# Berlin 2018 – wissenschaftliches Programm

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# MA: Fachverband Magnetismus

## MA 21: Poster I

### MA 21.69: Poster

### Dienstag, 13. März 2018, 09:30–13:00, Poster A

**Real-time dynamics of the Kosterlitz-Thouless transition in a magnetic layer on a metallic system** — •Simon Michel and Michael Potthoff — I. Institut für Theoretische Physik, Universität Hamburg

A theoretical approach is developed to study the real-time dynamics of topological excitations of a two-dimensional anisotropic magnetic layer which is coupled to a metallic substrate. To this end, we solve the equations of motion for three-component classical spins on the square lattice which mutually interact via a direct in-plane exchange. In addition there is a local exchange coupling to the local magnetic moments of a system of noninteracting conduction electrons.

As a first step we consider the spin-subsystem only and study the vortex-unbinding Kosterlitz-Thouless transition in the equilibrium phase diagram. Within the real-time approach, this is done by starting from a random initial state, followed by a fictitious dissipative dynamics using a Gilbert damping term to generate a typical equilibrium state with given total energy. Thermodynamical expectation values are given as time averages. Here, we discuss the temperature dependence of the spin correlations, of the vortex density and of the average vortex-antivortex distance.

Eventually, our goal is to understand, on an atomic level, how to control topological excitations with the tip of a scanning-tunnelling microscope. In our model approach, this shall be done by computations of the real-time dynamics of the spin-electron hybrid system which is initiated by a strong local perturbation.