Science China Physics, Mechanics & Astronomy最新文献

The Lamb shift of a quantum emitter in close proximity to a plasmonic nanostructure can be three or more orders of magnitude larger than that in the free space and is ultra-sensitive to the emitter position and polarization. We demonstrate that this large Lamb shift can be sensitively observed from the scattering or absorption spectrum dip shift of the coupled system when the plasmonic nanoparticle or tip scans the emitter. Using these observations, we propose a scanning optical scattering imaging method based on the plasmonic-enhanced Lamb shift with achieves sub-nanometer resolution. Our method is based on the scattering or absorption spectrum of the plasmon-emitter coupling system, which is free of the fluorescence quenching problem and easier to implement in a plasmon-emitter coupling system. In addition, our scheme works even if the quantum emitter is slightly below the dielectric surface, which can bring about broader applications, such as detecting atoms and molecules or quantum dots above or under a surface.

Because of the complexity and difficulty of realizing a multi-wavelength soliton state, reports on its internal dynamic characteristics are scarce. In this study, the switching and periodic soliton explosion processes of the multi-wavelength soliton state in a negative dispersion passively mode-locked fiber laser are realized. The generation of the multi-wavelength soliton state undergoes the process of noise, oscillation, and stable mode-locking, and the splitting and annihilation of solitons with different group velocities directly impact the generation and disappearance of three wavelengths. Positive and negative dispersion lead to different group velocities of solitons. The presence and displacement of solitons with different group velocities cause soliton collisions, which lead to soliton explosions. A soliton experiences relative phase oscillation, chaos, and oscillation, as well as convergence and separation before and after an explosion. With an increase in parameters related to pump power, single-soliton oscillation, multi-wavelength solitons, and chaos are found in experiments and simulations, proving the relevance and reliability between simulation and experimental results. This work promotes the dynamical study of multi-soliton collisions in nonlinear science and the development of chaos theory in multi-comb lasers.

Globular clusters harbor numerous millisecond pulsars, but long-period pulsars (P ≳ 100 ms) are rarely found. In this study, we employed a fast folding algorithm to analyze observational data from multiple globular clusters obtained by the Five-hundred-meter Aperture Spherical radio Telescope (FAST), aiming to detect the existence of long-period pulsars. We estimated the impact of the median filtering algorithm in eliminating red noise on the minimum detectable flux density (S_min) of pulsars. Subsequently, we successfully discovered two isolated long-period pulsars in M15 with periods approximately equal to 1.928451 and 3.960716 s, respectively. On the (P - dot P) diagram, both pulsars are positioned below the spin-up line, suggesting a possible history of partial recycling in X-ray binary systems disrupted by dynamical encounters later on. According to timing results, these two pulsars exhibit remarkably strong magnetic fields. If the magnetic fields were weakened during the accretion process, then a short duration of accretion might explain the strong magnetic fields of these pulsars.

In comparison to conventional hexagonal honeycomb structures, auxetic metamaterials with re-entrant configurations have exhibited superior mechanical properties in terms of energy absorption. To further enhance the energy absorption capacity of these materials, a novel re-entrant honeycomb configuration, named novel auxetic re-entrant honeycomb (NARH), is developed by incorporating “<>”-shaped cell walls into the conventional auxetic re-entrant honeycomb (ARH). Two analytical models for the plateau stress are formulated to consider the plastic deformation of NARH during quasi-static compression and the dynamic impact using the linear momentum theorem. Quasi-static compression tests on 3D printed NARH honeycomb specimens and finite element simulations are performed to verify the effectiveness of the theoretical models. NARH exhibits higher plateau stresses compared with ARH during compression, which can be attributed to the presence of more plastic hinges formed in NARH. These hinges, the embedded parts with inclined cell walls, not only improve stability by forming stable triangles during compression but also enhance the energy absorption capacity. A parametric study is conducted to analyze the effect of impact velocity, thickness, and incline angle of cell walls on crashworthiness. Numerical simulations demonstrate higher sensitivity of the mechanical properties to impact velocity and cell wall thickness. Adding ribs to the “<>”-shaped cell walls in NARH further reduces the initial peak force during dynamic crushing while maintaining high energy absorption. The research provides valuable guidelines for the design of energy absorption metamaterials.

Star clusters were historically considered simple stellar populations, with all stars sharing the same age and initial chemical composition. However, the presence of chemical anomalies in globular clusters (GCs), called multiple stellar populations (MPs), has challenged star formation theories in dense environments. Literature studies show that mass, metallicity, and age are likely controlling parameters for the manifestation of MPs. Identifying the limit between clusters with/without MPs in physical parameter space is crucial to reveal the driving mechanism behind their presence. In this study, we look for MP signals in Whiting 1, which is traditionally considered a young GC. Using the Magellan telescope, we obtained low-resolution spectra within λλ = 3850–5500 Å for eight giants of Whiting 1. We measured the C and N abundances from the CN and CH spectral indices. C and N abundances have variations comparable with their measurement errors (∼ 0.1 dex), suggesting that MPs are absent from Whiting 1. Combining these findings with literature studies, we propose a limit in the metallicity vs. cluster compactness index parameter space, which relatively clearly separates star clusters with/without MPs (GCs/open clusters). This limit is physically motivated. On a larger scale, the galactic environment determines cluster compactness and metallicity, leading to metal-rich, diffuse, old clusters formed ex situ. Our proposed limit also impacts our understanding of the formation of the Sagittarius dwarf galaxy: star clusters formed after the first starburst (age≲ 8–10 Gyr). These clusters are simple stellar populations because the enriched galactic environment is no longer suitable for MP formation.

The Five-hundred-meter Aperture Spherical radio Telescope (FAST) has the largest aperture and a 19-beam L-band receiver, making it powerful for investigating the neutral hydrogen atomic gas (Hi) in the universe. We present HiFAST (https://hifast.readthedocs.io), a dedicated, modular, and self-contained calibration and imaging pipeline for processing the Hi data of FAST. The pipeline consists of frequency-dependent noise diode calibration, baseline fitting, standing wave removal using an FFT-based method, flux density calibration, stray radiation correction, and gridding to produce data cubes. These modules can be combined as needed to process the data from most FAST observation modes: tracking, drift scanning, On-The-Fly mapping, and most of their variants. With HiFAST, the root-mean-square (RMS) noises of the calibrated spectra from all 19 beams were only slightly (∼5%) higher than the theoretical expectation. The results for the extended source M33 and the point sources are consistent with the results from Arecibo. The moment maps (0, 1 and 2) of M33 agree well with the results from the Arecibo Galaxy Environment Survey (AGES) with a fractional difference of less than 10%. For a common sample of 221 sources with signal-to-noise ratio S/N > 10 from the Arecibo Legacy Fast ALFA (ALFALFA) survey, the mean value of fractional difference in the integrated flux density, S_int, between the two datasets is approximately 0.005%, with a dispersion of 15.4%. Further checks on the integrated flux density of 23 sources with seven observations indicate that the variance in the flux density of the source with luminous objects (S_int > 2.5 Jy km s⁻¹) is less than 5%. Our tests suggest that the FAST telescope, with the efficient, precise, and user-friendly pipeline HiFAST, will yield numerous significant scientific findings in the investigation of the Hi in the universe.

We discuss a novel window to probe the origin of our universe via the mass functions of primordial black holes (PBHs). The mass functions of PBHs are simply estimated using the conventional Press-Schechter formalism for two paradigms of cosmic origin, including inflationary ΛCDM and bounce cosmology. The standard inflationary ΛCDM model cannot generate an appreciable number of massive PBHs; however, non-trivial inflation models with blue-tilted power spectra at small scales and matter bounce cosmology provide formation mechanisms for heavy PBHs, which in turn, may seed the observed supermassive black holes (SMBHs). By fitting the SMBH mass functions at high redshift (z ∼ 6) derived from Sloan Digital Sky Survey (SDSS) and Canada-France High-z Quasar Survey (CFHQS) quasars, for two paradigms of cosmic origin, we derive constraints on the PBH density fraction f_PBH at z ∼ 6 and the characteristic mass M_⋆, with the prior assumption that all SMBHs stem from PBHs. We demonstrate that this newly proposed procedure, relying on astronomical measurements that utilize deep-field surveys of SMBHs at high redshift, can be used to constrain models of cosmic origin. Additionally, although not the main focus of this paper, we evolve the mass function from z ∼ 6 to z ∼ 0 through an assumption of 3 × 10⁸-year Eddington’s accretion, and give a rough estimation of f_PBH at z ∼ 0.

Three-dimensional (3D) phononic topological insulators (TIs) featuring two-dimensional (2D) surface states and one-dimensional (1D) hinge states have opened up a new route for multi-dimensional robust wave transport, providing unprecedented methods for integrated acoustic sensors and energy harvesting devices. However, aiming at the elastic 3D phononic TI with gapless surface states and hinge states, the realization of elastic 3D phononic TIs with gapless surface states and hinge states is a significant challenge due to the complicated multi-mode polarization of elastic waves in 3D structures. In this study, we demonstrate an elastic 3D phononic TI with a Dirac hierarchy by elaborately operating the corresponding spatial symmetries of the chiral honeycomb lattice. First, a 3D double Dirac cone of elastic wave can be achieved by doubling the lattice along the out-of-plane direction to fold two iso-frequency Weyl points. The topological phase transitions and 2D gapless two-fold Dirac surface states of elastic wave are realized by breaking the half-lattice spatial translation symmetry. Subsequently, based on the Brillouin zone folding along the in-plane direction, the 2D gapless two-fold surface Dirac cones are folded into four-fold surface Dirac cones. Finally, by inducing the relative radius of adjacent holes to break the in-plane spatial inversion symmetry, the fourfold surface Dirac cones are gapped and associated with a surface state inversion, in which the gapless 1D hinge Dirac dispersion is achieved. This research offers a route for engineering the hierarchies of TIs in 3D elastic wave systems and provides new possibilities for designing 3D ultrasonic devices with unconventional functions.

Two-dimensional systems that simultaneously harbor superconductivity and nontrivial band topology may serve as appealing platforms for realizing topological superconductivity with promising applications in fault-tolerant quantum computing. Here, based on first-principles calculations, we show that monolayered CoN and CoP with the isovalent FeSe-like structure are stable in freestanding form, even though their known bulk phases have no resemblance to layering. The two systems are further revealed to display intrinsic band inversions due to crystal field splitting, and such orderings are preserved with the inclusion of spin-orbit coupling (SOC), which otherwise is able to open a curved band gap, yielding a non-zero Z₂ topological invariant in each case. Such a mechanism of topologicalization is distinctly contrasted with that identified recently for the closely related monolayers of CoX (X = As, Sb, Bi), where the SOC plays an indispensable role in causing a nontrivial band inversion. Next, we demonstrate that, by applying equi-biaxial tensile strain, the electron-phonon coupling strength in monolayered CoN can be significantly enhanced, yielding a superconducting transition temperature (T_c) up to 7–12 K for the Coulomb pseudopotential of μ* = 0.2–0.1, while the CoP monolayer shows very low T_c even under pronounced strain. Their different superconducting behaviors can be attributed to different variations in lattice softening and electronic density of states around the Fermi level upon pressuring. Our central findings enrich the understanding of different mechanisms of band inversions and topologicalization and offer platforms for achieving the coexistence of superconductivity and nontrivial band topology based on two-dimensional systems.

Devices that surpass the restriction of reciprocity of classical physical waves have brought intriguing possibilities for wave modulation. Non-reciprocal acoustic devices that rely on the viscosity of the medium or nonlinear effect have low efficiency and distortion problems respectively, and poor immunity to defects. The appearance of acoustic topological insulators achieves non-reciprocal transport with high robustness. However, the local nature of topological states means that their appearance depends on a system with a larger dimension. That is, most of the area of a topological device is occupied by useless lattices that do not directly contribute to non-reciprocal transport. The extra cost of topology protection severely limits the application scenarios of topology states, decreases the cost-effectiveness of topology devices, and is not conducive to device miniaturization and integration. In this work, we construct an acoustic three-layer heterojunction by introducing two types of domain walls into a conventional quantum Hall effect acoustic topological insulator, and successfully construct a non-reciprocal scattering network that forms topological modes spanning the interlayer domain. These extended states are still protected by bulk-band topology, making their non-reciprocity robust against disorder. This structure flawlessly realizes the path broadening in a two-dimensional topological system and can accomplish functions such as non-reciprocal acoustic splitting and multichannel transmission. Our work opens up opportunities for developing topological-insulator-based non-reciprocal devices in acoustics.