ISBN 9783843944748

978-3-8439-4474-8, Reihe Physik

Jakob Gollwitzer
Magnon-Photon Interactions: From X-ray Mapping of Standing Spin Waves to Fano Interference in Cavity Electromagnonics

150 Seiten, Dissertation Universität Hamburg (2020), Softcover, A5

Zusammenfassung / Abstract

This thesis describes two types of light-matter interactions in magnetic thin films. In the first part, it focuses on the resonant interaction of hard X-rays with 57Fe nuclei in a microstructured magnetic element. Specifically, the resonant nuclear scattering from 57Fe nuclei is used to investigate the spatial dependence of magnetization dynamics in a thin, microstructured magnetic stripe. We develop a quasi incoherent scattering model that allows spatial resolution of a standing spin wave profile in this stripe. These results open up new perspectives for depth dependent investigations of laterally varying dynamic spin structures via nuclear resonant scattering.

In the second part of this thesis, the focus moves from light as a spatial probe of the magnetization to the interaction of a photonic cavity mode with the Kittel mode of a magnetic thin film. This change of role occurs in the framework of the novel field of cavity electromagnonics, which utilizes a quantum optical model to describe coupled microwave photon-magnon systems. Here, we extend this model to show that a generalized form of Fano interference emerges from the photonic cavity mode interacting with the Kittel mode at low coupling strengths. This is confirmed experimentally by coupling the Kittel mode of a permalloy film to a microwave cavity in the Purcell regime. In addition, we demonstrate that the developed generalized Fano form reveals a coherent contribution representing interference between the magnon and photon channels and an incoherent contribution due to mode coupling. Finally, we show that a Fano phase picture describes well how generalized Fano interference between the magnonic and photonic systems gives way to mode hybridization as the coupling strength increases. These results offer a new perspective on magnon photon coupling and relate the observed reflectivity lineshapes to the quantum optical model of cavity electromagnonics in a physically meaningful way.