RESUMO
Solomon rings, upholding the symbol of wisdom with profound historical roots, were widely used as decorations in ancient architecture and clothing. However, it was only recently discovered that such topological structures can be formed by self-organization in biological/chemical molecules, liquid crystals, etc. Here, we report the observation of polar Solomon rings in a ferroelectric nanocrystal, which consist of two intertwined vortices and are mathematically equivalent to a [Formula: see text] link in topology. By combining piezoresponse force microscopy observations and phase-field simulations, we demonstrate the reversible switching between polar Solomon rings and vertex textures by an electric field. The two types of topological polar textures exhibit distinct absorption of terahertz infrared waves, which can be exploited in infrared displays with a nanoscale resolution. Our study establishes, both experimentally and computationally, the existence and electrical manipulation of polar Solomon rings, a new form of topological polar structures that may provide a simple way for fast, robust, and high-resolution optoelectronic devices.
RESUMO
Stimuli-responsive micro/nanostructures that can dynamically and reversibly adapt their configurations according to external stimuli have stimulated a wide scope of engineering applications, ranging from material surface engineering to micromanipulations. However, it remains a challenge to achieve a precise local control of the actuation to realize applications that require heterogeneous and on-demand responses. Here, a new experimental technique is developed for large arrays of hybrid magnetic micropillars and achieve precise local control of actuation using a simple magnetic field. By manipulating the spatial distribution of magnetic nanoparticles within individual elastomer micropillars, a wide range of the magnetomechanical responses from less than 5% to ≈50% for the ratio of the bending deflection to the original length of the pillars is realized. It is demonstrated that the micropillars with different degrees of bending deformation can be configured in any spatial pattern using a photomask-assisted template-casting technique to achieve heterogeneous, site-specific, and programmed bending actuations. This unprecedented local control of the micropillars offers exciting novel applications, as demonstrated here in encryptable surface printing and stamping, direction- and track-programmable microparticle/droplet transport, and smart magnetic micro-tweezers. The hybrid magnetic micropillars reported here provide a versatile prototype for heterogeneous and on-demand actuation using programmable stimuli-responsive micro/nanostructures.
RESUMO
Time-dependent Ginzburg-Landau equations were solved by the finite difference scheme for a superconducting sample in steady and oscillating magnetic fields for 3D geometry. The dynamic behaviour of penetrating and leaving magnetic vortices in superconductor with the oscillating magnetic field was simulated. Carrier concentration density and the average magnetization of the sample were studied as a function of the external oscillating magnetic field. Anomalies in carrier concentrations at certain magnetic field values were observed and discussed. It was also observed that the area swept by magnetization versus external magnetic field is magnetic oscillation frequency dependent, which increases with increasing frequencies. It was suggested that this effect may cause instability in the superconducting characteristics of the sample over a number of cycles. Calculated energy patterns showed consistency with vortex patterns in the steady magnetic field. Magnetic oscillations initiated oscillations in energy components, ripples in superconducting energy are subjected to the entrance and leaving of vortices, while instability observed in interaction energy is referred to vortex relaxation time.
