物理与天体物理最新文献

The Talbot effect describes the periodic revivals of field patterns, and is ubiquitous across wave systems. In optics, it is mostly known for its manifestations in space and time, but it is also observed in the wavevector and frequency spectra owing to the Fourier duality. Recently, the Talbot self-imaging has been shown separately in the azimuthal angle and orbital angular momentum (OAM) domains. Here we reveal the missing link between them and demonstrate the generalized angle–OAM Talbot effect. Versatile transformations of petal fields and OAM spectra are experimentally demonstrated, based on the synergy of angular Talbot phase modulation and light propagation in a ring-core fibre. Moreover, the generalized self-imaging concept leads to new realizations in mode sorting, which separate OAM modes in a modulo manner, theoretically free from any crosstalk within the congruence classes of OAM modes. We design and experimentally construct various mode sorters with excellent performance, and show the unconventional behaviour of Talbot-based sorters where neighbouring OAM modes can be mapped to positions that are far apart. Besides its fundamental interest, our work has applications in OAM-based information processing, and implies that the physical phenomena in time–frequency and angle–OAM domains are broadly connected and that their processing techniques may be borrowed interchangeably.

We analyse divergences of the scalar curvature R of the vector multiplet moduli space of type IIA string theory compactified on a Calabi-Yau X, along infinite-distance large volume limits. Extending previous results, we classify the origin of the divergence along trajectories which implement decompactifications to F-theory on X and/or emergent heterotic string limits. In all cases, the curvature divergence can be traced back to a 4d rigid field theory that decouples from gravity along the limit. This can be quantified via the asymptotic relation R ~ (Λ_WGC/Λ_sp)^2ν, with Λ_WGC ≡ g_rigidM_P and Λ_sp the species scale. In the UV, the 4d rigid field theory becomes a higher-dimensional, strongly-coupled rigid theory that also decouples from gravity. The nature of this UV theory is encoded in the exponent ν, and it either corresponds to a 5d SCFT, 6d SCFT or a Little String Theory.

The longitudinal electron transport in a multilayer superconducting structure SF₁S₁F₂sN, where S is a superconductor, F is a ferromagnet, s is a thin superconducting layer, and N is a normal metal, has been theoretically studied. Calculations have shown that the rotation of the magnetization of ferromagnetic layers relative to each other makes it possible to smoothly change the kinetic inductance of the structure by several times. A feature of the electronic state of the structure in the region of system parameters corresponding to its transition from a state with the 0 stable Josephson phase to a state with the π stable phase (0–π transition) has been discovered. This feature leads to the decrease in the singlet component of the pairing amplitude and to an increase in the kinetic inductance of the entire structure. The study of the effect of the finite longitudinal current on the charge transport has shown that the destruction of superconductivity in different layers occurs step-by-step, and the dependence of the kinetic inductance L_k on the total transport current J exhibits several plateaus with an almost constant inductance.

The hypergeometric amplitude is a one-parameter deformation of the Veneziano amplitude for four-point tachyon scattering in bosonic string theory that is consistent with S-matrix bootstrap constraints. In this article we construct a similar hypergeometric generalization of the Veneziano amplitude for type-I superstring theory. We then rule out a large region of the (r, m², D) parameter space as non-unitary, and establish another large subset of the (r, m², D) parameter space where all of the residue’s partial wave coefficients are positive. We also analyze positivity in various limits and special cases. As a corollary to our analysis, we are able to directly demonstrate positivity of a wider set of Veneziano amplitude partial wave coefficients than what has been presented elsewhere.

The thermodynamic stability and the magnetic and electronic properties of a new two-dimensional magnetic compound (Cr_1 − xFe_x)₃C₂ belonging to the MXen family have been analyzed using ab initio calculations and the cluster approximation. The most stable structure and magnetic configuration of (Cr_1 − xFe_x)₃C₂ have been proposed taking into account the functionalization of the surface with fluorine and oxygen. For the first time, a stable and promising ferrimagnetic MXene (Cr_1/3Fe_2/3)₃C₂ with a high magnetic moment per cell has been discovered, both in the pure form and with the fluorine-functionalized surface.