title: Topological, non-topological and instanton droplets driven by spin-transfer torque in materials with perpendicular magnetic anisotropy and Dzyaloshinskii-Moriya Interaction.
abstract: The interfacial Dzyaloshinskii-Moriya Interaction can modify the topology of droplets excited by a localized spin-polarized current. Here, we show that, in addition to the stationary droplet excitations with skyrmion number either one (topological) or zero (non-topological), there exists, for a fixed current, an excited mode with a non-stationary time behavior. We call this mode "instanton droplet", which is characterized by time domain transitions of the skyrmion number. These transitions are coupled to an emission of incoherent spin-waves that can be observed in the frequency domain as a source of noise. Our results are interesting from a fundamental point of view to study spin-wave emissions due to a topological transition in current-driven systems, and could open the route for experiments based on magnetoresistance effect for the design of a further generation of nanoscale microwave oscillators.
authors.affiliation: Department of Electrical and Information Engineering, Politecnico di Bari, via E. Orabona 4, I-70125 Bari, Italy.
authors.forename: Mario
authors.initials: M
authors.lastname: Carpentieri
authors.affiliation: Department of Computer Science, Modelling, Electronics and System Science, University of Calabria, via P. Bucci 41C, I-87036, Rende (CS), Italy.
authors.forename: Riccardo
authors.initials: R
authors.lastname: Tomasello
authors.affiliation: Department of Electrical and Information Engineering, Politecnico di Bari, via E. Orabona 4, I-70125 Bari, Italy.|Department of Physics and Earth Sciences and CNISM Unit of Ferrara, University of Ferrara, Ferrara, via Saragat 1, I-44122, Ferrara, Italy.
authors.forename: Roberto
authors.initials: R
authors.lastname: Zivieri
authors.affiliation: Department of Electronic Engineering, Industrial Chemistry and Engineering, University of Messina, c.da di Dio, I-98166, Messina, Italy.
authors.forename: Giovanni
authors.initials: G
authors.lastname: Finocchio