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We use scanning gate microscopy to study electron transport through an open, gate-defined resonator in a Ga(Al)As heterostructure. Raster-scanning the voltage-biased metallic tip above the resonator, we observe distinct conductance modulations as a function of the tip position and voltage. Quantum-mechanical simulations reproduce these conductance modulations and reveal their relation to the partial local density of states in the resonator. Our measurements illustrate the current frontier between possibilities and limitations in imaging the local density of states in buried electron systems using scanning gate microscopy., Physical Review Research, 3 (3), ISSN:2643-1564

We measure electronic transport through point contacts in the high-mobility electron gas in a Ga[Al]As heterostructure at different temperatures and bulk electron densities. The conductance through all point contacts increases with increasing temperature in a temperature window around $T \sim 10 K$ for all investigated electron densities and point contact widths. For high electron densities this conductance exceeds the fundamental ballistic limit (Sharvin limit). These observations are in agreement with a viscous electron transport model and previous experiments in graphene., 5 pages, 2 figures

The Kondo effect is a cornerstone in the study of strongly correlated fermions. The coherent exchange coupling of conduction electrons to local magnetic moments gives rise to a Kondo cloud that screens the impurity spin. Here we report on the interplay between spin–orbit interaction and the Kondo effect, that can lead to a underscreened Kondo effects in quantum dots in bilayer graphene. More generally, we introduce a different experimental platform for studying Kondo physics. In contrast to carbon nanotubes, where nanotube chirality determines spin–orbit coupling breaking the SU(4) symmetry of the electronic states relevant for the Kondo effect, we study a planar carbon material where a small spin–orbit coupling of nominally flat graphene is enhanced by zero-point out-of-plane phonons. The resulting twoelectron triplet ground state in bilayer graphene dots provides a route to exploring the Kondo effect with a small spin–orbit interaction., Nature Communications, 12, ISSN:2041-1723

Graphene has evolved as a platform for quantum transport that can compete with the best and cleanest semiconductor systems. Recently, many interesting local properties of carrier transport in graphene have been investigated by various scanning probe techniques. Here, we report on the observation of distinct electronic jets emanating from a narrow split-gate defined channel in bilayer graphene. We find that these jets, which are visible via their interference patterns, occur predominantly with an angle of 60{\deg} between each other. This observation is related to the specific bandstructure of bilayer graphene, in particular trigonal warping, which leads to a valley-dependent selection of momenta for low-energy conduction channels. This experimental observation of electron jetting has consequences for carrier transport in graphene in general as well as for devices relying on ballistic and valley selective transport.

Due to the growing value of software technology in our every-day life, young professionals and undergraduates need to be well-qualified for Software Engineering (SE) careers. Additionally, its didactic basis is a recent development.

Software process models are important in software projects in order to give the work of a project guidelines or a framework. However, teaching process models in higher education seems to be quite challenging. This has to do with the fact that undergraduates have no experience with projects in which process models are used. The theoretical mediation of process models is initially on a very abstract level. For this reason, we chose to combine two didactic approaches, namely problem-based learning and project work. Various traditional plan-driven process models have been expanded in courses in Software Engineering with agile process models. The Scrum Framework is the focus of consideration of this paper. Three Universities of Applied Sciences which cooperate in the EVELIN project focused on Scrum as a process model and integrated it into their teaching. Since the respective concepts of implementation differ, they should be presented and compared in this article to presents some practice approaches. The goal of this presentation of is a uniform evaluation in order to obtain insights from different perspectives. This comparison can draw conclusions for possible necessary improvements of the respective concepts.

In multivalley semiconductors, the valley degree of freedom can be potentially used to store, manipulate and read quantum information, but its control remains challenging. The valleys in bilayer graphene can be addressed by a perpendicular magnetic field which couples by the valley g-factor. However, control over the valley g-factor has not been demonstrated yet. We experimentally determine the energy spectrum of a quantum point contact realized by a suitable gate geometry in bilayer graphene. Using finite bias spectroscopy we measure the energy scales arising from the lateral confinement as well as the Zeeman splitting and find a spin g-factor of 2. The valley g-factor can be tuned by a factor of 3 using vertical electric fields, reaching values between 40 and 120. The results are quantitatively explained by a calculation considering topological magnetic moment and its dependence on confinement and the vertical displacement field.

The objective of our study was to investigate the effects of benzalkonium chloride (BC) adaptation of L. monocytogenes on the susceptibility to antimicrobial agents and on the viable but non culturable (VBNC) state of the bacterial cells. We adapted L. monocytogenes SLCC2540 to BC by applying BC below minimum inhibitory concentration (MIC) to above minimum bactericidal concentration (MBC). The culturable fractions and the susceptibility of adapted and parental cells to BC were assessed. In addition, cell membrane permeability and glucose uptake were analyzed by multi parametric flow cytometry using the fluorescent agents SYTO9, propidium iodide, and 2-deoxy-2-[(7-nitro-2,1,3-benzoxadiazol-4-yl)amino]-D-glucose (2-NBDG). Adapted cells displayed a two-fold MIC increase of BC and reduced antibiotic susceptibility. At high BC concentrations, the decrease in the number of colony forming units was significantly lower in the population of adapted cells compared to parental cells. At the same time, the number of metabolically active cells with intact membranes was significantly higher than the number of culturable cells. Growth-independent viability assays revealed an adapted subpopulation after BC application that was not culturable, indicating increased abundance of viable but nonculturable (VBNC) cells. Moreover, adapted cells can outcompete non-adapted cells under sublethal concentrations of disinfectants, which may lead to novel public health risks.

Thin nanomaterials are key constituents of modern quantum technologies and materials research. The identification of specimens of these materials with the properties required for the development of state-of-the-art quantum devices is usually a complex and tedious human task. In this work, we provide a neural-network-driven solution that allows for accurate and efficient scanning, data processing, and sample identification of experimentally relevant two-dimensional materials. We show how to approach the classification of imperfect and imbalanced data sets using an iterative application of multiple noisy neural networks. We embed the trained classifier into a comprehensive solution for end-to-end automatized data processing and sample identification.

The objective of our study was to investigate the effects of benzalkonium chloride (BC) adaptation of L. monocytogenes on the susceptibility to antimicrobial agents and on the viable but non culturable (VBNC) state of the bacterial cells. We adapted L. monocytogenes SLCC2540 to BC by applying BC below minimum inhibitory concentration (MIC) to above minimum bactericidal concentration (MBC). The culturable fractions and the susceptibility of adapted and parental cells to BC were assessed. In addition, cell membrane permeability and glucose uptake were analyzed by multi parametric flow cytometry using the fluorescent agents SYTO9, propidium iodide, and 2-deoxy-2-[(7-nitro-2,1,3-benzoxadiazol-4-yl)amino]-D-glucose (2-NBDG). Adapted cells displayed a two-fold MIC increase of BC and reduced antibiotic susceptibility. At high BC concentrations, the decrease in the number of colony forming units was significantly lower in the population of adapted cells compared to parental cells. At the same time, the number of metabolically active cells with intact membranes was significantly higher than the number of culturable cells. Growth-independent viability assays revealed an adapted subpopulation after BC application that was not culturable, indicating increased abundance of viable but nonculturable (VBNC) cells. Moreover, adapted cells can outcompete non-adapted cells under sublethal concentrations of disinfectants, which may lead to novel public health risks.

openaire: EC/H2020/766025/EU//QuESTech Crystal fields occur due to a potential difference between chemically different atomic species. In van der Waals heterostructures such fields are naturally present perpendicular to the planes. It has been realized recently that twisted graphene multilayers provide powerful playgrounds to engineer electronic properties by the number of layers, the twist angle, applied electric biases, electronic interactions, and elastic relaxations, but crystal fields have not received the attention they deserve. Here, we show that the band structure of large-angle twisted double bilayer graphene is strongly modified by crystal fields. In particular, we experimentally demonstrate that twisted double bilayer graphene, encapsulated between hBN layers, exhibits an intrinsic band gap. By the application of an external field, the gaps in the individual bilayers can be closed, allowing to determine the crystal fields. We find that crystal fields point from the outer to the inner layers with strengths in the bottom/top bilayer Eb = 0.13 V/nm ≈ -Et = 0.12 V/nm. We show both by means of first-principles calculations and low energy models that crystal fields open a band gap in the ground state. Our results put forward a physical scenario in which a crystal field effect in carbon substantially impacts the low energy properties of twisted double bilayer graphene, suggesting that such contributions must be taken into account in other regimes to faithfully predict the electronic properties of twisted graphene multilayers.

To handle heterogeneity within students, to foster needed generic competencies, to motivate them, and to increase their employability, Pair Programming seems to be a suitable didactical method to teach and learn programming. In this context, Pair Programming was used in programming lessons and its effectiveness was evaluated. This paper presents the results of the evaluations in order to derive whether Pair Programming is a suitable method to meet the mentioned challenges in a didactically meaningful way.

Internally differentiated instructional tasks are a strategy to handle the heterogeneity of learners’ individual knowledge levels. The use of differentiated learning tasks can make an important contribution to teaching/learning management in order to efficiently promote the individual competency development of students. This paper covers the first formative evaluation results of implementing an inner differentiation approach covering instructional tasks in the basics of programming in an engineering bachelors’ degree program.

Internal differentiation is a didactic answer to the growing heterogeneity of the knowledge-base of students based on the rising permeability in higher education (e.g., different qualifications for access to university). As part of an appropriate didactic setting, learning tasks are an essential component, among many other factors. The use of differentiated learning tasks as a reaction to heterogeneity can make an important contribution to teaching/learning. The competency development of students can thus be promoted efficiently. As this diversity is discoverable considering coding in particular among software engineering students, this paper focuses on a beginners' programming course.

This paper deals with the identification of learning obstacles using the questionnaire method. Therefore, two iterations were proceeded: The first one was part of a survey that was carried out at four locations at universities of applied sciences. We asked students about obstructive facts in general providing items for five learning obstacle dimensions that were set up before; emotional/motivational, epistemological/cognitive, didactical, resource-related and meta-cognitive learning obstacle dimensions. After the general part, we asked them to answer the same question, but in relation to the — in their opinion — most difficult learning content. With this question, we aim to get indications regarding to epistemological obstacles. In a second step, we used the "Motivated Strategies for Learning Questionnaire", which was developed by Pintrich [1] as a basis to develop a questionnaire that extracts learning obstacles. In its original version, the "Motivated Strategies for Learning Questionnaire" was intended to measure students' learning strategies, but, as the obstacle dimensions were partly derived from learning strategy classification, we chose this already validated questionnaire [2]. Within this iteration, we could confirm a five-factor structure of the questionnaire that could be mapped to the five before set learning obstacle dimensions.

The pattern of branched electron flow revealed by scanning gate microscopy shows the distribution of ballistic electron trajectories. The details of the pattern are determined by the correlated potential of remote dopants with an amplitude far below the Fermi energy. We find that the pattern persists even if the electron density is significantly reduced such that the change in Fermi energy exceeds the background potential amplitude. The branch pattern is robust against changes in charge carrier density, but not against changes in the background potential caused by additional illumination of the sample., New Journal of Physics, 20, ISSN:1367-2630

We measure transport through a Ga[Al]As heterostructure at temperatures between 0.1 K and 30 K. Increasing the temperature enhances the electron-electron scattering rate and viscous effects in the two-dimensional electron gas arise. To probe this regime we measure so-called vicinity voltages and use a voltage-biased scanning tip to induce a movable local perturbation. We find that the scanning gate images differentiate reliably between the different regimes of electron transport. Our data are in good agreement with recent theories for interacting electron liquids in the ballistic and viscous regimes stimulated by measurements in graphene. However, the range of temperatures and densities where viscous effects are observable in Ga[Al]As are very distinct from the graphene material system., With attached supplemental material and journal reference

To handle heterogeneity within students, to foster needed generic competencies, to motivate them, and to increase their employability, a didactical method to teach and learn programming in non-major degree programs shall be found. Therefore, this paper covers strategies and the theoretical underpinning concerning these four challenges and gives solutions how to cope with them. Finally, Pair Programming is presented as a method that addresses the issues introduced here.

We demonstrate an experimental method for measuring quantum state degeneracies in bound state energy spectra. The technique is based on the general principle of detailed balance, and the ability to perform precise and efficient measurements of energy-dependent tunnelling-in and -out rates from a reservoir. The method is realized using a GaAs/AlGaAs quantum dot allowing for the detection of time-resolved single-electron tunnelling with a precision enhanced by a feedback-control. It is thoroughly tested by tuning orbital and spin-degeneracies with electric and magnetic fields. The technique also lends itself for studying the connection between the ground state degeneracy and the lifetime of the excited states., Accepted for publication as a Letter in Physical Review Letters

Language — spoken and written — is the medium for information and knowledge sharing; and it is almost always even a role of every subject in (higher) education. The language therefore plays an important part in teaching and learning. This is further underlined by the fact that "discipline-specific language" — which is "the uses of language in university discipline learning and teaching and in professional life in a particular discipline" [1, p. 1] — can be understood as a link between knowledge and generic/personal/interpersonal competencies; especially communication skills. In this paper a research proposal is outlined to enable an enhanced and conscious approach to the use of language and special terms in Software Engineering in higher education. This is done by a two-piece approach that considers terminology from a linguistic and a didactical point of view. All of this combined is intended to contribute toward the development of a terminology in Software Engineering and, in a wider context, to reach the top goal of this research agenda: To be able to obtain recommendations for action for teaching and learning methods to improve the quality and sustainability of teaching and learning in this discipline.