Highlights
Abstract +
The eigenstate thermalization hypothesis describes the nonequilibrium dynamics of an isolated quantum many-body system, during which a pure state becomes locally indistinguishable from a thermal ensemble. The discovery of quantum many-body scars (QMBS) shows a weak violation of ergodicity, characterized by coherent oscillations of local observables after a quantum quench. These states consist of the tower of regular eigenstates which are equally spaced in the energy spectrum. Although subextensive entanglement scaling is a primary feature widely used to detect QMBS numerically as entropy outliers, rainbow scars exhibit volume-law scaling, which may challenge this property. In this work, we construct the rainbow scar state in the fracton model on a two-leg ladder. The fracton model is composed of four-body ring-exchange interactions, exhibiting global time-reversal symmetry $ \hat{{{\cal{T}}}}={{\cal{K}}} {\mathrm{i}} \hat{\sigma}^y $ and subsystem $ {\hat{U}(1)}=\displaystyle \prod\nolimits_{j \in \{\text {row/col}\}} {\mathrm{exp}}\Big({{\mathrm{i}} \dfrac{\theta}{2} \hat{\sigma}_j^z}\Big)$ symmetry. The subsystem symmetry constrains particle mobility, hindering the establishment of thermal equilibrium and leading to a series of anomalous dynamical processes. We construct the rainbow scar state with distributed four-body GHZ states whose entanglement entropy follows the volume law. By calculating the eigenstates of the fracton model with exact diagonalization, the rainbow scar state consists of a series of degenerate high-energy excited states that are not significant outliers among other eigenstates in the spectrum. By introducing the on-site interaction to break the time-reversal symmetry, the degeneracy of rainbow scar states is lifted into an equally spaced tower of states, ensuring the revival of the initial state. However, when subsystem $\hat U(1) $ symmetry is broken, the scar state is quickly thermalized, indicating that the weak thermalization may be protected by subsystem $\hat U(1) $ symmetry. Additionally, we propose a scheme for preparing the rainbow scar state by modulating the strength of the four-body interaction and $ \hat{\sigma}^z$ operations, analyzing the influence of noise on the strength of the four-body interaction. This work provides new insights into the weak thermalization processes in fracton model and aids in understanding the nature of ETH-violation in various nonequilibrium systems.
EDITOR'S SUGGESTION
2025, 74 (10): 107401.
doi: 10.7498/aps.74.20250037
Abstract +
The epitaxial orientation of YBa2Cu3O7–δ grown via the oxygen partial pressure jump pathway in transient liquid-phase assisted chemical solution deposition (TLAG-CSD) depends on the barium-to-copper ratio in the precursor phase. To explore the mechanism behind this phenomenon, in this work we investigate the effects of different oxygen partial pressures and barium-to-copper ratio components on the barium-copper-oxygen liquid phase ([Ba-Cu-O]L) and the intermediate phase transition in the medium-high temperature heat treatment process. The research shows that the formation of the liquid phase exhibits a point-to-surface characteristic; the temperature and morphological differences in the liquid phase are mainly determined by the composition, with oxygen partial pressure only playing a supporting role. Y∶Ba∶Cu = 0∶3∶7 (0-3-7) components all appear before Y∶Ba∶Cu = 0∶2∶3 (0-2-3) components in the liquid phase, with a temperature difference of 20 ℃ (high oxygen partial pressure) or 40 ℃ (low oxygen partial pressure). Experimental results indicate that there are differences in the intermediate phase properties between these two components. Under high oxygen partial pressure, the intermediate phase BaCuO2 exhibits a single characteristic peak in the 0-3-7 component, with large and dispersed grains; the 0-2-3 component has multiple characteristic peaks, with small and dense grains. The surface area of the liquid phase region in the 0-3-7 component is smaller than that in the 0-2-3 component, resulting in different supersaturation levels of Y3+ in the liquid phases of the two components and causing orientation differences in YBCO. Finally, the basic model for the formation of fluorine-free liquid phase is summarized, and the complete [Ba-Cu-O]L film can be generated from the 0-2-3 component at high oxygen partial pressure and 750 ℃.
EDITOR'S SUGGESTION
2025, 74 (10): 107802.
doi: 10.7498/aps.74.20250109
Abstract +
Radar cross section (RCS), a crucial physical quantity that characterizes the backscattering intensity of targets under radar illumination, is the primary metric for assessing stealth capabilities. With the development of radar detection technologies, RCS reduction has become a forefront research topic in radar stealth, aiming to minimize target detectability. With the maturity of radar networking technology, the bistatic radar RCS reduction is becoming increasingly important in future electromagnetic stealth countermeasures compared with the monostatic radar RCS reduction. Artificial electromagnetic metasurfaces have introduced innovative technical approaches for realizing the bistatic radar RCS reduction. However, current metasurface designs still face challenges related to inefficiency and suboptimal performance, mainly due to the time-consuming nature of large-scale array optimization and the global extremum characteristics of bistatic radar RCS reduction. To overcome these limitations, this study proposes a few-shot convolutional neural network (CNN)-based approach, which achieves uniform full-space radar echo scattering by directionally optimizing metasurface phase distributions, thereby enabling effective bistatic radar RCS reduction. This approach integrates convolutional feature extraction, residual enhancement, and fully connected optimization modules with a customized loss function to efficiently capture the complex multidimensional relationships between diffuse reflection phases and the full-space RCS extrema. Theoretical calculations, full-wave simulations, and experimental tests show that the metasurface designed with this approach can achieve over 10 dB of Bistatic Radar RCS reduction in a frequency range from 7.26 GHz to 10.74 GHz. The method also ensures uniform diffuse reflection across the full space for various incidence angles (30°, 45°, 60°). Compared with traditional optimization algorithms, this method enhances RCS reduction by 17.2% while significantly improving computational efficiency. This approach provides a promising new technical paradigm for achieving full-space electromagnetic stealth in advanced weapon systems.
EDITOR'S SUGGESTION
2025, 74 (10): 108101.
doi: 10.7498/aps.74.20241668
Abstract +
In this paper, a method of designing broadband reconfigurable polarization-converting metasurface operating in L-band is proposed. This method can also be used to directly modulate the information by using two modulation modes: binary amplitude shift keying (BASK) and binary phase shift keying (BPSK). Switching the ON/OFF state of PIN diode can be used to modify the amplitude and phase responses of the cross-polarized reflection of the element in a frequency band of 1.17–1.66 GHz, thereby creating a 1-bit digital coding meta-atom. By changing the real-time coding patterns of amplitude and phase, the reconfigurable metasurface can control beams and information modulation. Simulation results show that by changing the coding patterns of the metasurface, twin-beams and four-beams with different reflection angles can be obtained which fully validates the control ability of dynamic far-field beam. As an experimental verification, a reconfigurable metasurface consisting of 10×10 meta-atoms is fabricated, and its beam control and information modulation functions are tested. The far-field patterns of the metasurface with different coding phase distributions are measured. Furthermore, modulation signals of varying high/low voltage levels and rates are loaded onto the metasurface, in order to control its modulation mode and rate. The modulated signals reflected from metasurface are captured by a high-speed radio-frequency (RF) oscilloscope at varying rates and reflection angles, and then demodulated so as to recover the original information. On this basis, a metasurface wireless communication system based on BASK and BPSK is constructed to transmit digital image information in a real-world environment. In the experiment, the image is first represented by a sequence of 0 bit and 1 bit, corresponding to the operational state sequence of the metasurface used for transmitting information. The field programmable gate array (FPGA) is then used to generate signals with high and low voltage levels in real time according to the sequence of working states of the metasurface, and to modulate the carrier signal irradiated onto the metasurface. Therefore, the signal is converted into a modulated signal and received by the antenna. Finally, the signal is demodulated by the universal software radio peripheral (USRP) and transmitted to the terminal equipment, yielding the constellation diagrams and enabling the recovering of the images. The image information recovered under both modulation schemes verifies that the system can achieve real-time modulation and transmission of digital information. The proposed metasurface and the design method may be used in many fields, such as satellite communications and digital broadcasting.
EDITOR'S SUGGESTION
2025, 74 (10): 102801.
doi: 10.7498/aps.74.20250017
Abstract +
EDITOR'S SUGGESTION
2025, 74 (10): 104701.
doi: 10.7498/aps.74.20241499
Abstract +
The manta ray is a large marine species, which has the ability of gliding efficiently and flapping rapidly. It can autonomously switch between various motion modes, such as gliding, flapping, and group swimming, based on ocean currents and seabed conditions. To address the computational resource and time constraints of traditional numerical simulation methods in modeling the manta ray’s three-dimensional (3D) large-deformation flow field, this study proposes a novel generative artificial intelligence approach based on a denoising probabilistic diffusion model (surf-DDPM). This method predicts the surface flow field of the manta ray by inputting a set of motion parameter variables. Initially, we establish a numerical simulation method for the manta ray’s flapping mode by using the immersed boundary method and the spherical function gas kinetic scheme (IB-SGKS), generating an unsteady flow dataset comprising 180 sets under frequency conditions of 0.3–0.9 Hz and amplitude conditions of 0.1–0.6 body lengths. Data augmentation is then performed. Subsequently, a Markov chain for the noise diffusion process and a neural network model for the denoising generation process are constructed. A pretrained neural network embeds the motion parameters and diffusion time step labels into the flow field data, which are then fed into a U-Net for model training. Notably, a transformer network is incorporated into the U-Net architecture to enable the handling of long-sequence data. Finally, we examine the influence of neural network hyperparameters on model performance and visualize the predicted pressure and velocity fields for multi-flapping postures that were not included in the training set, followed by a quantitative analysis of prediction accuracy, uncertainty, and efficiency. The results demonstrate that the proposed model achieves fast and accurate predictions of the manta ray’s surface flow field, characterized by extensive high-dimensional upsampling. The minimum PSNR value and SSIM value of the predictions are 35.931 dB and 0.9524, respectively, with all data falling within the 95% prediction interval. Compared with CFD simulations, the single-condition simulations by using AI model show that the prediction efficiency is enhanced by 99.97%.
EDITOR'S SUGGESTION
2025, 74 (10): 107301.
doi: 10.7498/aps.74.20241756
Abstract +
The normal metal-quantum dots-superconductor hybrid system is a good platform for studying the mechanism of thermoelectric conversion. In terms of non-equilibrium Keldysh Green’s function formalism and linear response theory, the charge and spin thermoelectric transport characteristics of a normal-double quantum dot-superconductor hybrid system with spin-orbit coupling are studied in this work. We delve into the relationship between thermoelectric coefficients and the system parameters, and find both charge and spin thermoelectric coefficients exhibit distinct symmetry in the parameter space composed of temperature and energy. The increase in temperature leads to a decrease in conductance within the energy gap, which is attributed to the reduction in Andreev transport. However, outside the energy gap, the conductance gradually increases, and the thermal conductance is gradually enhanced. This is because more quasiparticles outside the energy gap participate in thermoelectric transport, and a large charge thermopower is generated in the region far from the energy gap. It is found that the thermoelectric figure of merit is greater than 1, indicating a strong violation of the Wiedemann-Franz law. With the increase of temperature, the large spin thermopower as well as spin thermoelectric figure of merit can be obtained outside the energy gap. The charge (spin) thermopower and the thermoelectric figure of merit show the rich evolutionary characteristics as functions of energy level and Zeeman energy. With the disappearance of the charge thermopower, the spin thermopower still has a finite value, which leads to the emergence of a pure spin Seebeck effect. This is helpful for designing a pure spin current thermoelectric generator. Due to a competitive mechanism between the spin-orbit coupling effect and the Zeeman field, thermoelectric coefficients decrease with the strength of spin-orbit interaction increasing, but one still can obtain the spin thermoelectric quantities which meet the practical needs by regulating the strength of spin-orbit coupling and the Zeeman energy. The evolution pattern of the thermoelectric coefficientss in the energy space indicates that the enhancement of thermoelectric conversion efficiency can be achieved by modulating the energy levels of double quantum dots. In addition, this hybrid system can act as a heat engine to achieve the conversion of heat into work. Although its power and efficiency do not evolve synchronously, thermodynamic performance that meets practical needs can still be obtained in certain parameter regions. The research results of this work hold theoretical and practical significance for understanding the thermoelectric transport and thermodynamic performance of hybrid thermoelectric systems.
EDITOR'S SUGGESTION
2025, 74 (10): 100303.
doi: 10.7498/aps.74.20250137
Abstract +
EDITOR'S SUGGESTION
2025, 74 (10): 107103.
doi: 10.7498/aps.74.20250150
Abstract +
Bi2Te3-based compounds are the thermoelectric materials available only commercially, but the research on their low-temperature performances below 300 K are still insufficient. The influences of Bi/Sb ratio modulation and Se substitution on the electrical and thermal transport properties of BixSb2–xTe3 and Bi0.4Sb1.6Te3–ySey materials are systematically investigated in this work, aiming to optimize their thermoelectric performance in cryogenic regions through combined bandgap tuning and defect engineering. Materials are synthesized using a melt-quenching and spark plasma sintering process, and then phase analysis is conducted via X-ray diffraction and microstructural characterization by electron probe microanalysis. First-principles calculations and Hall effect measurements are used to investigate their defect formation mechanisms and carrier transport behaviors. In the BixSb2–xTe3 system, the increase of Bi content reduces the bandgap from 0.168 eV for Bi0.4Sb1.6Te3 to 0.113 eV for Bi0.58Sb1.42Te3, shifting the peak ZT temperature to lower ranges. However, the enhancement of alloy scattering leads the carrier mobility to decrease from 332 to 109 cm2/(V·s) and power factor to fall from 4.58 to 1.12 mW/(m·K2). To solve this problem, Se is substituted for the Te lattice of Bi0.4Sb1.6Te3. First-principles calculations reveal that the Se substitution reduces the formation energy of SeTe + BiSb complex, thus effectively suppressing SbTe antisite defects. This will result in the carrier concentration decreasing from 3.32×1019 to 2.64×1019 cm–3 while maintaining high mobility at 279 cm2/(V·s). Concurrently, Se-induced point defects enhance phonon scattering, reducing lattice thermal conductivity from 0.46 to 0.38 W/(m·K), a decrease of 17%. Bi0.4Sb1.6Te2.97Se0.03 sample achieves a ZT value of 0.93 at 220 K, which is 16% higher than the pristine Bi0.4Sb1.6Te3 sample with a ZT value of 0.80. The peak ZT increases from 1.17 to 1.31 at 350 K, an increase of 12%. These improvements arise from the synergistic effects of band engineering, where flattened valence band edges increase effective mass, and defect engineering, where antisite defects and strengthens phonon scattering are suppressed. This work provides a dual optimization strategy for BiSbTe-based materials, i.e. balancing bandgap reduction by controlling defects to improve cryogenic performance. The findings are particularly significant for the applications of BiSbTe-based materials in infrared detectors and multistage thermoelectric cooling systems.
EDITOR'S SUGGESTION
2025, 74 (10): 107201.
doi: 10.7498/aps.74.20241601
Abstract +
Charge balances can influence the emission efficiency of exciplex-based organic light-emitting diodes (OLEDs), but so far, the physical mechanism behind this phenomenon is not fully understood. Here, organic magnetic field effects (OMFEs) including magneto-conductance (MC), magneto-electroluminescence (MEL), and magneto-efficiency (Mη) are used as fingerprint probing tools to study physical mechanism of influence of charge balance on the emission efficiency of exciplex-based OLEDs. Specifically, low- and high-field effects of MC traces [MCL (|B| ≤ 10 mT) and MCH (10 < |B| ≤ 300 mT)] from the unbalanced device are separately attributed to the magnetic field (B)-mediated intersystem crossing (ISC) process and the B-mediated triplet-charge annihilation (TCA) process between triplet exciplex states and excessive charge carriers, whereas those from the balanced device are respectively attributed to the B-mediated reverse intersystem crossing (RISC) process and the balanced carrier injection. As the injection current decreases from 200 to 25 μA, low-field effects of MEL traces (MELL) form the unbalanced device always reflect the B-mediated ISC process, but those from the balanced device exhibit a conversion from ISC process to RISC process. Furthermore, although low-field effects of Mη traces (MηL) from unbalanced device and balanced device are attributed to the B-mediated ISC process, MηL value in the balanced device is approximately one-fourth of that in the unbalanced device. These different MC, MEL, and Mη traces reveal that the balanced carrier injection can increase the number of triplet exciplex states via weakening the TCA process, which leads to the enhanced RISC process. Because RISC can convert dark triplet exciplex states into bright singlet exciplex states, the emission efficiency of the balanced device is higher than that of the unbalanced one. Obviously, in this work OMFEs are used to provide a new physical mechanism for charge balance that influences the emission efficiency of exciplex-based OLEDs.
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