Ph.D. Theses

Kesterite type materials are researched for their ability to form thin film solar cell absorbers from earth abundant and non-toxic elements. Main routes to increase their efficiencies to the level of competing materials include compositional variations such as deviations from stoichiometry and alloying. [...]

In the light of upcoming gravitational wave experiments like the Laser Interferometer SpaceAntenna (LISA) we aim to improve the understanding of early universe first-order phasetransitions.In this thesis, the central subject of study is the energy budget of phase transitions. Thisthermodynamic quantity can be studied microscopically in equilibrium finite temperaturequantum field theory. [...]

The first two decades of this century mark the beginning of the precision cosmologyand astrophysics era. Two remarkable cosmological results include the measurementsof the cosmic microwave background (CMB) anisotropies by the Planck satellite andof the baryonic acoustic oscillations (BAO) by the Sloan Digital Sky Survey. [...]

Conformal partial waves are fundamental objects in conformal field theory and their knowledge is a necessary prerequisite for the bootstrap programme. The study of partial waves is naturally a part of harmonic analysis on the conformal group. [...]

The upcoming generation of hard X-ray free-electron lasers (XFEL) delivers X-raypulses with unmatched brilliance at megahertz repetition rates based on supercon-ducting linear accelerators. The European XFEL, the first XFEL of this generation,accelerates bursts of up to 2700 electron bunches every tenth of a second over adistance of 1.7 km to energies as high as 17.5 GeV. [...]

This thesis deals with the impact of ultrashort near-infrared~(nIR) and extreme ultraviolet~(XUV) laser pulses on the magnetic multi-domain states of particularly thin Co/Pt multilayers. The laser induced magnetization dynamics are investigated with femtosecond time and nanometer spatial resolution utilizing time-resolved magnetic small-angle X-ray scattering~(TR-mSAXS) at the free-electron lasers~(FEL) FLASH in Hamburg and FERMI@Elettra in Trieste.One part of the thesis deals with ultrafast demagnetization in three different Co/Pt-multilayer samples with total film thicknesses in the range of the attenuation length of nIR radiation in Co and Pt. [...]

Free-electron lasers (FELs) are the fourth generation of synchrotron light sources operating in the ultraviolet and X-ray wavelength range. The large size and the high costs of such sources limit the handiness of them. [...]

Despite the great successes achieved by the Standard Model (SM) in explaining and predicting the behavior and existence of particles, multiple phenomena are yet to be given a satisfying explanation. Amongst these is Dark Matter (DM), a kind of matter that would permeate the whole Universe and that so far has been observed only via its gravitational interactions.One possible extension of the SM, which may contribute to solve the mystery of DM and/or explain some astrophysical anomalies, are Axion-Like Particles (ALPs). [...]

The results obtained at the LHC agree well with the predictions of the Standard Model of particle physics (SM). However, the need for Beyond the Standard Model (BSM) physics remains. [...]

This thesis describes general strategies to directly study the electrochemical Liquid Liquid Solid (ec-LLS) growth process using a suite of in-situ characterization techniques. The central goal of this work is to directly observe the ec-LLS process as it occurs to increase our understanding of the fundamental aspects of the technique.The first portion of this thesis details a general methodology for the study of electron beam stimulated ec-LLS nanowire growth via liquid cell transmission electron microscopy (LC-TEM). [...]