Accepted
Abstract +
SmCo12, with its large magnetic energy product, is a highly promising high-temperature permanent magnet that has attracted significant attention. However, the widespread ThMn12-type crystal structure in this system faces serious stability issues, which significantly hinder its practical engineering applications. Exploring novel SmCo12 structures that combine stability and excellent magnetic properties is crucial for overcoming this bottleneck. In this study, we systematically investigated the metastable phases of the SmCo12 system using a local particle swarm optimization algorithm combined with first-principles calculations. Theoretical calculations revealed a hexagonal phase structure (space group $P \overline{3} 1 m$) with a formation energy 90 meV/atom lower than that of the conventional ThMn12-type SmCo12. Its phonon spectrum shows no imaginary frequencies and its structure remains stable during Nosé-Hoover thermostat simulations at 1200 K, confirming its dynamic stability and thermodynamic stability. The electronic structure reveals this structureexhibits metallic characteristics, with a total magnetic moment as high as 21.81 µB/f.u. and a magnetocrystalline anisotropy constant up to 11.10 MJ/m3, significantly surpassing those of similar high-cobalt-content Sm-Co systems. Furthermore, theoretical predictions indicate that the hexagonal phase SmCo12 structure exhibits exceptionally outstanding magnetic properties, with maximum energy product, anisotropy field, and Curie temperature reaching 54.56 MGOe, 15.01 MA/m, and 1180 K, respectively. The newly discovered hexagonal SmCo12 phase provides a novel direction for addressing the stability issues of the ThMn12-type structure.
, , Received Date: 2025-03-22
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Organic cations in hybrid organic-inorganic perovskite solar cells are susceptible to decomposition under high temperatures and ultraviolet light, leading their power conversion efficiency (PCE) to decrease. All-inorganic perovskite solar cells exhibit both high PCE and superior photothermal stability, making them promising candidates for single-junction and tandem photovoltaic applications. The mixed-halide perovskite CsPbI2Br has received much attention as a top cell in semi-transparent and tandem solar cells due to its excellent thermal stability and suitable bandgap (1.90 eV). Although the PCE of CsPbI2Br-based solar cells is approaching its theoretical limit, the energy loss caused by non-radiative recombination remains a major barrier to further improving performance. This non-radiative recombination is mainly caused by inadequate band alignment between the absorption layer and the transport layer, resulting in the loss of open-circuit voltage (VOC) and decrease of short-circuit current density (JSC). Two-dimensional perovskite passivation formed through solution processing can mitigate interfacial recombination, but it can also impede efficient charge transport. Constructing three-dimensional perovskite structures not only provides an effective solution to these limitations but also enhances sunlight absorption and facilitates carrier transport. In this study, we propose a dual-absorption-layer perovskite heterojunction (DPHJ) strategy, which involves integrating a staggered type-II perovskite heterojunction (p-pCsPbI2Br-CsPbIBr2) into the absorption layer of the top cell in an all-perovskite tandem solar cell. The simulation result indicates that stacking a 100-nm-thick CsPbIBr2 layer atop a 300-nm-thick CsPbI2Br layer greatly enhances the PCE of the single-junction device from 19.46% to 22.29%. This improvement is mainly attributed to band bending at the CsPbI2Br/CsPbIBr2 interface, which enhances the built-in electric field, facilitates carrier transport, and suppresses non-radiative recombination within the absorption layer. Compared with the tandem solar cell utilizing a single-absorption-layer CsPbI2Br top cell, the DPHJ-based tandem solar cell significantly increases VOC from 2.16 to 2.25 V and JSC from 15.96 to 16.76 mA⋅cm–2. As a result, the DPHJ-based tandem solar cell achieves a high theoretical PCE of 32.47%. In addition, the DPHJ-based tandem solar cell exhibits a significantly enhanced external quantum efficiency in a wavelength range of 500—580 nm , which can be attributed to the band-edge absorption of CsPbIBr2. This enhanced absorption generates more photogenerated carriers, thereby significantly improving the JSC. The VOC and PCE values in this study exceed those experimentally reported values of current CsPbI2Br single-junction and all-perovskite tandem solar cells. Compared with the single-layer CsPbI2Br (E2=101.9 meV, electron-phonon coupling strength $ {\gamma _{{\text{ac}}}} = 1.2 \times {10^{ - 2}},{\text{ }}{\gamma _{{\text{LO}}}} = 6.9 \times {10^3} $), the double-absorption-layer film exhibits a high exciton binding energy (E2=110.7 meV) and reduced electron-phonon coupling strength ($ {\gamma _{{\text{ac}}}} = 1.1 \times {10^{ - 2}},{\text{ }}{\gamma _{{\text{LO}}}} = $$ 6.3 \times {10^3} $), which helps suppress phase segregation and enhance both optical and thermal stability, which is favorable for fabricating long-term stable all-perovskite tandem solar cells. This work provides new ideas and theoretical guidance for improving the efficiency and stability of all-perovskite tandem solar cells. In addition, it also proposes a universal design concept for optimizing absorption layers in all-perovskite multijunction cells, which is expected to further advance the research in this field.
, , Received Date: 2025-03-26
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, , Received Date: 2025-01-24
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Laser-produced plasma extreme ultraviolet (LPP-EUV) source is one of the key technologies in advanced lithography systems. Recently, solid-state lasers have been proposed as an alternative drive laser for the next-generation LPP-EUV source. Compared with currently used CO2 lasers, solid-state lasers have higher electrical-optical efficiency, more compact size, and better pulse shape tunability. Although limited to shorter operating wavelengths, the solid-state lasers have higher critical plasma density and optical depth. Consequently, re-absorption and spectral broadening cause lower conversion efficiency (CE). Therefore, to optimize EUV emission features and improve CE, a 0.532-μm pre-pulse laser is utilized in this work to modulate the plasma density distribution. The pre-pulse and a 1.064-μm Nd: YAG laser (the main pulse) are incident on an Sn slab target co-axially. The EUV energy and spectra of the Sn plasma are characterized at various delay times. It is demonstrated that compared with the 1.064-μm single pulse, the 0.532-μm pre-pulse laser with short delay times of 10 ns and 20 ns respectively results in a 4% increase in CE at 26° and 18% increase at 39°. The angular distribution of EUV energy is modulated by the 0.532-μm pre-pulse. An isotropic emission can be obtained within a certain delay time. The spectral feature near 13.5 nm is optimized, and a spectral purity of 12.2% is improved by 69%. The laser spot sizes of 0.3 mm and 1 mm for the pre-pulse are compared in the experiment. The results show that the 1-mm spot size has a better modulation effect on the EUV emission. Moreover, the time-resolved visible-band plasma profile is captured by an ICCD with 1.6-ns gate width. The plasma size and the distance to the target surface are increased by the 0.532-μm pre-pulse, which suggests that the energy of the main pulse is deposited in the low-density pre-plasma plume instead of in the plasma near the target surface. The lower plasma density leads to an increase in CE and spectral purity. The angular distribution of EUV energy is found to be closely related to the plasma morphology, and defined as the ratio of the longitudinal size to lateral size of the plasma. This indicates that the variation of plasma morphology can influence the angular distribution of EUV energy, which is caused by the 0.532-μm pre-pulse. This work has guiding significance for optimizing the emission characteristics of solid-state laser driven EUV sources.
, , Received Date: 2025-04-06
Abstract +
The channel plasma characteristics of an artificially triggered lightning in Guangdong, China, are analyzed using slit-free spectroscopy technology. Based on spectral diagnostic methods, the maximum and minimum values of the triggered lightning channel current are determined to be about 30.9 kA and 25.6 kA (minimum), respectively, and the current is simulated using a modified transmission line model with linear current decay (MTLL). To investigate the electric field distribution, the finite-difference time-domain (FDTD) method and transmission line (TL) model are employed. At a distance of 58 m, assuming a return stroke velocity of 1.3 × 108 m/s, the TL-predicted radiation electric field deviates from experimental electric field, but is very close to the FDTD-simulation of the vertical electric field. Moreover, the analyses of magnetic fields at 58 m, 90 m, and 1.6 km are compared using FDTD simulations, dipole approximation, and charge magnetic field limit (CMFL) estimation. The discrepancies between calculated value and experimental values appear at 58 m and 90 m, which may be due to the near-field interference and measurement limitation. However, they become small at 1.6 km. This work is helpful for the study of lightning electromagnetic field properties and spectral diagnosis.
, , Received Date: 2025-04-06
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Two-dimensional planar heterojunctions composed of single-layer transition metal dichalcogenides have great potential applications in low-power, high-performance, and flexible optoelectronic devices. The localized atomic structure and crystal defects at interface govern the electronic, magnetic, optical, catalytic, and topological quantum properties. However, accurate characterization of interface atomic structure is still a challenge, so far. To determine the accurate atomic position, a spherical aberration-corrected electron microscope with segmented detector is employed, and the calculation is performed by integrated differential phase contrast (iDPC) imaging algorithm. By using the iDPC method, the atomic structure of WS2-MoSe2 monolayer heterojunction interface is characterized, and the W, Se, Mo, and S atoms are imaged simultaneously. Statistics show that the angles between the lattices on both sides of the WS2-MoSe2 planar heterojunction are distributed around 29° and 35°. Additionally, it is found that the lattice near the boundary experiences the strains of approximately 4‰ and 2% in the two lattice vector directions, with significant distortion occurring only at the interface. In this work, several typical atomic configurations, including merge type, quadrilateral type, and pentagonal type are found. The interface atomic configuration can help to release stress at the lateral interface. This study provides a useful method for accurately characterizing the structures for planar heterojunctions of monolayer transition metal dichalcogenide. It is of great significance for in-depth research on the structure-property relationship at single-atom resolution in various interface structures.
, , Received Date: 2025-03-12
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Steam condensation is a common physical phenomenon in nature and plays an important role in various industrial processes. Therefore, the regulation mechanism of steam condensation process has been widely concerned by scholars in recent years. In this paper, the molecular dynamics simulation method is used to study the vapor condensation behavior of copper surface by establishing a secondary microstructure model. The influences of different geometrical characteristics on the condensation process are discussed by analyzing the nucleation and merging time of droplets, the vapor condensation snapshot, the total number of condensed water molecules, and the total number of water molecules in the maximum condensed drop. With the increase of column width or column height ratio, the molecular weight of the total condensed water first increases and then decreases.
, , Received Date: 2025-04-03
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, , Received Date: 2025-03-18
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, , Received Date: 2025-03-26
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With the development of hardware-optimized deployment of piking neural networks (SNNs), SNN processors based on field-programmable gate arrays (FPGAs) have become a research hotspot due to their efficiency and flexibility. However, existing methods rely on multi-timestep training and reconfigurable computing architectures, which increases computational and memory overhead, thus reducing deployment efficiency. This work presents an efficient and lightweight residual SNN accelerator that combines algorithm and hardware co-design to optimize inference energy efficiency. In terms of algorithm, we employ single-timesteps training, integrate grouped convolutions, and fuse batch normalization (BN) layers, thus compressing the network to only 0.69 M parameters. Quantization-aware training (QAT) further constrains all weights and activations to 8-bit precision. In terms of hardware, the reuse of intra-layer resource maximizes FPGA utilization, a full pipeline cross-layer architecture improves throughput, and on-chip block RAM (BRAM) stores network parameters and intermediate results to improve memory efficiency. The experimental results show that the proposed processor achieves a classification accuracy of 87.11% on the CIFAR-10 dataset, with an inference time of 3.98 ms per image and an energy efficiency of 183.5 FPS/W. Compared with mainstream graphics processing unit (GPU) platforms, it achieves more than double the energy efficiency. Furthermore, compared with other SNN processors, it achieves at least a fourfold increase in inference speed and a fivefold improvement in energy efficiency.
,
Abstract +
Charge transfer processes in ion-matter interactions are crucial for ion beam-driven high-energy density physics, materials irradiation damage and charge state stripping in accelerator techniques. Here we generated carbon ion beams with energies in the MeV energy range through TNSA (target normal sheath acceleration) mechanism, and measured the average charge state of 1.5 ~ 4.5 MeV carbon ion beams passing through porous C9H16O8 foam with 2 mg/cm3 volume density. The measured average charge states are compared with various semi-empirical formula and rate equation-predicted equilibrated average charge state. The results show that the rate equation predictions fully considering the ionization, capture, excitation, and de-excitation processes are in good agreement with experiment. The rate equation prediction using gas target cross-section data underestimated the experimental data, because the target density effects caused by the solid fiber filaments in foam-structured target increases the ionization probability through frequent collisions and decrease the electron capture probability, which leads to an enhancement of ion charge states. In the projectile energy range above 3 MeV, the experimental data agree with rate equation predictions employing solid-target cross-section data. However, a significant deviation emerges in the energy region below 3 MeV due to the fact that in this energy regime, the lifetime of ion excited states is shorter than the collisional time scale. In this case, excited electrons have time to de-excite to the ground state before the second collision occurs. Consequently, the target density effects are weakened, and the charge states was reduced. The experimental results agree well with predictions from the ETACHA code, which considers excitation and de-excitation processes in detail. This work provides data and references to better understand the ion-matter interactions and to discriminate the various charge exchange models.
, , Received Date: 2025-04-08
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Hyperentanglement, as a high-dimensional quantum entanglement phenomenon with multiple degrees of freedom, plays a critical role in quantum communication, quantum computing, and high-dimensional quantum state manipulation. Unlike entangled states in a single degree of freedom, hyperentangled states establish entanglement relationships simultaneously in multiple degrees of freedom, such as polarization, path, and orbital angular momentum. Through entanglement-based distribution techniques, high-dimensional quantum information networks can be constructed. On this basis, a fully connected quantum network with hyperentanglement is constructed in this work, and the polarization and time-bin degree-of-freedom hyperentanglement is realized through the process of second-harmonic generation and spontaneous parametric down-conversion in periodically poled lithium niobate (PPLN) waveguide cascades. The hyperentangled state is then multiplexed into a single-mode fiber by using dense wavelength division multiplexing (DWDM) technology for transmission to terminal users. The quality of the entangled states in the two degrees of freedom is characterized using Franson-type interference and photon-pair coincidence measurement techniques. Polarization entangled states are subjected to quantum state tomography, and entanglement distribution technology is employed to achieve long-distance distribution and quantum key transmission within the network. Experimental results show that the two-photon interference visibility of both polarization and time-bin entanglement is greater than 95%, demonstrating the high quality of the hyperentanglement in the network. After 100-km-entanglement distribution, the fidelity of the quantum states in both degrees of freedom remains above 88%, indicating the effectiveness of long-distance entanglement distribution in this network. Additionally, it is verified that this network supports the distribution of quantum keys over a distance of more than 50 km between users. These results confirm the feasibility of a fully connected quantum network with hyperentanglement and demonstrate the potential for constructing large-scale metropolitan networks by using hyperentanglement. As a higher-dimensional entanglement, hyperentangled states can significantly enhance the capacity and efficiency of quantum information processing. Although the quantum communication is still in its early stages of development, achieving stable storage and transmission of entangled states in large-scale metropolitan networks remains a great challenge. By utilizing the frequency conversion properties and high integration characteristics of the periodically poled lithium niobate waveguides, the three-user hyperentangled quantum network constructed in this work provides a new solution for developing the large-scale metropolitan networks with high-dimensional quantum information networks., It is expected to provide a new platform for quantum tasks such as superdense coding and quantum teleportation
, , Received Date: 2025-04-15
Abstract +
Topological pumping based on Thouless pumping can be effectively applied to optical waveguide array systems to achieve robust light manipulation with strong disturbance resistance. One of its typical models, the Rice-Mele (R-M) model, enables directional light field to transmit from the leftmost (rightmost) waveguide to the rightmost (leftmost) waveguide, which can be utilized to realize fabrication-tolerant optical couplers. Adiabatic evolution is a critical factor influencing the transport of topological eigenstates. However, it requires the system’s parameter variation to be sufficiently slow, which leads to excessively long waveguide lengths, limiting device compactness. To reduce the size, non-adiabatic evolution offers a feasible alternative. Meanwhile, the adiabatic properties of topological pumping models introduce new degrees of freedom, expanding possibilities for light manipulation. Based on the R-M model, this work analyzes the relationship between adiabatic property and structure length L, investigates light field evolution behavior when adiabatic condition is violated, and explores the transition from adiabatic to non-adiabatic regimes. When adiabatic condition is satisfied (L1 = 1000 μm), the light field evolution aligns with the eigen edge state. The output mode is manifested as an edge state and localized at the edge waveguide. As length shortens (L2 = 250 μm and L4 = 30 μm), the deviation between light field and eigen edge state arises, and the eigen bulk states get involved in the light field. The output modes are manifested as the superposition of edge state and bulk state, with energy spreading to other waveguides. At a specific length (L3 = 110 μm), the light-field undergoes non-adiabatic evolution: initially deviating from the edge state and later returning to the edge state. This phenomenon is termed adiabatic equivalent evolution. The output mode is localized at the edge waveguide, which is the same as the adiabatic evolution. By analyzing the fidelity between output mode and eigen edge state, we demonstrate that the adiabaticity can effectively regulate fidelity, achieving signal on/off at the edge waveguide. As structural length decreases, fidelity gradually declines and exhibits an oscillating behavior. When fidelity approaches to 1, the adiabatic equivalent evolution emerges. The first-order perturbation approximation reveals that these oscillations stem from destructive interference between edge and bulk states, thereby confirming their intrinsic origin in band interference. This mechanism enables eigen edge state output at shorter lengths than adiabatic requirements, providing a reliable approach for miniaturizing devices. Furthermore, the fabrication tolerance is analyzed. Within the whole waveguides width deviation range of –35–+30 nm (relative deviation range of –7%–+6%), the transmission of edge waveguide through the adiabatic equivalent evolution is larger than 0.9. This work analyses light-field evolution process and underlying physics for topological pumping in non-adiabatic regimes, supplements theoretical methods for analyzing non-adiabatic evolution, and provides strategies for achieving eigen edge state output at reduced lengths. This work provides some feasible principles for designing topological optical waveguide arrays, guiding the development of compact and robust on-chip photonic devices such as optical couplers and splitters, which have broad application prospects in integrated photonics.
, , Received Date: 2025-03-14
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In the face of the surge of air transport demand and the increasing risk of flight conflicts, it is very important to effectively manage flight conflicts and accurately identify key conflict aircraft. This paper presents a novel method for identifying critical nodes in flight conflict networks by integrating complex network theory with a weighted cycle ratio (WCR). By modeling aircraft as nodes and conflict relationships as edges, we construct a flight conflict network where the urgency of conflicts is reflected in edge weights. We extend the traditional cycle ratio (CR) concept to propose the WCR, which accounts for both the topological structure of the network and the urgency of conflicts. Furthermore, we combine the WCR with node strength (NS) to form an adjustable mixed indicator (MI) that adaptively balances the importance of nodes based on their involvement in cyclic conflict structure and their individual conflict strength. Through extensive simulations, including node deletion experiments and network robustness analyses, we demonstrate that our method can precisely pinpoint critical nodes in flight conflict networks. The results indicate that regulating these critical nodes can significantly reduce network complexity and conflict risks. Importantly, the effectiveness of our method increases with the complexity of the flight conflict network, making it particularly suitable for scenarios with high aircraft density and complex conflict patterns. Overall, this study not only deepens the theoretical understanding of complex aviation network analysis but also provides a practical tool for improving air traffic control efficiency and safety, thereby contributing to achieving more environmentally friendly and sustainable air transportation.
,
Abstract +
Our work constructs a non-Hermitian system with long range hopping under periodic driving. The Hamiltonian has chiral symmetry, which implies that the topological invariant can be defined. Based on the non-Bloch band theory and the Floquet method, relevant operators and topological number can be defined, providing quantitative approaches for studying topological properties. For example, by calculating the non-Bloch time-evolution factor, the Floquet operator, etc., it is found that the topological invariant is determined by the change of the phase of $U^{+}_{\epsilon=0,\pi}(\beta)$ as it moves along the generalized Brillouin zone, corresponding to the emergence of quasi-energy zero mode and $\pi$ mode.
Results show that the topological structure of the static system can be affected by periodic driving significantly. The topological phase boundary of the zero mode can be changed. When there is no periodic driving, there is no $\pi$ mode in the energy spectrum. After the introduction of periodic driving, a gap appears at the quasi-energy $\epsilon=\pi$, inducing a non-trivial $\pi$-mode phase and enriching the topological phase diagram. Further, the next nearest neighbor hopping has a unique effect in this system. It can induce large topological numbers. However, different from the static system, large topological numbers only appear in specific parameter intervals under periodic driving. As the strength of the next nearest neighbor hopping increases, the large topological number phase disappears instead, reflecting the non-monotonic regulation characteristics of the Floquet system. In addition, the introduction of the phase of the next nearest neighbor hopping can change the topological phase boundary, providing new ideas for experimentally regulating topological states.
This research is of significance in the field of topological phase transitions in non-Hermitian systems. Theoretically, it reveals the synergistic effect of long-range hopping and periodic driving, and improves the theoretical framework for the cross-research of long-range and dynamic regulation in non-Hermitian systems. From an application perspective, it provides theoretical support for experimentally realizing the controllable modulation of topological states, which is helpful to promote the development of fields such as low energy consumption electronic devices and topological quantum computing.
Results show that the topological structure of the static system can be affected by periodic driving significantly. The topological phase boundary of the zero mode can be changed. When there is no periodic driving, there is no $\pi$ mode in the energy spectrum. After the introduction of periodic driving, a gap appears at the quasi-energy $\epsilon=\pi$, inducing a non-trivial $\pi$-mode phase and enriching the topological phase diagram. Further, the next nearest neighbor hopping has a unique effect in this system. It can induce large topological numbers. However, different from the static system, large topological numbers only appear in specific parameter intervals under periodic driving. As the strength of the next nearest neighbor hopping increases, the large topological number phase disappears instead, reflecting the non-monotonic regulation characteristics of the Floquet system. In addition, the introduction of the phase of the next nearest neighbor hopping can change the topological phase boundary, providing new ideas for experimentally regulating topological states.
This research is of significance in the field of topological phase transitions in non-Hermitian systems. Theoretically, it reveals the synergistic effect of long-range hopping and periodic driving, and improves the theoretical framework for the cross-research of long-range and dynamic regulation in non-Hermitian systems. From an application perspective, it provides theoretical support for experimentally realizing the controllable modulation of topological states, which is helpful to promote the development of fields such as low energy consumption electronic devices and topological quantum computing.
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