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TT: Fachverband Tiefe Temperaturen

TT 53: Poster Session: Superconductivity 1

TT 53.22: Poster

Mittwoch, 22. März 2017, 15:00–19:00, P2-OG2

Kinetics of quasiparticles in conventional superconductors beyond mean field — •Frank Lengers, Peter Kettmann, Simon Hannibal, and Tilmann Kuhn — Institut für Festkörpertheorie, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Str. 10, 48149 Münster

Nonequilibrium dynamics of superconductors offer a versatile tool for understanding the underlying many particle interactions. Conventional superconductors can be excited into the nonadiabatic regime by THz pulses to study the Higgs mode in those materials. Theoretical modelling of those processes is typically done on the mean field level. Here we present a quantum kinetic treatment of the well-known BCS-model for conventional superconductors beyond the mean field approximation. We treat the quasiparticle correlations as independent variables in a density-matrix formalism by truncating the quantum mechanical BBGKY hierarchy at certain order. It is shown that the well-known mean field equations of motion are recovered at the lowest truncation level. The dynamics of a conventional superconductor after excitation into the nonadiabatic regime is modelled by a sudden quench of the coupling parameter of the BCS-model. Thereby we study the Higgs mode in a conventional superconductor and compare the results to the mean field case. In a second part we introduce semiclassical equations of motion. We observe that the resulting changes due to the extension of the model compared to the mean field case are rather small. Yet relaxation and dephasing behaviour of quasiparticles and coherences can be observed.