arXiv subjects

Clecio C. de Souza Silva

Publications and source records attributed to Clecio C. de Souza Silva.

4 recordsLinked to original sources

arXiv2025

Stability of (Active) Bilayer Skyrmions in Synthetic Antiferromagnets

Synthetic antiferromagnetic (SAF) skyrmions are nanoscale composite textures that exhibit high-speed, Hall-free current-driven motion and recently demonstrated self-propulsion. These remarkable properties rely on the stability of the SAF skyrmion's topological bound state, whose underlying mechanisms remain unclear. Here, using an atomistic spin model, we analyze the collapse pathways of bilayer SAF skyrmions in homochiral systems, where both ferromagnetic layers share the same Dzyaloshinskii-Moriya interaction (DMI) vectors, and in heterochiral systems, where the DMI vectors have opposite directions. We find that pair destruction occurs either by decoupling or by sequential collapse into the homogeneous antiferromagnetic state, so the activation energy is set by the smaller of these two barriers. By examining how these barriers vary with DMI strength, anisotropy, magnetic field, and interlayer exchange, we identify regimes of enhanced stability. In particular, increasing interlayer coupling strengthens homochiral skyrmions but weakens heterochiral ones, while reducing the anisotropy constant effectively stabilizes heterochiral SAF skyrmions. These results outline viable strategies to optimize SAF heterostructures for enhanced skyrmion stability in racetrack devices and emerging active skyrmionic systems.

cond-mat.mes-hall↗

arXiv2025

Emergent Self-propulsion of Skyrmionic Matter in Synthetic Antiferromagnets

Self-propulsion plays a crucial role in biological processes and nanorobotics, enabling small systems to move autonomously in noisy environments. Here, we theoretically demonstrate that a bound skyrmion-skyrmion pair in a synthetic antiferromagnetic bilayer can function as a self-propelled topological object, reaching speeds of up to a hundred million body lengths per second--far exceeding those of any known synthetic or biological self-propelled particles. The propulsion mechanism is triggered by the excitation of back-and-forth relative motion of the skyrmions, which generates nonreciprocal gyrotropic forces, driving the skyrmion pair in a direction perpendicular to their bond. Remarkably, thermal noise induces spontaneous reorientations of the pair and momentary reversals of the propulsion, mimicking behaviors observed in motile bacteria and microalgae.

cond-mat.soft↗

arXiv2012

Stability of fractional vortex states in a two-band mesoscopic superconductor

We investigate the stability of noncomposite fractional vortex states in a mesoscopic two-band superconductor within the two-component Ginzburg-Landau model. Our analysis explicitly takes into account the relationship between the model parameters and microscopic material parameters, such as partial density of states, fermi velocities and elements of the electron-phonon coupling matrix. We have found that states with different phase winding number in each band (L1 not equal to L2) and fractional flux can exist in many different configurations, including rather unconventional ones where the dominating band carries larger winding number and states where |L1-L2| > 1. We present a detailed analysis of the stability of the observed vortex structures with respect to changing the microscopic parameters, showing that, in the weak coupling case, fractional vortex states can be assessed in essentially the whole range of temperatures and applied magnetic fields in which both bands are active. Finally, we propose an efficient way of increasing the range of parameters for which these fractional vortex states can be stabilized. In particular, our proposal allows for observation of fractional vortex structures in materials with stronger coupling, where those states are forbidden at a homogeneous field. This is accomplished with the help of the stray fields of a suitably prepared magnetic dot placed nearby the superconducting disk.

cond-mat.supr-con↗

arXiv2005

Collective vortex rectification effects in films with a periodic pinning array

The vortex ratchet effect has been studied in Al films patterned with square arrays of submicron antidots. We have investigated the transport properties of two sets of samples: (i) asymmetrical antidots where vortices are driven by an unbiased ac current, and (ii) symmetrical antidots where in addition to the ac drive a dc bias was used. For each sample, the rectified (dc) voltage is measured as a function of drive amplitude and frequency, magnetic field, and temperature. As unambiguously shown by our data, the voltage rectification in the asymmetric antidots is induced by the intrinsic asymmetry in the pinning potential created by the antidots, whereas the rectification in the symmetric antidots is induced by the dc bias. In addition, the experiments reveal interesting collective phenomena in the vortex ratchet effect. At fields below the first matching field ($H_1$), the dc voltage--ac drive characteristics present two rectification peaks, which is interpreted as an interplay between the one-dimensional motion of weakly pinned incommensurate vortex rows and the two-dimensional motion of the whole vortex lattice. We also discuss the different dynamical regimes controlling the motion of interstitial and trapped vortices at fields slightly higher than $H_1$ and their implications for the vortex ratchet effect.

cond-mat.supr-con↗