SPECIAL TOPIC—Ultrafast physics in atomic, molecular and optical systems
EDITOR'S SUGGESTION
2025, 74 (15): 150201.
doi: 10.7498/aps.74.20250388
Abstract +
EDITOR'S SUGGESTION
2025, 74 (15): 150301.
doi: 10.7498/aps.74.20250483
Abstract +
Compton scattering is defined as an inelastic scattering process in which the interaction between strong laser fields and electrons in matter leads to photon emission. In recent years, with the rapid development of X-ray free-electron lasers, the intensity of X-ray lasers has steadily increased, and the photon energy in Compton scattering process has risen correspondingly. Previous studies focus on single-photon Compton scattering of free electrons. However, the mechanism of non-relativistic X-ray photon scattering by bound electrons remains to be elucidated. Therefore, we develop a frequency-domain theory based on non-perturbative quantum electrodynamics to investigate single-photon Compton scattering of bound electrons in strong X-ray laser fields. Our results show that the double-differential probability of Compton backscattering decreases with the increase of incident photon energy. This work establishes a relationship between Compton scattering and atomic ionization in high-frequency intense laser fields, thereby providing a platform for studying atomic structure dynamics under high-intensity laser conditions.
EDITOR'S SUGGESTION
2025, 74 (15): 153303.
doi: 10.7498/aps.74.20250459
Abstract +
EDITOR'S SUGGESTION
2025, 74 (15): 158702.
doi: 10.7498/aps.74.20250573
Abstract +
Femtosecond laser excitation of nonlinear materials is one of the key technologies for generating terahertz waves at present. Due to its advantages such as ultrashort time resolution and ultrabroad frequency spectrum, the technology has been widely used to characterize, measure, sense and image terahertz waves. However, the methods of controlling terahertz waves through microstructures can only regulate their transmission process, and they will face obstacles such as design difficulty and complex processes, making it hard to be widely used in industry. In this work, by introducing a pulse-shaping system to change the time dispersion of femtosecond laser pulses, the interaction process between femtosecond laser and lithium niobate crystals can be directly regulated, therefore the terahertz generation process can be directly controlled. Taking the second-order time dispersion for example, the terahertz signals generated by pump light with different second-order time dispersion in lithium niobate is detected by using the pump-probe phase-contrast imaging system. Meanwhile, the generation process of terahertz waves is simulated using the impact stimulated Raman scattering model and Huang-Kun equation, demonstrating the feasibility of using femtosecond laser pulses to adjust the time dispersion of terahertz waves. The experimental and simulation results show that when the time dispersion of femtosecond laser causes the pulse width to increase, the time in which the lithium niobate lattice is subjected to the impact stimulated Raman scattering force is prolonged, and the macroscopic polarization of the lithium niobate lattice is correspondingly extended. On the one hand, the longer duration of polarization results in a wider terahertz signal in the time domain and a narrower one in the frequency domain. On the other hand, since the impact stimulated Raman scattering force is proportional to the pump light intensity and is in the same direction during the interaction time, when the Raman scattering force ends, the lattice reaches a maximum displacement. The longer Raman scattering force causes the lattice to move to one side for a longer time, and correspondingly, the subsequent vibration of one period takes a longer time, ultimately resulting in a lower center frequency. In addition, this work also points out that the modulation of terahertz signals by pump light pulse width may be affected by the thickness of the wafer, and the modulation effect on thinner media may be more obvious. This result is of great reference significance for the active regulation of on-chip terahertz sources based on lithium niobate crystals in the future.
SPECIAL TOPIC—Instrumentation and metrology for ultrafast atomic and molecular spectroscopy
EDITOR'S SUGGESTION
2025, 74 (15): 150702.
doi: 10.7498/aps.74.20250534
Abstract +
In recent years, the attosecond extreme ultraviolet (XUV) pulse generation and advanced spectroscopic techniques have provided powerful tools for investigating electron dynamics. Researches on an attosecond timescale can realize real-time tracking of electronic motion in atoms and molecules, enabling the measurement of electron wave packet evolution and quantum characteristics, which are crucial for revealing complex dynamical processes within atomic and molecular systems. High-resolution photoelectron interferometers based on attosecond XUV pulse trains have played an important role in a wide range of applications due to their unique combination of high energy and temporal resolution. These applications include the characterization of attosecond pulse trains, the measurement of photoionization time delays in atoms and molecules, quantum state reconstruction of photoelectrons, and laser-induced electronic interference phenomena. By integrating attosecond temporal resolution with millielectronvolt level energy resolution, high-resolution photoelectron interferometric spectroscopy has emerged as a key technique for probing ultrafast dynamics and quantum state characterization. This review systematically summarizes recent advances in high-resolution attosecond photoelectron interferometry, with a focus on the experimental approaches and spectroscopic techniques required to access electron dynamics on an attosecond scale. These include the generation of narrowband attosecond XUV pulse trains, attosecond-stable Mach-Zehnder interferometers, high-energy resolution time-of-flight electron spectrometers, and quantum interference-based measurement schemes such as RABBIT and KRAKEN. This review discusses in detail the reconstruction of attosecond pulse sequences, shell-resolved photoionization time delay measurements in atoms, spectral phase evolution in Fano resonances, tomographic reconstruction of photoelectron density matrices on an attosecond timescale, and control experiments of laser-induced electronic dynamic interference effects. Through the analysis of recent studies, we demonstrate the powerful potential of attosecond high-energy resolution photoelectron interferometry in tracking ultrafast electron dynamics. Finally, the prospects of attosecond photoelectron spectroscopy in ultrafast dynamics and coherent manipulation of quantum systems are discussed.
EDITOR'S SUGGESTION
2025, 74 (15): 153301.
doi: 10.7498/aps.74.20250647
Abstract +
Attosecond ionization dynamics, a central topic in ultrafast science, largely depends on advances in experimental techniques and theoretical modeling to reveal the fundamental processes that control the evolution of matter on an ultrafast timescale. Among the cutting-edge approaches in this field, the strong-field multiphoton transition interferometry (SFMPTI) method stands out due to its ability to detect multiphoton ionization dynamics with attosecond time resolution via quantum path interference. This technique has been widely applied to the attosecond-scale measurements and characterizations of ionization time delays with quantum-state specificity, ranging from atomic systems to complex molecules. It provides a novel time-domain perspective in the study of strong-field physics. This article focuses on the application of the SFMPTI in probing strong-field multiphoton ionization time delays in atoms and molecules. We systematically present the quantum interference mechanisms behind the method: electrons undergo multi-photon above-threshold ionization (ATI) driven by a 400 nm laser pulse, while an additional 800 nm laser pulse induces the sideband signals through two-color interference. The relative phases encoding of these sidebands provides precise timing information about the ionization process. Furthermore, we summarize the recent advances in attosecond-resolved investigations of ATI dynamics and resonance-state-mediated time delays. For instance, the significant influence of resonance-enhanced multiphoton ionization processes involving different intermediate states in Ar atoms on ionization time delays is elucidated, highlighting the important influences of Freeman resonances on photoelectron emission dynamics in strong laser fields. Additionally, nuclear vibrations in NO molecules change ionization trajectories via nonadiabatic coupling of potential energy surfaces, leading to variations in time delay. Notably, the substantial influence of internuclear distance on ionization delay highlights the high sensitivity of electron-nuclear co-evolution to ultrafast phenomena. Finally, we discuss the potential applications and remaining challenges of this emerging technique, which will continue to open up new avenues for exploring attosecond electron dynamics in complex systems.
EDITOR'S SUGGESTION
2025, 74 (15): 153302.
doi: 10.7498/aps.74.20250546
Abstract +
Attosecond transient absorption spectroscopy (ATAS) is an all-optical pump-probe technique that employs attosecond pulses (from the extreme ultraviolet to soft X-ray) to excite or probe a system, enabling real-time tracking of electronic transitions, quantum state evolution, and energy transfer processes. This approach possesses some key advantages: 1) ultrafast temporal resolution (sub-femtosecond) combined with high spectral resolution (millielectronvolt level); 2) broadband excitation of multiple quantum states, allowing simultaneous detection of multiple energy levels; and 3) element- and site-specific insights provided by the measurements of inner-shell to valence transition reveal charge transfer dynamics, spin state changes, and local structural evolution. To date, significant breakthroughs have been achieved in atomic/molecular physics, electronic coherent dynamics, and strong-field physics by using ATAS. This paper systematically reviews the technical principles and theoretical models related to ATAS by using medium intensity near-infrared pulses, analyzes the recent progress of the applications in gas-phase systems and condensed-phase systems, and explores their future prospects in ultrafast physical chemistry and quantum materials. In gas-phase environments, the ATAS has demonstrated significant capabilities in probing energy level shifts and population transfers in atomic systems, as well as capturing nonadiabatic dynamics and charge migration in diatomic and polyatomic molecules. While in condensed-phase systems, this technique has been effectively used to study the ultrafast dynamics of carriers in semiconductors and to examine the interaction dynamics of localized electrons in insulators and transition metals. Given the rapid evolution of attosecond laser technologies and the unique advantages of the ATAS detection method, this paper also outlines potential future directions. These prospects are expected to further expand the frontiers of ultrafast spectroscopy and drive advancements in a range of disciplines in basic research and technological applications.
EDITOR'S SUGGESTION
2025, 74 (15): 153701.
doi: 10.7498/aps.74.20250415
Abstract +
With the continuous advancement and maturation of laser cooling techniques for atoms and molecules and full-dimensional electron and ion imaging technology, using momentum imaging techniques to investigate the characteristic properties of cold atoms and collision dynamics has emerged as a burgeoning research direction. This progress has driven the development of a series of high-resolution electron and ion detection devices, leading to innovative breakthroughs in fields such as cold molecule reactions, Rydberg atoms, nuclear decay, photoionization of Bose-Einstein condensates (BECs) and cold plasmas, collisions between cold atoms and ions/electrons, coherent control of cold atoms, and strong-field ultrafast physics. This article reviews representative instruments and their corresponding seminal achievements in the following domains: In cold molecular/cold chemical reactions, imaging technology has revealed new insights into reaction mechanisms; For cold Rydberg atom interactions, it demonstrates high-precision quantum state manipulation capabilities, advancing quantum information processing; In nuclear decay research, it provides ultra-sensitive detection methods, deepening understanding of decay processes; For BEC photoionization and cold plasma control, it can precisely monitor and manipulate microscopic processes; In cold atomic collision studies, it reveals new details in collision dynamics, refining collision theories; Regarding coherent control of cold atoms, it achieves accurate quantum state manipulation and interference; In strong-field ultrafast processes, it elucidates complex electron dynamics under intense fields, providing innovative methods for ultrafast laser control. Furthermore, this article summarizes the applications of imaging technologies in the aforementioned research areas involving cold atoms, and provides prospects for future developments in this evolving field.
EDITOR'S SUGGESTION
2025, 74 (15): 154202.
doi: 10.7498/aps.74.20250698
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EDITOR'S SUGGESTION
2025, 74 (15): 153201.
doi: 10.7498/aps.74.20250550
Abstract +
Transient absorption spectroscopy using soft X-ray coherent light sources as ultrafast probes holds significant potential applications in chemistry, biology, and materials science. This article presents the design of a transient absorption apparatus based on desktop soft X-ray light sources. A commercial femtosecond laser system (4.4 mJ, 25 fs, 800 nm, 1 kHz) drives an optical parametric amplifier, generating a 900 μJ, 28 fs, 1440 nm short-wavelength infrared (SWIR) pulse. This SWIR pulse is spectrally broadened and temporally compressed into a few-cycle pulse (400 μJ, 16.5 fs, 1530 nm) by a hollow-core fiber compressor. Then, few-cycle SWIR pulse drives the generation of attosecond soft X-ray high-order harmonic radiation, with the maximum photon energy extending into the water window region (>300 eV). The spectral resolution of the soft X-ray spectrometer is determined to be 334 meV at 243 eV. The remaining 800 nm pump pulse from the OPA system is combined with the high-order harmonic soft X-ray probe by using a hole mirror, forming a Mach-Zehnder interferometer with a time jitter of less than 10 fs during the one-hour data acquisition. This setup demonstrates the feasibility of performing time-resolved soft X-ray spectroscopy in a compact experimental configuration. Preliminary studies of transient absorption near the argon L-edge and carbon K-edge are conducted, demonstrating that this system can be used as a powerful tool for element-specific, time-resolved, and transition-channel-resolved investigations of electron dynamics.
SPECIAL TOPIC—Dynamics of atoms and molecules at extremes
EDITOR'S SUGGESTION
2025, 74 (15): 153401.
doi: 10.7498/aps.74.20250533
Abstract +
The scattering cross-sections and reaction rate coefficients are crucial parameters for elucidating the energy transfer mechanism of state-to-state collisions between molecular gases and also serve as a fundamental basis for modeling the non-equilibrium flow field. However, the database of kinetic processes related to nitrogen shock flows is still being developed. In this work, a detailed kinetic study of the N2 + O2 collision is carried out by combining the quasi-classical trajectory method (QCT) and neural network model (NN). Firstly, QCT is used to calculate 90 N2(v) + O2(w) processes with various initial vibrational states (v,w), and the contributions of all vibrational excitation and dissociation reaction channels are discussed. The following conclusions are drawn: 1) The contributions of the vibration-vibration (VV) energy exchange channel of O2 and N2 are similar, while the vibration-translational (VT) transition mainly occurs on O2; 2) The total dissociation cross-section primarily results from the O2 single-dissociation channel, followed by the exchange-dissociation channel, with relatively minor contributions from the N2 single- and double-dissociation channels. Then, based on the QCT dataset, a high-performance NN model (R-value of 0.99) is trained to predict the total dissociation cross-section caused by N2(v) + O2(w) collisions. Compared with the method that only uses QCT, the method that jointly uses OCT and NN model can achieve an approximately 91.94% reduction in computational cost. Finally, to facilitate use in kinetic modeling, Arrhenius-type fits for the VV/VT rate coefficients are provided over the temperature range of 5000–30000 K, and an exponential form related to the translational energy Et is used to fit the total dissociation cross-section.
EDITOR'S SUGGESTION
2025, 74 (15): 154102.
doi: 10.7498/aps.74.20250634
Abstract +
Charge transfer processes in ion-matter interactions are crucial for ion beam-driven high-energy density physics, material irradiation damage, and charge state stripping in accelerator techniques. Here we generate carbon ion beams in the MeV energy range through target normal sheath acceleration (TNSA) mechanism, and measure the average charge state of 1.5–4.5 MeV carbon ion beams passing through porous C9H16O8 foam with a volume density of 2 mg/cm3. The measured average charge states are compared with the average equilibrium charge-states predicted by semi-empirical formula and rate equation. The results show that the predictions from the rate equation that fully considers the ionization, capture, excitation, and de-excitation processes are in good agreement with experimental results. The prediction from the rate equation by using gas target cross-section data underestimates the experimental data, because the target density effect caused by the solid fiber filaments in the foam-structured target increases the ionization probability through frequent collisions, reduces the electron capture probability, and thus leads to an enhancement of ion charge states. In the projectile energy range above 3 MeV, the experimental data agree with the predictions from the rate equation using 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 range, the lifetime of ion excited states is shorter than the collisional time scale. In this case, excited electrons have time to de-excite the ground state before the second collision occurs. Consequently, the target density effects are weakened, and the charge states are reduced. The experimental results agree well with predictions from the ETACHA code that considers excitation and de-excitation processes in detail. This work provides the data and references for better understanding ion-matter interactions and distinguishing various charge exchange models.
SPECIAL TOPIC—Atomic, molecular and materials properties data
EDITOR'S SUGGESTION
2025, 74 (15): 152501.
doi: 10.7498/aps.74.20250581
Abstract +
EDITOR'S SUGGESTION
2025, 74 (15): 153102.
doi: 10.7498/aps.74.20250611
Abstract +
Li-like ions widely exist in astrophysical and laboratory plasmas, and their precise atomic parameters (e.g. excitation energies and transition rates) are very important for plasma diagnostics and spectral analysis. In this work, we employ the GRASP2018 software package, which is widely used in atomic structure calculations, to systematically compute the lowest 15 energy levels and the electric dipole (E1), magnetic dipole (M1), and electric quadrupole (E2) transition rates between them of 17 Li-like ions across the isoelectronic sequence (Z = 6–51: C3+, F6+, Mg9+, P12+, Ar15+, Sc18+, Cr21+, Co24+, Zn27+, As30+, Kr33+, Y36+, Mo39+, Rh42+, Cd45+, Sn37+, Sb38+). The calculations are based on the multi-configuration Dirac-Fock (MCDF) and configuration interaction (CI) method combined with high-order relativistic corrections and quantum electrodynamics effects such as Breit interaction, self-energy correction and vacuum polarization. The computational convergence is achieved. The calculated excitation energies and transition rates are compared with the NIST database and previous theoretical results. Due to the reasonable construction and larger scale of baseset, the current computational results show evident improvement compared with the results obtained using the same MCDF+CI method previously. Particularly for the two lowest excited states, [1s22p]1/2 and [1s22p]3/2, which exhibit slower convergence, the relative difference between current results and the NIST data is reduced by one to two orders of magnitude compared with previous MCDF+CI calculations. This accuracy even approaches that achieved by S-matrix methods specifically optimized for the ground state and these two lowest excited states. For transition rates, except for certain weak transitions with rates below $ {10}^{3}\;{{{\mathrm{s}}}}^{{-1}} $, the difference between our calculations and previous theoretical results obtained using the MCDF+CI method is still within 1%. Furthermore, our calculations accord with the NIST data within 5% for the majority of transitions. A comparison of NIST data with other previous theoretical results shows evident discrepancies between our calculations and the NIST data for some excitation energies and transition rates. Our results are consistent with other theoretical results for these specific values, indicating that these particular energy levels and transitions need more detailed theoretical and experimental investigation. This work provides highly accurate data for supporting experimental diagnostics and theoretical modeling of astrophysical and laboratory plasmas in future research. The datasets presented in this paper are openly available at https://www.doi.org/10.57760/sciencedb.j00213.00154 .
EDITOR'S SUGGESTION
2025, 74 (15): 153103.
doi: 10.7498/aps.74.20250568
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EDITOR'S SUGGESTION
2025, 74 (15): 153402.
doi: 10.7498/aps.74.20250541
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In this work, we systematically investigate single-electron capture process in the collision between N6+(1s) ions and H(1s) atoms in a wide energy range from 0.25 to 225 keV/u by using a two-electron semiclassical asymptotic-state close-coupling method. Spin-averaged and spin-resolved total cross sections, as well as n-resolved and $n\ell $-resolved partial cross sections, are calculated and comprehensively compared with existing experimental measurements and theoretical predictions. The results show at low energies (<10 keV/u), energy dependence of the total cross section is weak, and it follows a monotonically decreasing trend at higher energies. The analysis of $n\ell $-resolved cross sections reveals the strong coupling effects between various channels at low energies, while at high energies the relative $\ell $ distributions in each $n\ell $-resolved cross section approximately follow the statistical $\ell $ distribution, for which the electrons are therefore mainly captured into subshells of the maximum $\ell $. The present study demonstrates the importance of a two-electron treatment taking into account electronic correlation and the use of extended basis sets in the close-coupling scheme. However, substantial discrepancies exist among theoretical approaches at low energies. It is clear that further experimental and theoretical efforts are required to draw definite conclusions. Our work provides a complete and consistent set of cross sections in a broad range of collision energies, which can be used for various plasma diagnosis and modeling. The datasets presented in this paper are openly available at https://doi.org/10.57760/sciencedb.j00213.00143 .
EDITOR'S SUGGESTION
2025, 74 (15): 155203.
doi: 10.7498/aps.74.20250600
Abstract +
Experimental opacity data are used to evaluate the opacity models and their accuracy of the calculated results. In order to study the opacity of carbon material in the shell of the inertial confinement fusion ignition target, the experimental study of the spectrally-resolved opacity of radiatively heated carbon plasma is carried out on the Shenguang III prototype laser facility. Eight nanosecond lasers are injected into a conical-cylindrical gold hohlraum and converted into intense X-ray radiation, the high-temperature plasma is obtained by radiatively heating the CH film in the center of the hohlraum. Temporal evolutions of temperature and density of carbon plasma are simulated with the Multi-1D code. By using a spatially-resolved flat-field grating spectrometer combined with the ninth beam smoothing surface backlight technology, the absorption spectra of CH sample and the backlighter spectra are measured in one shot. Finally, the experimental transmission spectra of carbon plasma (with a temperature of 65 eV and density of 0.003 g/cm3) in a range of 300–500 eV are obtained and compared with the calculated results of a DCA/UTA opacity code. The datasets presented in this paper are openly available at https://doi.org/10.57760/sciencedb.j00213.00153 .
EDITOR'S SUGGESTION
2025, 74 (15): 156401.
doi: 10.7498/aps.74.20250569
Abstract +
We present a multi-phase equation of state (EOS) for lead (Pb, Z = 82) in wide ranges of densities and temperatures: $ {11}{.34}\;{\text{g}}/{\text{c}}{{\text{m}}^3} < \rho < 80\; {\text{g}}/{\text{c}}{{\text{m}}^3}{,} $ $ 300\;{\mathrm{K}} < T < 10\;{\mathrm{MK}}. $ The EOS model is based on a standard decomposition of the Helmholtz free energy that is regarded as a function of the specific volume and the temperature into cold term, ion-thermal term, and electronic excitation term. The cold term models both the compression and the expansion states; the ion-thermal term introduces the Debye approximation and the melting entropy; the electronic excitation term employs the Thomas-Fermi-Kirzhnits (TFK) model. The thermodynamic properties of the warm-dense lead are calculated using the extended first-principles molecular dynamics (ext-FPMD) method, with the density reaching five times that of ambient density and the temperature up to 0.4 MK. Our EOS model is used to predict the principle Hugoniot, the room-temperature isotherm, the melting curve, and the thermodynamic properties in the warm-dense region. A systematic comparison with the experimental data, the SESAME-3200 table, and the ext-FPMD calculations is made and shows that our EOS model is consistent with not only the various experimental data, but also the ext-FPMD calculations, indicating some superiority over the SESAME-3200 table in the warm-dense region. The datasets presented in this paper, including the tabular EOS consisting of internal energy and pressure at the different densities and temperatures, are openly available at https://www.doi.org/10.57760/sciencedb.j00213.00166 .
EDITOR'S SUGGESTION
2025, 74 (15): 157102.
doi: 10.7498/aps.74.20250574
Abstract +
Rare earth metals are of significant importance in engineering and technological applications, and their unique f-electron-related behaviors have attracted widespread interest in condensed matter physics. In this work, we investigate the elastic properties of rare earth metals ranging from Ce to Yb by combining first-principles calculations with systematic data compilation. Taking Ce and Yb as representative cases, we investigate the evolution of their elastic properties under high-pressure conditions (0–15 GPa), and we systematically compare the simulation performances of different f-electron treatment approaches. The results indicate a significant difference in ductility between light and heavy rare earth metals under ambient pressure. Under pressure, the elastic properties of Ce and Yb undergo marked changes in phase transitions. Specifically, the B/G ratio, a key indicator of ductility, decreases from about 2.0 in light lanthanides to around 1.5 in heavy lanthanides, crossing the critical threshold of 1.75. Notably, during the fcc iso-structural phase transition in Ce and the fcc-bcc phase transition in Yb, a significant brittle-ductile transition is observed. These transitions are closely related to the bonding characteristics modulated by atomic number or pressure condition. For instance, as the atomic number increases, the Cauchy pressure (C12–C44) decreases with the variation of s and d valence electrons, indicating an enhanced covalent bonding tendency. In addition, this study reveals that simulating f-electrons as core electrons can adequately describe the elastic properties and trends of rare earth metals under ambient pressure. However, when modeling high-pressure structural phase transitions and their related elastic evolution, the method of treating f-electrons as valence electrons and performing electron correlation correction shows better accuracy. The datasets presented in this paper are openly available at https://doi.org/10.57760/sciencedb.j00213.00150 .
GENERAL
2025, 74 (15): 150302.
doi: 10.7498/aps.74.20250108
Abstract +
Efficient and high-fidelity two-qubit gates are crucial to achieving fault-tolerant quantum computing and have become one of the key research topics in the quantum computing field. The fidelity of quantum gate is affected by many factors, such as quantum chip parameters and control waveforms. In theory, the chip paramters and waveforms can be precisely designed. However, in practice, the actual chip parameters and waveforms may deviate from the theoretical values. It is necessary to systematically study the effects of chip parameters, control waveforms, and other factors on the fidelity of two-qubit gate, and determine the magnitude and direction of the each factor’s effect. Here, we systematically study the effects of chip parameters, control waveforms, coupler start frequency, qubit frequency, etc. on the fidelity of CZ gate. On this basis, the response of gate fidelity to deviations in control parameters is further studied. At the chip design level, quantum chips based on CBQ parameters can achieve higher-fidelity CZ gate in shorter gate operation time. In terms of controlling waveforms, the three-level Fourier series wave is superior to the square wave and rounded trapezoidal wave in achieving lower gate error rate and shorter gate operation time, and can better meet the requirements for efficient implementation of high-fidelity quantum gates. Factors such as the coupler starting frequency and qubit frequency have relatively little effect on the fidelity of the CZ gate. In a wide frequency range, high-fidelity CZ gate can always be achieved by optimizing the control waveform parameters. It should be pointed out that slight deviations of control parameters will lead to a significant increase in gate error. This study is of great significance for clarifying the effects of various factors on the fidelity of the CZ gate. It can provide theoretical and technical support for designing superconducting quantum chips and realizing high-fidelity CZ gate, thereby promoting the engineering development of quantum computing.
2025, 74 (15): 150501.
doi: 10.7498/aps.74.20250554
Abstract +
To achieve multi-channel parallel transmission of complex signals and enhance spectral efficiency, this study presents a Rydberg atomic antenna system that can demonstrate multiplexed communication schemes. 852-nm and 509-nm lasers are used to excite cesium atoms into Rydberg states in a vapor cell, while employing differential detection techniques to suppress common-mode noise in order to obtain high signal-to-noise ratio electromagnetically induced transparency (EIT) spectra. Under weak electric field conditions, microwave field coupling causes atomic energy level shifts, resulting in two-photon detuning and rendering the EIT transmission intensity almost linearly dependent on the microwave electric field strength. Based on this effect, the integrated electrode configuration in the atomic cell generates a time-varying electric field, which can measure the waveforms, amplitudes, and frequencies of microwave and low-frequency electric fields. According to this principle, we decompose complex chaotic signals into three-dimensional orthogonal electric field components in order to demonstrate time-division multiplexing (TDM) of three-channel signals. Meanwhile, frequency-division multiplexing (FDM) is realized by modulating the x -, y -, z - channels with 3 kHz, 5 kHz, and 4 kHz carriers, respectively. The quantitative analysis of the parameters related to the transmition signal and the reference signal reveals high-fidelity reconstruction, with the fidelity levels reaching 95% for TDM and 90% for FDM. These results validate the feasibility of using optical atomic antennas to reconstruct complex signal waveforms and emphasize the potential of Rydberg-based systems in high-performance electromagnetic field sensing and communication applications.
2025, 74 (15): 150701.
doi: 10.7498/aps.74.20250517
Abstract +
Low-dimensional material systems benefit from their extremely high carrier mobility and flexible integrability, making them a subject of research in the terahertz detection field and demonstrating significant potential for applications. At present, software is mainly used to simulate and analyze the structures relied upon for semiconductor terahertz detection of bulk materials, while the simulation analysis for terahertz detection in low-dimensional material systems is still relatively unexplored. Due to the low degrees of freedom in carrier motion in low-dimensional materials, the probability of scattering caused by collisions between electrons and the lattice in the channel during electron movement is effectively reduced, making these materials have immense potential in high-sensitivity detection. Their low equivalent noise power and high signal-to-noise ratio performance in signal detection highlight the broad development prospects of these materials in the field of communication. This work simulates and analyzes the plasmon wave effect in a monolayer MoS2 field-effect transistor (FET) for THz detection for the first time, and systematically elucidates the principle and analysis process of using plasmon waves for THz detection. The transmission characteristic curve of the device is simulated and measured at a source-drain voltage of 0.5 V, and, a gate-to-drain voltage of –0.1 V is selected based on this curve to preliminarily investigate the THz response performance of the device. By adjusting key parameters such as Ugs, THz wave irradiation frequency, and HfO2 layer thickness, it is found that the monolayer MoS2 FET THz detector can produce a maximum DC voltage signal of 14 μV. This signal exhibits a complex variation trend related to the bias voltage between the gate and drain. This trend correlates with the bias voltage-induced changes in carrier concentration and the corresponding momentum relaxation time. The research results obtained in this paper can provide an important reference for designing low-dimensional material THz detectors. Furthermore, they lay a foundation for optimizing the performance of two-dimensional material THz detectors through simulation analysis, thereby providing deeper insights into the study of THz photoelectric responses in 2D materials.
COVER ARTICLE
COVER ARTICLE
2025, 74 (15): 150401.
doi: 10.7498/aps.74.20250582
Abstract +
This paper conducts numerical studies on superradiance and Hawking radiation of a specific rotating acoustic black hole model characterized by parameters A and B, within the framework of analogue gravity. The standard radial wave equation for scalar perturbations in the effective metric of this model is solved numerically by using an adaptive Runge-Kutta method with tortoise coordinates; this approach necessitates careful numerical inversion of the coordinate transformation near the horizon via a root-finding algorithm. By imposing appropriate boundary conditions, we extract the reflection coefficient $\mathcal{R}$ and transmission coefficient $\mathcal{T}$ in a range of frequencies ω. Our results clearly demonstrate superradiance, with the reflectivity $|\mathcal{R}|^2$ exceeding unity for $\omega < m\varOmega_{\rm{H}} = 1$ (where $m=-1$ and $\varOmega_{\rm{H}}=-1$), which confirms energy extraction from the rotating background. The high accuracy of our method is validated by the flux conservation relation, $|\mathcal{R}|^2 + $$ [(\omega - m\varOmega_{\rm{H}})/\omega]|\mathcal{T}|^2 = 1$, which typically has a numerical precision of $ 10^{-8}$. Furthermore, using the derived Hawking temperature and the rotation modified Bose-Einstein distribution, we calculate the Hawking radiation power spectrum $P_\omega$, and use the numerically obtained transmission coefficient $|\mathcal{T}|^2$ as the greybody factor of the model. A prominent feature of $P_\omega$ is its sharp enhancement (or divergence) as ω approaches the threshold $m\varOmega_{\rm{H}}$ from above, which is a characteristic directly related to the denominator of the Bose-Einstein factor. This research also reveals that superradiant amplification and Hawking spectrum characteristics are significantly dependent on the specific values of flow parameters A and B, even when the superradiant threshold $m\Omega_H$ is kept unchanged. This detailed numerical study provides quantitative results for the scattering and radiation properties of this model, and also for strong support for the analogue gravity framework.
ATOMIC AND MOLECULAR PHYSICS
2025, 74 (15): 153101.
doi: 10.7498/aps.74.20250417
Abstract +
Viscosity is an essential transport property in gas dynamics, especially the bulk viscosity, which exhibits more complex behavior. Carbon monoxide (CO) is a molecule of weak polarity, which exists in many important fields such as combustion and coke metallurgy. In order to effectively uncover the mechanism of the CO viscosity, this study dealt with it from a microscopic view. A transcale model is built which integrates density functional theory (DFT, first-principles) calculations with equilibrium molecular dynamics (EMD) simulations to establish a microscale foundation. Based on that, a fitted high-precision potential function is formed, then by using the Green-Kubo linear response theory, the shear and bulk viscosities of CO are achieved in a medium temperature range of 100–800 K. The MD simulation is implemented with C programming language, and an adaptive time-step algorithm is applied so that the computational efficiency is significantly enhanced. The resulting bulk viscosity exhibits quite obvious sensitivity to the potential function of the molecule system, while the shear viscosity shows little. Unlike the shear viscosity, which appears more linear, the bulk viscosity shows clear nonlinear behavior that changes with temperature. Correspondingly, traditional theoretic models and experimental results from different literature indicate that the bulk viscosity at medium temperatures is overestimated to various degrees. Fitting functions on the shear and bulk viscosities in the defined temperature range are established, respectively. Additionally, the lower system pressure and larger system size in the model effectively reduce statistical pressure fluctuations and improve the convergence of relevant laws. This work elucidates the microscopic mechanism of CO viscosity and provides a high-fidelity theoretical tool for modeling the viscosity of high-temperature nonequilibrium gas flows (e.g. hypersonic boundary layers, and plasma transport).
EDITOR'S SUGGESTION
2025, 74 (15): 153202.
doi: 10.7498/aps.74.20250505
Abstract +
This work is to investigate the single-photon scattering in a waveguide quantum electrodynamics system consisting of two dipole-coupled giant atoms, each interacting with a separate one-dimensional infinite waveguide at two distinct coupling points. Our primary objective is to establish a theoretical framework for manipulating photon propagation paths via quantum interference induced by multiple coupling points and local phase engineering. Unlike traditional chiral coupling schemes, an innovative method, in which the coupling phases are designed locally at each atom-waveguide interface, is used to achieve effective chiral coupling, thereby introducing novel quantum interference mechanisms. Using a real-space approach, we derive analytical expressions for four-port scattering amplitudes. We establish the conditions for achieving perfect directional routing to any output port and demonstrate the coherent control mechanisms implemented by geometric and local coupled phases. Continuous frequency tunability is primarily achieved through dipole-dipole interaction, and finely tuned through the accumulated phase and local coupling phases. Local phase differences precisely regulate port-specific probability distributions within the waveguides while preserving total routing efficiency. Furthermore, we elucidate the mechanisms of nonreciprocal transport and chiral scattering. The analysis reveals different governing principles: perfect nonreciprocity arises from the interplay of the accumulated phase, local coupling phases, photon-atom detuning, and dipole-dipole interaction. In contrast, perfect chiral scattering depends entirely on the accumulated phase and local coupling phases, and is independent of detuning. Notably, under the phase-matching conditions, the system achieves both perfect chiral and directional routing, and realizes frequency-selective path-asymmetric photon control. These findings provide a comprehensive framework for manipulating quantum interference in multi-atom waveguide systems, highlighting applications in quantum information processing, including tunable single-photon routers, isolators, and chiral quantum nodes. By implementing superconducting circuits, the local phase can be dynamically adjusted, thus proving the feasibility of the experiment.
ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
2025, 74 (15): 154101.
doi: 10.7498/aps.74.20250469
Abstract +
The technology of space-based wireless power transfer presents a potential solution for supplying energy to spacecraft. However, this method transmits energy through high-power electromagnetic pulses, which may pose a potential threat to gallium arsenide (GaAs) solar cells. Currently, the damage mechanisms affecting solar cells in these conditions remain unclear. To solve this issue, the thermo-electrical coupled damage mechanism of single-junction GaAs solar cells is investigated using a comprehensive multiphysics simulation model in this work. The damage characteristics of the solar cells under varying voltage and frequency inputs are simulated and analyzed. Furthermore, the relationship between burnout time and both input voltage and frequency are investigated, and the differences in damage mechanisms observed at different frequencies are elucidated. The results indicate that due to high current density and contact resistance, burnout mainly occurs at the cathode electrode contacts. Additionally, the PN junction and the anode contact experience significant temperature elevations, which is more likely to affect the cell performance. By deepening our understanding of how high-power electromagnetic pulses damage space solar cells, this study will provide support for designing electromagnetic protection systems for spacecraft power architectures.
EDITOR'S SUGGESTION
2025, 74 (15): 154201.
doi: 10.7498/aps.74.20250432
Abstract +
2025, 74 (15): 154301.
doi: 10.7498/aps.74.20250379
Abstract +
In recent years, people have increased their efforts to use spoof surface acoustic waves (SSAWs) to achieve subwavelength-scale modulation. However, obstacles on the transmission path often cause strong scattering of SSAWs, which limits their practical applications in communications and other fields. In this paper, we propose a new type of acoustic metasurface that supports the SSAWs’ propagation on both sides and design an acoustic stealth device based on such a metasurface. This metasurface is composed of periodically arranged Helmholtz resonators with bidirectional apertures, whose unique structure enables SSAWs to achieve interlayer transitions between the top surface and bottom surface. Remarkably, the total thickness of the structure is only 1/20 of the incident wavelength, exhibiting obvious subwavelength characteristics. We theoretically calculate the dispersion curve of SSAWs, and establish the dependency relationship between the propagation wave vector and the structural parameters. By optimizing the structural parameters of the double-sided metasurface, the wave vector matching during propagation is ensured, thereby achieving efficient transitions with minimal losses between the top and bottom surfaces. We construct a “sound-transparent path” through numerical simulations, allowing waves to bypass obstacles without scattering, and demonstrate that thermoviscous effects exert a negligible influence on transmission efficiency. Furthermore, an experiment is carried out to validate this metasurface’s dual-sided wave-manipulation capability, which demonstrates that the SSAWs maintain their wavefronts during interfacial propagation, showing excellent robustness against large-sized obstacles. The proposed stealth device possesses notable advantages, including a lightweight structure and high flexibility, providing new research perspectives and technical pathways for manipulating SSAWs and designing acoustic devices on a deep subwavelength scale.
2025, 74 (15): 154501.
doi: 10.7498/aps.74.20250272
Abstract +
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2025, 74 (15): 155201.
doi: 10.7498/aps.74.20250303
Abstract +
2025, 74 (15): 155202.
doi: 10.7498/aps.74.20250570
Abstract +
Rotating cylindrical cathodes possess high theoretical target utilization rates and have been widely used in thin film deposition in various industries. Regarding plasma research, the plasma discharge and transport processes of rotating cylindrical cathodes involve three-dimensional systems, unlike those of planar cathodes. Traditional plasma models applied to these systems require a large quantity of computational resources and have poor convergence, making simulation difficult. In this context, the plasma density and electric potential distributions are calculated by a two-dimensional particle-in-cell/Monte Carlo collision (PIC/MCC) model, and they are used as a self-consistent background field in this work. Furthermore, a three-dimensional electron Monte Carlo method is used to track electron motion, so that three-dimensional plasma discharge simulation can be performed. On this basis, using plasma density projection as the etching flux and the cellular automata method, the rotational etching process of the cylindrical cathode is decomposed into stepwise micro-element static etching, thereby achieving three-dimensional etching behavior simulation. Subsequently, the etched target morphology is equivalently treated as the emission flux of In and Sn atoms, and a three-dimensional test particle Monte Carlo method is employed to trace their motion, realizing three-dimensional particle deposition simulation. Thus, a comprehensive three-dimensional simulation system is constructed through incorporating the cathode magnetic field, plasma discharge, target etching, and thin-film deposition into a complete simulation chain. The results indicate that this three-dimensional simulation system can accurately predict the operating conditions of cylindrical cathodes. The plasma stably accumulates on the cylindrical cathode surface, forming a three-dimensional discharge race track. The simulated etching profile is consistent with experimental result, showing the precise matching of the feature points with the residual thickness of the target. The utilization rate of the target material is 85.81%, with an error of less than 2% compared with that of the measurement. The molar ratio of In/Sn on the substrate is 11.76, with an error of 6.6% compared with the results measured by energy dispersive spectroscopy. The particle distribution on the substrate matches the actual film thickness distribution, with a uniform deposition length of 1730 mm, representing an error of only 1.1% compared with corresponding actual value.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2025, 74 (15): 156201.
doi: 10.7498/aps.74.20250456
Abstract +
The rapid advancement of micro-nano acoustic devices has led their core acoustic structures to shrink to the nanoscale level. The influence of surface effects on the mechanical properties of thin-film materials on a nanoscale becomes increasingly prominent, and the classical elasticity theory struggles to accurately describe their mechanical behavior on this scale. In this paper, a mechanical model of nano-SiO2/Si heterostructured thin films that considers surface effects is developed using surface elasticity theory. This model incorporates the key parameter of surface energy density. In this paper, a mechanical model of heterostructured nano-SiO2/Si films is developed using the surface elasticity theory, incorporating surface effects through the introduction of surface energy density as a key parameter. Using the Fourier integral transform method, analytical expressions for stress and displacement fields under surface traction are systematically derived, revealing the influence of surface effects on the mechanical behavior of materials on a nanoscale by comparing the analytical solution with that from the classical theory. The results show that when the surface stress distribution deviates by 3% from that predicted by the classical theory, the microscopic properties of the material become significant, and the surface effect cannot be ignored in a range of five times the width of the excitation region 2a. As the size of the excitation region decreases, the surface effect is significantly increases and the stress distribution within the excitation region and near the boundary becomes more concentrated than the counterparts in the classical theory. The shear stress is no longer zero, and an extreme value is observed at the boundary, which is significantly different from that predicted by the classical theory of elasticity. The transverse and longitudinal displacements are reduced compared with those from the classical theory, and the surface stiffness and deformation resistance of the material are greatly enhanced. Significant surface effects occur on nano-heterostructure thin films, leading to large deviations in stress and displacement distributions from the results of elasticity theory. Therefore, the classical elasticity assumptions are no longer applicable in the corresponding nanoscale range. The results demonstrate that the propagation of ultrahigh-frequency nano- length acoustic waves in nanoscale solid film surfaces is significantly affected by the scale effect. The failure of the classical elastic wave theory on a nanoscale is of great value for the study of nanoscale acoustic theory. Furthermore, these findings provide a theoretical basis for the subsequent development of more precise models of interfacial effects and a more detailed investigation of the influence of the film-substrate modulus ratio.
2025, 74 (15): 156202.
doi: 10.7498/aps.74.20250555
Abstract +
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2025, 74 (15): 157101.
doi: 10.7498/aps.74.20250082
Abstract +
Plutonium dioxide, as one of the primary materials for nuclear fuel, serves as a critical component in fast neutron reactor fuel and mixed oxide (MOX) fuel due to its distinctive physical and chemical properties. It can significantly enhance the utilization efficiency of uranium and diminish the demand for natural uranium resources. Moreover, plutonium dioxide constitutes an essential component of spent nuclear fuel. However, during long-term storage, oxygen vacancies on its surface can facilitate hydrogen release under the influence of water molecules, thereby posing potential risks to nuclear safety. Therefore, it is crucial to have a deep understanding of the interaction mechanism between water molecules and the plutonium dioxide surface. Such insights provide valuable theoretical guidance for ensuring the safe storage of spent nuclear fuel., The adsorption behavior of H2O molecules on the PuO2 (111) and (110) surfaces, as well as the effects of oxygen vacancies and excess electrons on these surfaces, is investigated numerically based on the first-principles calculations in this work. The simulation results show that the PuO2 (111) surface is very stable compared with the PuO2 (110) surface, indicating that PuO2 (110) is more prone to oxygen vacancies. For the adsorption of water molecules on PuO2 (111) and (110) surfaces, the plutonium atom vertex site is identified as the only stable adsorption site, with one hydrogen atom of the water molecule preferentially bonding to a surface oxygen atom. Due to the higher reactivity of the PuO2 (110) surface than that of the stoichiometric PuO2 (111) surface, water molecules exhibit molecular adsorption configurations on the latter, while dissociative adsorption configurations are favored on the former. Using the CI-NEB method, the energy barriers for the dissociation of the first hydrogen atom on stoichiometric surfaces of PuO2 (111) and (110) are determined to be 0.11 eV and 0.008 eV, respectively. In contrast, the energy barriers for complete dissociation are 0.85 eV and 1.02 eV, respectively, which are significantly higher. For reduced PuO2 (111) surfaces containing surface oxygen vacancies, the energy barrier for H2 production via water decomposition is calculated to be 3.31 eV. On the over-hydrogenated PuO2 (111) surface, the energy barrier for H2 production decreases markedly to 1.92 eV, providing theoretical insights into the mechanism of hydrogen release during nuclear fuel storage.
2025, 74 (15): 157501.
doi: 10.7498/aps.74.20250482
Abstract +
The magnetoelectric (ME) antenna based on the piezoelectric resonance principle can solve the problems of large size and high power consumption of traditional low-frequency electrical antennas. However, the acoustic impedance mismatch between the adhesive layer in the magnetoelectric composite and the piezoelectric and ferromagnetic phases significantly hinders the stress transfer in the magneto-mechanical-electric coupling process, ultimately limiting the magnetic radiation intensity of the magnetoelectric composite. To improve the magnetic emission performance of the PZT MFC/Metglas magnetoelectric composite, in this work, the two-dimensional filler MoS2 is adopted to fill and modify the adhesive layer of the PZT MFC/Metglas magnetoelectric composite, aiming to improve the acoustic impedance match between the adhesive layer and the ferroelectric and ferromagnetic phases. The influence of the MoS2 content on the magnetic emission intensity of the PZT MFC/Metglas magnetoelectric composite is systematically studied. The results show that when the filling weight percent of MoS2 is 1%, the magnetic emission intensity of the PZT MFC/Metglas magnetoelectric composite can reach 331 μT under the optimal bias, which is 1.5 times higher than that of the magnetoelectric composite without MoS2 filling. At a distance of 1 m, the magnetic emission intensity can reach 2.7 nT. The stress wave transfer mechanism in the electro-mechanical-magnetic coupling is discussed in conjunction with acoustic impedance matching theory. In addition, the amplitude shift keying modulation method demonstrates the lossless signal transmission capability of the magnetoelectric antenna composed of MoS2-modified PZT MFC/Metglas magnetoelectric composite. This method of optimizing the interfacial adhesive layer is simple and effective to expand the magnetoelectric response by increasing the stress wave transfer efficiency. Meanwhile, it provides a feasible solution for communication systems such as low-frequency underwater communication, underground sensing, and distributed wireless networks.
2025, 74 (15): 157801.
doi: 10.7498/aps.74.20250488
Abstract +
Plasmon-induced transparency (PIT) is a class of electromagnetically induced transparency phenomenon that enhances the interaction between light and matter, thereby improving the performance of nano-optical devices. However, traditional PITs usually rely on near-field coupling between bright modes and dark modes. In order to break through the limitation of this mechanism, in this study we propose a dual-polarized graphene hypersurface structure, which consists of four groups of symmetric L-shaped graphene surrounding cross-shaped hollow graphene, forming a triple PIT through the synergistic effect between two single PITs. The accuracy of the results is verified by simulating the transmission spectra using the finite-difference time-domain, which is highly similar to that of the coupled-mode theory results. It is found that by modulating the Fermi energy levels and carrier mobility, this structure exhibits a group refractive index of up to 500 as a slow-light device, demonstrating excellent slow-light control capability. As a polarizing device, this structure has dual polarization characteristics and can generate a triple PIT window under both x and y polarized light incidence. In particular, the resonant frequency f6 is not affected by the direction of polarization of the incident light. This good stability and resistance to interference in various polarized light conditions are particularly important for designing polarization devices. Meanwhile, we adjust the length parameter of graphene L2 and find that the resonance frequency f6 is still highly stable, showing a better tolerance to structural changes. Therefore, in this study, a multifunctional integrated device with slow light modulation and polarization selection in one device is designed, providing new theoretical guidance and research directions for synergistic effects based on polarization insensitivity.
2025, 74 (15): 157901.
doi: 10.7498/aps.74.20250520
Abstract +
To improve the thermionic emission performance of the rare-earth refractory yttrium salt cathode used in the magnetron, the influence of Sc2O3 doping on its thermionic emission properties is investigated. Cathodes are fabricated by incorporating different weight percentages of Sc2O3 into the rare-earth refractory yttrium salt matrix, and their thermionic emission properties are systematically evaluated. The experimental findings reveal that the doping of Sc2O3 significantly enhances the thermionic emission capability of the cathode. Notably, Sc2O3 with a doping concentration of 3% has the most significant improvement in emission performance. The 3% Sc2O3-doped cathode can achieve a thermionic emission current density of 3.85 A/cm2 under an anode voltage of 300 V at 1600 ℃. In contrast, under the same conditions, the undoped cathode provides a current density of only 1.66 A/cm2, indicating a 132% increase in thermionic emission efficiency when doped with 3% Sc2O3. By using the Richardson line method coupled with data-fitting algorithms, the absolute zero work functions for undoped and Sc2O3-doped cathodes (3%, 7%, and 11%) are determined to be 1.42, 0.93, 0.98, and 1.11 eV, respectively. The lifespan assessment indicates that at 1400℃ the cathode doped with 3% Sc2O3 remains stable for over 4200 h under an initial load of 0.5 A/cm2 without significant degradation. Finally, those cathodes are analyzed by the XRD, SEM, EDS, AES respectively. The analyses show that during thermionic emission testing, the Sc2O3 and Y2Hf2O7 undergo substitutional solid solution reactions, forming the ScxY(2–x)Hf2O[7+(3/2)x] solid solution. This process causes lattice distortion in the Y2Hf2O7, which makes it in a high-energy state, thus reducing the work function on the cathode surface. At the same time, Sc from Sc2O3 displaces Y in the Y2Hf2O7 unit cells, with the displaced Y existing in the form of metal, which enhances the electrical conductivity of the cathode surface. Additionally, the ScxY(2–x)Hf2O[7+(3/2)x] solid solution generates a substantial number of Vo2+ oxygen vacancies and free electrons, thereby further augmenting surface conductivity. All in all, these mechanisms contribute to significantly improving the thermionic emission capability of the cathode.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2025, 74 (15): 158101.
doi: 10.7498/aps.74.20250595
Abstract +
The top-seeded solution growth (TSSG) method is a critical technique for growing low-defect and high-quality silicon carbide (SiC) single crystals. A comprehensive numerical analysis model including induction heating, heat and mass transfer is developed for growing 6-inch SiC single crystals. The coupling effects of Lorentz force, centrifugal force, thermal buoyancy force and surface tension on the solution flow are considered, and the effects of crystal rotation speed on the velocity field, temperature field, carbon concentration field, crystal growth rate and carbon dissolution and precipitation on the crucible wall are systematically investigated. The results indicate that the Lorentz force in the solution results in a more complex flow field at low crystal rotation speeds. The crystal rotation speed should be controlled within the appropriate range to ensure that the carbon concentration distribution beneath the growth interface determined by the transport mode is coordinated with that at the growth interface determined by the temperature, which is beneficial for the uniform and high growth rate of SiC single crystals. Low rotation speeds reduce the growth rate of SiC single crystals, while high rotation speeds lead radial uniformity of growth rate to decrease. At a rotation speed of 25 r/min, the average growth rate of SiC single crystals is higher and the radial distribution uniformity is better. Further analysis is conducted on the dissolution and precipitation of carbon at the solution-crucible interface, and the regions, where the crucible wall dissolves quickly and SiC polycrystalline particles are generated, are located. The transport directions of polycrystalline particles are predicted based on the velocity field. The research results provide a scientific basis for growing 6-inch SiC single crystals by TSSG method.
2025, 74 (15): 158102.
doi: 10.7498/aps.74.20250602
Abstract +
EDITOR'S SUGGESTION
2025, 74 (15): 158701.
doi: 10.7498/aps.74.20250616
Abstract +
The aggregation of Medin is closely related to the arterial wall degeneration and cerebrovascular dysfunction. In patients with vascular dementia or Alzheimer’s disease, the concentration of medin in cerebral arterioles increases, and Medin is co-localized with vascular amyloid-β (Aβ) deposits. Previous study demonstrates that Medin interacts directly with Aβ, forming heterologous fibrils with Aβ and promoting Aβ aggregation. However, the basic mechanism of the co-aggregation between Medin and Aβ remains largely elusive. Here, we explore the interactions and conformational ensembles of Aβ42/Medin trimers in different peptide environments (self-aggregation vs. co-aggregation) by performing all-atom replica exchange molecular dynamic simulation on Aβ42/Medin homotrimers and Aβ42-Medin heterotrimer with an accumulated simulation time of 72 μs. Our results reveal that Aβ42 exhibits higher affinity with Medin, and Aβ42 and Medin have similar molecular recognition sites in self-aggregation and co-aggregation. The N-terminus of Aβ42 and the C-terminus of Medin play critical roles in Aβ42-Medin cross-talk. More importantly, co-aggregation significantly changes the interaction strength, binding patterns and structural characteristics of Aβ42 and Medin. Intermolecular interactions of Aβ42 trimers are relatively weak among three trimers, and the binding sites are concentrated between N- and N-termini, between N- and C-termini, and between C- and C-termini of Aβ42. In contrast, intermolecular interactions of Medin trimers are the strongest, and the binding sites are widely and uniformly distributed in Medin peptides. Intermolecular interactions of Aβ42 in Aβ42-Medin heterotrimer decrease compared with those of Aβ42 trimers, only the binding of the hydrophobic core regions (16KLVFFA21) is retained and other regions of Aβ42 gain increase flexibility. Two-dimensional free energy landscapes reveal distinct conformational diversities between the homo- and heterotrimers, with the order of diversity being Medin/Aβ42-Medin trimers > Aβ42 trimers. The Rg of Aβ42 trimers is smaller than those of the other two trimers, implying that Aβ42 trimers possess a more compact structure, whereas Medin/Aβ42-Medin trimers exhibit a relatively loose conformation. The Aβ42 trimers possess the highest β content whereas Medin trimers exhibit the lowest β probability. It is found that Aβ42-Medin co-aggregation induces Medin to form more β-structures with longer lengths and fewer helices, while promoting Aβ42 to form more helices and fewer β-structures. High β-propensity regions of Medin in heterotrimers shift towards the C-terminus of Medin, suggesting that Medin utilizes its C-terminal β region as a core motif to drive its co-aggregation with Aβ42. These results elucidate the detailed influences of co-aggregation on the interactions and conformations of Aβ42 and Medin. This work provides key insights into the molecular mechanism of Aβ42-Medin co-aggregation and the pathological mechanisms of cross-linking between related diseases.
EDITOR'S SUGGESTION
2025, 74 (15): 158703.
doi: 10.7498/aps.74.20250484
Abstract +
Homologous recombination is a central mechanism for maintaining genome stability and biodiversity. RecA, as the first discovered homologous recombinase, plays a crucial role in homologous recombination strand exchange. In recent years, with the development of structural biology, significant breakthroughs have been made in understanding the static structure of the RecA nucleoprotein filament. However, research on the kinetic process of homologous recombination strand exchange mediated by RecA continues to encounter significant challenges. Research into the dynamic process has been ongoing for decades. In recent years, the use of single-molecule techniques has resulted in significant breakthroughs in this field. Among these techniques, single-molecule fluorescence resonance energy transfer (FRET) technology is widely used due to its ultra-high temporal and spatial resolution, making it well suitable for studying RecA-mediated homologous recombination strand exchange. However, the fluorescent labels required for FRET experiments may affect the RecA-mediated strand exchange process, which is often overlooked by researchers. Most of related articles focus on the effect of fluorescent labels on local structure. This paper primarily examines the effect of DNA fluorescent labeling on protein function, focusing on its effects on strand exchange from two perspectives: strand specificity and conformational sensitivity of the fluorescent labeling. Using experiments such as double-strand binding, single-strand invasion, and strand exchange, we develop a labeling scheme with the minimal effect—9 bp spaced C-strand double-base labeling in triplet— that can effectively improve the efficiency of studying the homologous recombination process. This result enhances the understanding of the effect of fluorescent labeling, allowing researchers to rapidly optimize the position and method of fluorescent labeling, and reduce its negative effects on the strand exchange process. Moreover, it provides some inspirations for other fluorescent labeling experiments.
