Berlin 2015 – scientific programme

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MA: Fachverband Magnetismus

MA 43: Magnetization / Demagnetization Dynamics III

MA 43.6: Talk

Thursday, March 19, 2015, 11:00–11:15, EB 301

Gilbert damping from nonperturbative partial summation — •David Vincent Altwein, Elena Y. Vedmedenko, and Roland Wiesendanger — University of Hamburg, Hamburg, Germany

We devise an exact way to recover the concept of Rayleigh-dissipation from the framework of quantum field theory (QFT) which is illustrated for magnetization dynamics. Initially, an effective hamiltonian for a subsystem is obtained by employing the inequivalent sets of canonical operators, generated by the system-bath-interactions, causing vacuum polarization which gives rise to a geometric expansion in a complexe quantity. The latter’s imaginary part is intimately connected to the irreducible polarization and self-energy operators of the problem and appears as a damping parameter which contains nonperturbative information. Remarkably, we obtain the Landau-Lifshitz-Gilbert-Equation with its correct scaling of the gyromagnetic ratio γ, stemming directly from the renormalization of charge e and mass m of the problem whilst lowest order perturbation theory in the interaction strength was used to derive the Landau-Lifshitz-Equation microscopically. Conceptually, our approach shares certain similarities with the known truncation schemes, employed in the QFT framework for dissipation and it uses a smaller set of assumptions than many popular system-bath-approaches in the literature.