Böcker i Springer Theses-serien

By projecting first to 13 and then 15 m HgCdTe growth, values of fundamental properties of the material that would minimize tunneling dark currents were determined through careful modeling of the dark current-reverse bias voltage curves, as well as the dark current-temperature curves.

This thesis demonstrates the potential of two platforms to explore experimentally the emerging field of quantum thermodynamics that has remained mostly theoretical so far.

This book addresses the development of both DNA-sequence-selective and DNA-form-selective ligands, with the aim of creating potential molecular probes and therapeutic agents for non-canonical DNA structure-caused human diseases.

This book explores efficient syntheses of indole alkaloids based on gold-catalyzed cascade cyclizations, presenting two strategies for total synthesis of these natural products based on gold-catalyzed reactions of conjugated diyne or ynamide.

This work presents some essential techniques that constitute the modern strategy for computing scattering amplitudes. It begins with an introductory chapter to fill the gap between a standard QFT course and the latest developments in the field. The author then tackles the main bottleneck: the computation of the loop Feynman integrals. The most efficient technique for their computation is the method of the differential equations. This is discussed in detail, with a particular focus on the mathematical aspects involved in the derivation of the differential equations and their solution. Ample space is devoted to the special functions arising from the differential equations, to their analytic properties, and to the mathematical techniques which allow us to handle them systematically.  The thesis also addresses the application of these techniques to a cutting-edge problem of importance for the physics programme of the Large Hadron Collider: five-particle amplitudes at two-loop order. It presents the first analytic results for complete two-loop five-particle amplitudes, in supersymmetric theories and QCD. The techniques discussed here open the door to precision phenomenology for processes of phenomenological interest, such as three-photon, three-jet, and di-photon + jet production.

Non-collinear spin textures have attracted significant attention due to their topological nature, emergent electromagnetic properties, and potential spintronic and magnonic device applications. This book explores the physical properties of distinct spin textures in D2d compounds. The main goals of the work are (a) discovering new spin textures in D2d Heusler compounds and studying their detailed properties to enrich the field of non-collinear magnetism (b) optimizing the nano-track geometry and generating isolated and single chains of nano-objects that will establish new hallmarks for technological applications (c) studying the stability of spin textures with magnetic fields and temperatures and finding a way to observe the striking behavior of spin textures near the specimen edges. The first few chapters provide a brief overview of spin textures such as Bloch and Neel skyrmions. In the experimental methods section, the author shows how to identify the single-crystalline grains of a polycrystalline sample, how to make single-crystalline thin specimens and nano-tracks, and then provides explicit descriptions of different imaging techniques performed on a transmission electron microscope. This part will be valuable for beginners wishing to conduct research in experimental nano-magnetism and transmission electron microscope imaging. The core results of the book are presented in four chapters, describing the discovery of several new and unanticipated spin textures, namely square-shaped antiskyrmions, elliptical Bloch skyrmions, fractional antiskyrmions, fractional Bloch skyrmions and elongated (anti)skyrmions in a single D2d Heusler compound. It is shown that these textures can be understood by a combination of dipole-dipole interactions and a chiral vector exchange that makes it possible to stabilize various spin textures even in the same compound. The D2d compounds are the first non-centrosymmetric systems shown to host several co-existing non-collinear spin textures.

The structure of quantum theory permits interference of indistinguishable paths. At the same time, however, it also limits such interference to certain orders and any higher-order interference is prohibited. This thesis develops and studies concepts to test quantum theory with higher-order interference using many-particle correlations, the latter being generally richer and typically more subtle than single-particle correlations. It is demonstrated that quantum theory in general allows for interference up to order 2M in M-particle correlations. Depending on the mutual coherence of the particles, however, the related interference hierarchy can terminate earlier. In this thesis, we show that mutually coherent particles can exhibit interference of the highest orders allowed. We further demonstrate that interference of mutually incoherent particles truncates already at order M+1, although interference of the latter is principally more multifaceted than their coherent counterpart. We introduce two families of many-particle Sorkin parameters, whose members are expected to be all zero when quantum mechanics holds. As proof of concept, we demonstrate the disparate vanishing of such higher-order interference terms as a function of coherence in experiments with mutually coherent and incoherent sources. Finally, we investigate the influence of exotic kinked or looped quantum paths, which are permitted by Feynman's path integral approach, in such setups.

The thesis presents a systematic study of the Mpemba effect in a colloidal system with a micron-sized particle diffusing in a water bath. While the Mpemba effect, where a system's thermal relaxation time is a non-monotonic function of the initial temperature, has been observed in water since Aristotle's era, the underlying mechanism of the effect is still unknown. Recent studies indicate that the effect is not limited to water and has been studied both experimentally and numerically in a wide variety of systems. By carefully designing a double-well potential using feedback-based optical tweezers, the author demonstrates that an initially hot system can sometimes cool faster than an initially warm system. The author also presents the first observation in any system of another counterintuitive effect-the inverse Mpemba effect-where the colder of the two samples reaches the thermal equilibrium at a hot temperature first. The results for both the observations agree with theoretical predictions based on the Fokker-Planck equation. The experiments reveal that, for carefully chosen conditions, a strong version of both of the effects are observed where a system can relax to the bath temperature exponentially faster than under typical conditions.

This thesis explores the physics of non-equilibrium quantum dynamics in homogeneous two-dimensional (2D) quantum gases. Ultracold quantum gases driven out of equilibrium have been prominent platforms for studying quantum many-body physics. However, probing non-equilibrium dynamics in conventionally trapped, inhomogeneous atomic quantum gases has been a challenging task because coexisting mass transport and spreading of quantum correlations often complicate experimental analyses. In this work, the author solves this technical hurdle by producing ultracold cesium atoms in a quasi-2D optical box potential. The exquisite optical trap allows one to remove density inhomogeneity in a degenerate quantum gas and control its dimensionality. The author also details the development of a high-resolution, in situ imaging technique to monitor the evolution of collective excitations and quantum transport down to atomic shot-noise, and at the length scale of elementary collective excitations. Meanwhile, tunable Feshbach resonances in ultracold cesium atoms permit precise and dynamical control of interactions with high temporal and even spatial resolutions. By employing these state-of-the-art techniques, the author performed interaction quenches to control the generation and evolution of quasiparticles in quantum gases, presenting the first direct measurement of quantum entanglement between interaction quench generated quasiparticle pairs in an atomic superfluid. Quenching to attractive interactions, this work shows stimulated emission of quasiparticles, leading to amplified density waves and fragmentation, forming 2D matter-wave Townes solitons that were previously considered impossible to form in equilibrium due to their instability. This thesis unveils a set of scale-invariant and universal quench dynamics and provides unprecedented tools to explore quantum entanglement transport in a homogenous quantum gas.

This work systematically investigates the use of high-quality (high-Q) resonators as coding particles of chipless cooperative radar targets to overcome clutter. Due to their high-Q, the backscattered signature can outlast clutter and permit reliable readouts in dynamic environments as well as its integration in other types of cooperative radar targets for joint identification, sensing, and ranging capabilities.This is first demonstrated with temperature and pressure sensors in the microwave frequency range, which include the characterization of a novel temperature sensor for machine tool monitoring up to 400 (deg)C, as well as inside the machine. Afterwards, the thesis proposes and demonstrates the use of metallic as well as dielectric Electromagnetic BandGap (EBG) structures to enable the realization and to enhance the capabilities at mm-Wave and THz frequencies compared to microwave frequencies with compact monolithic multi-resonator cooperative radar targets. Furthermore, this work studies the integration of resonators as coding particles inside larger retroreflective configurations such as Luneburg lenses to achieve long-range and high accuracy for localization and, at the same time, frequency coding robust against clutter for identification. Finally, the successful readout of these cooperative radar targets is demonstrated in cluttered dynamic environments, as well as with readers based on Frequency-Modulated Continuous-Wave (FMCW) radars.

This thesis describes in-depth studies of the remarkable electronic transport within the ultrahigh conductivity delafossite metals PtCoO_2 and PdCoO_2 using the tool of focused ion beam (FIB) microstucturing. Despite being first synthesised over 50 years ago, important questions remain regarding both the origin of the unusually high conductivity of these compounds and the consequences of their unique properties for unconventional electronic transport, such as that within the ballistic regime. The thesis explores both these areas.High-energy electron irradiation is used to examine the effects of deliberately introducing point defects into PdCoO_2 and PtCoO_2, demonstrating that the extremely low resistivity of these materials stems from an extreme purity as high as 1 defect in 120,000 atoms, rather than a novel scattering suppression mechanism. In addition, studies of the electronic transport in micron-scale squares of these metals show that their broadly hexagonal Fermi surfaces lead not only to long range ballistic behaviour but novel ballistic regime phenomena which cannot be observed in materials with a higher-symmetry Fermi surface.

This book presents a comprehensive study covering the design and application of models and algorithms for assessing the joint device failures of telecommunication backbone networks caused by large-scale regional disasters. At first, failure models are developed to make use of the best data available; in turn, a set of fast algorithms for determining the resulting failure lists are described; further, a theoretical analysis of the complexity of the algorithms and the properties of the failure lists is presented, and relevant practical case studies are investigated. Merging concepts and tools from complexity theory, combinatorial and computational geometry, and probability theory, a comprehensive set of models is developed for translating the disaster hazard in informative yet concise data structures. The information available on the network topology and the disaster hazard is then used to calculate the possible (probabilistic) network failures. The resulting sets of resources that are expected to break down simultaneously are modeled as a collection of Shared Risk Link Groups (SRLGs), or Probabilistic SRLGs. Overall, this book presents improved theoretical methods that can help predicting disaster-caused network malfunctions, identifying vulnerable regions, and assessing precisely the availability of internet services, among other applications.

The thesis contains several pioneering results at the intersection of state-of-the-art materials characterization techniques and machine learning. The use of machine learning empowers the information extraction capability of neutron and photon spectroscopies. In particular, new knowledge and new physics insights to aid spectroscopic analysis may hold great promise for next-generation quantum technology. As a prominent example, the so-called proximity effect at topological material interfaces promises to enable spintronics without energy dissipation and quantum computing with fault tolerance, yet the characteristic spectral features to identify the proximity effect have long been elusive. The work presented within permits a fine resolution of its spectroscopic features and a determination of the proximity effect which could aid further experiments with improved interpretability. A few novel machine learning architectures are proposed in this thesis work which leverage the case when the data is scarce and utilize the internal symmetry of the system to improve the training quality. The work sheds light on future pathways to apply machine learning to augment experiments.

This book describes a detailed multi-scale approach integrating nano- (active site), meso- (porous catalyst architecture) and macroscale (reactor) efforts, to address the challenges of producing a better epoxidation catalyst. It contains an in-depth study of the design and synthesis of gold nanoparticles and their application as a catalyst for direct gas phase propylene epoxidation. "e;Direct"e; means using only hydrogen and oxygen in one step, which is key for sustainable manufacturing, as opposed to commercialised, more complex production routes requiring multiple steps, or integration with another chemical plant. The insights gained can be used for rational design for stable and selective catalysts for other reactions. It also details the step-by-step process to build an epoxidation reactor system with a focus on safety aspects, which can be used as a guidebook for undergraduate and graduate students in chemical engineering. Beyond heterogeneous catalysis, the new, easily accomplished methodology for synthesising atomically precise nanoparticles is shown to be relevant to electrocatalysis and to healthcare applications, such as anti-microbial surfaces.This book will be of interest to researchers, engineers and experts in the related areas of chemical engineering, chemistry, material science and electrochemistry.

This thesis investigates the detection efficiency of field-resolved measurements of ultrashort mid-infrared waves via electro-optic sampling for the first time. Employing high-power gate pulses and phase-matched upconversion in thick nonlinear crystals, unprecedented efficiencies are achieved for octave-spanning fields in this wavelength range. In combination with state-of-the art, high-power, ultrashort mid-infrared sources, this allows to demonstrate a new regime of linear detection dynamic range for field strengths from mV/cm to MV/cm-levels. These results crucially contribute to the development of field-resolved spectrometers for early disease detection, as fundamental vibrational modes of (bio-)molecules lie in the investigated spectral range.The results are discussed and compared with previous sensitivity records for electric-field measurements and reference is made to related implementations of the described characterization technique. Including a detailed theoretical description and simulation results, the work elucidates crucial scaling laws, characteristics and limitations. The thesis will thus serve as an educational introduction to the topic of field-resolved measurements using electro-optic sampling, giving detailed instructions on simulations and experimental implementations. At the same time, it showcases the state-of-the-art in terms of detection sensitivity for characterizing mid-infrared waves.

This book presents an innovative methodology to fabricate nanostructured piezoelectric composite fibers with wearable technologies application as an energy generator and/or sensors. It reports on methods of piezoelectric fiber formation and development of novel textile structures (weave, knit, braid, coil) with embedded electrodes. The flexibility and small diameter of the final fiber make it possible to use them in garment without affecting structure of comfort. The performance of the fiber generators was evaluated through different applications such as air and water sensor, health and movement monitoring, and energy generator. The book targets a wide readership including materials scientists, electrical engineering, soft robotics, Internet of things, electronic textiles, and wearable technology.

This thesis presents significant new observations of nuclear wobbling, and thus expands our understanding of nuclear triaxiality and its prevalence in the nuclear chart. Triaxial nuclear shapes are a very rare phenomena and their experimental identification often relies on two unique signatures - nuclear wobbling motion and chiral rotation. While nuclear chirality is a well-studied phenomenon, experimental observations of wobbling nuclei are rather limited. With the identification of 135Pr and 187Au as wobblers, this work establishes triaxiality to be a general phenomenon present in different regions of the nuclear chart, irrespective of any particular spin or deformation. A major focus of this work is the detailed investigation of the different kinds of wobbling modes. Depending on the geometry of the nuclear system, wobbling can be classified into two types - longitudinal and transverse. This work has, for the first time, reported evidence of the possible coexistence of both forms of wobbling in a single nucleus. Another important result reported in this work is the very first observation of co-existing chiral and wobbling modes in the 135Pr nucleus. This thesis details the experimental methods that led to this breakthrough, along with pertinent theoretical interpretations.

This thesis outlines the principles, device physics, and technological applications of electronics based on the ultra-wide bandgap semiconductor aluminum nitride. It discusses the basic principles of electrostatics and transport properties of polarization-induced two-dimensional electron and hole channels in semiconductor heterostructures based on aluminum nitride. It explains the discovery of high-density two-dimensional hole gases in undoped heterojunctions, and shows how these high conductivity n- and p-type channels are used for high performance nFETs and pFETs, along with wide bandgap RF, mm-wave, and CMOS applications. The thesis goes on to discuss how the several material advantages of aluminum nitride, such as its high thermal conductivity and piezoelectric coefficient, enable not just high performance of transistors, but also monolithic integration of passive elements such as high frequency filters, enabling a new form factor for integrated RF electronics.

This book presents novel observational evidence toward detecting and characterizing the products of massive, interacting binary stars. As a majority of massive stars are born in close binary systems, a large number of so-called massive binary interaction products are predicted to exist; however, few have been identified so far. Based on observations with the largest telescopes around the world, equipped with state-of-the-art instrumentation, this book helps to remedy this situation. In her outstanding PhD-thesis Julia Bodensteiner identifies a new class of post-interaction binaries in a short-lived phase just briefly after the initially more massive star has been stripped of part of its envelope. She further provides new evidence for the Be phenomenon to largely result from binary interactions. These results represented a new and testable prediction for the evolution of these stars and opened up a new way forward for identifying hundreds of post-interaction products.Finally, using the MUSE integral field spectrograph at the Very Large Telescope in Chile, the author presents a novel spectroscopic campaign focusing on the 40 Myr-old star cluster NGC 330 in the Small Magellanic Clouds. Combined with photometric observations from the Hubble Space Telescope, the MUSE data allow to characterize the entire massive star population of NGC 330, revealing their multiplicity properties and rotational velocities and providing unique observational constraints on their (binary) evolution history. This is made possible by the developments of novel numerical methods allowing to extract star spectra from the MUSE integral field spectroscopic data and to characterize their properties by the simultaneous comparison of MUSE spectroscopy and Hubble photometry with atmospheric models.This book is a partly re-written version of the author's thesis offering a highly readable coherent text presenting not only new insights into the properties of binary interaction products but also giving students an excellent introduction into the field.

This thesis addresses the feasibility of the production of ultra-high-energy cosmic rays in starburst galaxies and active galactic nuclei. These astrophysical objects were theoretically proposed as candidate sources a long time ago. Nevertheless, the interest in them has been recently renewed due to the observational data collected by the Pierre Auger Observatory and the Telescope Array. In this work, a comprehensive review of the current status of the research on cosmic rays accelerators is provided, along with a summary of the principal concepts needed to connect these relativistic particles with electromagnetic and neutrino observations in the multi-messenger era. On one hand, the hypothesis of accelerating particles with energies above 10' eV in starburst superwinds is carefully revisited, taking into account the constraints imposed by the most recent electromagnetic observations. On the other hand, an alternative new model for the gamma emission of the nearby active galaxy NGC 1068 is presented. The implications of the results of these studies are discussed in terms of the contemporary observatories and prospects for future experiments are offered.

This thesis makes significant advances towards an understanding of superconductivity in the cuprate family of unconventional, high-temperature superconductors. Even though the high-temperature superconductors were discovered over 35 years ago, there is not yet a general consensus on an acceptable theory of superconductivity in these materials. One of the early proposals suggested that collective magnetic excitations of the conduction electrons could lead them to form pairs, which in turn condense to form the superconducting state at a critical temperature Tc. Quantitative calculations of Tc using experimental data were, however, not available to verify the applicability of this magnetic mechanism. In this thesis, the author constructed an angle-resolved photoemission apparatus that could provide sufficiently accurate data of the electronic excitation spectra of samples in the normal state, data which was furthermore unusually devoid of any surface contamination. The author also applied the Bethe-Salpeter method to his uncommonly pristine and precise normal state data, and was able to predict the approximate superconducting transition temperatures of different samples. This rare combination of experiment with sophisticated theoretical calculations leads to the conclusion that antiferromagnetic correlations are a viable candidate for the pairing interaction in the cuprate superconductors.

This PhD thesis reports on investigations of several oxide-based materials using advanced infrared and Raman spectroscopy techniques and in combination with external stimuli such as high magnetic or electric field, sptial confinement in thin film heterostructures and the radiation with UV light. This leads to new results in the fields of superconductivity, electronic polarization states and nanoscale phenomena.Among these, the observation of anomalous polar moments is of great relevance for understanding the electric-field-induced metal-to-insulator transistion; and the demonstration that confocal Raman spectroscopy of backfolded acoustic photons in metal-oxide multilayers  can be used as a powerful characterization tool for monitoring their interface properties and layer thickness is an important technical development for the engineering of such functional oxide heterostructures. 

This thesis provides the first atomic length-scale observation of the structural transformation (referred to as lattice reconstruction) that occurs in moire superlattices of twisted bilayer transition metal dichalcogenides (TMDs) at low (I < 2Es) twist angles. Such information is essential for the fundamental understanding of how manipulating the rotational twist-angle between two adjacent 2-dimensional crystals subsequently affects their optical and electrical properties.Studies using Scanning transmission electron microscopy (STEM), a powerful tool for atomic-scale imaging, were limited due to the complexity of the (atomically-thin) sample fabrication requirements. This work developed a unique way to selectively cut and re-stack monolayers of TMDs with a controlled rotational twist angle which could then be easily suspended on a TEM grid to meet the needs of the atomically thin sample requirements. The fabrication technique enabled the study of the two common stacking-polytypes including 3R and 2H (using MoS2 and WS2 as the example) as well as their structural evolution with decreasing twist-angle.Atomic-scale studies were followed by a comprehensive investigation of their electronic properties using scanning probe microscopy and electrical transport measurements of the artificially-engineered structures. The electronic structure of two common stacking-polytypes (3R and 2H) were strikingly different, as revealed by conductive atomic force microscopy. Further studies focused on the 3R-stacking polytype to reveal room-temperature out-of-plane ferroelectricity using tools such as kelvin probe force microscopy, scanning electron microscopy and electrical transport measurements. This work highlights that the unique intrinsic properties of TMDs (i.e. semiconductors with strongly light-matter interaction) combined with the additional twisted degree-of-freedom has great potential to create atomically thin transistors/LEDs with built-in memory storage functions and will further aid in the development of the next generation of optoelectronics.

This book presents the latest theoretical studies giving new predictions and interpretations on the quantum correlation in molecular dynamics induced by ultrashort laser pulses. The author quantifies the amount of correlation in terms of entanglement by employing methods developed in quantum information science, in particular applied to the photoionization of a hydrogen molecule. It is also revealed that the photoelectron-ion correlation affects the vibrational dynamics of the molecular ion and induces the attosecond-level time delay in the molecular vibration. Furthermore, the book also presents how molecular vibration can couple to photons in a plasmoic nanocavity.Physicists and chemists interested in the ultrafast molecular dynamics would be the most relevant readers. They can learn how we can employ the quantum-information-science tools to understand the correlation in the molecular dynamics and why we should consider the correlation between the photoelectron and the molecular ion to describe the ion's dynamics. They can also learn how to treat a molecule coupled to photons in a nanocavity. All the topics are related to the state-of-the-art experiments, and so, it is important to publish these results to enhance the understanding and to induce new experiments to confirm the theory presented. 

This book presents experimental studies on emergent transport and magneto-optical properties in three-dimensional topological insulators with two-dimensional Dirac fermions on their surfaces. Designing magnetic heterostructures utilizing a cutting-edge growth technique (molecular beam epitaxy) stabilizes and manifests new quantization phenomena, as confirmed by low-temperature electrical transport and time-domain terahertz magneto-optical measurements. Starting with a review of the theoretical background and recent experimental advances in topological insulators in terms of a novel magneto-electric coupling, the author subsequently explores their magnetic quantum properties and reveals topological phase transitions between quantum anomalous Hall insulator and trivial insulator phases; a new topological phase (the axion insulator); and a half-integer quantum Hall state associated with the quantum parity anomaly. Furthermore, the author shows how these quantum phases can be significantly stabilized via magnetic modulation doping and proximity coupling with a normal ferromagnetic insulator. These findings provide a basis for future technologies such as ultra-low energy consumption electronic devices and fault-tolerant topological quantum computers.