Fluctuations and Pinning for Individually Manipulated Skyrmions

We numerically examine the dynamics of individually dragged skyrmions interacting simultaneously with an array of other skyrmions and quenched disorder. For drives just above depinning, we observe a broadband noise signal with a 1/f characteristic, while at higher drives, narrowband or white noise appears. Even in the absence of quenched disorder, the threshold force that must be applied to translate the driven skyrmion is finite due to elastic interactions with other skyrmions. The depinning threshold increases as the strength of the quenched disorder is raised. Above the depinning force, the skyrmion moves faster in the presence of quenched disorder than in a disorder-free system since the pinning sites prevent other skyrmions from being dragged along with the driven skyrmion. For strong pinning, we find a stick-slip motion of the driven skyrmion which produces a telegraph noise signature. The depinning threshold increases monotonically with skyrmion density in the absence of quenched disorder, but when pinning is present, the depinning threshold changes nonmonotonically with skyrmion density, and there are reentrant pinned phases due to a competition between pinning induced by the quenched disorder and that produced by the elastic interactions of the skyrmion lattice.

The Effect of Hyperbolic Two-temperatures Model on Waves Propagation in a Semi-conductor Medium Containing Spherical Cavities

This article is interested in the study of the carrier density, the redial displacement, the conductive temperature, thermodynamic temperature and the stresses in a semi-conductor material containing a spherical hole. This investigation deals with the photo-thermo-elastic interactions in a semi-conductor medium in the context of the new hyperbolic two-temperatures model with one relaxation time. The Laplace transform technique are used to obtain the problem analytical solution by the eigenvalues methods and the inversions of the Laplace transform were performed numerically. Numerical results for semi-conductor materials are shown graphically and discussed.

Adhesive Wear Regimes on Rough Surfaces and Interaction of Micro-contacts

We develop an analytical model of adhesive wear between two unlubricated rough surfaces, forming micro-contacts under normal load. The model is based on an energy balance and a crack initiation criteria. We apply the model to the problem of self-affine rough surfaces under normal load, which we solve using the boundary element method. We discuss how self-affinity of the surface roughness, and the complex morphology of the micro-contacts that emerge for a given contact pressure, challenge the definition of contact junctions. Indeed, in the context of adhesive wear, we show that elastic interactions between nearby micro-contacts can lead to wear particles whose volumes enclose the convex hull of these micro-contacts. We thereby obtain a wear map describing the instantaneous produced wear volume as a function of material properties, roughness parameters and loading conditions. Three distinct wear regimes can be identified in the wear map. In particular, the model predicts the emergence of a severe wear regime above a critical contact pressure, when interactions between micro-contacts are favored.

Addressing single spin crossover molecules in a two-dimensional monolayer

Bistable spin-crossover molecules are particularly interesting to the development of innovative electronic and spintronic devices as they present two spin states that can be controlled by external stimuli. In this purpose, being able to switch at will the spin state of a single molecule in a dense molecular array is a key milestone. However, the elastic interactions between the molecules favour more cooperative behaviour where patches of neighbouring molecules switches simultaneously. We demonstrate here that the interaction of iron II spin-crossover molecules with a metallic substrate can strongly reduce their cooperative behaviour until addressing independently single molecular spin state. Mechanoelastic model is able to reproduce well such findings.

Novel Soliton Molecules and Wave Interactions for A (3+1)-Dimensional Nonlinear Evolutionary Equation

New wave excitations are revealed for a (3+1)-dimensional nonlinear evolution equation to enrich nonlinear wave patterns in nonlinear systems. Based on a new variable separation solution with two arbitrary variable separated functions obtained by means of the multilinear variable separation approach, localized excitations of N dromions, N x M lump lattice and N x M ring soliton lattice are explored. Interestingly, it is observed that soliton molecules can be composed of diverse "atoms" such as the dromions, lumps and ring solitons, respectively. Elastic interactions between solitons and soliton molecules are graphically demonstrated.

Directing the far-from-equilibrium assembly of nanoparticles in confined liquid crystals by hydrodynamic fields

The assembly of nematic colloids relies on long-range elastic interactions that can be manipulated through external stimuli.