong Chen(陈关荣)

2023 (6): 60502-060502. doi: 10.1088/1674-1056/acc44e

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Noise and time delay are inevitable in real-world networks. In this article, the framework of master stability function is generalized to stochastic complex networks with time-delayed coupling. The focus is on the effects of noise, time delay, and their inner interactions on the network synchronization. It is found that when there exists time-delayed coupling in the network and noise diffuses through all state variables of nodes, appropriately increasing the noise intensity can effectively improve the network synchronizability; otherwise, noise can be either beneficial or harmful. For stochastic networks, large time delays will lead to desynchronization. These findings provide valuable references for designing optimal complex networks in practical applications.

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Synchronization-desynchronization transitions in networks of circle maps with sinusoidal coupling

Yun Zhai(翟云), Jinghua Xiao(肖井华), and Zhigang Zheng(郑志刚)

2023 (6): 60505-060505. doi: 10.1088/1674-1056/acc062

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Coupled phase oscillators are adopted as powerful platforms in studying synchrony behaviors emerged in various systems with rhythmic dynamics. Much attention has been focused on coupled time-continuous oscillators described by differential equations. In this paper, we study the synchronization dynamics of networks of coupled circle maps as the discrete version of the Kuramoto model. Despite of its simplicity in mathematical form, it is found that discreteness may induce many interesting synchronization behaviors. Multiple synchronization and desynchronization transitions of both phases and frequencies are found with varying the coupling among circle-map oscillators. The mechanisms of these transitions are interpreted in terms of the mean-field approach, where collective bifurcation cascades are revealed for coupled circle-map oscillators.

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Semi-analytical steady-state response prediction for multi-dimensional quasi-Hamiltonian systems

Wen-Wei Ye(叶文伟), Lin-Cong Chen(陈林聪), Zi Yuan(原子), Jia-Min Qian(钱佳敏), and Jian-Qiao Sun(孙建桥)

2023 (6): 60506-060506. doi: 10.1088/1674-1056/acae7c

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The majority of nonlinear stochastic systems can be expressed as the quasi-Hamiltonian systems in science and engineering. Moreover, the corresponding Hamiltonian system offers two concepts of integrability and resonance that can fully describe the global relationship among the degrees-of-freedom (DOFs) of the system. In this work, an effective and promising approximate semi-analytical method is proposed for the steady-state response of multi-dimensional quasi-Hamiltonian systems. To be specific, the trial solution of the reduced Fokker-Plank-Kolmogorov (FPK) equation is obtained by using radial basis function (RBF) neural networks. Then, the residual generated by substituting the trial solution into the reduced FPK equation is considered, and a loss function is constructed by combining random sampling technique. The unknown weight coefficients are optimized by minimizing the loss function through the Lagrange multiplier method. Moreover, an efficient sampling strategy is employed to promote the implementation of algorithms. Finally, two numerical examples are studied in detail, and all the semi-analytical solutions are compared with Monte Carlo simulations (MCS) results. The results indicate that the complex nonlinear dynamic features of the system response can be captured through the proposed scheme accurately.

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Modeling differential car-following behavior under normal and rainy conditions: A memory-based deep learning method with attention mechanism

Hai-Jian Bai(柏海舰), Chen-Chen Guo(过晨晨), Heng Ding(丁恒), Li-Yang Wei(卫立阳), Ting Sun(孙婷), and Xing-Yu Chen(陈星宇)

2023 (6): 60507-060507. doi: 10.1088/1674-1056/acaa2f

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In order to analyze and learn the difference in car-following behavior between normal and rainy days, we first collect car-following trajectory data of an urban elevated road on normal and rainy days by microwave radar and analyze the differences in speed, relative speed, acceleration, space headway, and time headway among data through statistics. Secondly, owing to the time-series characteristics of car-following data, we use the long short-term memory (LSTM) neural network optimized by attention mechanism (AM) and sparrow search algorithm (SSA) to learn the different car-following behaviors under different weather conditions and build corresponding models (ASL-Normal, ASL-Rain, where ASL stands for AM-SSA-LSTM), respectively. Finally, the simulation test shows that the mean square error (MSE) and reciprocal of time-to-collision (RTTC) of the ASL model are better than those of LSTM and intelligent diver model (IDM), which is closer to the real data. The ASL model can better learn different driving behaviors on normal and rainy days. However, it has a higher sensitivity to weather conditions from cross test on normal and rainy data-sets which need classification training or sample diversification processing. In the car-following platoon simulation, the stability performances of two models are excellent, which can describe the basic characteristics of traffic flow on normal and rainy days. Comparing with ASL-Rain model, the convergence time of ASL-Normal is shorter, reflecting that cautious driving behavior on rainy days will reduce traffic efficiency to a certain extent. However, ASL-Normal model produces a more severe and frequent traffic oscillation within a shorter period because of aggressive driving behavior on normal days.

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Influence of acceleration on relativistic nonlinear Thomson scattering in tightly focused linearly polarized laser pulses

Yifan Chang(常一凡), Yubo Wang(王禹博), Chang Wang(王畅), Yuting Shen(申雨婷), and Youwei Tian(田友伟)

2023 (6): 63201-063201. doi: 10.1088/1674-1056/ac89e6

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The influence of acceleration of electrons on relativistic nonlinear Thomson scattering in tightly focused linearly polarized laser pulses is investigated for the first time. In the framework of classical electrodynamics, it is deduced and found that the more severe the change in the electron transverse acceleration, the stronger the asymmetry of the radiation angle distribution, and the greater the transverse acceleration, the greater the radiation energy. Tightly focused, ultrashort, and high-intensity lasers lead to violent electron acceleration processes, resulting in a bifurcated radiation structure with asymmetry and higher energy. Additionally, a change in the initial phase of the laser brings about periodic change of the acceleration, which in turn makes the radiation change periodically with the initial phase. In other cases, the radiation is in a symmetrical double-peak structure. These phenomena will help us to modulate radiation with more energy collimation.

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High harmonic generation in crystal SiO₂ by sub-10-fs laser pulses

Shuai Wang(王帅), Jiawei Guo(郭嘉为), Xinkui He(贺新奎), Yueying Liang(梁玥瑛), Baichuan Xie(谢百川), Shiyang Zhong(钟诗阳), Hao Teng(滕浩), and Zhiyi Wei(魏志义)

2023 (6): 63301-063301. doi: 10.1088/1674-1056/acc452

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The high harmonic generation (HHG) by few-cycle laser pulses is essential for research in strong-field solid-state physics. Through comparison of high harmonic spectra of solids generated by laser pulses with varying durations, we discovered that lasers with good dispersion compensation are capable of producing a broad spectrum of high harmonics. As the pulse duration is further compressed, several interference peaks appear in the broad spectrum. Moreover, we conducted simulations using the semiconductor Bloch equation, considering the effect of Berry curvature, to better understand this process. Our work provides a valuable approach for studying HHG by few-cycle laser pulses in solid materials, expanding the application of HHG in attosecond physics.

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Generation of quasi-chirp-free isolated attosecond pulses from atoms under the action of orthogonal two-color combined pulse of fundamental frequency and higher intensity second harmonic fields

Rui-Xian Yu(蔚瑞贤), Yue Qiao(乔月), Ping Li(李萍), Jun Wang(王俊), Ji-Gen Chen(陈基根), Wei Feng(冯伟), Fu-Ming Guo(郭福明), and Yu-Jun Yang(杨玉军)

2023 (6): 63302-063302. doi: 10.1088/1674-1056/acc80a

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The intrinsic chirp of high-order harmonic generation is an important factor limiting the production of ultrashort attosecond pulses. Based on numerically solving the time-dependent Schrödinger equation, the generation process of high-order harmonic from the He atom under the action of orthogonal two-color combined pulse of fundamental frequency and higher intensity second harmonic fields is studied. In this paper, we propose to achieve quasi-chirp-free isolated attosecond pulses by superimposing a higher second-harmonic field on the orthogonal direction of the fundamental frequency field. It is found that the high-energy part of its harmonic emission exhibits small chirp characteristics, which can be used to synthesize isolated attosecond pulses. Through the analysis of the wave packets evolution and the classical motion trajectories of the electron, it is demonstrated that the quasi-chirp-free harmonic can be attributed to the simultaneous return of electrons ionized at different times to the parent particle. The influence of the relative phase of the two pulses on the harmonics is further analyzed, and it is observed that this phenomenon is sensitive to the relative phase, but it can still generate isolated attosecond pulses within a certain phase.

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Electron-impact ionization of W⁹⁺ and W¹⁰⁺

Runjia Bao(鲍润家), Junkui Wei(魏军奎), Lei Chen(陈雷), Bowen Li(李博文), and Ximeng Chen(陈熙萌)

2023 (6): 63401-063401. doi: 10.1088/1674-1056/aca14d

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Electron-impact single-ionization (EISI) cross sections for W$^{q+}$ ($q=9$, 10) ions have been calculated by using the level-to-level distorted-wave (LLDW) method with emphasis on the contribution of metastable states to the total ionization cross sections. Contributions from direct-ionization (DI) and excitation-autoionization (EA) processes are taken into account. The calculated cross sections include the contributions from both the ground configuration and the long-lived metastable states with lifetimes exceeding 10$^{-6}$ s. Calculated cross sections are in good agreement with experimental measurements when the influence of metastable states on the total ionization cross section are well considered.

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Complex-amplitude Fourier single-pixel imaging via coherent structured illumination

Hong-Yun Hou(侯红云), Ya-Nan Zhao(赵亚楠), Jia-Cheng Han(韩佳成), De-Zhong Cao(曹德忠),Su-Heng Zhang(张素恒), Hong-Chao Liu(刘宏超), and Bao-Lai Liang(梁宝来)

2023 (6): 64201-064201. doi: 10.1088/1674-1056/ac8e9a

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We propose a method of complex-amplitude Fourier single-pixel imaging (CFSI) with coherent structured illumination to acquire both the amplitude and phase of an object. In the proposed method, an object is illustrated by a series of coherent structured light fields, which are generated by a phase-only spatial light modulator, the complex Fourier spectrum of the object can be acquired sequentially by a single-pixel photodetector. Then the desired complex-amplitude image can be retrieved directly by applying an inverse Fourier transform. We experimentally implemented this CFSI with several different types of objects. The experimental results show that the proposed method provides a promising complex-amplitude imaging approach with high quality and a stable configuration. Thus, it might find broad applications in optical metrology and biomedical science.

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Generation of spectrally uncorrelated biphotons via fiber nonlinear quantum interference

Zhengtong Wei(卫正统), Chuan Qu(瞿川), Tian'an Wu(吴天安), Yuanyuan Li(李媛媛), Bo Li(李博), and Shenghai Zhang(张胜海)

2023 (6): 64202-064202. doi: 10.1088/1674-1056/acb767

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Spectrally uncorrelated biphotons are the essential resources for achieving various quantum information processing protocols. We theoretically investigate the generation of spectrally uncorrelated biphotons emitted by spontaneous four-wave mixing from a fiber nonlinear interferometer which consists of an N-stage nonlinear gain fiber and an (N-1)-stage dispersion modulation fiber. The output biphoton states of nonlinear interference are the coherent superposition of various biphoton states born in each nonlinear fiber, and thus the interference fringe will reshape the biphoton joint spectra. As a result, resorting to Taylor expansion to first order for phase mismatching, we theoretically verify that the orientation of phase matching contours will rotate in a specific way with only varying the length of dispersion modulation fiber. The rotation in orientation of phase matching contours may result in spectrally uncorrelated biphotons and even arbitrary correlation biphotons. Further, we choose micro/nanofiber as the nonlinear gain fiber and single-mode communication fiber as dispersion modulation fiber to numerically simulate the generation of spectrally uncorrelated biphotons from spontaneous fourwave mixing. Here, due to significant frequency detuning (hundreds of THz), Raman background noise can be considerably suppressed, even at room temperature, and photons with largely tunable wavelengths can be achieved, indicating a practicability in many quantum fields. A photon mode purity of 97.2% will be theoretically attained without weakening the heralding nature of biphoton sources. We think that this fiber nonlinear interference with the flexibly engineered quantum state can be an excellent practical source for quantum information processing.

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Principle of subtraction ghost imaging in scattering medium

Qin Fu(付芹), Yanfeng Bai(白艳锋), Wei Tan(谭威), Xianwei Huang(黄贤伟), Suqin Nan(南苏琴), and Xiquan Fu(傅喜泉)

2023 (6): 64203-064203. doi: 10.1088/1674-1056/acb202

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Scattering medium in light path will cause distortion of the light field, resulting in poor signal-to-noise ratio (SNR) of ghost imaging. The disturbance is usually eliminated by the method of pre-compensation. We deduce the intensity fluctuation correlation function of the ghost imaging with the disturbance of the scattering medium, which proves that the ghost image consists of two correlated results: the image of scattering medium and the target object. The effect of the scattering medium can be eliminated by subtracting the correlated result between the light field after the scattering medium and the reference light from ghost image, which verifies the theoretical results. Our research may provide a new idea of ghost imaging in harsh environment.

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A 54-fs diode-pumped Kerr-lens mode-locked Yb:LuYSiO₅laser

Yang Yu(于洋), Yuehang Chen(陈月航), Wenlong Tian(田文龙), Li Zheng(郑立), Geyang Wang(王阁阳), Chuan Bai(白川), Xuan Tian(田轩), Haijing Mai(麦海静), Yulong Su(苏玉龙), Jiangfeng Zhu(朱江峰), and Zhiyi Wei(魏志义)

2023 (6): 64204-064204. doi: 10.1088/1674-1056/acb9ed

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We demonstrate a Kerr-lens mode-locked Yb:LuYSiO₅ (Yb:LYSO) laser with the pulse duration of 54 fs, corresponding to a spectral bandwidth of 25 nm centered at 1062 nm. To the best of our knowledge, this is the shortest pulse duration obtained from Yb:LYSO laser. At the repetition rate of 378.3 MHz, an output power of 111.6 mW is obtained using an output coupler with 0.6% transmittance, which can maintain long-time stable mode-locking more than 13 h.

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Antimonene-based saturable absorber for a soliton mode-locked and Q-switched fiber laser in the 2 μm wavelength region

H Ahmad, B Nizamani, M Z Samion, N Yusoff, and M F Ismail

2023 (6): 64205-064205. doi: 10.1088/1674-1056/ac891f

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We demonstrate antimonene as a saturable absorber (SA) to generate an ultrafast mode-locked and Q-switched laser in the 2 μm wavelength region. The two antimonene-based SAs were prepared and inserted separately in a thulium-holmium-doped fiber laser to produce the pulsed laser. Antimonene was coated onto a tapered fiber to generate soliton mode-locked pulses and used in thin-film form for the generation of Q-switched pulses. The mode-locking was stable within a pump power of 267 mW-511 mW, and the laser operated at a central wavelength of 1897.4 nm. The mode-locked laser had a pulse width of 1.3 ps and a repetition rate of 12.6 MHz, with a signal-to-noise ratio of 64 dB. Q-switched laser operation was stable at a wavelength of 1890.1 nm within a pump power of 312 mW-381 mW. With the increase in pump power from 312 mW to 381 mW, the repetition rate increased to a maximum of 56.63 kHz and the pulse width decreased to a minimum value of 2.85 μs. Wide-range tunability of the Q-switched laser was also realized within the wavelength range of 1882 nm-1936 nm.

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Ultraviolet metalens and metalens array of focused vortex beams

Jinping Zhang(张金平), Yan Wang(王焱), Huan Yuan(袁欢), Zehao Wang(王泽豪), Yang Deng(邓阳),Chengzhi Huang(黄承志), Jiagui Wu(吴加贵), and Junbo Yang(杨俊波)

2023 (6): 64206-064206. doi: 10.1088/1674-1056/ac9d87

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The solar-blind ultraviolet (UV) wavelength is particularly interesting within the range of 200 nm-300 nm. Here, we propose a focusing metalens, focusing vortex beam (VB) metalens and metalens array that specifically work in the UV band to focus a beam or VB. Firstly, a high numerical aperture (NA) focusing metalens working at a wavelength of 214.2 nm was designed, and the NA reached 0.83. The corresponding conversion efficiency of the unit structure reached as high as 94%, and the full width at half maximum was only 117.2 nm. Metalenses with large NA can act as optical tweezers and can be applied to trap ultracold atoms and molecules. Secondly, a focused VB metalens in the wavelength range of 200 nm-300 nm was also designed, which can convert polarized light into a VB and focus the VB simultaneously. Finally, a metalens array was developed to focus VBs with different topological charges on the same focal plane. This series of UV metalenses could be widely used in UV microscopy, photolithography, photonics communication, etc.

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Theoretical research on the transverse spin of structured optical fields inside a waveguide

Zhiyong Wang(王智勇), Xiangru Wang(汪相如), Anran Li(李岸然), Kaiqiang Zhang(张开强), Yukun Ji(纪玉坤), and Mingyu Zhong(钟明玉)

2023 (6): 64207-064207. doi: 10.1088/1674-1056/acbf28

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Structured optical fields inside a waveguide possess the transverse spin, i.e., the spin angular momentum perpendicular to the direction of the waveguide. The physical origin of the transverse spin can be attributed to the presence of an effective rest mass of photons in guided waves, or equivalently, to the existence of a longitudinal field component, such that the transverse and longitudinal fields together form an elliptical polarization plane. In contrary to the traditional viewpoint, the transverse spin of photons in guided waves is also quantized, and its quantization form is related to the ellipticity of the polarization ellipse. The direction of the transverse spin depends on the propagation direction of electromagnetic waves along the waveguide, such a spin-momentum locking may have important applications in spin-dependent unidirectional optical interfaces. By means of a coupling between the transverse spin of guided waves and some physical degrees of freedom, one can develop an optical analogy of spintronics, i.e., spinoptics.

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Compact TE-pass polarizer based on lithium-niobate-on-insulator assisted by indium tin oxide and silicon nitride

Jia-Min Liu(刘家敏) and De-Long Zhang(张德龙)

2023 (6): 64208-064208. doi: 10.1088/1674-1056/ac960b

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An indium tin oxide (ITO) and silicon nitride (Si₃N₄) assisted compact TE-pass waveguide polarizer based on lithium-niobate-on-insulator is proposed and numerically analyzed. By properly designing the ITO and Si₃N₄ assisted structure and utilizing the epsilon-near-zero effect of ITO, the TM mode is strongly confined in the ITO layer with extremely high loss, while the TE mode is hardly affected and passes through the waveguide with low loss. The simulation results show that the polarizer has an extinction ratio of 22.5 dB and an insertion loss of 0.8 dB at the wavelength of 1.55 μm, and has an operating bandwidth of about 125 nm (from 1540 nm to 1665 nm) for an extinction ratio of >20 dB and an insertion loss of <0.95 dB. Moreover, the proposed device exhibits large fabrication tolerances. More notably, the device is compact, with a length of only 7.5 μm, and is appropriate for on-chip applications.

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Single-event-transient effect in nanotube tunnel field-effect transistor with bias-induced electron-hole bilayer

Xue-Ke Wang(王雪珂), Ya-Bin Sun(孙亚宾), Zi-Yu Liu(刘子玉), Yun Liu(刘赟), Xiao-Jin Li(李小进), and Yan-Ling Shi(石艳玲)

2023 (6): 64209-064209. doi: 10.1088/1674-1056/ac9180

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The single event transient (SET) effect in nanotube tunneling field-effect transistor with bias-induced electron-hole bilayer (EHBNT-TFET) is investigated by 3-D TCAD simulation for the first time. The effects of linear energy transfer (LET), characteristic radius, strike angle, electrode bias and hit location on SET response are evaluated in detail. The simulation results show that the peak value of transient drain current is up to 0.08 mA for heavy ion irradiation with characteristic radius of 50 nm and LET of 10 MeV·cm²/mg, which is much higher than the on-state current of EHBNT-TFET. The SET response of EHBNT-TFET presents an obvious dependence on LET, strike angle, drain bias and hit location. As LET increases from 2 MeV·cm²/mg to 10 MeV·cm²/mg, the peak drain current increases monotonically from 0.015 mA to 0.08 mA. The strike angle has an greater impact on peak drain current especially for the smaller characteristic radius. The peak drain current and collected charge increase by 0.014 mA and 0.06 fC, respectively, as the drain bias increases from 0.1 V to 0.9 V. Whether from the horizontal or the vertical direction, the most sensitive hit location is related to w_t. The underlying physical mechanism is explored and discussed.

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Dynamic light storage based on controllable electromagnetically induced transparency effect

Liu-Ying Zeng(曾柳莹), Jun-Fang Wu(吴俊芳), and Chao Li(李潮)

2023 (6): 64213-064213. doi: 10.1088/1674-1056/acd2bd

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We analytically and numerically investigate a signal light storing mechanism based on the controllable electromagnetically induced transparency (EIT) effect. We demonstrate that the isolation between the waveguide and the cavities cannot be achieved instantly as soon as the two cavities are tuned into resonance, no matter the index tuning rate is ultrafast or slow. We also investigate the temporal evolution features of the intracavity energy when the pulse during time is prolonged. We find many periodical oscillations of the trapped energy in both cavities, and they are entirely complementary. Our analysis shows that the adiabatic wavelength conversion in both cavities and a phase difference π between them play critical roles in this phenomenon.

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Characteristic analysis of scattering field in two-layer media by Green's function

Ping Zhang(张萍), Zhi-Ying Liu(刘智颖), Shou-Guo Yan(阎守国), Juan Huang(黄娟), and Bi-Xing Zhang(张碧星)

2023 (6): 64301-064301. doi: 10.1088/1674-1056/aca3a0

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The problem of three-dimensional (3D) acoustic scattering in a complex medium has aroused considerable interest of researchers for many years. An ultrasonic scattered field calculating technique is proposed to study the scattering echo from strongly scattered materials in a two-layer medium in this work. Firstly, with the high frequency stationary phase method, the Green's function of two-layer fluid media is derived. And then based on the idea of integral equation discretization, the Green's function method is extended to two-layer fluid media to derive the scattering field expression of defects in a complex medium. With this method, the scattering field of 3D defect in a two-layer medium is calculated and the characteristics of received echoes are studied. The results show that this method is able to solve the scattering P wave field of 3D defect with arbitrary shape at any scattering intensity in two-layer media. Considering the circumstance of water-immersion ultrasonic non-destructive test (NDT), the scattering sound field characteristics of different types of defects are analyzed by simulation, which will help to optimize the detection scheme and corresponding imaging method in practice so as to improve the detection quality.

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Effect of magnetic field on expansion of ferrofluid-encapsulated microbubble

Zhiwei Du(杜芷玮), Fan Li(李凡), Ruiqi Pan(潘瑞琪), Runyang Mo(莫润阳), and Chenghui Wang(王成会)

2023 (6): 64302-064302. doi: 10.1088/1674-1056/acc1d2

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Magnetic microbubbles (MMBs) have great potential applications in drug delivery and target therapy because they can be controlled by magnetic fields. In this paper, dynamic equations are derived by Lagrangian formalism and the behavior of MMBs subject to a combination field of magnetic and ultrasound field in an incompressible infinite fluid is analyzed numerically. The results show that the magnetic field can promote bubble expansion and hinder its translational motion, and both the enhancement and obstruction effects will weaken with the decrease of bubble size. The initial translational velocity has almost no effect on bubbles motion. Besides, the maximum expansion radius of MMBs increases with the ferrofluid shell thickness, while that of the common MBs is just the opposite. In addition, the periodic change of Levich viscous drag caused by the rebound leads to the step-like translational motion. Finally, the ferrofluid-shell model can be replaced by the model of non-magnetic microbubbles in magnetic liquid at high driving frequency.

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Bubble nucleation in spherical liquid cavity wrapped by elastic medium

Xian-Mei Zhang(张先梅), Fan Li(李凡), Cheng-Hui Wang(王成会), Jing Hu(胡静), Run-Yang Mo(莫润阳), Zhuang-Zhi Shen(沈壮志), Jian-Zhong Guo(郭建中), and Shu-Yu Lin(林书玉)

2023 (6): 64303-064303. doi: 10.1088/1674-1056/acaa30

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According to classical nucleation theory, gas nuclei can generate and grow into a cavitation bubble when the liquid pressure exceeds a threshold. However, classical nucleation theory does not include boundary effects. An enclosed spherical liquid cavity surrounded by elastic medium is introduced to model the nucleation process in tissue. Based on the equilibrium pressure relationship of a quasi-static process, the expressions of the threshold and the modified nucleation rate are derived by considering the tissue elasticity. It is shown that the constraint plays an important role in the nucleation process. There is a positive correlation between nucleation threshold pressure and constraint, which can be enhanced by an increasing tissue elasticity and reducing the size of the cavity. Meanwhile, temperature is found to be a key parameter of nucleation process, and cavitation is more likely to occur in confined liquids at temperature T >100 ℃. In contrast, less influences are induced by these factors, such as bulk modulus, liquid cavity size, and acoustic frequency. Although these theoretical predictions of the thresholds have been demonstrated by many previous researches, much lower thresholds can be obtained in liquids containing dissolved gases, e.g., the nucleation threshold is about -21 MPa in a liquid of 0.8-nm gas nuclei at room temperature. Moreover, when there is a gas nucleus of 20 nm, the theoretical threshold pressure might be less than 1 MPa.

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Helical particle manipulation based on power-exponent-phase acoustic vortices generated by a sector transducer array

Qingdong Wang(王青东), Yantao Hu(胡彦涛), Shengli Wang(王胜利), and Hongyu Li(李洪宇)

2023 (6): 64304-064304. doi: 10.1088/1674-1056/acc800

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The characteristics of traditional acoustic vortices (AVs) were verified by the cross-sectional axisymmetric pressure distributions with perfect phase spirals around the center pressure null. In order to generate a non-axisymmetric pressure distribution, the concept of power-exponent-phase was first introduced into the formation of AV beams, named "power-exponent-phase acoustic vortices (PAVs)" in this paper. Based on a ring-array of sector transducers, the helical distribution of the low-pressure valley in cross-sections of PAVs, which enables particles to move from a distant position to the center low-potential well along a certain spiral passageway, was proved theoretically. The particle manipulation behavior for PAVs with a power order of 2 is numerically modeled and experimentally confirmed. The results show that PAVs with a non-axisymmetric spiral pressure distribution can be used to realize the directional transport of particles in an enlarged scope, suggesting prospective application potential in biomedical engineering.

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An optimized smearing scheming for first Brillouin zone sampling and its application on thermal conductivity prediction of graphite

Chengye Li(李承业), Changying Zhao(赵长颖), and Xiaokun Gu(顾骁坤)

2023 (6): 64401-064401. doi: 10.1088/1674-1056/ac9223

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We propose an optimized scheme to determine the smearing parameter in the Gaussian function that is used to replace the Dirac δ function in the first Brillouin zone sampling. The broadening width is derived by analyzing the difference of the results from the phase-space method and Gaussian broadening method. As a demonstration, using the present approach, we investigate the phonon transport in a typical layered material, graphite. Our scheme is benchmarked by comparing with other zone sampling methods. Both the three-phonon phonon scattering rates and thermal conductivity are consistent with the prediction from the widely used tetrahedron method and adaptive broadening method. The computational efficiency of our scheme is more than one order of magnitude higher than the two other methods. Furthermore, the effect of four-phonon scattering in phonon transport in graphite is also investigated. It is found that four-phonon scattering reduces the through-plane thermal conductivity by 10%. Our methods could be a reference for the prediction of thermal conductivity of anisotropic material in the future.

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Rayleigh-Taylor instability of viscoelastic self-rewetting film flowing down a temperature-controlled inclined substrate

Siyi An(安思亦) and Yongjun Jian(菅永军)

2023 (6): 64701-064701. doi: 10.1088/1674-1056/acc78b

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Rayleigh-Taylor (RT) instability of gravity-driven viscoelastic self-rewetting film flowing under an inclined substrate uniformly heated or cooled is considered. The surface tension of self-rewetting film is considered as a quadratic function of temperature. The long wave hypothesis is used to derive a nonlinear free surface evolution equation of the thin viscoelastic film. Linear stability analysis shows that for a prescribed the viscoelastic coefficient, substrate cooling products instability, while substrate heating remains stability. Furthermore, we analyze the influence of viscoelastic coefficient on RT instability. Results show that the viscoelastic coefficient reinforces the RT instability whether the substrate is heated or cooled. Moreover, we use the line method to numerically simulate the nonlinear evolution equation and systematically examine the space-time variation of the film free surface. The numerical results illustrate that increasing the viscoelastic coefficient can enhance the disturbance amplitude and wave frequency. This means that the viscoelastic coefficient makes the system unstable, which is consistent with result of the linear stability analysis. In addition, the oscillation tends to accumulate downstream of the inclined substrate when the evolution time is long enough. Finally, the variation of film thickness with related parameters for different viscoelastic coefficients is investigated.

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Effect of particle shape on packing fraction and velocity profiles at outlet of a silo

Qing-Qing Gao(高庆庆), Yu-Chao Chen(陈玉超), and Lin Hu(胡林)

2023 (6): 64702-064702. doi: 10.1088/1674-1056/aca204

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Many studies on how the particle shape affects the discharge flow mainly focus on discharge rates and avalanche statistics. In this study, the effect of the particle shape on the packing fraction and velocities of particles in the silo discharge flow are investigated by using the discrete element method. The time-averaged packing fraction and velocity profiles through the aperture are systematically measured for superelliptical particles with different blockinesses. Increasing the particle blockiness is found to increase resistance to flow and reduce the flow rate. At an identical outlet size, larger particle blockiness leads to lower velocity and packing fraction at the outlet. The packing fraction profiles display evidently the self-similar feature that can be appropriately adjusted by fractional power law. The velocity profiles for particles with different shapes obey a uniform self-similar law that is in accord with previous experimental results, which is compatible with the hypothesis of free fall arch. To further investigate the origin of flow behaviors, the packing fraction and velocity field in the region above the orifice are computed. Based on these observations, the flow rate of superelliptical particles is calculated and in agreement with the simulated data.

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Experimental and numerical analyses of electrohydrodynamic force according to air pressure

Rong-Hui Quan(全荣辉), Bo Wang(王博), and Yun-Jia Yao(姚韵佳)

2023 (6): 65201-065201. doi: 10.1088/1674-1056/acac11

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Electrohydrodynamic (EHD) force produced by corona discharge is considered as a new thrust for solar-powered aircraft and stratosphere balloons in near space. However, its performance at low air pressures remains to be clarified. An experiment of measuring the EHD force at 0.02 atm-1.0 atm (1 atm=1.01325×10⁵ Pa) is carried out with the wire-to-cylinder geometric structure. The ion distribution is analyzed by using the drift-diffusion model with two-dimensional numerical simulation. The experimental result shows that the EHD force is not linearly related to the corona discharge current at low air pressures. Numerical simulation finds that the proportion of ions in the counter-direction electric field increases from approximately 0.36% to 30% when the pressure drops from 1.0 atm to 0.2 atm. As a result, the EHD force with a constant power supply drops faster than the previous theoretical prediction in the ground experiment, suggesting that the consideration of counter-direction EHD force is necessary to improve the ionic wind propulsion efficiency in near-space applications.

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Nonlinear mixing-based terahertz emission in inclined rippled density plasmas

K Gopal, A P Singh, and S Divya

2023 (6): 65202-065202. doi: 10.1088/1674-1056/aca9c9

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We propose to investigate the THz field generation using nonlinear mixing mechanism of laser beat wave with inclined rippled density plasmas. Two laser pulses with frequencies $(\omega_1, \omega_2)$ and wave vectors $(k_1, k_2)$ co-propagate and resultant laser beat wave forms at beat frequency $(\omega_1-\omega_2)$. Laser beat wave imparts a nonlinear force on the ambient electrons and pushes them outward with nonlinear velocity $v_{\rm NL}$. Coupling of induced density perturbation and nonlinear velocity $v_{\rm NL}$ generates nonlinear currents at laser beat frequency that further generates electromagnetic field $E_{(\omega_1-\omega_2)}$ in terahertz (THz) range. In the present scheme, density ripples are introduced at an angle with respect to laser propagation and flat Gaussian index ($f$) is introduced in laser field profile that transform curved top of Gaussian field envelope into flat top field envelope. The combined effect of flat laser pulses with inclined density ripples in plasmas shows 10-fold enhancement in THz field amplitude when flat-Gaussian index ($f$) varies from 1 to 4. Also, the THz field intensifies when density ripples inclination increases upto a certain angle and then decreases.

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Effects of atomic corrugations on electronic structures in Pb_1-xBi_x thin films

Pengju Li(李鹏举), Kun Xie(谢鹍), Yumin Xia(夏玉敏), Desheng Cai(蔡德胜), and Shengyong Qin(秦胜勇)

2023 (6): 66101-066101. doi: 10.1088/1674-1056/acbf29

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We carried out experimental investigations of the geometric effect on the electronic behavior in Pb$_{1-x}$Bi$_{x}$ thin films by scanning tunneling microscopy and spectroscopy. Single crystal monolayer Pb$_{0.74}$Bi$_{0.26}$ and two-monolayer Pb$_{0.75}$Bi$_{0.25}$ Pb$_{1-x}$Bi$_{x}$ thin films were fabricated by molecular beam epitaxy, where large surface corrugations were observed. Combined with tunneling spectroscopic measurements, it is found that atomic corrugations can widely change the electronic behaviors. These findings show that the Pb$_{1-x}$Bi$_{x}$ system can be a promising platform to further explore geometry-decorated electronic behavior in two-dimensional metallic thin films.

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Probing the effects of lithium doping on structures, properties, and stabilities of magnesium cluster anions

Xiao-Yi Zhang(张小义), Ya-Ru Zhao(赵亚儒), Hong-Xing Li(李红星), Kai-Ge Cheng(成凯格), Zi-Rui Liu(刘子锐), Zhi-Ping Liu(刘芷萍), and Hang He(何航)

2023 (6): 66102-066102. doi: 10.1088/1674-1056/acc51f

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Bimetallic clusters have aroused tremendous interest because the property changes like structure, size, and composition have occurred. Herein, a structural search of the global minimum for anionic LiMg$_{n}^{-}$ ($n=2$-11) clusters is performed using an efficient crystal structure analysis by particle swarm optimization (CALYPSO) structural searching program with subsequent density functional theory (DFT) calculations. A great variety of low energetic isomers are converged, and the most stable ones are confirmed by comparing their total energy of each size. It is found that the LiMg$_{n}^{-}$ clusters are structurally consistent with corresponding Mg clusters anions except for LiMg$_{5}^{-}$ and LiMg$_{7}^{-}$. In all the doped clusters, the Li atom prefers to occupy the convex position. Simulated photoelectron spectra (PES), Infrared (IR), and Raman spectra of LiMg$_{n}^{-}$ could be used as an essential evidence for identifying cluster structures experimentally in the future. Stability study reveals that a tower-like structure of LiMg$_{9}^{-}$ has prominent stability and can be identified as a magic number cluster. The reason might be that there are both closed-shell 1S$^{2}$1P$^{6}$1D$^{10}$2S$^{2}$ electronic configurations and stronger Li-Mg bonds caused by sp hybridization in the LiMg$_{9}^{-}$ cluster.

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Er intercalation and its impact on transport properties of epitaxial graphene

Mingmin Yang(杨明敏), Yong Duan(端勇), Wenxia Kong(孔雯霞), Jinzhe Zhang(章晋哲), Jianxin Wang(王剑心), and Qun Cai(蔡群)

2023 (6): 66103-066103. doi: 10.1088/1674-1056/acbc6a

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Intercalation of atomic species is a practicable method for epitaxial graphene to adjust the electronic band structure and to tune the coupling between graphene and SiC substrate. In this work, atomically flat epitaxial graphene is prepared on 4H-SiC(0001) using the flash heating method in an ultrahigh vacuum system. Scanning tunneling microscopy, Raman spectroscopy and electrical transport measurements are utilized to investigate surface morphological structures and transport properties of pristine and Er-intercalated epitaxial graphene. It is found that Er atoms are intercalated underneath the graphene layer after annealing at 900 ℃, and the intercalation sites of Er atoms are located mainly at the buffer-layer/monolayer-graphene interface in monolayer domains. We also report the different behaviors of Er intercalation in monolayer and bilayer regions, and the experimental results show that the diffusion barrier for Er intercalated atoms in the buffer-layer /monolayer interface is at least 0.2 eV higher than that in the first/second graphene-layer interface. The appearance of Er atoms is found to have distinct impacts on the electronic transports of epitaxial graphene on SiC(0001).

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Dislocation mechanism of Ni₄₇Co₅₃ alloy during rapid solidification

Yun-Chun Liu(刘云春), Yong-Chao Liang(梁永超), Qian Chen(陈茜), Li Zhang(张利), Jia-Jun Ma(马家君), Bei Wang(王蓓), Ting-Hong Gao(高廷红), and Quan Xie(谢泉)

2023 (6): 66104-066104. doi: 10.1088/1674-1056/aca7ea

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Dislocations and other atomic-level defects play a crucial role in determining the macroscopic properties of crystalline materials, but it is extremely difficult to observe the evolution of dislocations due to the limitations of the most advanced experimental techniques. Therefore, in this work, the rapid solidification processes of Ni₄₇Co₅₃ alloy at five cooling rates are studied by molecular dynamics simulation, and the evolutions of their microstructures and dislocations are investigated as well. The results show that face-centered cubic (FCC) structures are formed at the low cooling rate, and the crystalline and amorphous mixture appear at the critical cooling rate, and the amorphous are generated at the high cooling rate. The crystallization temperature and crystallinity decrease with cooling rate increasing. Dislocations are few at the cooling rates of 1×10¹¹ K/s, 5×10¹² K/s, and 1×10¹³ K/s, and they are most abundant at the cooling rates of 5×10¹¹ K/s and 1×10¹² K/s, in which their dislocation line lengths are both almost identical. There appear a large number of dislocation reactions at both cooling rates, in which the interconversion between perfect and partial dislocations is primary. The dislocation reactions are more intense at the cooling rate of 5×10¹¹ K/s, and the slip of some dislocations leads to the interconversion between FCC structure and hexagonal close packed (HCP) structure, which causes the twin boundaries (TBs) to disappear. The FCC and HCP are in the same atomic layer, and dislocations are formed at the junction due to the existence of TBs at the cooling rate of 1×10¹² K/s. The present research is important in understanding the dislocation mechanism and its influence on crystal structure at atomic scales.

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Sensitivity study of the SiGe heterojunction bipolar transistor single event effect based on pulsed laser and technology computer-aided design simulation

Ya-Hui Feng(冯亚辉), Hong-Xia Guo(郭红霞), Xiao-Yu Pan(潘霄宇), Jin-Xin Zhang(张晋新),Xiang-Li Zhong(钟向丽), Hong Zhang(张鸿), An-An Ju(琚安安),Ye Liu(刘晔), and Xiao-Ping Ouyang(欧阳晓平)

2023 (6): 66105-066105. doi: 10.1088/1674-1056/ac8f3b

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The single event effect of a silicon-germanium heterojunction bipolar transistor (SiGe HBT) was thoroughly investigated. By considering the worst bias condition, the sensitive area of the proposed device was scanned with a pulsed laser. With variation of the collector bias and pulsed laser incident energy, the single event transient of the SiGe HBT was studied. Moreover, the single event transient produced by laser irradiation at a wavelength of 532 nm was more pronounced than at a wavelength of 1064 nm. Finally, the impact of the equivalent linear energy transfer of the 1064 nm pulsed laser on the single event transient was qualitatively examined by performing technology computer-aided design simulations, and a good consistency between the experimental data and the simulated outcomes was attained.

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Hydrogen evolution reaction between small-sized Zr_n (n = 2–5) clusters and water based on density functional theory

Lei-Lei Tang(唐雷雷), Shun-Ping Shi(史顺平), Yong Song(宋永), Jia-Bao Hu(胡家宝), Kai Diao(刁凯), Jing Jiang(蒋静), Zhan-Jiang Duan(段湛江), and De-Liang Chen(陈德良)

2023 (6): 66106-066106. doi: 10.1088/1674-1056/aca7ec

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Density functional theory (DFT) is used to calculate the most stable structures of Zr$_{n }$ ($n=2$-5) clusters as well as the adsorption energy values of Zr$_{n }$ ($n=2$-5) clusters after adsorbing single water molecule. The results reveal that there is a significant linear relationship between the adsorption energy values and the energy gaps of the Zr$_{n }$ ($n=2$-5) clusters. Furthermore, the calculations of the reaction paths between Zr$_{n}$ ($n=2$-5) and single water molecule show that water molecule can react with Zr$_{n}$ ($n=2$-5) clusters to dissociate, producing hydrogen, and O atoms mix with the clusters to generate Zr$_{n}$O ($n=2$-5), all of which are exothermic reactions. According to the released energy, the Zr$_{4}$ cluster is the most efficient in Zr$_{n}$ ($n=2$-5) clusters reacting with single water molecule. The natural population analysis (NPA) and density of states (DOS) demonstrate the production of hydrogen and orbital properties in different energy ranges, respectively, jointly forecasting that Zr$_{n}$O ($n= 2$-5) will probably continue to react with more water molecules. Our findings contribute to better understanding of Zr's chemical reactivity, which can conduce to the development of effective Zr-based catalysts and hydrogen-production methods.

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Layer thickness dependent plastic deformation mechanism in Ti/TiCu dual-phase nano-laminates

Minrong An(安敏荣), Yuefeng Lei(雷岳峰), Mengjia Su(宿梦嘉), Lanting Liu(刘兰亭), Qiong Deng(邓琼), Haiyang Song(宋海洋), Yu Shang(尚玉), and Chen Wang(王晨)

2023 (6): 66201-066201. doi: 10.1088/1674-1056/acb48f

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Crystalline/amorphous nanolaminate is an effective strategy to improve the mechanical properties of metallic materials, but the underlying deformation mechanism is still under the way of exploring. Here, the mechanical properties and plastic deformation mechanism of Ti/TiCu dual-phase nanolaminates (DPNLs) with different layer thicknesses are investigated using molecular dynamics simulations. The results indicate that the influence of the layer thickness on the plastic deformation mechanism in crystalline layer is negligible, while it affects the plastic deformation mechanism of amorphous layers distinctly. The crystallization of amorphous TiCu is exhibited in amorphous parts of the Ti/TiCu DPNLs, which is inversely proportional to the layer thickness. It is observed that the crystallization of the amorphous TiCu is a process driven by stress and heat. Young's moduli for the Ti/TiCu DPNLs are higher than those of composite material due to the amorphous/crystalline interfaces. Furthermore, the main plastic deformation mechanism in crystalline part: grain reorientation, transformation from hexagonal-close-packed-Ti to face-centered cubic-Ti and body-centered cubic-Ti, has also been displayed in the present work. The results may provide a guideline for design of high-performance Ti and its alloy.

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Structural phase transition and transport properties in topological material candidate NaZn₄As₃

Qing-Xin Dong(董庆新), Bin-Bin Ruan(阮彬彬), Yi-Fei Huang(黄奕飞), Yi-Yan Wang(王义炎), Li-Bo Zhang(张黎博), Jian-Li Bai(白建利), Qiao-Yu Liu(刘乔宇), Jing-Wen Cheng(程靖雯), Zhi-An Ren(任治安), and Gen-Fu Chen(陈根富)

2023 (6): 66501-066501. doi: 10.1088/1674-1056/acbe2f

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We report a comprehensive study on a layered-structure compound of NaZn₄As₃, which has been predicted to be an ideal topological semimetal (TSM) candidate. It is found that NaZn₄As₃ undergoes a structural transformation from high temperature rhombohedral to a low temperature monoclinic phase. The electric resistivity exhibits a metal-to-insulator-like transition at around 100 K, and then develops a plateau at low temperature, which might be related to the protected topologically conducting surface states. Our first-principles calculation confirms further that NaZn₄As₃ is a topological insulator (TI) for both different phases rather than a previously proposed TSM. The Hall resistivity reveals that the hole carriers dominate the transport properties for the whole temperature range investigated. Furthermore, an obvious kink possibly associated to the structure transition has been detected in thermopower around ～ 170 K. The large thermopower and moderate κ indicate that NaZn₄As₃ and /or its derivatives can provide a good platform for optimizing and studying the thermoelectric performance.

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Molecular dynamics study on the dependence of thermal conductivity on size and strain in GaN nanofilms

Ying Tang(唐莹), Junkun Liu(刘俊坤), Zihao Yu(于子皓), Ligang Sun(孙李刚), and Linli Zhu(朱林利)

2023 (6): 66502-066502. doi: 10.1088/1674-1056/acbf26

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The thermal conductivity of GaN nanofilm is simulated by using the molecular dynamics (MD) method to explore the influence of the nanofilm thickness and the pre-strain field under different temperatures. It is demonstrated that the thermal conductivity of GaN nanofilm increases with the increase of nanofilm thickness, while decreases with the increase of temperature. Meanwhile, the thermal conductivity of strained GaN nanofilms is weakened with increasing the tensile strain. The film thickness and environment temperature can affect the strain effect on the thermal conductivity of GaN nanofilms. In addition, the analysis of phonon properties of GaN nanofilm shows that the phonon dispersion and density of states of GaN nanofilms can be significantly modified by the film thickness and strain. The results in this work can provide the theoretical supports for regulating the thermal properties of GaN nanofilm through tailoring the geometric size and strain engineering.

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Strain effects on Li⁺ diffusion in solid electrolyte interphases: A molecular dynamics study

Xiang Ji(姬祥) and Junqian Zhang(张俊乾)

2023 (6): 66601-066601. doi: 10.1088/1674-1056/ac9606

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Dilithium ethylene dicarbonate (Li₂EDC) and dilithium butylene dicarbonate (Li₂BDC) are the common organic compositions of the solid electrolyte interphase (SEI) layers in rechargeable lithium-ion batteries. The Li⁺ diffusion in the amorphous and ordered phases of Li₂EDC and Li₂BDC under various strains has been investigated by using molecular dynamics simulations. It is found that different strains lead to diverse changes in Li⁺ diffusivity. The tensile strain makes the Li⁺ diffusion coefficients increase in amorphous and ordered Li₂EDC or Li₂BDC, and the compressive strain makes the Li⁺ diffusion coefficients decrease in them. The average Li⁺ coordination number calculation, ion conductivity calculation and the calculation of the residence autocorrelation function in amorphous and ordered Li₂EDC or Li₂BDC are performed to further analyze the strain effects on Li⁺ transport in them. The factors influencing Li⁺ diffusion in amorphous and ordered Li₂EDC or Li₂BDC under the strain are discussed.

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A first-principles study on remote van der Waals epitaxy through a graphene monolayer on semiconductor substrates

Rui Hou(侯锐) and Shenyuan Yang(杨身园)

2023 (6): 66801-066801. doi: 10.1088/1674-1056/ac92d6

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To investigate the mechanism of remote epitaxy, where the overlayer can follow the same crystalline structure as the underlying semiconductor substrate through a thin two-dimensional interlayer, we systematically study the potential fluctuations of graphene covered Si, GaAs, and GaN substrates from first-principles. We find that the uneven semiconductor surface, the distorted graphene, and the non-uniform interface charge transfer make significant contributions to the potential fluctuation. The semiconductor substrate with different surface reconstructions and orientations will generate different potential fluctuations through the graphene interlayer. We also calculate and compare the adsorption of adatoms on graphene covered substrates. The adsorption energies of adatoms not only depend on their distances to the underlying semiconductor surface, but are also sensitive to the direction of the charge transfer at the graphene/substrate interface. Changing the semiconductor reconstruction or orientation could even reverse the order of the adsorption energies of cation and anion adatoms by reversing the interface charge transfer direction, leading to a change in the growth orientation of the overlayer. Our study improves the understanding of the mechanism of remote epitaxy, and reveals that it is possible to control the initial nucleation and orientation of overlayers by changing the semiconductor reconstructions and/or orientations in remote epitaxy.

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Grand canonical Monte Carlo simulation study of hydrogen storage by Li-decorated pha-graphene

Meng-Meng Zhang(张蒙蒙), Feng Zhang(张凤), Qiang Wu(吴强), Xin Huang(黄欣), Wei Yan(闫巍),Chun-Mei Zhao(赵春梅), Wei Chen(陈伟), Zhi-Hong Yang(杨志红),Yun-Hui Wang(王允辉), and Ting-Ting Wu(武婷婷)

2023 (6): 66803-066803. doi: 10.1088/1674-1056/ac8ce2

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Grand canonical Monte Carlo simulation (GCMCs) is utilized for studying hydrogen storage gravimetric density by pha-graphene at different metal densities, temperatures and pressures. It is demonstrated that the optimum adsorbent location for Li atoms is the center of the seven-membered ring of pha-graphene. The binding energy of Li-decorated pha-graphene is larger than the cohesive energy of Li atoms, implying that Li can be distributed on the surface of pha-graphene without forming metal clusters. We fitted the force field parameters of Li and C atoms at different positions and performed GCMCs to study the absorption capacity of $\rm{H_{2}}$. The capacity of hydrogen storage was studied by the differing density of Li decoration. The maximum hydrogen storage capacity of 4Li-decorated pha-graphene was 15.88 wt% at 77 K and 100 bar. The enthalpy values of adsorption at the three densities are in the ideal range of 15 kJ$\cdot$mol$^{-1}$-25 kJ$\cdot$mol$^{-1}$. The GCMC results at different pressures and temperatures show that with the increase in Li decorative density, the hydrogen storage gravimetric ratio of pha-graphene decreases but can reach the 2025 US Department of Energy's standard (5.5 wt%). Therefore, pha-graphene is considered to be a potential hydrogen storage material.

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Structural and mass transport properties of liquid ytterbium in the temperature range 1123 K-1473 K

D D Satikunvar, N K Bhatt, and B Y Thakore

2023 (6): 67101-067101. doi: 10.1088/1674-1056/ac8cd9

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We have studied the structural and atomic transport properties of liquid f-shell Yb in the temperature range 1123 K-1473 K. Pair interactions between atoms are derived using a local pseudopotential. The potential parameters are fitted to the phonon dispersion curve at room temperature. The local pseudopotential used in the present study is computationally more efficient with only three parameters, and it is found to be transferable to the liquid phase without changing the parameters. Since the various computed properties agree with reported theoretical and experimental findings, the adopted fitting scheme is justified. As a significant outcome of the study, we find that (i) the melting in Yb is governed by the Lindemann's law, (ii) the mass transport mechanism obeys the Arrhenius law, (iii) the role of the three-particle correlation function in deriving the velocity autocorrelation function is small, (iv) the mean-square atomic displacement is more sensitive to the choice of interaction potential than the other bulk properties, and (v) liquid Yb does not show liquid-liquid phase transition within the studied temperature range. Further, due to the good description of the structural and mass transport properties, we propose that Yb remains divalent at reduced density.

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Two-dimensional CrP₂ with high specific capacity and fast charge rate for lithium-ion battery

Xiaoyun Wang(王晓允), Tao Jing(荆涛), and Dongmei Liang(梁冬梅)

2023 (6): 67102-067102. doi: 10.1088/1674-1056/acc5e0

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The electrode material is regarded as one of the key factors that determine the performance of lithium-ion batteries (LIBs). However, it is still a challenge to search for an anode material with large capacity, low diffusion barrier, and good stability. In the present work, two new CrP$_{2}$ monolayers ($Pmmn$-CrP$_{2}$ and $Pmma$-CrP$_{2})$ are predicted by means of first principles swarm structure search. Our study shows that both the two CrP$_{2}$ monolayers have high dynamical and thermal stability, as well as excellent electron conductivity. Additionally, $Pmmn$-CrP$_{2}$ exhibits a remarkably high storage capacity of 705 mA$\cdot$h$\cdot$g$^{-1}$ for Li, meanwhile the diffusion energy barrier of Li on the surface of this monolayer is 0.21 eV, ensuring it as a high-performance anode material for LIBs. We hope that our study will inspire researchers to search for new-type two-dimensional (2D) transition metal phosphides for the electrode materials of LIBs.

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Symmetry-constrained quantum coupling in non-Fermi-liquid transport

Rong Li(李荣) and Zhen-Su She(佘振苏)

2023 (6): 67104-067104. doi: 10.1088/1674-1056/acc0f4

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Finding the common origin of non-Fermi liquids (NFLs) transport in high-temperature superconductors (HTSCs) has proven to be fundamentally challenging due to the prominence of various collective fluctuations. Here, we propose a comprehensive non-Hermitian Hamiltonian (NHH) for quantum coupling of multiple scattering mechanisms associated with four types of order fluctuations. It predicts that the anticommutation symmetry of the spinor fermions constrains the scattering rate to a unified quadrature scaling, i.e., $ǎrGamma=ǎrGamma_{\rm I} + \sqrt{ǎrGamma_{\rm Q}^{2}+(\mu k_{\rm B}T)^{2}+(\nu\mu_{\rm B}B )^{2} + ( \gamma_{E}E )^{2}}$. This scaling yields a comprehensive and accurate description of two widespread NFL behaviors in HTSCs, i.e., a temperature-scaling crossover between quadratic and linear laws and the quadrature magnetoresistance, validated by several dozens of data sets for broad phase regimes. It reveals that the common origin of these behaviors is the spinor-symmetry-constrained quantum coupling of spin-wave and topological excitations of mesoscopic orders. Finally, we show that this NHH can be easily extended to other complex quantum fluids by specifying the corresponding symmetries. It is concluded that this work uncovers a critical organization principle (i.e., the spinor symmetry) underlying the NFL transport, thus providing a novel theoretical framework to advance the transport theory of correlated electron systems.

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Ga intercalation in van der Waals layers for advancing p-type Bi₂Te₃-based thermoelectrics

Yiyuan Chen(陈艺源), Qing Shi(石青), Yan Zhong(钟艳), Ruiheng Li(李瑞恒), Liwei Lin(林黎蔚), Ding Ren(任丁), Bo Liu(刘波), and Ran Ang(昂然)

2023 (6): 67201-067201. doi: 10.1088/1674-1056/acc2af

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Tetradymite-structured chalcogenides, such as Bi$_{2}$Te$_{3}$ and Sb$_{2}$Te$_{3}$, are quasi-two-dimensional (2D) layered compounds, which are significant thermoelectric materials applied near room temperature. The intercalation of guest species in van der Waals (vdW) gap implemented for tunning properties has attracted much attention in recent years. We attempt to insert Ga atoms in the vdW gap between the Te layers in p-type Bi$_{0.3}$Sb$_{1.7}$Te$_{3}$ (BST) for further improving thermoelectrics. The vdW-related defects (including extrinsic interstitial and intrinsic defects) induced by Ga intercalation can not only modulate the carrier concentration but also enhance the texture, thereby yielding excellent electrical properties, which are reflected in the power factor ${PF} \sim 4.43 $ mW$\cdot$m$^{-1}\cdot$K$^{-2}$. Furthermore, the intercalation of Ga produces multi-scale lattice imperfections such as point defects, Te precipitations, and nanopores, realizing the low lattice thermal conductivity in BST-Ga samples. Ultimately, a peak ${zT} \sim 1.1$ at 373 K is achieved in the BST-1% Ga sample and greatly improved by $\sim 22%$ compared to the pristine BST. The weak bonding of vdW interlayer interaction can boost the synergistic effect for advancing BST-based or other layered thermoelectrics.

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High-performance spin-filtering and spin-rectifying effects in Blatter radical-based molecular spintronic device

Chun-Xu Tong(童春旭), Peng Zhao(赵朋), and Gang Chen(陈刚)

2023 (6): 67202-067202. doi: 10.1088/1674-1056/acc16d

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We design a Blatter radical-based molecular spintronic device, and investigate its spin-polarized transport properties using density functional theory and non-equilibrium Green's function technique. High-performance spin-rectifying and spin-filtering effects are realized. The physical mechanism is explained by the spin-resolved bias voltage-dependent transmission spectra, the energy levels of the corresponding molecular projected self-consistent Hamiltonian orbitals, and their spatial distributions. The results demonstrate that the Blatter radical has great potential in the development of high-performance multifunctional molecular spintronic devices.

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Thickness-dependent exciton relaxation dynamics of few-layer rhenium diselenide

Chang-Fu Huo(霍唱福), Tiantian Yun(云田田), Xiao-Qing Yan(鄢小卿), Zewen Liu(刘泽文), Xin Zhao(赵欣), Wenxiong Xu(许文雄), Qiannan Cui(崔乾楠), Zhi-Bo Liu(刘智波), and Jian-Guo Tian(田建国)

2023 (6): 67203-067203. doi: 10.1088/1674-1056/acc1d3

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Rhenium diselenide (ReSe₂) has gathered much attention due to its low symmetry of lattice structure, which makes it possess in-plane anisotropic optical, electrical as well as excitonic properties and further enables ReSe₂ have an important application in optoelectronic devices. Here, we report the thickness-dependent exciton relaxation dynamics of mechanically exfoliated few-layer ReSe₂ flakes by using time-resolved pump-probe transient transmission spectroscopies. The results reveal two thickness-dependent relaxation processes of the excitons. The fast one correlates with the exciton formation (i.e., the conversion of hot carriers to excitons), while the slow one is attributed to the exciton recombination dominated by defect-assisted exciton trapping besides photon emission channel. The decrease of scattering probability caused by defects leads to the increase of fast lifetime with thickness, and the increase of slow lifetime with thickness is related to the trap-mediated exciton depopulation induced by surface defects. Polarization-dependent transient spectroscopy indicates the isotropic exciton dynamics in the two-dimensional (2D) plane. These results are insightful for better understanding of excitonic dynamics of ReSe₂ materials and its application in future optoelectronic and electronic devices.

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Two-dimensional tetragonal ZnB: A nodalline semimetal with good transport properties

Yong-Chun Zhao(赵永春), Ming-Xin Zhu(朱铭鑫), Sheng-Shi Li(李胜世), and Ping Li(李萍)

2023 (6): 67301-067301. doi: 10.1088/1674-1056/ac8f33

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Nodal-line semimetals have become a research hot-spot due to their novel properties and great potential application in spin electronics. It is more challenging to find 2D nodal-line semimetals that can resist the spin-orbit coupling (SOC) effect. Here, we predict that 2D tetragonal ZnB is a nodal-line semimetal with great transport properties. There are two crossing bands centered on the $S$ point at the Fermi surface without SOC, which are mainly composed of the ${\rm p}_{xy}$ orbitals of Zn and B atoms and the ${\rm p}_{z}$ orbitals of the B atom. Therefore, the system presents a nodal line centered on the $S$ point in its Brillouin zone (BZ). And the nodal line is protected by the horizontal mirror symmetry $M_{z}$. We further examine the robustness of a nodal line under biaxial strain by applying up to $-4%$ in-plane compressive strain and 5% tensile strain on the ZnB monolayer, respectively. The transmission along the $a$ direction is significantly stronger than that along the $b$ direction in the conductive channel. The current in the $a$ direction is as high as 26.63 μA at 0.8 V, and that in the $b$ direction reaches 8.68 μA at 0.8 V. It is interesting that the transport characteristics of ZnB show the negative differential resistance (NDR) effect after 0.8 V along the $a (b)$ direction. The results provide an ideal platform for research of fundamental physics of 2D nodal-line fermions and nanoscale spintronics, as well as the design of new quantum devices.

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Exploring plasmons weakly coupling to perovskite excitons with tunable emission by energy transfer

Guo-Dong Yan(严国栋), Zhen-Hua Zhang(张振华), Heng Guo(郭衡), Jin-Ping Chen(陈金平),Qing-Song Jiang(蒋青松), Qian-Nan Cui(崔乾楠), Zeng-Liang Shi(石增良), and Chun-Xiang Xu(徐春祥)

2023 (6): 67302-067302. doi: 10.1088/1674-1056/ac921b

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Localized surface plasmon resonance (LSPR) has caused extensive concern and achieved widespread applications in optoelectronics. However, the weak coupling of plasmons and excitons in a nanometal/semiconductor system remains to be investigated via energy transfer. Herein, bandgap tunable perovskite films were synthesized to adjust the emission peaks, for further coupling with stable localized surface plasmons from gold nanoparticles. The degree of mismatch, using steady-state and transient photoluminescence (PL), was investigated systematically in two different cases of gold nanoparticles that were in direct contacting and insulated. The results demonstrated the process of tuning emission coupled to LSPR via wavelength-dependent photoluminescence intensity in the samples with an insulating spacer. In the direct contact case, the decreased radiative decay rate involves rapid plasmon resonance energy transfer to the perovskite semiconductor and non-radiative energy transfer to metal nanoparticles in the near-field range.

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An integrated split and dummy gates MOSFET with fast turn-off and reverse recovery characteristics

Weizhong Chen(陈伟中), Liuting Mou(牟柳亭), Haifeng Qin(秦海峰), Hongsheng Zhang(张红升), and Zhengsheng Han(韩郑生)

2023 (6): 67303-067303. doi: 10.1088/1674-1056/ac9045

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A power MOSFET with integrated split gate and dummy gate (SD-MOS) is proposed and demonstrated by the TCAD SENTAURUS. The split gate is surrounded by the source and shielded by the dummy gate. Consequently, the coupling area between the split gate and the drain electrode is reduced, thus the gate-to-drain charge ($Q_{\rm GD}$), reverse transfer capacitance ($C_{\rm RSS}$) and turn-off loss ($E_{\rm off}$) are significantly decreased. Moreover, the MOS-channel diode is controlled by the dummy gate with ultra-thin gate oxide $t_{\rm ox}$, which can be turned on before the parasitic P-base/N-drift diode at the reverse conduction, then the majority carriers are injected to the N-drift to attenuate the minority injection. Therefore, the reverse recovery charge ($Q_{\rm RR}$), time ($T_{\rm RR}$) and peak current ($I_{\rm RRM}$) are effectively reduced at the reverse freewheeling state. Additionally, the specific on-resistance ($R_{\rm on,sp}$) and breakdown voltage ($BV$) are also studied to evaluate the static properties of the proposed SD-MOS. The simulation results show that the $Q_{\rm GD}$ of 6 nC/cm$^{2}$, the $C_{\rm RSS}$ of 1.1 pF/cm$^{2}$ at the $V_{\rm DS}$ of 150 V, the $Q_{\rm RR}$ of 1.2 μC/cm$^{2}$ and the $R_{\rm on,sp}$ of 8.4 m$\Omega \cdot$cm$^{2}$ are obtained, thus the figures of merit (FOM) including $Q_{\rm GD} \times R_{\rm on,sp}$ of 50 nC$\cdot$m$\Omega $, $E_{\rm off} \times R_{\rm on,sp}$ of 0.59 mJ$\cdot$m$\Omega $ and the $Q_{\rm RR} \times R_{\rm on,sp}$ of 10.1 μC$\cdot$m$\Omega $ are achieved for the proposed SD-MOS.

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Research on self-supporting T-shaped gate structure of GaN-based HEMT devices

Peng Zhang(张鹏), Miao Li(李苗), Jun-Wen Chen(陈俊文), Jia-Zhi Liu(刘加志), and Xiao-Hua Ma(马晓华)

2023 (6): 67305-067305. doi: 10.1088/1674-1056/acaa27

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A self-supporting T-shaped gate (SST-gate) GaN device and process method using electron beam lithography are proposed. An AlGaN/GaN high-electron-mobility transistor (HEMT) device with a gate length of 100 nm is fabricated by this method. The current gain cutoff frequency ($f_{\rm T})$ is 60 GHz, and the maximum oscillation frequency ($f_{\rm max})$ is 104 GHz. The current collapse has improved by 13% at static bias of ($V_{\rm GSQ}$, $V_{\rm DSQ}) = (-8 {\rm V}, 10 {\rm V})$, and gate manufacturing yield has improved by 17% compared with the traditional floating T-shaped gate (FT-gate) device.

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Generalization properties of restricted Boltzmann machine for short-range order

M A Timirgazin and A K Arzhnikov

2023 (6): 67401-067401. doi: 10.1088/1674-1056/ac989c

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A biased sampling algorithm for the restricted Boltzmann machine (RBM) is proposed, which allows generating configurations with a conserved quantity. To validate the method, a study of the short-range order in binary alloys with positive and negative exchange interactions is carried out. The network is trained on the data collected by Monte-Carlo simulations for a simple Ising-like binary alloy model and used to calculate the Warren-Cowley short-range order parameter and other thermodynamic properties. We demonstrate that the proposed method allows us not only to correctly reproduce the order parameters for the alloy concentration at which the network was trained, but can also predict them for any other concentrations.

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Extremely fast vortex dynamics in Bi₂Sr₂Ca₂Cu₃O_10+δ crystalline nanostrip

A B Yu(于奥博), C T Lin(林成天), X F Zhang(张孝富), and L X You(尤立星)

2023 (6): 67402-067402. doi: 10.1088/1674-1056/acb425

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The maximum velocity of a mobile vortex in movement is generally limited by the phenomenon of flux-flow instability (FFI), which necessitates weak vortex pinning and fast heat removal from non-equilibrium electrons. We here demonstrate exfoliations and nano-fabrications of Bi₂Sr₂Ca₂Cu₃O_10+δ crystalline nanostrips, which possess a rather weak pinning volume of vortices, relatively low resistivity, and large normal electron diffusion coefficient. The deduced vortex velocity in Bi₂Sr₂Ca₂Cu₃O_10+δ crystalline nanostrips can be up to 300 km/s near the superconducting transition temperature, well above the speed of sound. The observed vortex velocity is an order of magnitude faster than that of conventional superconducting systems, representing a perfect platform for exploration of ultra-fast vortex matter and a good candidate for fabrications of superconducting nanowire single photon detectors or superconducting THz modulator.

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Crystal growth of CeMn_0.85Sb₂: Absence of magnetic order of Ce-sublattice

Yong Li(李勇), Shan-Shan Miao(苗杉杉), Hai Feng(冯海),Huai-Xin Yang(杨槐馨), and You-Guo Shi(石友国)

2023 (6): 67501-067501. doi: 10.1088/1674-1056/acc060

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Single crystals of CeMn$_{0.85}$Sb$_{2}$ have been successfully synthesized by using the Bi as flux. Analysis of single crystal x-ray diffraction data confirms that CeMn$_{0.85}$Sb$_{2}$ crystallizes in the HfCuSi$_{2}$-type structure with the space group $P4/nmm$ (No. 129). In the case of $H\parallel c$, CeMn$_{0.85}$Sb$_{2}$ displays a robust antiferromagnetic transition at $\sim 160 $ K for Mn-sublattice, and there is no sign of magnetic order regarding Ce-sublattice. In the case of $H\bot c$, the Mn-sublattice shows signs of magnetic order at 160 K and 116 K, indicating a possible spin reorientation. There is no sign of magnetic order for the Ce-sublattice either, but, alternating current magnetic susceptibility measurements reveal a spin glass state below 18 K in the case of $H\bot c$. Isothermal magnetization curves measured below magnetic order with $H\bot c$ show saturation and even large hysteresis at 2 K, indicating the presence of a ferromagnetic component. In addition, a field-induced spin-flop transition is observed in the case of $H\bot c$, indicating a field-induced spin reorientation of Mn spins. Electrical resistivity measurements indicate a metallic nature for CeMn$_{0.85}$Sb$_{2}$ and large anisotropy which is consistent with its quasi-two-dimensional layered structure.

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Gate-voltage control of alternating-current-driven skyrmion propagation in ferromagnetic nanotrack devices

Xin-Yi Cai(蔡心怡), Zhi-Hua Chen(陈志华), Hang-Xiao Yang(杨航霄), Xin-Yan He(何鑫岩), Zhen-Zhen Chen(陈珍珍), Ming-Min Zhu(朱明敏), Yang Qiu(邱阳), Guo-Liang Yu(郁国良), and Hao-Miao Zhou(周浩淼)

2023 (6): 67502-067502. doi: 10.1088/1674-1056/acb420

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Magnetic skyrmions, with topologically protected particle-like magnetization configurations, are promising information carriers for future spintronics devices with ultralow energy consumption. Generally, during motion, skyrmions suffer from the skyrmion Hall effect (SkHE) wherein the skyrmions deflect away from the intended path of the driving force. Numerous methods have been proposed to avoid this detrimental effect. In this study, we propose controllable alternating current (AC)-driven skyrmion propagation in a ferromagnetic nanowire based on combination of gate-voltage-controlled magnetic anisotropy (VCMA) and SkHE. Micromagnetic simulations show that a skyrmion oscillatory closed-loop-like in situ motion driven by AC can be transformed into directional ratchet-like propagation along the nanotrack by creating a VCMA-gate barrier. Additionally, we show that the skyrmion propagation conditions depend on the gate barrier potential and driving AC parameters, and they can be used for the optimal design of nanotrack devices. Moreover, this mechanism could be used to control skyrmion macroscopic propagation directions by dynamically alternating the voltage of another series of gates. We further show the dynamic control of the long-distance propagation of skyrmions along with the pinning state. The study results provide a promising route for designing future skyrmion-based spintronics logical and memory devices.

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Magnonic band-pass and band-stop filters with structurally modulated waveguides

Lai-He Feng(冯来和), Mang-Yuan Ma(马莽原), Zhi-Hua Liu(刘智华), Kai-Le Xie(解凯乐), and Fu-Sheng Ma(马付胜)

2023 (6): 67503-067503. doi: 10.1088/1674-1056/ac8afb

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Magnonics is a fascinating and emerging field, which mainly studies processing information with spin waves. Magnonic devices with in-plane magnetization have recently been realized. Because of the isotropic propagation, magnonic devices based on perpendicular magnetization are attracting extensive interest. Here, we numerically demonstrate two magnonic filters with out-of-plane magnetization using micromagnetic simulations. The band-pass and the band-stop functions have been realized in two structurally modulated waveguides, respectively. The intensity of spin waves is manipulated when they arrive at the uniformly/non-uniformly magnetized modulators, which results in the variation of transmission coefficients. It is found that the proposed filters can work at multiple frequencies, which can be further adjusted by the external magnetic field. Our designed magnonic devices with Néel-type skyrmion could promote the development of spin wave computing using spin textures.

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Magnetic ordering induced magnetodielectric effect in Ho₂Cu₂O₅ and Yb₂Cu₂O₅

Hao Jin(金昊), Shuai Huang(黄帅), Kai-Qi Wan(万凯奇), Chang-Ming Zhu(朱长明),Hai-Ou Wang(王海欧), Kun-Peng Su(苏昆朋), and De-Xuan Huo(霍德璇)

2023 (6): 67504-067504. doi: 10.1088/1674-1056/ac904a

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Materials with strongly coupled magnetic and electronic degrees of freedom provide new possibilities for practical applications. In this paper, we have investigated the structure, magnetic property, and magnetodielectric (MD) effect in Ho$_{2}$Cu$_{2}$O$_{5}$ and Yb$_{2}$Cu$_{2}$O$_{5}$ polycrystalline samples, which possess a non-centrosymmetric polar structure with space group $Pna$2$_{1}$. In Ho$_{2}$Cu$_{2}$O$_{5}$, Ho$^{3+}$ and Cu$^{2+}$ sublattices order simultaneously, exhibiting a typical paramagnetic to antiferromagnetic transition at 13.1 K. While for Yb$_{2}$Cu$_{2}$O$_{5}$, two magnetic transitions which originate from the orderings of Yb$^{3+}$ (7.8 K) and Cu$^{2+}$ (13.5 K) sublattices are observed. A magnetic field induced metamagnetic transition is obtained in these two cuprates below Néel temperature ($T_{\rm N}$). By means of dielectric measurement, distinct MD effect is demonstrated by the dielectric anomaly at $T_{\rm N}$. Meanwhile, the MD effect is found to be directly related to the metamagnetic transition. Due to the specific spin configuration and different spin evolution in the magnetic field, a positive MD effect is formed in Ho$_{2}$Cu$_{2}$O$_{5}$, and a negative one is observed in Yb$_{2}$Cu$_{2}$O$_{5}$. The spontaneous dielectric anomaly at $T_{\rm N}$ is regarded as arising from the shifts in optical phonon frequencies, and the magnetoelectric coupling is used to interpret the magnetic field induced MD effect. Moreover, an $H$-$T$ phase diagram is constructed for Ho$_{2}$Cu$_{2}$O$_{5}$ and Yb$_{2}$Cu$_{2}$O$_{5}$ based on the results of isothermal magnetic and dielectric hysteresis loops.

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Electric-field control of perpendicular magnetic anisotropy by resistive switching via electrochemical metallization

Yuan Yuan(袁源), Lu-Jun Wei(魏陆军), Yu Lu(卢羽), Ruo-Bai Liu(刘若柏), Tian-Yu Liu(刘天宇), Jia-Rui Chen(陈家瑞), Biao You(游彪), Wei Zhang(张维), Di Wu(吴镝), and Jun Du(杜军)

2023 (6): 67505-067505. doi: 10.1088/1674-1056/acbde8

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Electric-field control of perpendicular magnetic anisotropy (PMA) is a feasible way to manipulate perpendicular magnetization, which is of great importance for realizing energy-efficient spintronics. Here, we propose a novel approach to accomplish this task at room temperature by resistive switching (RS) via electrochemical metallization (ECM) in a device with the stack of Si/SiO$_{2}$/Ta/Pt/Ag/Mn-doped ZnO (MZO)/Pt/Co/Pt/ITO. By applying certain voltages, the device could be set at high-resistance-state (HRS) and low-resistance-state (LRS), accompanied with a larger and a smaller coercivity ($H_{\rm C}$), respectively, which demonstrates a nonvolatile E-field control of PMA. Based on our previous studies and the present control experiments, the electric modulation of PMA can be briefly explained as follows. At LRS, the Ag conductive filaments form and pass through the entire MZO layer and finally reach the Pt/Co/Pt sandwich, leading to weakening of PMA and reduction of $H_{\rm C}$. In contrast, at HRS, most of the Ag filaments dissolve and leave away from the Pt/Co/Pt sandwich, causing partial recovery of PMA and an increase of $H_{\rm C}$. This work provides a new clue to designing low-power spintronic devices based on PMA films.

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Multiferroic monolayers VOX (X = Cl, Br, I): Tunable ferromagnetism via charge doping and ferroelastic switching

Hong-Chao Yang(杨洪超), Peng-Cheng Liu(刘鹏程), Liu-Yu Mu(穆鎏羽), Ying-De Li(李英德), Kai Han(韩锴), and Xiao-Le Qiu(邱潇乐)

2023 (6): 67701-067701. doi: 10.1088/1674-1056/acaa2b

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The fascinating properties arising from the interaction between different ferroic states of two-dimensional (2D) materials have inspired tremendous research interest in the past few years. Under the first-principles calculations, we predict the coexistence of antiferromagnetic and ferroelastic states in VO$X$ ($X={\rm Cl}$, Br, I) monolayers. The results illustrate that the VO$X$ monolayers exhibit indirect bandgap characteristics, $i.e.$, their gaps decrease with the halide elements changing from Cl to I. The ground states of all these VO$X$ monolayers are antiferromagnetic (AFM) with the magnetic moments contributed by the V 3d electrons. Furthermore, the magnetic ground state changing from AFM to ferromagnetism (FM) can be realized by doping carriers. In addition, the moderate ferroelastic transition barrier and reversible switching signal ensure their high performances of nonvolatile memory devices. Our findings not only offer an ideal platform for investigating the multiferroic properties, but also provide candidate materials for potential applications in spintronics.

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An ultrafast spectroscopy system for studying dynamic properties of superconductors under high pressure and low temperature conditions

Jian Zhu(朱健), Ye-Xi Li(李叶西), Deng-Man Feng(冯登满), De-Peng Su(苏德鹏), Dong-Niu Fan(范东牛),Song Yang(杨松), Chen-Xiao Zhao(赵辰晓), Gao-Yang Zhao(赵高扬), Liang Li(李亮),Fang-Fei Li(李芳菲), Ying-Hui Wang(王英惠), and Qiang Zhou(周强)

2023 (6): 67801-067801. doi: 10.1088/1674-1056/acc0f5

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An ultrafast pump-probe spectroscopy system combined with a cryogenic diamond anvil cell (DAC) instrument is developed to investigate the photo-excitation dynamic properties of condensed materials under low temperature and high pressure (LTHP) conditions. The ultrafast dynamics study is performed on Bi₂Sr₂CaCu₂O_8+δ (Bi-2212) thin film under LTHP conditions. The superconducting (SC) phase transition has been observed by analyzing the ultrafast dynamics of Bi-2212 as a function of pressure and temperature. Our results suggest that the pump-probe spectroscopy system combined with a cryogenic DAC instrument is an effective method to study the physical mechanism of condensed matter physics at extreme conditions, especially for the SC phase transition.

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Probing photocarrier dynamics of pressurized graphene using time-resolved terahertz spectroscopy

Yunfeng Wang(王云峰), Shujuan Xu(许淑娟), Jin Yang(杨金), and Fuhai Su(苏付海)

2023 (6): 67802-067802. doi: 10.1088/1674-1056/acc2b1

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Graphene hosts intriguing photocarrier dynamics such as negative transient terahertz (THz) photoconductivity, high electron temperature, benefiting from the unique linear Dirac dispersion. In this work, the pressure effects of photocarrier dynamics of graphene have been investigated using in situ time-resolved THz spectroscopy in combination with diamond anvil cell exceeding 9 GPa. We find that the negative THz conductivity maintains in our studied pressure range both for monolayer and bilayer graphene. In particular, the amplitude of THz photoconductivity in monolayer graphene manifests an extraordinary dropping with pressure, compared with that from the counterparts such as bulk silicon and bilayer graphene. Concomitantly, the time constant is reduced with increasing pressure, highlighting the pressure-induced hot carrier cooling. The pressure dependence of photocarrier dynamics in monolayer graphene is likely related with the enhancement of the interfacial coupling between diamond surface and sample, allowing for the activity of new electron-phonon scattering. Our work is expected to provide an impetus for the studies of high-pressure THz spectroscopy of two-dimensional materials.

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Back interface passivation for ultrathin Cu(In,Ga)Se₂ solar cells with Schottky back contact: A trade-off of electrical effects

Ye Tu(涂野), Yong Li(李勇), and Guanchao Yin(殷官超)

2023 (6): 68101-068101. doi: 10.1088/1674-1056/acc05b

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Back interface passivation reduces the back recombination of photogenerated electrons, whereas aggravates the blocking of hole transport towards back contact, which complicate the back interface engineering for ultrathin CIGSe solar cells with a Schottky back contact. In this work, theoretical explorations were conducted to study how the two contradictory electrical effects impact cell performance. For ultrathin CIGSe solar cells with a pronounced Schottky potential barrier (E_h> 0.2 eV), back interface passivation produces diverse performance evolution trends, which are highly dependent on cell structures and properties. Since a back Ga grading can screen the effect of reduced recombination of photogenerated electrons from back interface passivation, the hole blocking effect predominates and back interface passivation is not desirable. However, when the back Schottky diode merges with the main pn junction due to a reduced absorber thickness, the back potential barrier and the hole blocking effect is much reduced on this occasion. Consequently, cells exhibit the same efficiency evolution trend as ones with an Ohmic contact, where back interface passivation is always advantageous. The discoveries imply the complexity of back interface passivation and provide guidance to manipulate back interface for ultrathin CIGSe solar on TCOs with a pronounced Schottky back contact.

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Oxidation behavior of Ti_0.2Zr_0.2Hf_0.2Nb_0.2Ta_0.2C–M_xC (M = Ti, Zr, Hf, Nb, Ta) composite ceramic at high temperature

Shuai Xu(徐帅), Tao Wang(王韬), Xingang Wang(王新刚), Lu Wu(吴璐),Zhongqiang Fang(方忠强), Fangfang Ge(葛芳芳), Xuan Meng(蒙萱),Qing Liao(廖庆), Jinchun Wei(魏金春), and Bingsheng Li(李炳生)

2023 (6): 68102-068102. doi: 10.1088/1674-1056/ac9a38

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Ti$_{0.2}$Zr$_{0.2}$Hf$_{0.2}$Nb$_{0.2}$Ta$_{0.2}$C-$M_{x}$C composite ceramic was prepared by hot press sintering, with the Ti$_{0.2}$Zr$_{0.2}$Hf$_{0.2}$Nb$_{0.2}$Ta$_{0.2}$C high-entropy carbide as the main phase. Secondary phase $M_{x}$C ($M={\rm Ti}$, Zr, Hf, Nb, Ta) was found to be distributed relatively uniform in the composite ceramic. The oxidation behavior of the ceramic was examined after exposure to 923 K and 1173 K. Morphology of the surface and cross sections of all oxidation samples were observed. The characteristics of the oxidation behavior of the high-entropy carbide and the secondary phase $M_{x}$C were compared and analyzed. The secondary phases (such as Ti-rich carbide or Hf-rich carbide) in the material were seriously oxidized at 923 K and 1173 K, which reflects the superior oxidation performance of the high-entropy carbide. The nano high-entropy oxides with Ti, Zr, Hf, Nb, Ta, and O elements were discovered by oxidation of the composite ceramic. This research will help deepen the understanding of the oxidation mechanism of high-entropy carbide and composite ceramic.

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Morphological features and nanostructures generated during SiC graphitization process

Wen-Xia Kong(孔雯霞), Yong Duan(端勇), Jin-Zhe Zhang(章晋哲),Jian-Xin Wang(王剑心), and Qun Cai(蔡群)

2023 (6): 68103-068103. doi: 10.1088/1674-1056/acb766

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Surface morphological features and nanostructures generated during SiC graphitization process can significantly affect fabrication of high-quality epitaxial graphene on semiconductor substrates. In this work, we investigate the surface morphologies and atomic structures during graphitization process of 4H-SiC (0001) using scanning tunneling microscopy. Our high-magnified scanning-tunneling-microscope images exhibit the appearance and gradual developments of SiC ($1\times 1$) nanostructures after 1100 $^\circ$C cleaning treatments, irregularly distributed among carbon nanocaps and $(\sqrt {3} {\times }\sqrt {3} )$ reconstruction domains. A model for the formation and growth progression of SiC ($1\times 1$) nanostructures has been proposed. When post-annealing temperature reaches 1300 $^\circ$C, the nanoholes and nanoislands can be observed on the surface, and multilayer graphene is often detected lying on the top surface of those nanoislands. These results provide profound insights into the complex evolution process of surface morphology during SiC thermal decomposition and will shed light on fabrication of SiC nanostructures and graphene nanoflakes.

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Enhanced xylene sensing performance of hierarchical flower-like Co₃O₄ via In doping

Jing Zhang(张京), Jianyu Ling(凌剑宇), Kuikun Gu(谷魁坤), Georgiy G. Levchenko, and Xiao Liang(梁霄)

2023 (6): 68104-068104. doi: 10.1088/1674-1056/acbe30

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Metal ions doping is a typical approach for tuning sensing properties of metal oxide semiconductors based gas sensors. Herein, hierarchical flower-like pure and In-doped Co₃O₄ nanostructures assembled by porous two-dimensional (2D) nanosheets are synthesized via a solvothermal method and annealing process. The sensing measurements display that the In@Co₃O₄-4 based sensor possesses high response value of 55.9 toward 100 ppm xylene at 150 ℃, which is nearly 3.8 times larger than that of pure Co₃O₄ sensor. Furthermore, it possesses good selectivity and anti-humidity properties. Combined with the results of DFT calculations, the mechanism of enhanced gas sensing performance is analyzed systematically.

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Structural, electronic, and Li-ion mobility properties of garnet-type Li₇La₃Zr₂O₁₂ surface: An insight from first-principles calculations

Jing-Xuan Wang(王靖轩), Bao-Zhen Sun(孙宝珍), Mei Li(李梅), Mu-Sheng Wu(吴木生), and Bo Xu(徐波)

2023 (6): 68201-068201. doi: 10.1088/1674-1056/acc05d

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Garnet-type Li₇La₃Zr₂O₁₂ (LLZO) is a promising solid-state electrolyte for Li-ion batteries, but Li-dendrite's formation greatly limits the applications. In this paper, we systematically investigate the stability, electronic properties, and Li-ion mobility of the LLZO surface by the first-principles calculations. We consider the (110) and (001) slab structures with different terminations in the t- and c-LLZO. Our results indicate that both (110) and (001) surfaces prefer to form Li-rich termination due to their low surface energies for either t- or c-LLZO. Moreover, with the decrease of Li contents the stability of Li-rich surfaces is improved initially and degrades later. Unfortunately, the localized surface states at the Fermi level can induce the formation of metallic Li on the Li-rich surfaces. In comparison, Li/La-termination has a relatively low metallic Li formation tendency due to its rather low diffusion barrier. In fact, Li-ion can spontaneously migrate along path II (m Li3→Li2) on the Li/La-T(001) surface. In contrast, it is more difficult for Li-ion diffusion on the Li-T(001) surface, which has a minimum diffusion barrier of 0.50 eV. Interestingly, the minimum diffusion barrier decreases to 0.34 eV when removing four Li-ions from the Li-T(001) surface. Thus, our study suggests that by varying Li contents, the stability and Li-ion diffusion barrier of LLZO surfaces can be altered favorably. These advantages can inhibit the formation of metallic Li on the LLZO surfaces.

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A non-quasi-static model for nanowire gate-all-around tunneling field-effect transistors

Bin Lu(芦宾), Xin Ma(马鑫), Dawei Wang(王大为), Guoqiang Chai(柴国强),Linpeng Dong(董林鹏), and Yuanhao Miao(苗渊浩)

2023 (6): 68501-068501. doi: 10.1088/1674-1056/acbe32

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Nanowires with gate-all-around (GAA) structures are widely considered as the most promising candidate for 3-nm technology with the best ability of suppressing the short channel effects, and tunneling field effect transistors (TFETs) based on GAA structures also present improved performance. In this paper, a non-quasi-static (NQS) device model is developed for nanowire GAA TFETs. The model can predict the transient current and capacitance varying with operation frequency, which is beyond the ability of the quasi-static (QS) model published before. Excellent agreements between the model results and numerical simulations are obtained. Moreover, the NQS model is derived from the published QS model including the current-voltage (I-V) and capacitance-voltage (C-V) characteristics. Therefore, the NQS model is compatible with the QS model for giving comprehensive understanding of GAA TFETs and would be helpful for further study of TFET circuits based on nanowire GAA structure.

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Synergistic effect of total ionizing dose on single-event gate rupture in SiC power MOSFETs

Rongxing Cao(曹荣幸), Kejia Wang(汪柯佳), Yang Meng(孟洋), Linhuan Li(李林欢), Lin Zhao(赵琳), Dan Han(韩丹), Yang Liu(刘洋), Shu Zheng(郑澍), Hongxia Li(李红霞), Yuqi Jiang(蒋煜琪), Xianghua Zeng(曾祥华), and Yuxiong Xue(薛玉雄)

2023 (6): 68502-068502. doi: 10.1088/1674-1056/acbde7

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The synergistic effect of total ionizing dose (TID) and single event gate rupture (SEGR) in SiC power metal-oxide-semiconductor field effect transistors (MOSFETs) is investigated via simulation. The device is found to be more sensitive to SEGR with TID increasing, especially at higher temperature. The microscopic mechanism is revealed to be the increased trapped charges induced by TID and subsequent enhancement of electric field intensity inside the oxide layer.

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Orderly hysteresis in field-driven robot swarm active matter

Yanping Liu(刘艳萍), Gao Wang(王高), Peilong Wang(王培龙), Daming Yuan(袁大明), Shuaixu Hou(侯帅旭), Yangkai Jin(金阳凯), Jing Wang(王璟), and Liyu Liu(刘雳宇)

2023 (6): 68701-068701. doi: 10.1088/1674-1056/acc803

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Boundary effect and time-reversal symmetry are hot topics in active matter. We present a biology-inspired robot-environment-interaction active matter system with the field-drive motion and the rules of resource search, resource consumption, and resource recovery. In an environmental compression-expansion cycle, the swarm emerges a series of boundary-dependent phase transitions, and the whole evolution process is time-reversal symmetry-breaking; we call this phenomenon "orderly hysteresis". We present the influence of the environmental recovery rate on the dynamic collective behavior of the swarm.

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Comparison of sleep timing of people with different chronotypes affected by modern lifestyle

Ying Li(李莹), Ji-Chen Guo(郭纪辰), and Xue Wang(王雪)

2023 (6): 68702-068702. doi: 10.1088/1674-1056/acbf1f

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Circadian rhythm is an endogenous rhythmic behavior of organisms which can be entrained by daily light-dark cycles. The timing of human sleep-cycle is regulated by endogenous circadian rhythm and homeostatic processes. Light exposure affects both sleep timing and circadian rhythm. Now humans can extend lighting time by turning on artificial lights and wake up time is usually triggered by alarm clocks to meet social schedules. This modern lifestyle is believed to be related with a temporal mismatch between sleep and circadian rhythmicity (social jet-lag) and insufficient sleep, which lead to ill mental and physical health outcomes. At present, the impacts of self-selection of light exposure and social constrains on sleep timing is far from clear. According to preferred sleep-wake schedule, there are three different chronotypes. In this paper, we apply a mathematical model to get a quantitative comparison of sleep timing of people with different chronotypes with the effects of modern light consumption and social constrains. The results show that the prolonged day light and evening light exposure both delay preferred sleep timing with the sleep duration almost unchanged. People of evening-type or with longer intrinsic periods are most expected to be vulnerable to evening light. Increasing light exposure can offset the effect of evening light to some extent, but it is most difficult for evening-type people. Social constrains cause the largest social jet-lag in people of evening-type, which increases with evening light intensity or intrinsic periods. Morning-type people's sleep symptoms worsens, while that of evening-type people improves with age. This study provides a theoretical reference for preventing and treating sleep disorder and social jet-lag for individuals with different chronotypes.

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A progressive surrogate gradient learning for memristive spiking neural network

Shu Wang(王姝), Tao Chen(陈涛), Yu Gong(龚钰), Fan Sun(孙帆), Si-Yuan Shen(申思远), Shu-Kai Duan(段书凯), and Li-Dan Wang(王丽丹)

2023 (6): 68704-068704. doi: 10.1088/1674-1056/acb9f6

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In recent years, spiking neural networks (SNNs) have received increasing attention of research in the field of artificial intelligence due to their high biological plausibility, low energy consumption, and abundant spatio-temporal information. However, the non-differential spike activity makes SNNs more difficult to train in supervised training. Most existing methods focusing on introducing an approximated derivative to replace it, while they are often based on static surrogate functions. In this paper, we propose a progressive surrogate gradient learning for backpropagation of SNNs, which is able to approximate the step function gradually and to reduce information loss. Furthermore, memristor cross arrays are used for speeding up calculation and reducing system energy consumption for their hardware advantage. The proposed algorithm is evaluated on both static and neuromorphic datasets using fully connected and convolutional network architecture, and the experimental results indicate that our approach has a high performance compared with previous research.

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Identification of key recovering node for spatial networks

Zijian Yan(严子健), Yongxiang Xia(夏永祥), Lijun Guo(郭丽君), Lingzhe Zhu(祝令哲), Yuanyuan Liang(梁圆圆), and Haicheng Tu(涂海程)

2023 (6): 68901-068901. doi: 10.1088/1674-1056/acb75f

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Many networks in the real world have spatial attributes, such as location of nodes and length of edges, called spatial networks. When these networks are subject to some random or deliberate attacks, some nodes in the network fail, which causes a decline in the network performance. In order to make the network run normally, some of the failed nodes must be recovered. In the case of limited recovery resources, an effective key node identification method can find the key recovering node in the failed nodes, by which the network performance can be recovered most of the failed nodes. We propose two key recovering node identification methods for spatial networks, which are the Euclidean-distance recovery method and the route-length recovery method. Simulations on homogeneous and heterogeneous spatial networks show that the proposed methods can significantly recover the network performance.

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Robust multi-task distributed estimation based on generalized maximum correntropy criterion

Qian Hu(胡倩), Feng Chen(陈枫), and Ming Ye(叶明)

2023 (6): 68902-068902. doi: 10.1088/1674-1056/acb9fc

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False data injection (FDI) attacks are common in the distributed estimation of multi-task network environments, so an attack detection strategy is designed by combining the generalized maximum correntropy criterion. Based on this, we propose a diffusion least-mean-square algorithm based on the generalized maximum correntropy criterion (GMCC-DLMS) for multi-task networks. The algorithm achieves gratifying estimation results. Even more, compared to the related work, it has better robustness when the number of attacked nodes increases. Moreover, the assumption about the number of attacked nodes is relaxed, which is applicable to multi-task environments. In addition, the performance of the proposed GMCC-DLMS algorithm is analyzed in the mean and mean-square senses. Finally, simulation experiments confirm the performance and effectiveness against FDI attacks of the algorithm.

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Corrigendum to “Peptide backbone-copper ring structure: A molecular insight into copper-induced amyloid toxicity”

Jing Wang(王静), Xiankai Jiang(姜先凯), Xiurong Su(苏秀榕), Xingfei Zhou(周星飞), Yu Wang(王宇), Geng Wang(王耿), Heping Geng(耿和平), Zheng Jiang(姜政), Fang Huang(黄方), Gang Chen(陈刚), Chunlei Wang(王春雷), and Haiping Fang(方海平)

2023 (6): 69901-069901. doi: 10.1088/1674-1056/acd329

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The author list originally given in Wang et al. Chin. Phys. B 31 108702 (2022) has been amended to remove four authors, Hua Li, Bin Wu, Jun Guo and Chenqi Xu, who believe their contributions are more suitable to be credited in the acknowledgments.

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