Berlin 2018 – scientific programme

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MA: Fachverband Magnetismus

MA 52: Poster II

MA 52.14: Poster

Thursday, March 15, 2018, 15:00–18:00, Poster C

Relaxation of a classical spin coupled to a conventional superconductor — •Cassian Plorin and Michael Potthoff — I. Institut für Theoretische Physik, Universität Hamburg

The effect of a superconducting substrate on the real-time dynamics of the local magnetic moment of an adatom is investigated numerically within a variant of the s-d exchange model. To this end, we solve the equations of motion for a classical spin, which is exchange-coupled to the local magnetic moment of a conduction-electron system. The electron system is given as a negative-U Hubbard model and treated by a mean-field decoupling. Its real-time dynamics is governed by a von-Neumann-type equation for the normal and for the anomalous blocks of the one-particle reduced density matrix.

We study the time dependence of the classical spin, of the electron spin density and of the local s-wave order parameter after a sudden flip of the direction of a magnetic field coupling to the spin. The spin relaxation and the alignment to the new field direction is found to be strongly U-dependent. Incomplete relaxation is observed when the superconducting gap exceeds a certain value. This effect is beyond a Landau-Lifschitz-Gilbert-type approach but can be understood on the level of linear-response theory in the exchange coupling. The feedback of the spin dynamics on the superconducting order parameter, however, is beyond linear-response theory.