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 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 Real-space spectroscopy of interacting quasiparticles in exotic semimetals(2022) He, Qingyu; Takagi, Hidenori (Prof. Dr.)Item Open Access High quality graphene for magnetic sensing(2022) Herlinger, Patrick; Smet, Jurgen (Dr.)In this thesis, we investigated the reliable fabrication of high quality graphene and its use as Hall transducer material. Charged impurities and random strain fluctuations were identified as main culprits that deteriorate the electrical properties of graphene devices. It was shown that these extrinsic sources of disorder can be reduced through optimized device processing steps as well as the use of a proper substrate material for graphene such as hexagonal boron nitride (hBN). This insulating material is atomically flat and possesses a very low intrinsic density of charged impurities. By performing Raman spectroscopy and electrical transport measurements, both without and with applied magnetic field, on a large number of different types of graphene devices, it was demonstrated that the encapsulation of graphene between hexagonal boron nitride thin films is the best way to obtain high quality graphene devices. However, even for these hBN-encapsulated devices, we still observed a notable sample-to-sample variation of the electrical properties. Therefore, we developed a post-processing technique that allows us to improve the electrical properties of such devices both significantly and reliably. Since our technique is applied after device fabrication, we could also demonstrate its beneficial effect by comparing one and the same device before and after treatment. We then assessed the application of such high quality graphene as Hall transducer material. The dependencies on and between all relevant operating parameters were explored. This allowed us to develop a deep understanding and empirical model for graphene Hall elements, including the interplay between thermal and 1/f noise in these devices. All key performance indicators for Hall sensors were measured and their typical values reported. For comparable device dimensions, hBN-encapsulated graphene Hall elements were found to have the potential to become a strong competitor to existing materials that are used in today's commercial Hall sensors. Unfortunately, the large-scale fabrication of hBN thin films still remains an unresolved challenge for the industrialization of large area, high quality graphene Hall elements. Also, the Si CMOS integration demands further development. Even though the application of graphene in Hall devices is promising, as shown in this work, this use case alone does likely not justify the significant efforts and investments we expect to be necessary to industrialize the fabrication of high quality graphene devices. Instead, these efforts and costs must be shared by developing a common technology platform for 2D materials that can address several commercially attractive applications where graphene or another 2D material offers superior performance as well. We hope that the insights provided in this work can help to accelerate this process.Item Open Access Heterodyne sensing of microwaves with a quantum sensor(2021) Meinel, Jonas; Vorobyov, Vadim; Yavkin, Boris; Dasari, Durga; Sumiya, Hitoshi; Onoda, Shinobu; Isoya, Junichi; Wrachtrup, JörgDiamond quantum sensors are sensitive to weak microwave magnetic fields resonant to the spin transitions. However, the spectral resolution in such protocols is ultimately limited by the sensor lifetime. Here, we demonstrate a heterodyne detection method for microwaves (MW) leading to a lifetime independent spectral resolution in the GHz range. We reference the MW signal to a local oscillator by generating the initial superposition state from a coherent source. Experimentally, we achieve a spectral resolution below 1 Hz for a 4 GHz signal far below the sensor lifetime limit of kilohertz. Furthermore, we show control over the interaction of the MW-field with the two-level system by applying dressing fields, pulsed Mollow absorption and Floquet dynamics under strong longitudinal radio frequency drive. While pulsed Mollow absorption leads to improved sensitivity, the Floquet dynamics allow robust control, independent from the system’s resonance frequency. Our work is important for future studies in sensing weak microwave signals in a wide frequency range with high spectral resolution.Item Open Access High space‐bandwidth‐product (SBP) hologram carriers toward photorealistic 3D holography(2024) Li, Jin; Li, Xiaoxun; Huang, Xiangyu; Kaissner, Robin; Neubrech, Frank; Sun, Shuo; Liu, Na3D holography capable of reproducing all necessary visual cues is considered the most promising route to present photorealistic 3D images. Three elements involving computer‐generated hologram (CGH) algorithms, hologram carriers, and optical systems are prerequisites to create high‐quality holographic displays for photorealistic 3D holography. Especially, the hologram carrier directly determines the holographic display capability and the design of high space‐bandwidth‐product (SBP) optical systems. Currently, two categories of hologram carriers, i.e., spatial light modulators (SLM) and metasurfaces, are regarded as promising candidates for photorealistic 3D holography. However, most of their SBP capability still cannot match the amount of information generated by the CGH. To address this issue, tremendous efforts are made to improve the capability of hologram carriers. Here, the main hologram carriers (from SLM to metasurfaces) that are widely utilized in holography systems to achieve high SBP capability (high resolution, wide viewing angles, and large sizes) are reviewed. The purpose of this review is to identify the key challenges and future directions of SLM‐based and metasurface‐based holography for photorealistic 3D holographic images.Item Open Access X-ray and Raman scattering studies of novel phases in 3d and 4d transition metal oxides(2020) Fürsich, Katrin; Keimer, Bernhard (Prof. Dr.)Item Open Access Readout and control of an endofullerene electronic spin(2020) Pinto, Dinesh; Paone, Domenico; Kern, Bastian; Dierker, Tim; Wieczorek, René; Singha, Aparajita; Dasari, Durga; Finkler, Amit; Harneit, Wolfgang; Wrachtrup, Jörg; Kern, KlausAtomic spins for quantum technologies need to be individually addressed and positioned with nanoscale precision. C60 fullerene cages offer a robust packaging for atomic spins, while allowing in-situ physical positioning at the nanoscale. However, achieving single-spin level readout and control of endofullerenes has so far remained elusive. In this work, we demonstrate electron paramagnetic resonance on an encapsulated nitrogen spin (14N@C60) within a C60 matrix using a single near-surface nitrogen vacancy (NV) center in diamond at 4.7 K. Exploiting the strong magnetic dipolar interaction between the NV and endofullerene electronic spins, we demonstrate radio-frequency pulse controlled Rabi oscillations and measure spin-echos on an encapsulated spin. Modeling the results using second-order perturbation theory reveals an enhanced hyperfine interaction and zero-field splitting, possibly caused by surface adsorption on diamond. These results demonstrate the first step towards controlling single endofullerenes, and possibly building large-scale endofullerene quantum machines, which can be scaled using standard positioning or self-assembly methods.Item Open Access Long-range order, bosonic fluctuations, and pseudogap in strongly correlated electron systems(2022) Bonetti, Pietro Maria; Metzner, Walter (Prof. Dr.)Item Open Access Quantum Fourier transform for nanoscale quantum sensing(2021) Vorobyov, Vadim; Zaiser, Sebastian; Abt, Nikolas; Meinel, Jonas; Dasari, Durga; Neumann, Philipp; Wrachtrup, JörgThe quantum Fourier transformation (QFT) is a key building block for a whole wealth of quantum algorithms. Despite its proven efficiency, only a few proof-of-principle demonstrations have been reported. Here we utilize QFT to enhance the performance of a quantum sensor. We implement the QFT algorithm in a hybrid quantum register consisting of a nitrogen-vacancy (NV) center electron spin and three nuclear spins. The QFT runs on the nuclear spins and serves to process the sensor - i.e., the NV electron spin signal. Specifically, we show the application of QFT for correlation spectroscopy, where the long correlation time benefits the use of the QFT in gaining maximum precision and dynamic range at the same time. We further point out the ability for demultiplexing the nuclear magnetic resonance (NMR) signals using QFT and demonstrate precision scaling with the number of used qubits. Our results mark the application of a complex quantum algorithm in sensing which is of particular interest for high dynamic range quantum sensing and nanoscale NMR spectroscopy experiments.