Resources for and from Research, Teaching and Studying
Recent Submissions
In this work, we are searching for supersymmetric extensions of the Standard Model (SM) of particle physics which are asymptotically safe. Such models are well-defined at all energy scales and provide hints for the scale at which supersymmetry gets broken. The combination of supersymmetry and asymptotic safety hereby turns out to strongly restrict the space of possible models. Within extensions of the minimal supersymmetric SM (MSSM), we perturbatively find candidates which all have a specifi...
The successful implementation of nanoscale materials in next generation optoelectronic devices crucially depends on our ability to functionalize and design low dimensional materials according to the desired field of application. Recently, organic adsorbates have revealed an enormous potential to alter the occupied surface band structure of tunable materials by the formation of tailored molecule-surface bonds. Here, we extend this concept of adsorption-induced surface band structure engineerin...
Organic photovoltaic devices operate by absorbing light and generating current. These two processes are governed by the optical and transport properties of the organic semiconductor. Despite their common microscopic origin—the electronic structure—disclosing their dynamical interplay is far from trivial. Here we address this issue by time-resolved photoemission to directly investigate the correlation between the optical and transport response in organic materials. We reveal that optical gener...
The discovery and realization of graphene as an ideal two-dimensional (2D) material has triggered extensive efforts to create similar 2D materials with exciting spin-dependent properties. Here, we report on a novel Sn 2D superstructure on Au(111) that shows similarities and differences to the expected electronic features of ideal stanene. Using spin- and angle-resolved photoemission spectroscopy, we find that a particular Sn/Au superstructure reveals a linearly dispersing band centered at the ...
The quantification of the electronic transport energy gap of a molecular semiconductor is essential for pursuing any challenge in molecular optoelectronics. However, this remains largely elusive because of the difficulties in its determination by conventional spectroscopic methods. This communication presents an in-device molecular spectroscopy (i-MOS) technique, which permits measuring this gap seamlessly, in real device operative conditions, at room temperature and without any previous know...
Marcus’s theory of electron transfer, initially formulated six decades ago for redox reactionsin solution, is now of great importance for very diverse scientific communities. The molecularscale tunability of electronic properties renders organic semiconductor materials in principlean ideal platform to test this theory. However, the demonstration of charge transfer indifferent Marcus regions requires a precise control over the driving force acting on the chargecarriers. Here, we make use of a ...
Colloidal particles suspended in liquid crystals can exhibit various effective anisotropic interactions that can be tuned and utilized in self-assembly processes. We simulate a two-dimensional system of hard disks suspended in a solution of dense hard needles as a model system for colloids suspended in a nematic lyotropic liquid crystal. The novel event-chain Monte Carlo technique enables us to directly measure colloidal interactions in a microscopic simulation with explicit liquid crystal pa...
We investigate the nonlinear optical response of a thin film of ion-implanted VO2 nanocrystals with open aperture z-scans involving femtosecond near-infrared pulses. Beyond the established nonlinearity related to the insulator-metal phase transition of VO2, the metallic state features a pronounced saturable absorption for 100 fs pulses from a modelocked Yb:fiber source at = 1036 nm. In contrast, we find a pronounced reverse saturable absorption for 90 fs pulses in the telecom window at...
The individual monitoring service at the Materialprüfungsamt North Rhine-Westphalia and the TU Dortmund are developing the compact dosemeter system TL-DOS based on thin-layer thermoluminescence detectors as well as an associated glow curve analysis tool. Various dosemeters of the system measure different dose quantities and types of radiation. This thesis focuses on the TL-DOS neutron dosemeter to measure the whole body dose. The system is optimized in terms of LiF:Mg,Ti detectors, an albedo...
Modern computer processors are nowadays approaching limits due to their quantum limitations. The basic principle of modern electronics is measuring a small electrical charge of electrons passing through electronic circuits. An alternative approach based on novel materials could be the solution, which instead relies on the fundamental quantum- mechanical property – spin. The fundamental requirements that apply to a device based on quantum spin qubits include the ability to scale a quantum syst...
High energy gamma-ray astronomy probes the most extreme phenomena in our universe: super novae and their remnants as well as supermassive black holes at the center of far away galaxies. The First G-APD Cherenkov Telescope (FACT) is a small, prototype Imaging Air Cherenkov Telescope (IACT) operating since 2011 at the Roque de los Muchachos, La Palma, Spain. It specializes in continuously monitoring the brightest known sources of gamma rays. In this thesis, I present a new, open analysis c...
Quantum computers have the potential to speed up certain problems that are hard for classical computers. Hybrid systems, such as the nitrogen vacancy (NV) center in diamond, are among the most promising systems to implement quantum computing, provided the control of the different types of qubits can be efficiently implemented. In the case of the NV center, the anisotropic hyperfine interaction allows one to control the nuclear spins indirectly, through gate operations targeting the elect...
The combination of magnetic resonance with laser spectroscopy provides some interesting options for increasing the sensitivity and information content of magnetic resonance. This review covers the basic physics behind the relevant processes, such as angular momentum conservation during absorption and emission. This can be used to enhance the polarization of the spin system by orders of magnitude compared to thermal polarisation as well as for detection with sensitivities down to the level of ...
In the mitotic spindle microtubules attach to kinetochores via catch bonds during metaphase, and microtubule depolymerization forces give rise to stochastic chromosome oscillations. We investigate the cooperative stochastic microtubule dynamics in spindle models consisting of ensembles of parallel microtubules, which attach to a kinetochore via elastic linkers. We include the dynamic instability of microtubules and forces on microtubules and kinetochores from elastic linkers. A one-sided mode...
Electron paramagnetic resonance (EPR) is a spectroscopic technique to study the interaction between free electrons and the local molecular environment. Over the past 60 years, EPR instrumentation and methodology has been developed to study, for example, the structure and dynamics of proteins, chemical reactions of organic-based radicals, transition-metal chemistry, catalytic reactions, electron transfer processes, and metalloenzymes. Because of these past developments, EPR has become a p...
Die Frage nach dem Verhalten magnetischer Störstellen in Materialien bei tiefen Temperaturen ist aktueller als je zuvor bedingt durch den Schritt hin zu Nanotechnologie und Spintronik. Im ersten Teil dieser Arbeit befassen wir uns mit Störstellen in Graphen motiviert durch experimentelle Arbeiten. Die angesprochenen Störstellen entstehen, wenn einzelne Kohlenstoffatome aus der Gitterstruktur gelöst werden. Wir fassen zusammen, wie in solchen Defekten magnetische Momente entstehen, und,...
Hybrid quantum registers, such as electron-nuclear spin systems, have emerged as promising hardware for implementing quantum information and computing protocols in scalable systems. Nevertheless, the coherent control of such systems still faces challenges. Particularly, the lower gyromagnetic ratios of the nuclear spins cause them to respond slowly to control fields, resulting in gate times that are generally longer than the coherence time of the electron. Here, we demonstrate a scheme for ci...
Initializing quantum registers with high fidelity is a fundamental precondition for many applications like quantum information processing and sensing. The electronic and nuclear spins of a Nitrogen-Vacancy (NV) center in diamond form an interesting hybrid quantum register that can be initialized by a combination of laser, microwave, and radio-frequency pulses. However, the laser illumination, which is necessary for achieving electron spin polarization, also has the unwanted sideeffect of depo...
Synchrotron radiation sources have become an essential part of modern science. The ongoing development to reach higher performance levels with improved quality of synchrotron light demands upgrades of current synchrotron radiation facilities or even construction of new accelerators. During this process, new challenges, both technological and in the accelerator physics, need to be addressed to achieve a higher light quality in terms of brightness, coherence, pulse duration, etc. This includes ...
This thesis investigates the variation of signal transmission in topological phases as well as their robustness in one- and two-dimensional systems. For this purpose, multiple approaches in different systems are pursued. First, the possibility of designed modifications at the boundaries is explored in order to change the Fermi velocity at edge states of topological phases. The Fermi velocity as a quantity of the transport behavior describes the speed of signal transmission. The main ide...