Chenglong Hu | Searcharxiv

arXiv2025

Passive scalar dispersion along porous stratum with natural convection

We investigate horizontal dispersion of a passive scalar in a porous stratum with Rayleigh-Darcy convection initiated by a geothermal gradient. While increasing Rayleigh number ($Ra$) keeps enhancing convection, the horizontal dispersion coefficient ($\hat{D}$) only scales with Ra in a narrow range, and saturates at $Ra \gtrsim 2500$. We rationalize this two-stage behavior: at low Ra, passive scalar migrates through bulk circumflex; at high Ra, boundary micro-plume layer becomes the dominant scalar pathway. Theory gives saturate $\hat{D}$ value proportional to the Lewis number $Le$ and molecular diffusivity $D_0$.

physics.flu-dyn↗

arXiv2023

Controllable Creation of Skyrmion Bags in a Ferromagnetic Nanodisk

Skyrmion bags are composed of an outer skyrmion and arbitrary inner skyrmions, which have recently been observed in bulk chiral magnets, but still remain elusive in magnetic films. Here, we propose a method of creating skyrmion bags in a thin-film nanodisk, which includes three steps. Firstly, the size of outer skyrmion is enlarged by a vertical magnetic field, then inner skyrmions are nucleated at an off-center area by local current injection, and the system is finally reconstructed due to multiple inter-skyrmion potentials. Thus, skyrmion bags with topological charge up to forty can be created. Simulated Lorentz transmission electron microscopy images are given to facilitate the experimental demonstration. Our proposal is expected to inspire relevant experiments in magnetic films, and pave the way for potential spintronic applications based on skyrmion bags.

cond-mat.mes-hall↗