DESY NanoLab

The DESY NanoLab is a facility providing access to nano-characterization, nano-structuring and nano-synthesis techniques which are complementary to the advanced X-ray techniques available at DESY’s light sources. It comprises state-of-the art scanning probe microscopy and focused ion beam manufacturing, as well as surface sensitive spectroscopy techniques for chemical analysis. Specialized laboratory x-ray diffraction setups are available for a successful sample pre-characterization before the precious synchrotron beamtimes. Future upgrades will include as well characterization of magnetic properties

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

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

Connecting Fano interference and the Jaynes-Cummings model in cavity magnonics

We show that Fano interference can be realized in a macroscopic microwave cavity coupled to a spin ensemble at room temperature. Via a formalism developed from the linearized Jaynes-Cummings model of cavity electromagnonics, we show that generalized Fano interference emerges from the photon–magnon interaction at low cooperativity. In this regime, the reflectivity approximates the scattering cross-section derived from the Fano-Anderson model. Although asymmetric lineshapes in this system are often associated with the Fano formalism, we show that whilst Fano interference is actually present, an exact Fano form cannot be achieved from the linear Jaynes-Cummings model. In the Fano model an additional contribution arises, which is attributed to decoherence in other systems, and in this case is due to the resonant nature of the photonic mode. The formalism is experimentally verified and accounts for the asymmetric lineshapes arising from the interaction between magnon and photon channels. As the magnon–photon coupling strength is increased, these channels merge into hybridized magnon–photon modes and the generalized Fano interference picture breaks down. Our results are universally applicable to systems underlying the linearized Jaynes-Cummings Hamiltonian at low cooperativity and connect the microscopic parameters of the quantum optical model to generalized Fano lineshapes

Die Komplexität der Natur entschlüsseln

In der Materialforschung bricht ein neues Zeitalter an. Gekennzeichnet ist es durch die Suche nach einem tieferen Verständnis von komplexen, hierarchisch strukturierten oder ungeordneten Materialien. Solche Materialien spielen in der Natur, etwa in lebender Materie, eine zentrale Rolle, zunehmend aber auch in vielfältigen technischen Anwendungen. Ihre Erforschung erfordert abbildende Methoden, die alle Größenskalen von der Makro- bis zur Mikrowelt der Atome erfassen können. Ideal hierfür sind wenige Mikrometer feine Röntgenstrahlen mit einem hohen Anteil an kohärentem Licht. Dieses Röntgenlicht sollen zukünftige rein beugungsbegrenzte Synchrotron-Strahlungsquellen liefern. Mit dem Umbau des PETRA III-Speicherrings zu PETRA IV soll 2027 die weltweit leistungsfähigste Strahlungsquelle dieser Art in Betrieb gehen. Sie soll auch hochaufgelöste Einblicke in dynamische Prozesse, etwa chemische Reaktionen oder Phasenumwandlungen, ermöglichen

Atomic Resolution Incoherent Diffractive Imaging (IDI) via Intensity-IntensityCorrelations of Hard X-rays

The advent of accelerator-driven x-ray free-electron lasers has opened new avenues for high resolution structure determination via diffraction methods that go far beyond conventional x-ray crystallography methods. While these techniques rely on coherent scattering, incoherent processes like Compton scattering and fluorescence emission - the predominant scattering mechanism in the x-ray regime - are generally considered detrimental for imaging applications. Here we show that exploiting intensity correlations of incoherent x-ray fluorescence radiation allows one to image the full 3D structure of the fluorescing atoms with at least double the resolution of conventional crystallography measurements. We will study the application of this approach to image transition metal clusters in biologically relevant molecules like nitrogenases and dehydrogenases. Once successful, this method would eventually reveal hitherto unknown reaction steps in photosynthesis or nitrogen fixation that go along with subtle changes of the metal-cluster structure. The high-resolution determination of the metal atom positions will also assist phasing methods in macromolecular crystallography similar to anomalous dispersion methods. Incoherent diffractive imaging via fluorescence detection bears a number of properties that are conceptually superior to those of coherent methods