Not found SPECIAL TOPIC — Celebrating the 100th Anniversary of Physics Discipline of Xiamen University

    This Special Topic was organized to celebrate the Centenary of Physics Discipline of Xiamen University.

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    Accelerator-mode islands and superdiffusion in double-kicked rotor
    Fengdi Wang(王风涤) and Ping Fang(方萍)
    Chin. Phys. B, 2023, 32 (6): 060504.   DOI: 10.1088/1674-1056/accb4b
    Abstract132)   HTML4)    PDF (3009KB)(126)      
    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.
    Fragmentation dynamics of electron-impact double ionization of helium
    Shiwei Liu(刘士炜), Difa Ye(叶地发), and Jie Liu(刘杰)
    Chin. Phys. B, 2023, 32 (6): 063402.   DOI: 10.1088/1674-1056/acbe33
    Abstract139)   HTML5)    PDF (1807KB)(98)      
    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.
    Broadband and wide-angle plane focal surface Luneburg lens
    Jue Li(李珏), Yangyang Zhou(周杨阳), and Huanyang Chen(陈焕阳)
    Chin. Phys. B, 2023, 32 (6): 064210.   DOI: 10.1088/1674-1056/ac8e9e
    Abstract149)   HTML3)    PDF (1618KB)(46)      
    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.
    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)
    Chin. Phys. B, 2023, 32 (6): 064211.   DOI: 10.1088/1674-1056/ac8726
    Abstract155)   HTML3)    PDF (835KB)(94)      
    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.
    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)
    Chin. Phys. B, 2023, 32 (6): 064212.   DOI: 10.1088/1674-1056/acb203
    Abstract135)   HTML4)    PDF (2079KB)(110)      
    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.
    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)
    Chin. Phys. B, 2023, 32 (6): 064402.   DOI: 10.1088/1674-1056/acc78c
    Abstract139)   HTML5)    PDF (1892KB)(52)      
    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.
    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)
    Chin. Phys. B, 2023, 32 (6): 066107.   DOI: 10.1088/1674-1056/acae74
    Abstract137)   HTML3)    PDF (1152KB)(98)      
    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.
    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)
    Chin. Phys. B, 2023, 32 (6): 067205.   DOI: 10.1088/1674-1056/ac89db
    Abstract178)   HTML3)    PDF (2424KB)(70)      
    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.
    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)
    Chin. Phys. B, 2023, 32 (6): 066602.   DOI: 10.1088/1674-1056/accd4b
    Abstract92)   HTML3)    PDF (1966KB)(75)      
    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.
    Customizing topological phases in the twisted bilayer superconductors with even-parity pairings
    Conghao Lin(林丛豪), Chuanshuai Huang(黄传帅), and Xiancong Lu(卢仙聪)
    Chin. Phys. B, 2023, 32 (8): 087401.   DOI: 10.1088/1674-1056/acd3e3
    Abstract112)   HTML0)    PDF (1613KB)(80)      
    We investigate the topological properties of twisted bilayer superconductors with different even-parity pairings in each layer. In the presence of spin-orbit coupling, the Hamiltonian is mapped into an effective odd-parity superconductor. Based on this, we deduce the topological properties by examining the relative configuration between Fermi surface and Dirac pairing node. We show that mixed Rashba and Dresselhaus spin-orbit coupling and anisotropic hopping terms, which break the C4 symmetry of the Fermi surface, can induce first-order topological superconductors with non-zero bulk Chern number. This provides a versatile way to control the topological phases of bilayer superconductors by adjusting the twisted angle and chemical potential. We demonstrate our results using a typical twisted angle of 53.13°, at which the translation symmetry is restored and the Chern number and edge state are calculated using the Moiré momentum.
    Improving physical properties of poly(vinyl alcohol)/montmorillonite nanocomposite hydrogels via the Hofmeister effect
    Rongrong Guo(郭蓉蓉), Deshuai Yu(余德帅), Yifan Huang(黄一帆), Sen Wang(王森), Cong Fu(付聪), Shuihong Zhu(朱水洪), Jia Yi(易佳), Hanqi Wang(王涵淇), and Youhui Lin(林友辉)
    Chin. Phys. B, 2023, 32 (8): 088103.   DOI: 10.1088/1674-1056/acdfc2
    Abstract74)   HTML1)    PDF (2469KB)(28)      
    Hydrogel is a kind of three-dimensional crosslinked polymer material with high moisture content. However, due to the network defects of polymer gels, traditional hydrogels are usually brittle and fragile, which limits their practical applications. Herein, we present a Hofmeister effect-aided facile strategy to prepare high-performance poly(vinyl alcohol)/montmorillonite nanocomposite hydrogels. Layered montmorillonite nanosheets can not only serve as crosslinking agents to enhance the mechanical properties of the hydrogel but also promote the ion conduction. More importantly, based on the Hofmeister effect, the presence of (NH4)2SO4 can endow nanocomposite hydrogels with excellent mechanical properties by affecting PVA chains' aggregation state and crystallinity. As a result, the as-prepared nanocomposite hydrogels possess unique physical properties, including robust mechanical and electrical properties. The as-prepared hydrogels can be further assembled into a high-performance flexible sensor, which can sensitively detect large-scale and small-scale human activities. The simple design concept of this work is believed to provide a new prospect for developing robust nanocomposite hydrogels and flexible devices in the future.
    Pressure-driven membrane inflation through nanopores on the cell wall
    Qi Zhong(钟祺), Chen-Xu Wu(吴晨旭), and Rui Ma(马锐)
    Chin. Phys. B, 2023, 32 (8): 088704.   DOI: 10.1088/1674-1056/acd7cc
    Abstract72)   HTML0)    PDF (1484KB)(43)      
    Walled cells, such as in plants and fungi, compose an important part of the model systems in biology. The cell wall primarily prevents the cell from over-expansion when exposed to water, and is a porous material distributed with nanosized pores on it. In this paper, we study the deformation of a membrane patch by an osmotic pressure through a nanopore on the cell wall. We find that there exists a critical pore size or a critical pressure beyond which the membrane cannot stand against the pressure and would inflate out through the pore and further expand. The critical pore size scales linearly with the membrane tension and quadratically with the spontaneous curvature. The critical pressure is inversely proportional to the pore radius. Our results also show that the fluid membrane expansion by pressure is mechanically different from the solid balloon expansion, and predict that the bending rigidity of the membrane in walled cells should be much larger than that of the mammalian cells so as to prevent membrane inflation through the pores on the cell wall.