Science China Physics, Mechanics & Astronomy最新文献

To accurately obtain the waveform template of gravitational waves, substantial computational resources and extremely high precision are often required. In a previous study, we employed the confluent Heun function to obtain an exact solution to the Teukolsky equation. This approach allowed us to efficiently and accurately calculate the gravitational wave flux for a particle in circular orbits around a Schwarzschild black hole. Building on this method, we now extend its application to calculate the asymptotic gravitational wave fluxes from a particle in generic orbits around a near-extreme Kerr black hole. Our extended method proves particularly effective in handling computational challenges associated with large eccentricities (e = 0.9), higher spins (a = 0.999), higher harmonic modes, and strong-field regions. The results we obtained significantly outperform those derived from the numerical integration method based on the Mano-Suzuki-Takasugi method.

Multidimensional Floquet-driven alignment systems with dynamical symmetry present various exotic phenomena and applications. However, there are challenges in directly characterizing large-spin dynamical symmetry from spectra. Here, we first observe the symmetry-protected selection rules of dynamical high-dimensional parity in a large-spin (F = 4) system. We theoretically construct a Floquet-driven alignment system that can be used to reveal high-dimensional spatiotemporal symmetry. In the experiment, the system is implemented in Cs atomic gas subjected to two-dimensional Floquet-modulated magnetic resonance driving. By developing Floquet detection protocols of alignment double-sided spectra, we directly verify symmetry-protected selection rules of dynamical high-dimensional parity for large-spin systems. This work advances the exploration of dynamical symmetry to large spins, and unravels a universal Floquet scheme for the investigation of symmetry-protected selection rules.

Superconducting SnTe-type topological crystalline insulators (TCIs) are predicted to host multiple Majorana zero modes (MZMs) which can coexist in a single vortex. Fermi level (FL) close to the Dirac points of topological surface states is helpful for detecting MZMs. However, the TCI SnTe is a heavily p-type semiconductor which is very difficult to modify to n-type via doping or alloying. In this work, we fabricate the atomically flat Sn_1-xPb_xTe/Pb heterostructure by molecular beam epitaxy, and make the p-type Sn_1-xPb_xTe become n-type through changing the interface roughness. Using scanning tunnelling microscope, we find the Dirac points of Sn_1-xPb_xTe/Pb heterostructure are always above the FL due to the Fermi level pinning (FLP) induced by topological surface states at atomically flat interface. After increasing the interface roughness, the FLP effect is suppressed and then the Dirac points of p-type Sn_1-xPb_xTe can be tuned very close to or even below the FL. Our work provides a new method for tuning the FL of SnTe-type TCI which has potential application in novel topological superconductor device.

Superluminous supernovae (SLSNe) are a class of intense celestial events that can be standardized for measuring cosmological parameters, bridging the gap between type Ia supernovae and the cosmic microwave background. In this work, we discuss the cosmological applications of SLSNe from the Chinese Space Station Telescope (CSST). Our estimation suggests that SLSNe rate is biased tracing the cosmic star formation rate, exhibiting a factor of (1 + z)^1.2. We futher predict that CSST is poised to observe ∼ 360 SLSNe in the 10 square degrees ultra-deep field survey within a span of 2.5 years. A stringent constraint on cosmological parameters can be derived from their peak-color relationship. CSST is anticipated to uncover a substantial number of SLSNe, contributing to a deeper understanding of their central engines and shedding light on the nature of dark energy at high redshifts.

Kagome metals exhibit rich quantum states by the intertwining of lattice, charge, orbital and spin degrees of freedom. Recently, a novel charge density wave (CDW) ground state was discovered in kagome magnet FeGe and was revealed to be driven by lowering magnetic energy via large Ge1-dimerization. Here, based on DFT calculations, we show that such mechanism will yield infinitely many metastable CDWs in FeGe due to different ways to arrange the Ge1-dimerization in enlarged superstructures. Intriguingly, utilizing these metastable CDWs, innumerable polymorphs of kagome magnet LiFe₆Ge₆ can be stabilized by filling Li atoms in the voids right above/below the dimerized Ge1-sites in the CDW superstructures. Such polymorphs are very stable due to the presence of magnetic-energy-saving mechanism, in sharp contrast to the non-magnetic “166” kagome compounds. In this way, a one-to-one mapping of the metastable CDWs of FeGe to stable polymorphs of LiFe₆Ge₆ is established. On one hand, the fingerprints of these metastable CDWs, i.e., the induced in-plane atomic distortions and band gaps, are encoded into the corresponding stable polymorphs of LiFe₆Ge₆, such that further study of their properties becomes possible. On the other hand, such innumerable polymorphs of LiFe₆Ge₆ offer great degrees of freedom to explore the rich physics of magnetic kagome metals. We thus reveal a novel connection between the unusually abundant CDWs and structural polymorphism in magnetic kagome materials, and establish a new route to obtain structural polymorphism on top of CDW states.

Layered materials exhibit different electronic and phonon properties along in-plane and out-of-plane directions; existing studies focus on their in-plane behaviors, and the influence of such anisotropies on the dynamics of photocarriers and phonons is unknown. Here, we fabricate layered PdSe₂ crystals with flat edge surfaces and compare the time-resolved ultrafast spectroscopies on their basal and edge surfaces. Pronounced differences in the transient reflection spectroscopies reveal the inconsistent photocarrier and phonon dynamics behaviors on the two surfaces: the slow hot carrier relaxation process is accelerated and the thermoelasticity-induced longitudinal coherent acoustic phonon oscillation completely vanishes on the edge surface, as compared with the basal surface. Theoretical analysis reveals that the inconsistent hot carrier dynamics originate from the anisotropic properties of low-energy phonons in PdSe₂, and the absence of phonon oscillation on the edge surface results from the wavevector-limited sensitivity of acoustic B_1u mode. Moreover, polarization-dependent spectroscopies indicate the diverse optical anisotropies beyond the in-plane of PdSe₂. This work provides a new method to explore unique physical properties and modulate the optical anisotropy of layered materials.

The infinite-layer cuprate ACuO₂ (A = Ca, Sr, Ba) possesses the simplest crystal structure among numerous cuprate superconductors and can serve as a prototypical system to explore the unconventional superconductivity. Based on the first-principles electronic structure calculations, we have studied the electronic and magnetic properties of the infinite-layer cuprate SrCuO₂ from a phonon perspective. We find that interesting fluctuations of charges, electrical dipoles, and local magnetic moments can be induced by the atomic displacements of phonon modes in SrCuO₂ upon the hole doping. Among all optical phonon modes of SrCuO₂ in the antiferromagnetic Néel state, only the A_1g mode that involves the full-breathing O vibrations along the Cu-O bonds can cause significant fluctuations of local magnetic moments on O atoms and dramatic charge redistributions between Cu and O atoms. Notably, due to the atomic displacements of the A_1g mode, both the charge fluctuations on Cu and the electrical dipoles on O show a dome-like evolution with increasing hole doping, quite similar to the experimentally observed behavior of the superconducting T_c; in comparison, the fluctuations of local magnetic moments on O display a monotonic enhancement along with the hole doping. Further analyses indicate that around the optimal doping, there exists a large softening in the frequency of the A_1g phonon mode and a van Hove singularity in the electronic structure close to the Fermi level, suggesting potential electron-phonon coupling. Our work reveals the important role of the full-breathing O phonon mode playing in the infinite-layer SrCuO₂, which may provide new insights in understanding the cuprate superconductivity.

The advancement of integrated optical communication networks necessitates the deployment of on-chip beam splitters for efficient signal interconnections at network nodes. However, the pursuit of micron-scale beam splitting with large corners and reducing the device footprint to boost connection flexibility often results in phase mismatches. These mismatches, which stem from radiation modes and backward scattering, pose significant obstacles in creating highly integrated and interference-resistant connections. To address this, we introduce a solution based on the topological valley-contrasting state generated by photonic crystals with opposing valley Chern numbers, manifested in a harpoon-shaped structure designed to steer the splitting channels. This approach enables adiabatic mode field evolution over large corners, capitalizing on the robust phase modulation capabilities and topological protection provided by the subwavelength-scale valley-contrasting state. Our demonstration reveals that beam splitters with large corners of 60°, 90°, and 120° exhibit insertion loss fluctuations below 2.7 dB while maintaining a minimal footprint of 8.8 µm × 8.8 µm. As a practical demonstration, these devices facilitate three-channel signal connections, successfully transmitting quadrature phase shift keying signals at 3.66 Tbit/s with bit error rates below the forward error correction threshold, demonstrating performance comparable to that in defects scenarios. By harnessing the unidirectional excitation feature, we anticipate significant enhancements in the capabilities of signal distribution and connection networks through a daisy chain configuration.

The atomic-to-molecular gas conversion is a critical step in the baryon cycle of galaxies, which sets the initial conditions for subsequent star formation and influences the multi-phase interstellar medium. We compiled a sample of 94 nearby galaxies with observations of multi-phase gas contents by utilizing public Hi, CO, and optical IFU data from the MaNGA survey together with new FAST Hi observations. In agreement with previous results, our sample shows that the global molecular-to-atomic gas ratio ((R_{text{mol}}equivtext{log} M_{rm{H}_{2}}/M_{rm{H}_{1}})) is correlated with the global stellar mass surface density μ_* with a Kendall’s τ coefficient of 0.25 and p < 10⁻³, less tightly but still correlated with stellar mass and NUV–r color, and not related to the specific star formation rate (sSFR). The cold gas distribution and kinematics inferred from the Hi and CO global profile asymmetry and shape do not significantly rely on R_mol. Thanks to the availability of kpc-scale observations of MaNGA, we decompose galaxies into Hii, composite, and AGN-dominated regions by using the BPT diagrams. With increasing R_mol, the fraction of Hii regions within 1.5 effective radius decreases slightly; the density distribution in the spatially resolved BPT diagram also changes significantly, suggesting changes in metallicity and ionization states. Galaxies with high R_mol tend to have high oxygen abundance, both at one effective radius with a Kendall’s τ coefficient of 0.37 (p < 10⁻³) and their central regions. Among all parameters investigated here, the oxygen abundance at one effective radius has the strongest relation with global R_mol. The dependence of gas conversion on gas distribution and galaxy ionization states is weak. In contrast, the observed positive relation between oxygen abundance (μ_*) and R_mol indicates that the gas conversion is efficient in regions of high metallicity (density).

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.