Spin effects in the magneto-drag between double quantum wells

We report on the selectivity to spin in a drag measurement. This selectivity to spin causes deep minima in the magneto-drag at odd fillingfactors for matched electron densities at magnetic fields and temperatures at which the bare spin energy is only one tenth of the temperature. For mismatched densities the selectivity causes a novel 1/B-periodic oscillation, such that negative minima in the drag are observed whenever the majority spins at the Fermi energies of the two-dimensional electron gasses (2DEGs) are anti-parallel, and positive maxima whenever the majority spins at the Fermi energies are parallel.Comment: 4 pages, 3 figure

Excitons in coupled 2d electron and hole gases

Gegenstand der Arbeit ist die Herstellung und Untersuchung von gekoppelten 2d Elektronen- und Lochsystemen. Für solche Systeme werden bei ausreichend geringem Abstand zwischen der Elektronen- und der Lochschicht auf Grund der anziehenden Coulombwechselwirkung neuartige Zustände des Vielteilchensystems erwartet. Bei tiefen Temperaturen sollen sich räumlich indirekte Exzitonen bilden und einen Kosterlitz Thouless Phasenübergang zeigen. Es wurden Abstnde zwischen dem Elektronen- und dem Lochsystem bis herunter zu 15,3 nm realisiert. Zunächst wird eingehend beschrieben, wie im GaAs/AlGaAs Materialsystem ein Transistor aufgebaut werden kann, bei dem sich eine Elektronen- und eine Lochschicht in unmittelbarer Nähe zueinander befinden. Beide leitfähigen Schichten besitzen mehrere Kontakte; zu deren Herstellung wurde ein Verfahren aufgebaut und entwickelt, das auf der Kombination von Molekularstrahlepitaxie und fokussierter Ionenstrahlimplantation, die während einer Wachstumsunterbrechung durchgeführt wird, basiert. Im weiteren wird beschrieben, wie die Prozessierung der Probe durchgeführt werden muß und die Kontakte angeschlossen werden. Es werden Transportmessungen gezeigt und die grundsätzlichen Eigenschaften des neuartigen Doppellagentransistors demonstriert. Im zweiten Teil der Arbeit werden die thermodynamischen Eigenschaften des 2d Elektronen- und Lochsystems mit Hilfe von Kapazitätsmessungen untersucht. Die Magnetooszillationen der Kapazitätsmessungen lassen die unabhängige Bestimmung der Dichte des Ladungssystems zu und sind durch die magnetfeldabhängige Kompressibilität des Elektronensystems verständlich. Bei geringsten und identischen Dichten zwischen dem Elektronen- und dem Lochsystem zeigt sich bei tiefsten Temperaturen ein Peak in der Kapazität, der durch die Bildung von Exzitonen erklärt werden kann. Das Verhalten des Peaks in Abhängigkeit der Temperatur und dem Magnetfeld wird diskutiert.The subject of this work is the fabrication and investigation of coupled 2d electron- and hole systems. For this type of systems at sufficiently low distance between the electron and the hole layer new states of the many particle system are expected due to the attractive Coulomb interaction. At low temperatures spatially indirect excitons should form and condense in a Kosterlitz Thouless type of phase transition. Distances between the electron and the hole system as low as 15.3 nm have been realized. First it is shown, how to build a transistor in the GaAs/AlGaAs material system, in which an electron and an hole layer are in this low distance. Both conducting layers have several contacts; for their fabrication a process was developped which is based on a combination of molecular beam epitaxy and focussed ion beam implantation, which is performed during a growth interuption. After that it is described, how the processing is done and how the contacts are connected. Transport measurements are shown and the general features of the new kind of double layer transistor are demonstrated. In the second part of this work the thermodynamic properties of the coupled 2d electron- and hole system are investigated with capacity measurements. The magnetooscillations of the capacity measurements allow for the independent determination of the density of the charge system and can be understood as consequence of the magnetic field dependent compressibility of the electron system. At the lowest and identical densities of the electron- and the hole system a peak appears at the lowest densities in the capacitance, which can be explained by the formation of excitons. The dependence on temperature and magnetic field of the peak is discussed

Recognition of Human Activities in Hybrid Teamwork with Industrial Robot Systems

Pohlt C. Recognition of Human Activities in Hybrid Teamwork with Industrial Robot Systems. Bielefeld: Universität Bielefeld; 2022.The effort that is required to establish automation imposes a limitation to traditional production environments. This yields a lack of flexibility, which gains significance due to the changing consumer market. To overcome these limitations, a fundamental shift has been initiated towards a new era known as Industry 4.0. This shift is supported by rapidly evolving technological opportunities that enable novel forms of hybrid teamwork between humans and robots with significant implications for operators. Hybrid teamwork refers to the interaction of operators and robot systems in order to complete a work task in a robot cell. Cells are coherent environments that include robot systems with end-effectors, sensors and devices such as monitors. Due to the traditional isolation of robots within the cells, the design is often technology-centered rather than human-centered. However, the novel forms introduce more dynamic and uncertainty into teamwork, and consequently the way people and robots approach a given task must adapt to the evolving conditions. The challenge is to enable shared work tasks to be completed with as few agreements and interruptions as possible. Therefore, robot systems need to recognize human activities to interact, coordinate actions and avoid waiting times as well as confusion. In order to enable this, a (re)design of traditional environments towards increased flexibility and human-centered teamwork is required. In this thesis, I present my research on hybrid teamwork in industrial robot cells. This involves the recognition of human activities such as gestures or body movements to coordinate robot system actions. However, in order to establish hybrid teamwork, a number of research gaps still need to be addressed. This involves the analysis of human and hybrid teams in terms of internal and external relationships, the desired behavior of robot systems, and frequent human activities in typical teamwork situations. With regard to the realization of robot cells, a holistic view without shortcuts in the implementation and usable domain-specific datasets are missing. Therefore, I define industrial requirements, provide operator training strategies, integrate cognitive skills, and establish realistic domain-specific datasets as a foundation for robot training. Finally, the state-of-the-art in human activity recognition does not provide solutions that meet the requirements of Industry 4.0. The approaches lack flexibility as they are difficult to transfer, especially between initially unknown sources, and require large domain specific datasets to ensure acceptable reliabilities. I provide approaches that enable high performance under industrial conditions, cross-modality fusion of unknown sources, and weakly-supervised learning from unprepared samples. For the evaluation and training, generic datasets are used to improve transferability, along with realistic and limited domain-specific datasets to prove applicability. The finally introduced weakly-supervised fusion increases reliability by incorporating additional, but initially unknown, modalities in conjunction with flexibility and reliability by incorporating additional unprepared samples. Overall, this work contributes to the improvement of hybrid teamwork and identifies challenges of human-centered design in an industrial context

Human Work Activity Recognition for Working Cells in Industrial Production Contexts

Pohlt C, Schlegl T, Wachsmuth S. Human Work Activity Recognition for Working Cells in Industrial Production Contexts. In: 2019 IEEE International Conference on Systems, Man and Cybernetics (SMC). Bari, Italy. October 6-9, 2019 . Piscataway, NJ: IEEE; 2019: 4225-4230

Impact of Spontaneous Human Inputs during Gesture based Interaction on a Real-World Manufacturing Scenario

Pohlt C, Hell S, Schlegl T, Wachsmuth S. Impact of Spontaneous Human Inputs during Gesture based Interaction on a Real-World Manufacturing Scenario. In: Wrede B, ed. Proceedings of the 5th International Conference on Human Agent Interaction. New York: ACM; 2017: 347-351