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TY - THES AU - Ortmanns, Lara Celine TI - From 2d-van der Waals magnets to superconductor hybrid devices VL - 5348 PB - RWTH Aachen University VL - Dissertation CY - Aachen M1 - RWTH-2023-06360 SN - 978-91-7905-882-1 T2 - Doktorsavhandlingar vid Chalmers tekniska högskola SP - 1 Online-Ressource : Illustrationen, Diagramme PY - 2023 N1 - Druckausgabe: 2023. - Auch veröffentlicht auf dem Publikationsserver der RWTH Aachen University. - Cotutelle-Dissertation N1 - Dissertation, RWTH Aachen University, 2023. - Dissertation, Chalmers University of Technology Göteburg, 2023 AB - In this thesis, we focus on two distinct topics in different lines of research within mesoscopic physics, the first is related to spin-waves in 2d-van der Waals magnets, the second to the transient dynamics of a quantum dot device attached to a normal metal and proximized with a superconducting material. Based on our earlier work on the magnon dispersion in bilayers of 2d-ferromagnets, in this thesis we complement the earlier work by further analyzing the competing interactions in the Hamiltonian. Moreover, we explain the magnon dispersion degeneracy and the topology of the magnon spectrum in terms of an underlying PT-symmetry. As a result, we can exclude a magnon (thermal) Hall effect for our type of exchange anisotropy spin model, but indicate extensions of our model that would allow for non-trivial topological effects. The analysis of this first topic amounts to a study of equilibrium properties of 2d bulk materials, which exhibit magnetic order. The relevant excitations of interest are magnons, which are bosons. Differently, for the second topic we deal with the transient dynamics of a quantum dot device after a switch in gate voltage, where instead of magnetic order we have superconducting order in the lead attached, which induces a pronounced proximity effect on the sensitive quantum dot. The main degrees of freedom here are fermions. In our limit of interest, we do not resolve coherences in the description of the dynamics and determine the kernel of the time-evolution operator based on Fermi’s Golden rule and the electrostatics of the device. In spite of this simplification, we show that it is still advantageous to formulate the traditional approach in Liouville space to study the transient dynamics instead of the stationary state. In the large gap limit, we make use of a dissipative symmetry, termed fermionic duality, that refers to a generalized hermiticity relation of the time-evolution kernel. The duality leads to non-trivial relations between the quantities that determine the state and transport evolution. It is then the duality that further facilitates the analysis, as the transient behavior of the quantum dot can be understood in great detail in terms of stationary quantities of the real and dual system. In particular the heat current is an interesting transport observable, as it probes the interplay of Coulomb interaction and superconducting pairing. Based on a microscopic understanding of the underlying processes, we describe how to control the charge and heat currents in these NDS-devices by a suitable choice of the parameters. We give outlooks to further extensions of our approach to quantum dots attached to two superconductors, which promise interesting physics both from a theoretical and experimental perspective. LB - PUB:(DE-HGF)11 ; PUB:(DE-HGF)3 DO - DOI:10.18154/RWTH-2023-06360 UR - https://publications.rwth-aachen.de/record/960727 ER -