Dipolar wavevector interference induces a polar skyrmion lattice in strained BiFeO3 films
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Current-induced motion of nanoscale magnetic torons over the wide range of the Hall angle
Current-driven dynamics of topological spin textures plays a pivotal role in potential applications for electronic devices. While two-dimensional magnetic skyrmions have garnered significant interest, their practical use is hindered by the skyrmion Hall effect—a transverse motion to the current direction that occurs as a counteraction to the topological Hall effect of electrons arising from the Berry phase effect. Here, we explore current-driven dynamics of three-dimensional topological spin textures, magnetic torons, composed of layered skyrmions with two singularities called Bloch points at their ends. Through extensive numerical simulations, we show that torons exhibit a unique Hall motion ranging from the zero Hall effect, a purely longitudinal motion, to the perfect Hall effect, a purely transverse motion accompanied by no longitudinal motion. Such flexible and controllable behaviors stem from anisotropic potential barriers on the discrete lattice for nanoscale torons. Our results provide a method to probe the topology of three-dimensional magnetic textures and contribute to advanced topological spintronics beyond the realm of skyrmions.
Stiff, lightweight, and programmable architectured pyrolytic carbon lattices via modular assembling
Recent advances in additive manufacturing have enabled the creation of three-dimensional (3D) architectured pyrolytic carbon (PyC) structures with ultrahigh specific strength and energy absorption capabilities. However, their scalability is limited by reduced strength at larger sizes. Here we introduce a modular assembling approach to scale up PyC lattice structures while retaining strength. Three assembling mechanisms—adhesive, Lego-adhesive, and mechanical interlocking—are explored, demonstrating notably increased specific compressive strength and modulus as size increases, driven by energy release from assembly joint fractures. Practical application is demonstrated by using assembled PyC lattices as the core of an aerospace sandwich structure, significantly enhancing indentation resistance compared to conventional aramid paper honeycomb core. The method also enables versatile designs, including curved structures for space debris protection and bio-scaffold applications. This scalable approach offers a promising pathway for integrating PyC structures into large-scale engineering applications requiring superior mechanical properties and programmability in complicated shape design.
Controlling the wavefront aberration of a large-aperture and high-precision holographic diffraction grating
The scanning interference field exposure technique is an effective method to fabricate holographic diffraction grating with meter-level size and nano-level precision. The main problems of fabricating large-aperture and high-precision grating by this technique are the high-precision displacement measurement of the stage, the high-precision control of the interference fringe and the real time compensation of the grating phase error. In this paper, the influence of grating groove error on the wavefront aberration is analyzed. In order to improve the precision of the stage with displacement range more than one meter, an integrated displacement measurement combining grating sensing and laser interferometry is proposed, which suppresses the influence of environment on measurement precision under long displacement range. An interference fringe measurement method is proposed, which combines the diffraction characteristics of the measuring grating with the phase-shifting algorithm. By controlling the direction, period and phase nonlinear errors of the interference fringe, high quality interference fringe can be obtained. Further, a dynamic phase-locking model is established by using heterodyne interferometry to compensate grating phase error caused by stage motion error in real time. A grating with the aperture of 1500 mm × 420 mm is fabricated. The wavefront aberration reaches 0.327λ @ 632.8 nm and the wavefront gradient reaches 16.444 nm/cm. This research presents a novel technique for the fabrication of meter-level size and nano-level precision holographic grating, which would further promote the development of chirped pulse amplification systems, high-energy laser and ultra-high precision displacement measurement.
Improving the thermoelectric performance of scandium nitride thin films by implanting helium ions
Ion implantation is a widely used technique to introduce defects in low-dimensional materials and tune their properties. Here, we investigate the thermoelectric properties of scandium nitride thin films implanted with helium ions, revealing a positive impact of defect engineering on thermoelectric performance. Transport properties modeling and electron microscopy provide insights on the defect distribution in the films. The electrical resistivity and Seebeck coefficient increase significantly in absolute values after implantation and partially recover upon annealing as some of the implantation-induced defects heal. The thermal conductivity decreases by 46 % post- implantation due to the formation of extended defects and nanocavities. Consequently, the thermoelectric figure of merit zT doubles for the sample annealed at 673 K. These findings highlight the potential of controlled ion implantation to enhance thermoelectric properties in thin films, paving the way for further optimization through defect engineering.
Ultrafast exciton-phonon coupling and energy transfer dynamics in quasi-2D layered Ruddlesden-Popper perovskites
Understanding the performance of perovskite solar cells is critical for advancing sustainable energy solutions. Hot-drop casted quasi-2D Ruddlesden-Popper perovskites (RPPs) exhibit remarkable efficiency and stability, making them promising for commercial applications. However, the ultrafast energy transfer and exciton-phonon interactions in these materials remain unclear. Here, we show that using advanced techniques like two-dimensional electronic spectroscopy (2DES) and transient grating (TG), we can unravel energy dynamics in hot-drop casted RPP films. Our study reveals rapid energy transfer between perovskite layers occurring within 100–220 femtoseconds and highlights how exciton-phonon coupling drives structural changes in the material. Coherent vibrational signals identify key lattice and organic cation modes, providing insights into their role in energy dissipation. These findings deepen our understanding of how 2D perovskites work and pave the way for improving the efficiency and stability of next-generation optoelectronic devices.
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