Dresden 2017 – scientific programme

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MA: Fachverband Magnetismus

MA 16: Spin Dynamics: Magnetic relaxation and Gilbert Damping

MA 16.4: Talk

Monday, March 20, 2017, 18:15–18:30, HSZ 401

Relaxation of a classical spin coupled to a strongly correlated electron system — •Mohammad Sayad, Roman Rausch, and Michael Potthoff — I. Institut für Theoretische Physik, Universität Hamburg

Electron correlations are expected to have qualitatively new effects on the spin dynamics. Up to now, this has been studied only indirectly by computing the effect of the Coulomb interaction on the Gilbert damping. Here, we investigate correlation effects beyond an LLG-type approach. To this end, we consider a prototypical model with a classical spin which is anti-ferromagnetically exchange coupled to a Hubbard system and study the spin dynamics as a function of the local Coulomb interaction U. To address this quantum-classical hybrid problem, we propose a combination of a non-Markovian linear-response theory for the spin dynamics with time-dependent density-matrix renormalization group for the correlated electron system. In the metallic phase at quarter filling, we find two different channels for energy and spin dissipation, namely dissipation via correlated hopping and via excitations of local magnetic moments. For strong U, these become active on largely different time scales. While the overwhelming contribution to the Gilbert damping is due to magnetic excitations in the strong-U limit, the magnetic contribution is much smaller in general and even vanishes for infinite U as it is never activated. At half-filling and strong U, electron correlations lead to an incomplete spin relaxation on intermediate time scales. This represents a novel effect in a quantum-classical hybrid model which is similar to prethermalization.