Highlights
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SPECIAL TOPIC—Correlated electron materials and scattering spectroscopy
EDITOR'S SUGGESTION
2025, 74 (1): 017401.
doi: 10.7498/aps.74.20241534
Abstract +
SPECIAL TOPIC—Correlated electron materials and scattering spectroscopy
EDITOR'S SUGGESTION
2025, 74 (1): 012501.
doi: 10.7498/aps.74.20241412
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Inelastic neutron scattering is a pivotal technique in materials science and physics research, revealing the microscopic dynamic properties of materials by observing the changes in energy and momentum of neutrons interacting with matter. This technique provides important information for quantitatively describing the phonon dispersion and magnetic excitation of materials. Inelastic neutron scattering spectrometers can be divided into triple-axis spectrometers and time-of-flight spectrometers, according to the method of selecting monochromatic neutrons. The former has high signal-to-noise ratio, flexibility, and precise tracking capabilities for specific measurement points, while the latter significantly improves experimental efficiency through various measures. The application of inelastic neutron scattering spectrometers is quite extensive, playing an indispensable role in advancing frontier scientific research in the study of mechanisms in various materials such as magnetism, superconductivity, thermoelectrics, and catalysis. The high-energy inelastic spectrometer at the China Spallation Neutron Source is the first time-of-flight neutron inelastic spectrometer in China, achieving high resolution and multi-energy coexistence with its innovative Fermi chopper design. Additionally, the number of available single neutron beams in the experiment of this facility has reached the international leading level.
SPECIAL TOPIC—Correlated electron materials and scattering spectroscopy
EDITOR'S SUGGESTION
2025, 74 (1): 012801.
doi: 10.7498/aps.74.20241178
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SPECIAL TOPIC—Correlated electron materials and scattering spectroscopy
EDITOR'S SUGGESTION
2025, 74 (1): 017301.
doi: 10.7498/aps.74.20241163
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Due to the unique crystal structures and excellent transport properties, the Zintl phase thermoelectric materials have aroused extensive interest in energy storage and conversion. To explore the origins of those excellent performances, a series of experimental and theoretical techniques have been applied, such as neutron scattering, thermal conductivity, and molecular dynamics simulations with machine learning. In this paper, the progress of neutron scattering research on the structure and dynamics of Zintl phase is summarized, for example A14MPn11 compounds with zero-dimensional (0D) substructures, 1D chains-based compounds, 2D layered A2BX2 compounds (including the binary Mg3Sb2) and their structural variants, as well as AB4X3, and ZrBeSi-type compounds. The underlying mechanisms of intrinsically low lattice thermal conductivity in those Zintl phase are discussed in detail. These compounds generally exhibit the following characteristics: 1) strong anharmonicity, which is characterized by strong atomic vibrations and anharmonic phonon-phonon scattering; 2) weak chemical bonding, which usually leads to low sound velocity and interatomic force constants, and corresponding to low-energy phonon branches; 3) intrinsic vacancy defect, which weakens the bond strengths, softens the lattice, and enhances anharmonic phonon-phonon scattering. Neutron diffraction is applied to studying crystal structures, lattice parameters, atomic occupancies, and atomic displacement parameters. Inelastic neutron scattering measures the lattice dynamics, and density of states, which are related to lattice thermal conductivity. Hence, the physical mechanisms of Zintl compounds are analyzed for optimizing material properties and designing new functional materials.
INSTRUMENTATION AND MEASUREMENT
EDITOR'S SUGGESTION
2025, 74 (1): 017801.
doi: 10.7498/aps.74.20241491
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Photoluminescence (PL) spectroscopy has been widely used in the ultraviolet-near-infrared spectral range for over seventy years since its early reporting in the 1950’s, because it not only reveals the electronic structure information about such as band gap and impurity energy levels of semiconductor materials, but also serves as an efficient tool for analyzing interfacial structures, carrier lifetime, and quantum efficiency. However, in the infrared band beyond about 4 μm, the study of PL spectrum has been limited for decades due to strong thermal background interference, weak PL signals and low detection capability. In this review, a traditional PL method is introduced based on a Fourier transform infrared (FTIR) spectrometer, and a continuous-scan FTIR spectrometer-based double-modulation PL (csFTIR-DMPL) method is briefly described which was proposed in 1989 for breaking through the dilemma of the infrared band, and developed continuously in the later more than 20 years, with its limitations emphasized. Then, a step-scan FTIR spectrometer-based infrared modulated PL (ssFTIR-MPL) method reported in 2006 is analyzed with highlights on its advantages of anti-interference, sensitivity and signal-to-noise ratio. The effectiveness demonstration and application progress of this method in many research groups around the world are listed. Further developments in recent years are then summarized of wide-band, high-throughput scanning imaging and spatial micro-resolution infrared modulated PL spectroscopic experimental systems, and the technological progresses are demonstrated of infrared-modulated PL spectroscopy from 0.56–20 μm visible-far-infrared broadband coverage to >1000 high-throughput spectra imaging and ≤2–3 μm spatial micro-resolution. Typical achievements of collaborative research are enumerated in the visible-far-infrared semiconductor materials of dilute nitrogen/dilute bismuth quantum wells, HgCdTe epitaxial films, and InAs/GaSb superlattices. The results presented demonstrate the advancement of infrared modulated PL spectroscopy and the effectiveness of the experimental systems, and foresee further application and development in the future.
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The development trend of spallation damage mechanics is to construct a physical model that couples information with micro-mesoscale structure of materials, which also promotes the development of numerical calculation methods, experimental techniques and theoretical research. The mechanism responsible for plastic deformation and failure of structural metal materials at high strain rates is complex and ainfluenced by heterogeneities in the micro-mesoscale structure that comprises the distribution of grain boundaries, interfaces, and pre-existing densities voids. The distribution of these mesoscale heterogeneities can provide either strengthening behavior or void nucleation sites and influence spall failure behavior. Due to the lack of evolutionary information of micro-mesoscopic void distribution characteristics, the current spallation damage model is not only restricted in its application in extreme environments with high strain rates, high pressures, and shock, but also does not effectively provide some information about the correlation between material damage and final material fragmentation particle size, which is of very concern in engineering. Therefore, it is urgent to develop a spallation damage model that can reflect the variation law of micro-mesoscopic void distribution characteristics in damaged materials. The probability distribution function of void nucleation based on cosine function is given in this work by analyzing various influencing factors in the process of void nucleation, combining the characteristics of early void growth, and considering the convenience of analytical solution. The analytical calculation results of the new probability function of void nucleation are consistent not only with the results of the variation of void number with time calculated by molecular dynamics, but also with the experimental results of tantalum spallation in the early stage of damage development, that is to say, the new probability function of void nucleation can reflect the variation law of micro-void distribution characteristics in the early stage of spallation damage to a certain extent.
EDITOR'S SUGGESTION
2025, 74 (1): 014203.
doi: 10.7498/aps.74.20241458
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Fractional-order vortex beams possess fractional orbital angular momentum (FOAM) modes, which theoretically have the potential to increase transmission capacity infinitely. Therefore, they have significant application prospects in the fields of measurement, optical communication and microparticle manipulation. However, when fractional-order vortex beams propagate in free space, the discontinuity of the helical phase makes them susceptible to diffraction in practical applications, thereby affecting the accuracy of OAM mode recognition and severely limiting the use of FOAM-based optical communication. Achieving machine learning recognition of fractional-order vortex beams under diffraction conditions is currently an urgent and unreported issue. Based on ResNetA, a deep learning (DL) method of accurately recognizing the propagation distance and topological charge of fractional-order vortex beam diffraction process is proposed in this work. Utilizing both experimentally measured and numerically simulated intensity distributions, a dataset of vortex beam diffraction intensity patterns in atmospheric turbulence environments is created. An improved 101-layer ResNet structure based on transfer learning is employed to achieve accurate and efficient recognition of the FOAM model at different propagation distances. Experimental results show that the proposed method can accurately recognize FOAM modes with a propagation distance of 100 cm, a spacing of 5 cm, and a mode spacing of 0.1 under turbulent conditions, with an accuracy of 99.69%. This method considers the effect of atmospheric turbulence during spatial transmission, allowing the recognition scheme to achieve high accuracy even in special environments. It has the ability to distinguish ultra-fine FOAM modes and propagation distances, which cannot be achieved by traditional methods. This technology can be applied to multidimensional encoding and sensing measurements based on FOAM beam.
EDITOR'S SUGGESTION
2025, 74 (1): 015201.
doi: 10.7498/aps.74.20241118
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Microwave plasma thruster (MPT) is a kind of electrothermal thruster. Inside its cylindrical cavity, the plasma process, microwave electric field distribution, and TM011 mode resonant state are important factors affecting the performance of MPT seriously. According to previous MPT formed through continuous regulation in the resonant sate of cylindrical cavity, the research is needed on a newly fixed and simple MPT, which will simplify the resonant state regulation and lays an important foundation for further study. Therefore the plasma process is analyzed to find the optimal gas discharge condition, and the microwave electric field intensity and power density distribution inside the cavity running in TM011 resonant sate are calculated to analyse how the parameters are influenced by the cavity dimensions. The resonant state is finely regulated to study how it is influenced by the dimensions of cylindrical cavity and microwave coupling probe with ball and half ball structure. The results of theoretical analysis and calculation show that the discharge power of helium gas is the lowest under the condition of 489 Pa and when the ratio of length to diameter is greater than 1, the microwave electric density distribution inside the cavity is beneficial. Owing to the appropriate length and radius of microwave coupling ball probe, the experiment on resonant state regulation shows that the shortest cylinder cavity is in the optimal resonant sate, with a resonance frequency very close to 2.45 GHz. The helium discharge experiment proves that the cavity and matching ball probe enable high microwave utilization and easy helium gas discharge, and the structure scheme is correct and reliable.
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