08 Fakultät Mathematik und Physik
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/9
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Item Open Access Exploring the growth of refractory metal and sapphire films by thermal laser epitaxy(2024) Majer, Lena N.; Mannhart, Jochen (Prof. Dr.)Item Open Access Self-organized structures and excitations in dipolar quantum fluids(2024) Hertkorn, Jens; Pfau, Tilman (Prof. Dr.)Quantum many-body phenomena at a macroscopic scale, such as superfluidity and superconductivity, are rooted in the interplay between microscopic particles, governed by the laws of quantum mechanics. Exploring how this interplay leads to quantum behavior at a large scale allows us to gain a deeper understanding of nature and to discover new quantum phases. An elusive quantum phase in which the frictionless flow of superfluids and the crystal structure of solids coexists - the supersolid - was recently realized with quantum droplets in dipolar Bose-Einstein condensates. In this thesis we investigate self-organized structures, their formation mechanism, and excitations in dipolar quantum fluids created from such Bose-Einstein condensates. We show that the supersolid formation mechanism is driven by density fluctuations due to low-energy roton excitations, leading to a crystal structure of quantum droplets that are immersed in a superfluid background. These roton excitations split into a Goldstone mode and a Higgs amplitude mode, associated to the broken translational symmetry in the supersolid. We investigate the symmetry breaking of dipolar quantum fluids in a range of confinement geometries and establish a comprehensive description of elementary excitations across the superfluid to supersolid droplet phase transition. The droplets are stabilized by an interplay between interactions and the presence of quantum fluctuations. We show how this interplay can be used to find regimes where droplets are immersed in a high superfluid background, allowing for frictionless flow throughout the crystal. Moreover we show that towards higher densities beyond the quantum droplet phase, this interplay leads to several new self-organized structures in the phase diagram of dipolar quantum fluids. We theoretically predict new supersolid honeycomb, amorphous labyrinth, and other phases in oblate dipolar quantum fluids. Finally, we present a new experimental setup for the exploration of self-organized phases in dipolar quantum fluids and which also lays the foundation for the implementation of a quantum gas microscope. The results of this thesis present a complete framework for understanding and creating exotic phases in dipolar quantum fluids. The versatile structure formation, governed by a competition of controllable interactions and the presence of quantum fluctuations, positions dipolar quantum fluids as a model system for exploring self-organized equilibrium in weakly-interacting quantum many-body systems.Item Open Access Nanoscale magnetic resonance spectroscopy with nitrogen-vacancy centers in diamond(2021) Paone, Domenico; Wrachtrup, Jörg (Prof. Dr.)Stickstoff-Fehlstellen (NV-Zentren) in Diamant bilden interessante Quantensysteme, welche für Quanten-Sensing Protokolle genutzt werden können. In der vorliegenden Arbeit, werden NV-Zentren genutzt, um einzelne Molekülsysteme auszulesen und supraleitende Proben lokal zu charakterisieren. Zusätzlich werden Methoden entwickelt, um die Spineigenschaften der NV-Zentren zu optimieren, welche dann Einfluss auf das Sensorikverhalten des Systems haben.Item Open Access Spin-orbit coupled states arising in the half-filled t2g shell(2023) Schönleber, MarcoStrongly correlated and spin-orbit coupled t2g systems have been extensively investigated. By coupling orbital and spin angular momentum into one quantity, spin-orbit coupling (SOC) tends to reduce orbital degeneracy, e.g. for the widely studied case of one hole in the t2g shell. However, the opposite has to be expected at half filling. Without spin-orbit coupling, all orbitals are half filled, no orbital degree of freedom is left and coupling to the lattice can be expected to be small. At dominant spin-orbit coupling, in contrast, one of the j=3/2 states is empty and the system couples to the lattice. We investigate this issue. One finding is that the low-energy manifold evolves smoothly from the four S=3/2 states in the absence of SOC to the four j=3/2 states with dominant SOC. These four states are always separated from other states by a robust gap. We then discuss a relevant superexchange mechanism to assess the interplay between spin-orbit coupling and coupling to the lattice.Item Open Access Quantum fluctuations in one-dimensional supersolids(2023) Bühler, Chris; Ilg, Tobias; Büchler, Hans PeterItem Open Access The role of dimensionality and geometry in quench-induced nonequilibrium forces(2021) Nejad, Mehrana Raeisian; Khalilian, Hamidreza; Rohwer, Christian M.; Moghaddam, Ali GhorbanzadehWe present an analytical formalism, supported by numerical simulations, for studying forces that act on curved walls following temperature quenches of the surrounding ideal Brownian fluid. We show that, for curved surfaces, the post-quench forces initially evolve rapidly to an extremal value, whereafter they approach their steady state value algebraically in time. In contrast to the previously-studied case of flat boundaries (lines or planes), the algebraic decay for curved geometries depends on the dimension of the system. Specifically, steady-state values of the force are approached in time as t-d/2 in d-dimensional spherical (curved) geometries. For systems consisting of concentric circles or spheres, the exponent does not change for the force on the outer circle or sphere. However, the force exerted on the inner circles or sphere experiences an overshoot and, as a result, does not evolve to the steady state in a simple algebraic manner. The extremal value of the force also depends on the dimension of the system, and originates from curved boundaries and the fact that particles inside a sphere or circle are locally more confined, and diffuse less freely than particles outside the circle or sphere.Item Open Access Long wave approximation over and beyond the natural time scale(2024) Hofbauer, Sarah; Schneider, Guido (Prof. Dr.)Item Open Access Polarized neutron reflectometry study of complex magnetism and hydrogen incorporation in thin-film structures(2022) Guasco, Laura; Keimer, Bernhard (Prof. Dr.)In this thesis, we present the study of the structural and magnetic properties of simple metals and complex oxide thin films by means of polarized neutron reflectometry. The nuclear and electronic properties of thin films were modified via two routes, namely via hydrogen incorporation, in the case of niobium systems and complex oxide layers, and via depth modulated hole doping, in the case of manganite heterostructures.Item Open Access Thermodynamic uncertainty relation for stochastic field theories : general formulation and application to the Kardar-Parisi-Zhang equation(2022) Niggemann, Oliver; Seifert, Udo (Prof. Dr.)Item Open Access Bell-state measurement exceeding 50% success probability with linear optics(2023) Bayerbach, Matthias J.; D’Aurelio, Simone E.; Loock, Peter van; Barz, Stefanie