Science China Physics, Mechanics & Astronomy最新文献

Tungsten disulfide (WS₂) has been reported to show negligible stacking dependence under ambient conditions, impeding its further explorations on physical properties and potential applications. Here, we realize efficient modulation of interlayer coupling in bilayer WS₂ with 3R and 2H stackings by high pressure, and find that the pressure-triggered interlayer coupling and pressure-induced resonant-to-nonresonant transition exhibit prominent stacking dependence, which are experimentally observed for the first time in WS₂. Our work may unleash the stacking degree of freedom in designing WS₂ devices with tailored properties correlated to interlayer coupling.

In this paper, triple quasi-zero stiffness (QZS) passive vibration isolators whose restoring force curve has a three-stage softening effect are proposed. Multi-coupled SD oscillators with three independent geometrical parameters are used as negative stiffness mechanisms to achieve QZS characteristics at the origin and symmetrical positions on both sides of the origin. Isolation performances of different triple QZS isolators are analyzed to show influences of the selection of QZS regions away from the origin on the range of isolation regions. Pareto optimizations of system parameters are carried out to get a larger range of small restoring force regions and small stiffness regions. Isolation performances of two triple QZS isolators are discussed to show the influence of different Pareto optimization solutions through the comparisons with single and double QZS isolators. Results showed that triple QZS isolators have both the advantages of single and double QZS isolators which results in better isolation performances under both small and large excitation amplitudes. An improvement in isolation performances for triple QZS isolators is found with the decrease in average stiffness due to the appearance of two symmetrical QZS regions away from the origin. Larger displacements of QZS regions away from the origin result in better isolation performances when excitation amplitude is large, and triple QZS characteristics are similar to double QZS isolators at this time. Smaller restoring forces of QZS regions away from the origin lead to better isolation performances when excitation amplitude is small, and triple QZS characteristics are similar to single QZS isolators at this moment. Compared with the decrease in average stiffness, the improvement of isolation performances shows a hysteresis phenomenon due to the difference between static and dynamic characteristics.

Cosmic shear statistics, such as the two-point correlation function (2PCF), can be evaluated with the PDF-SYM method instead of the traditional weighted-sum approach. It makes use of the full PDF information of the shear estimators, and does not require weightings on the shear estimators, which can in principle introduce additional systematic biases. This work presents our constraints on S₈ and Ω_m from the shear-shear correlations using the PDF-SYM method. The data we use is from the z-band images of the Dark Energy Camera Legacy Survey (DECaLS), which covers about 10000 deg² with more than 100 million galaxies. The shear catalog is produced by the Fourier_Quad method, and well tested on the real data itself with the field-distortion effect. Our main approach is called quasi-2D as we do use the photo-z information of each individual galaxy, but without dividing the galaxies into redshift bins. We mainly use galaxy pairs within the redshift interval between 0.2 and 1.3, and the angular range from 4.7 to 180 arcmin. Our analysis yields S₈ = 0.762 ± 0.026 and Ω_m = 0.234 ± 0.075, with the baryon effects and the intrinsic alignments included. The results are robust against redshift uncertainties. We check the consistency of our results by deriving the cosmological constraints from auto-correlations of γ₁ and γ₂ separately, and find that they are consistent with each other, but the constraints from the γ₁ component are much weaker than that from γ₂. It implies a much worse data quality of γ₁, which is likely due to additional shear uncertainties caused by CCD electronics (according to the survey strategy of DECaLS). We also perform a pure 2D analysis, which gives S₈ = 0.81^+0.03_−0.04 and Ω_m = 0.25^+0.06_−0.05. Our findings demonstrate the potential of the PDF-SYM method for precision cosmology.

The superconducting ground state of kagome metals AV₃Sb₅ (where A stands for K, Rb, or Cs) emerges from an exotic charge density wave (CDW) state that potentially breaks both rotational and time reversal symmetries. However, the specifics of the Cooper pairing mechanism, and the nature of the interplay between these two states remain elusive, largely due to the lack of momentum-space (k-space) superconducting energy gap structure. By implementing Bogoliubov quasiparticle interference (BQPI) imaging, we obtain k-space information on the multiband superconducting gap structure Δⁱ_SC(k) in pristine CsV₃Sb₅. We show that the estimated energy gap on the vanadium ({d_{x{y mathord{left/ {vphantom {y {{x^{rm{2}}} - {y^{rm{2}}}}}} right.} {{x^{rm{2}}} - {y^{rm{2}}}}}}}) orbital is anisotropic but nodeless, with a minimal value located near the M point. Interestingly, a comparison of Δⁱ_SC(k) with the CDW gap Δⁱ_CDW(k) obtained by angle-resolved photoemission spectroscopy (ARPES) reveals direct k-space competition between these two order parameters, i.e., the opening of a large (small) CDW gap at a given momentum corresponds to a small (large) superconducting gap. When the long-range CDW order is suppressed by replacing vanadium with titanium, we find a nearly isotropic energy gap on both the V and Sb bands. This information will be critical for identifying the microscopic pairing mechanism and its interplay with intertwined electronic orders in this kagome superconductor family.

Space-borne gravitational wave (GW) detectors can detect the merger of massive black holes. The early warning and localization of GW events before merging can be used to inform electromagnetic telescopes and conduct multimessenger observations. However, this requires real-time data transmission and analysis capabilities. The geocentric orbit of the space-borne GW detector TianQin makes it possible to conduct real-time data transmission. In this study, we develop a search and localization pipeline for massive black hole binaries (MBHBs) with TianQin under both regular and real-time data transmission modes. We demonstrate that, with real-time data transmission, MBHBs can be accurately localized on the fly. With the approaching merger, each analysis can be finished in only 40 min. For an MBHB system at a distance of 1 Gpc, if we receive data every hour, then we can pinpoint its location to within less than 1 deg² on the final day before the merger.

Holography can provide the desired wavefront phase and/or amplitude for imaging, particle manipulation, bacteria trapping, and cell patterning in optics and acoustics. However, previous work on acoustic holography is mostly based on local design optimization, either using active control of the sound source or relying on the structural design to provide the desired wavefront. Achieving precise control over the acoustic field remains a significant challenge. Here, we realize refined single-plane symmetric binary amplitude, asymmetric intensity gradient amplitude, and bi-objective hologram through the non-local holographic imaging theory that considers the acoustic coupling of structural units in detail. By taking into account the self-radiation and mutual radiation between many small units on a plate of well-designed thickness, as well as the transmission through the plate’s apertures, we can effectively regulate the sound field behind the plate. We demonstrate the effectiveness of our approach through numerical simulations and experiments, showcasing a circle, a black hole, and a bi-objective with a circle and a square hologram. Notably, the acoustic black hole hologram precisely reconstructs the intensity gradient distribution at two bright spots. This non-local holographic imaging theory is valuable for the fine-intensity regulation of the sound field and is expected to be applied in ultrasound diagnosis and treatment, medical imaging, and other fields.

Hyperpolarized ³He nuclei have emerged as a significantly important approach in quantum precision measurement techniques, with extensive applications in fundamental physics, magnetometry, metrology, and beyond. In this study, we report on the design and implementation of a ³He polarization system at the China Mianyang Research Reactor (CMRR), utilizing the metastability-exchange optical pumping (MEOP) method. We employed a Merritt coil system consisting of four square coils to furnish a uniform holding field. We deployed a 2 W fiber laser to pump the metastable ³He atoms and conducted free induction decay (FID) detection of the polarized ³He nuclei using both pickup coil and optical methods. For the optical method, we used a 50 mW linearly polarized distributed Bragg reflector (DBR) laser as the probe. We applied transverse light absorption polarimetry to measure the absolute nuclear polarization of the ground-state ³He. We have developed cell fabrication capabilities at the CMRR, and cells at various pressures ranging from 100 to 1000 Pa have been fabricated and evaluated. For a typical borosilicate cell with 100 Pa pressure, the absolute polarization is measured as P_n ≈ 70%, and the transverse relaxation time is estimated as T₂ ≈ 0.5 s. Moreover, we constructed a few aluminosilicate cells, each carefully filled with pure ³He at a pressure of 100 Pa. Subsequently, we conducted a comprehensive evaluation of their performance in the context of MEOP.

Freestanding oxide perovskites possess strong interlayer coupling between adjacent atomic layers, thus exerting a determinative effect on the magnetism and ferroelectricity of these atomic-scale materials. Here, we propose an effective strategy to manipulate magnetism and ferroelectricity in freestanding rare-earth orthorhombic perovskite via modulation of layer thickness. By performing first-principles calculations, an even-odd oscillation is demonstrated in few-layer GdAlO₃ perovskite (GAP). Specifically, odd-layer systems with charged atomic layers are ferromagnetic polar metals, while even-layer systems are antiferromagnetic ferroelectric semiconductors. This thickness-dependent magnetic phase transition originates from carrier doping, as rationalized by the Stoner criterion. Furthermore, we demonstrate the promotion of in-plane ferroelectricity via the concurrent application of two distinct antiferrodistortive displacements, each driven by formation and breaking of bonds. Analogous multiferroic phases may emerge in other transition metal oxide perovskites supporting multiple valence states, e.g., few-layer GdMO₃ (M = V, Cr, Mn, and Ni). This work puts forward a strategy for layer thickness engineering of magnetism and ferroelectricity in 2D oxide perovskite multiferroic materials.

In a perfect quantum key distribution (QKD) protocol, quantum states should be prepared and measured with mutually unbiased bases (MUBs). However, in a practical QKD system, quantum states are generally prepared and measured with imperfect MUBs using imperfect devices, possibly reducing the secret key rate and transmission distance. To analyze the security of a QKD system with imperfect MUBs, we propose virtual MUBs to characterize the quantum channel against collective attack, and analyze the corresponding secret key rate under imperfect state preparation and measurement conditions. More generally, we apply the advantage distillation method for analyzing the security of QKD with imperfect MUBs, where the error tolerance and transmission distance can be sharply improved. Our analysis method can be applied to benchmark and standardize a practical QKD system, elucidating the security analysis of different QKD protocols with imperfect devices.

Independent manipulation of transmitted and reflected light fields is a key technology for the realization of multifunctional optical applications, which can be implemented based on multilayered plasmonic or supercell subwavelength structures. However, the former is not suitable for the optical bands, while the latter is insufficient in generating large phase gradients. Here, an adjoint-optimization-based inverse design methodology is proposed, which utilizes the polarization-selective local interference between individual meta-atoms and enables monolayer dielectric metasurfaces to decouple the wavefront of transmitted and reflected optical fields. Moreover, this methodology serves to mitigate the aperiodic electromagnetic crosstalk inherent between adjacent meta-atoms, consequently leading to a significant enhancement in the performance of meta-devices. We analyzed the physical mechanism of adjoint optimization and proposed the concept of phase factors, highlighting their importance in the rapid inverse design of meta-devices-an aspect often overlooked in previous research. To demonstrate the feasibility and robustness of our method, we optimize monolayer metasurfaces with different initial structures. These devices efficiently focus and deflect x-linearly and y-linearly polarized incident light in transmission and reflection spaces, respectively. Overall, this methodology holds immense potential for designing multifunctional, high-performing metasurfaces that meet multiple constraints, opening up broad prospects for applications.