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- ItemDFG final project report: Lattice QCD investigation of a b-bar b-bar u d tetraquark resonance(Hannover : Technische Informationsbibliothek, 2025) Wagner, MarcQuarks typically appear in pairs, known as mesons, or in triplets, known as baryons, with protons and neutrons as well-known representatives of the latter. However, there are also exotic combinations of four quarks, known as tetraquarks, which have gained significant interest, particularly in recent years. This interest arises from the fact that they can be both detected in modern accelerator experiments and increasingly well understood and precisely predicted on a theoretical level with modern numerical calculations. The goal of this project was to study the existence and properties of specific tetraquark systems, consisting of two heavy antiquarks and two light quarks, based on first principles quantum chromodynamics, using numerical lattice field theory calculations. Investigating a $\bar b \bar b u d$ tetraquark resonance with quantum numbers $I(J^P) = 0(1^-)$ proved to be particularly challenging. Within the scope of this project, it was understood through the Born-Oppenheimer approximation that the tetraquark resonance is not located slightly above the lower $B B$ threshold, as previously expected, but considerably higher, above the $B^\ast B^\ast$ threshold. Final results with full lattice QCD calculations beyond the Born-Oppenheimer approximation have yet to be achieved, as this requires the numerical solution of a complex two-channel scattering problem involving a $B B$ and a $B^\ast B^\ast$ channel. However, essential technical steps for such a future computation have been implemented. For the two $\bar b \bar c u d$ tetraquark systems with quantum numbers $I(J^P) = 0(0^+)$ and $I(J^P) = 0(1^+)$, a rigorous finite-volume scattering analysis based on full lattice QCD computations was performed for the first time. This led to the prediction of a weakly bound but stable tetraquark for each of the two systems, as well as a tetraquark resonance approximately $100 \, \text{MeV}$ above the lowest meson-meson threshold ($B D$ or $B^\ast D$, respectively).
- ItemTopological transport control of colloidal particles(Hannover : Technische Informationsbibliothek, 2025) de las Heras, Daniel; Fischer, Thomas M.We have studied experimentally and with computer simulations the transport of magnetic particles on top of magnetic patterns. The motion is driven by either a modulation loop of the orientation of a uniform external magnetic field or by a drift force. The application of an adiabatic modulation loop of the direction of an external magnetic field to magnetic colloids or macroscopic magnetic particles on a periodic pattern offers unprecedented control over the motion and assembly of such colloids or particles. The motion is topologically protected since only those loops that wind around special orientations of the external field induce particle transport. The set of winding numbers around the special orientations is the topological invariant that protects the motion. The colloidal or macroscopic particles are sorted into topological classes and the transport of each class can be controlled independently and simultaneously with the other topological classes. The use of non-periodic patterns facilitates the transport of identical colloidal particles independently and simultaneously. The complexity of the loop can be imprinted in either the pattern or the modulation loop. In twisted magnetic patterns high mobility peaks of non-topologically driven particles emerge at non generic magic angles, but these mo- bility peaks in contrast to topologically driven systems are very fragile and can be easily destroyed via the analogue of an Anderson transition.
- ItemDFG final report for the Walter Benjamin Programme : Stationary and time-dependent radiative heat transfer with cylindrical waveguides(Hannover : Technische Informationsbibliothek, 2025) Asheichyk, KirylFollowing the progress in development of micro- and nanodevices, the physics of thermal radiation at these small length scales has been studied intensively in the current century. It requires more sophisticated theories and obeys different laws compared to radiative heat exchange at large scales, for example, between the Sun and the Earth. Yet main questions remain similar: How to improve the efficiency of radiative heat transfer, suppress or enhance the cooling rate of an object, thermally isolate a part of a system? Another important and only recently emerged research area concerns systems subject to nonstationary conditions, such as time-dependent temperatures or material properties of the objects, where the heat fluxes can depend on time and show fundamentally different properties compared to the stationary case. In this project, we addressed the aforementioned questions for the stationary heat transfer between two nanoparticles placed close to a nanowire or inside a cylindrical cavity. In the former case, the heat transfer was shown to decay logarithmically with the interparticle distance, thus greatly outperforming the transfer without an additional object or in the presence of objects of other shapes. In the latter case, a cylindrical cavity can largely suppress or resonantly enhance the heat flow, depending on its radius. If we consider that one particle starts to radiate at a certain time, the heat flux to another one is no longer stationary, which requires an extension of the existing theoretical formalisms. Making this extension, we derived a formula for the time-dependent flux, numerically demonstrating it for two isolated nanoparticles, where picosecond-scale oscillatory exponential relaxation to the stationary value was observed. In addition to the aforementioned studies of radiative heat flow through vacuum, we also developed a theory for computing this flow inside media, and derived the corresponding thermal conductivity tensor for an arbitrary object. In agreement with recent experiments, it was found that the radiative part of conductivity of a nanosheet can be larger compared to the phononic part due to the electromagnetic surface waves contribution. The developed theoretical frameworks can be used to further advance the subject area, while the found results may be relevant for practical applications, such as thermal microscopy, thermal logic, or nanomedicine.
- ItemBerechnung, Messung und Kontrolle der Energiebarrieren und der lichtinduzierten Kinetik des ASi-Sii-Defektes(Hannover : Technische Informationsbibliothek, 2025-04-09) Lauer, KevinDie Siliziumtechnologie hat umfangreiche Anwendungsmöglichkeiten, die sich im gegenwärtigen Alltag überall wiederfinden. Anwendungen wie Computer, Smartphones, Sensoren, Detektoren, Solarzellen und viele mehr sind nur möglich geworden durch jahrzehntelange Erforschung des Siliziums und der nötigen technologischen Prozesse. Nichtsdestotrotz gibt es noch immer unverstandene Phänomene und Mechanismen, speziell im Bereich der Defekte und der Degradation. Ein besseres Verständnis ist notwendig, da Defekte zum einen notwendig für die Funktionsweise von Bauelementen sind, sich aber auch negativ auswirken können. Das Projekt untersuchte eine besondere Kategorie von Defekten, die einen Akzeptor und interstitielles Silizium involvieren, so genannte ASi-Sii-Defekte. Sie tragen vermutlich maßgeblich zur licht-induzierten Degradation von Solarzellen und Detektorbauelemente bei. Konkret wurden in diesem Projekt die Energiebarrieren zwischen verschiedenen Defektzuständen der ASi-Sii-Defekte, die teilweise erst identifiziert werden mussten, in enger Zusammenarbeit von Experiment und Theorie erforscht und bestimmt. Die Barrierenhöhen haben einen direkten Einfluss auf die Defektkinetik und -stabilität, weshalb ihre Kenntnis essentiell ist. Gelingt es, die Barrierenhöhen gezielt zu beeinflussen (z.B. durch Wahl des Akzeptors), so können Bauelementeigenschaften ggf. gezielt eingestellt werden, z.B. zur Effizienzsteigerung oder Lebenszeitverlängerung von Solarzellen. Zudem erscheint es reizvoll künftig zu untersuchen, inwieweit Defekte aus dieser Kategorie als Qubit Verwendung finden können und somit für die Silizium-basierte Quantentechnologie interessant sind. Das Projekt hat erfolgreich einen Beitrag zum grundlegenden Verständnis der ASi-Sii-Defekte geleistet und legt den Grundstein für die weitere Erforschung dieser interessanten Defektkategorie.
- ItemCollaborative Research Center 917 : Resistively Switching Chalcogenides for Future Electronics : Structure, Kinetics, and Device Scalability : Final report : 2019/2-2020-2021-2022-2023/1(Hannover : Technische Informationsbibliothek, 2025-03-25) Wuttig, Matthias; Waser, Rainer; Dronskowski, Richard; Dittmann, Regina; Simon, Ulrich; Mayer, JoachimThe goal of SFB 917 has been the development of novel nanoswitches that can be reproducibly and reversibly changed between two states on very short time and length scales. Such nanoswitches can enable new storage and memory devices as well as neuro-inspired architectures for information technology. In the third and final funding period of SFB 917 we have witnessed and contributed to three major trends. The exponential growth in the demand for data storage and processing has continued. Hardware improvements are therefore urgently needed to meet the increased demands for data storage and processing as well as the related increase in energy consumption. SFB 917 strives to realize novel storage devices by exploiting the full potential of chalcogenide-based nanoswitches. Yet, it has become increasingly clear in the last few years, that improvements in device performance alone are insufficient to deal with the exponential growth mentioned above. The advance of Large Language Models (LLMs) like ChatGPT and related software has produced a further increase in data processing related energy consumption. This is a major challenge considering the expected further increase of professional and private usage of such machine learning tools. To minimize the related energy consumption, particularly energy-efficient software and hardware developments are mandatory. Within SFB9917, we have this intensified our efforts to work on effects related to a reduction in energy consumption. While energy-efficient devices can help, an improvement in hardware architecture offers significantly more leverage. We have thus explored the potential of chalcogenide based nano-switches in neuro-inspired computer architectures. To this end, several new large-scale research projects have been initiated (NeuroSys and NeuroTec), which extend our research on these devices in increasingly more complex architectures, offering new opportunities to harvest the findings of SFB 917 in new applications. To tailor chalcogenide-based nano-switches, major advances in instrumentation as well as an in-depth understanding of the origin of underlying phenomena and unconventional properties in these materials have been mandatory. Challenges included the characterization of switching in these materials on nanosecond time and nanometer length scales. Sophisticated tools have been built and utilized. Understanding unconventional properties are required building a bridge between concepts of inorganic chemistry and material properties leading to novel treasure maps which help to identify and tailor chalcogenides for specific applications. These successes are described in detail in the present report. To demonstrate that these findings are also relevant for industry, close cooperation with industrial partners has been established to ensure that the findings made within SFB 917 can also be implemented on the shortest possible time scales.