ABSTRACT In this study, standard general relativity ( GR ) is modified for a non‐minimally linked bumblebee vector field that gets a nonzero vacuum prediction value in theories where the Lorentz symmetry of gravity is spontaneously disrupted. We study precise solutions in the context of bumblebee gravity that describe static, spherically symmetric charged black holes encircled by a string cloud. We examine the standard temperature, modified temperature and emission energy of this black hole solution under the Lorentz‐violating factors that modify conventional findings. We explore tunneling properties based on the semi‐classical approach, where the quantum gravity parameter is introduced into the conventional quantum tunneling probability using the WKB approximation under the generalized uncertainty principle ( GUP ). In order to provide possible observable indicators of Lorentz violation and investigate the photon sphere and black hole shadow under the impact of non‐magnetized plasma. Lastly, we investigate how Lorentz‐violating factors affect observational limitations. A framework to investigate novel physics beyond general relativity through the interaction between Lorentz violation, black hole physics, and a cloud of strings.
ABSTRACT Building on the recent work in [K. L. Tsakmakidis, et al., Nature Communications 16, 5719 (2025)], we analyze the therein introduced Pauli‐matrix first‐order formulation pertaining to the Engquist‐Majda one‐way wave problem. We show that the Pauli formulation provides a local doubled matrix factorization whose Hamiltonian is unitarily equivalent to a rotated Weyl Hamiltonian. Because the doubled system contains both longitudinal roots, exact recovery of one scalar one‐way branch requires a nonlocal spectral projector. For homogeneous Maxwell fields, the auxiliary branch space should be distinguished from the two‐dimensional physical polarization space, leading to a four‐component polarization‐preserving lift. Numerical snapshots illustrate one‐way directional propagation in the selected sector.
ABSTRACT Although the Zintl compound NaMgBi has been synthesized in the tetragonal PbFCl‐type phase, its accurate electronic structure is still unknown. This calculation is difficult because the conventional density functional theory (DFT) underestimates the bandgap, and the strong spin–orbit coupling (SOC) decreases the bandgap as well. Consequently, the usual DFT+SOC calculation predicts a false semimetallic band structure. Here, the GW approximation is used to calculate the accurate electronic structure of NaMgBi including the SOC. Our eigenvalue self‐consistent () results show that NaMgBi has a direct bandgap of 0.47 eV instead of an indirect one predicted by the DFT calculations neglecting the SOC. Although our calculations based on the results indicate that NaMgBi is trivial topologically, the solution of the Bethe–Salpeter equation shows that its exciton binding energy is 0.14 eV and the excitonic absorption coefficient can reach 10–10 in the infrared and visible light range, making it a promising optoelectronic material.
ABSTRACT The influences of a Ta buffer layer and film thickness on the perpendicular magnetic anisotropy (PMA) of Pt/Co 2 FeSi (CFS)/Pt multilayers was systematically investigated. Insertion of a Ta underlayer significantly improves interface quality and extends the CFS thickness window for strong PMA from 0.8–1.0 to 0.8–1.2 nm. The optimal PMA is achieved at a CFS thickness of 1.0 nm, yielding an effective anisotropy energy density (K e ff ) of 1.89 × 10 6 erg/cm 3 —a 56.1% enhancement over samples without the Ta layer. Further optimization of the Ta and Pt layer thicknesses to 8 nm and 16 nm, respectively, results in a pronounced increase in PMA, with K e ff reaching 3.86 × 10 6 erg/cm 3 . In asymmetric CFS (0.8 nm)/Pt/CFS (1.2 nm) trilayers, increasing the Pt spacer thickness above 3 nm drives a transition from ferromagnetic coupling to a magnetically decoupled state. Moreover, with increasing repetition number (n), the out‐of‐plane hysteresis loops develop a pinched character, indicating a crossover in the magnetization reversal mechanism from domain‐wall motion to nucleation‐dominated behavior. The identified correlations between interfacial structure, layer thickness, and magnetic anisotropy provide a rational design framework for Co 2 FeSi‐based perpendicular multilayer systems.
ABSTRACT The mathematician Sophie Germain identified the mean curvature as the essential quantity for describing the shapes of vibrating plates in the early nineteenth century. Her intuition that the elasticity of thin sheets was governed by geometry was a radical one at the time, as it was in opposition to the prevailing “molecular mentality.” In her correspondence with Gauss, she proposed a geometric measure that constructs a “sphere of mean curvature” at each point. Her hypothesis eventually led to the equations governing thin, elastic plates. Beyond elasticity, we now recognize the importance of this geometric measure in fluid dynamics, geometrical optics, biophysics, and materials science. Despite her pioneering contributions, Germain has not been fully credited for recognizing the mathematical and physical significance of mean curvature.
