Science China Physics, Mechanics & Astronomy最新文献

Since the discovery of a superconducting state in La₃Ni₂O₇ with T_c = 80 K under high pressure, numerous experimental and theoretical studies have been initiated on this material. In this paper, we study the candidate superconducting states in this system, i.e., interlayer s-wave pairing and intralayer d-wave pairing, in response to the parallel magnetic field. We find that the interlayer s-wave state effectively screens the parallel magnetic field, thereby forming a Fulde-Ferrell (FF) state. Conversely, the intralayer d-wave state cannot efficiently screen the magnetic field, leading to minor perturbations in the spatial distribution of the order parameters. We propose a method utilizing Josephson junctions to distinguish these two distinct superconducting states. Our findings are anticipated to enrich the understanding of superconducting phases.

A slender rod suffers global vibration in impact. In this study, we present the experimental, numerical, and theoretical studies of the axial responses of a 316 stainless steel rod during vertical impact with a rigid flat. Combining the contact models and the one-dimensional (1D) wave equation, we first develop a semi-analytical vertical impact model for the rods based on a unified theoretical framework, which considers different geometries of the impacting end including the hemispherical nose, the truncated conical nose, and the flat end. Furthermore, we perform free-drop experiments on these rods and numerical simulations to verify the theoretical models. The results show that the strain-rate effect hardens the rod nose and should not be ignored even at a velocity as low as a few meters per second. After the proposal of a dynamic correction factor to adjust the quasi-static contact model, the theoretical, numerical, and experimental results agree well with one another. Also, the three-dimensional (3D) FEM simulations show that the slight deviations between the experimental and the predicted results are due to the slight obliqueness of the rods in the drop. Additionally, we leverage the theoretical tool and FEM simulations to compare the mechanical responses of rods with different impacting ends, and suggestions about the selection of rod noses are obtained.

Interaction between metallic droplets and picosecond laser pre-pulse can shape the droplet into a target more favorable for the main pulse to efficiently generate extreme ultraviolet (EUV) light for nanolithography. After the radiation of the pre-pulse, flow pattern and wave propagation in the droplet are responsible for the deformation and fragmentation of the droplet at a late time. In this study, we numerically investigate the acoustic response and dynamic behaviors of a droplet subjected to a localized heat pulse in the vicinity of the droplet surface, which models the energy deposition of a picosecond (ps) laser pre-pulse. A second-order conservative sharp interface method is adopted to simulate corresponding compressible inviscid two-phase flows. Based on the numerical results, we find that a wave structure of compression-expansion-compression waves propagates in the spherical droplet, and that the asymmetry of the heat source around the droplet surface accounts for the occurrence of the secondary compression wave. Then, we assess the occurrence and propagation of the wave structures, and correlate the wave amplitude with the intensity of the deposited energy. In particular, a theoretical model for the wave propagation is established under the small perturbation assumption, and indicates that the minimum pressure should be inversely proportional to its distance to the droplet center. This theoretical prediction is in good agreement with the numerical results with low intensity of heat source. With the increase of intensity of heat source, the numerical results gradually deviate from the theoretical prediction, because of the failure of the small perturbation assumption at high deposition energy and the effect of asymmetry in geometry on the wave propagation. This study provides an insight into the physical mechanisms of a droplet radiated by a ps laser pulse, which may be helpful in designing the desirable target for efficient laser-induced EUV light generation.

The kagome metal FeGe provides a rich platform for understanding the mechanisms behind competing orders, as it exhibits charge order (CO) emerging deep within the antiferromagnetic phase. To investigate the intrinsic origin of this behavior, we examine the evolution of the low-energy electronic structure across the phase transition in annealed FeGe samples using angle-resolved photoemission spectroscopy. We find no evidence supporting a conventional nesting mechanism, such as Fermi surface nesting or van Hove singularities. However, we observe two notable changes in the band structure: an electron-like band around the K point and another around the A point, both shifting upward in energy when CO forms. These findings are consistent with our density-functional theory calculations, which suggest that the charge order in FeGe is primarily driven by magnetic energy savings due to a lattice distortion involving Ge1-dimerization. Our results provide photoemission evidence supporting this novel mechanism for CO formation in FeGe, in contrast to the conventional nesting-driven mechanisms.

In two-dimensional van der Waals magnetic materials, the interplay between magnetism and electron correlation can give rise to new ground states and lead to novel transport and optical properties. A fundamental question in these materials is how the electron correlation manifests and interacts with the magnetic orders. In this study, we demonstrate that the recently discovered 2D antiferromagnetic material, CrSBr is a Mott insulator, through the combined use of resonant and temperature-dependent angle-resolved photoemission spectroscopy techniques, supplemented by dynamical mean-field theory analysis. Intriguingly, we found that as the system transitions from the antiferromagnetic to the paramagnetic phases, its Mott bands undergo a reconfiguration, and a coherent-incoherent crossover, driven by the dissolution of the magnetic order. Our findings reveal a distinctive evolution of band structure associated with magnetic phase transitions, shedding light on the investigation of the intricate interplay between correlation and magnetic orders in strongly correlated van der Waals magnetic materials.

The characteristics and images of Einstein-Maxwell-dilaton (EMD) black holes are examined in this paper, focusing on their effective potential, photon trajectories, and images with both thin and thick accretion disks. We find that the shadow and photon sphere radii decrease as the dilaton charge increases. As the observation inclination increases, the direct and secondary images become distinct, with the direct image appearing hat-shaped. Simulations indicate that the brightness of the shadow and photon ring is higher in static spherical accretion flows compared to infalling ones. The study also shows that in thin disk accretion flows, direct emission predominantly influences the observed luminosity, while photon ring emission is less significant. Additionally, the appearance of black hole images varies with the observer’s inclination angle.

Photolithography is a foundational technique for manufacture compact chips in semiconductor industries. Regulating and cleaning contaminants in lithographic processes are crucial for achieving the higher resolution and smaller feature sizes, which contain a variety of physical phenomena related to fluid dynamics. In this review, we will first introduce the basic principles of two mainstream lithography, namely deep ultraviolet (DUV) lithography and extreme ultraviolet (EUV) lithography. We critically review several types of contaminants such as droplets, bubbles, particles and chemical organic pollutants, highlighting the advanced techniques for identifying the nano-substances and fluid behaviours. Then the control strategies for mitigating contaminants are reviewed, especially for the contamination removal on photomask, the improvement on the purity of immersion liquid and efficient cleaning treatment for wafer surface. This review underscores the critical need for advanced contaminant management strategies in photolithography, integrating innovative cleaning techniques that promise to elevate lithographic performance and drive future developments in semiconductor technology.

In extreme ultraviolet (EUV) lithography, mitigation of tin (Sn) debris contamination during EUV light generation is an important issue. In practice, the high-speed jet flows are used to transport debris away from the collector mirror, thereby protecting it and improving system performance. Since EUV light is generated in a near-vacuum environment, understanding jet flow behavior in these extreme conditions is crucial for effective contamination control. In this study, we introduce a new facility designed to investigate jet extruded into near-vacuum environments using particle image velocimetry (PIV) and particle tracking velocimetry (PTV). Our results reveal a significantly extended potential core and a “top-hat” velocity profile with an inlet flow rate of 0.28 standard liter per minute (SLPM) and ambient pressure of 13.9 Pa. We also investigate the effects of inlet flow rate, ambient pressure, and jet diameter on the centerline streamwise velocity of the jet flow. These findings aim to guide the design of equipment operating in vacuum conditions.

Future gravitational wave (GW) observatories, such as the Einstein Telescope, are anticipated to encounter overlapping GW signals, presenting considerable obstacles to GW data processing techniques, including signal identification and parameter estimation. In this letter, we propose a scheme of combining deep learning and Bayesian analysis to disentangle overlapping GW signals. The deep learning part takes a data-driven approach that employs an encoder-separation-decoder framework which is powerful enough to extract the shape of the signal even when the GW signals completely align. The Bayesian analysis part takes the matched filtering technique to extract the amplitude of the GW signals. Our scheme can facilitate the utilization of existing GW detection and parameter estimation methods for future instances of overlapping strain. This methodology effectively reduces biases in parameter estimation when handling multiple intertwined signals. Remarkably, this marks the first known instance where deep learning has been successfully utilized to disentangle overlapping GW signals.