Nonuniform and coherent motion of superconducting vortices in the picometer-per-second regime

We investigated vortex dynamics in a single-crystal sample of type-II superconductor NbSe$_{2}$ using scanning tunneling microscopy at 4.2 K. The decay of the magnetic field at a few nT/s in our superconducting magnet induced the corresponding motion of vortices at a few pm/s. Starting with an initial magnetic field of 0.5 T, we continued to observe motion of vortices within a field of view of 400$\times$400 nm$^2$ subject to decay of the magnetic field over a week. Vortices moved collectively, and maintained triangular lattices due to strong vortex-vortex interactions during the motion. However, we observed two peculiar characteristics of vortex dynamics in this superconductor. First, the speed and direction of the vortex lattice motion were not uniform in time. Second, despite the non-uniform motion, we also found that there exists an energetically favored configuration of the moving vortices in the single-crystal sample of NbSe$_{2}$ based on the overlaid trajectories and their suppressed speeds. We model the system with weak bulk pinning, strong bulk pinning, and edge barrier effects.Comment: 6 pages, 4 figures, Physical Review B (R) in press (2011

Grüne Mitte Essen. Räume, Ressourcen, Verflechtungen

Städte sind Knotenpunkte wirtschaftlichen, sozialen und politischen Lebens, und als solche verändern sie sich permanent: Häuser werden gebaut und abgerissen, Bäume werden gepflanzt und wieder gefällt. Menschen kommen hinzu, bleiben oder ziehen weiter, kehren zurück oder kommen zu Besuch. Jede Stadt hat ihre ganz eigenen Voraussetzungen, die mit darüber entscheiden, wie lokale und globale Entwicklungen vor Ort wirksam werden: Die geographische Lage, die vorhandenen Ressourcen, die historisch gewachsenen sozialen und politischen Verhältnisse. Häuser werden in einer bestimmten Lage aus bestimmten Materialien, von bestimmten Menschen und für bestimmte Menschen gebaut. In diesem Büchlein werden die lokalen und globalen Prägungen und Verflechtungen eines ganz konkreten Ortes angeschaut: Die Grüne Mitte Essen. Mit ihrer recht großen Grünfläche, zwei großen Wasserbecken, Wohnungsneubau und einigen Gewerbeflächen wird die Grüne Mitte Essen als „hochwertiges, lebendiges, grünes und urbanes Viertel zum Wohnen, Arbeiten und Erholen“ beworben. Damit gehört sie zur großen Transformation des Ruhrgebiets: Vom ehemaligen Kohle-, Arbeiter- und Industriegebiet soll es sich zum grünen Technologie- und Forschungsstandort wandeln. Die hier vorgelegte Arbeit ist Ergebnis der interdisziplinären Arbeitsgruppe „Glokale Verflechtungen im Ruhrgebiet“ der Global Young Faculty VII, finanziert durch das Mercator Research Center Ruhr 2021–2023

Simulation study of Non-ergodicity Transitions: Gelation in Colloidal Systems with Short Range Attractions

Computer simulations were used to study the gel transition occurring in colloidal systems with short range attractions. A colloid-polymer mixture was modelled and the results were compared with mode coupling theory expectations and with the results for other systems (hard spheres and Lennard Jones). The self-intermediate scattering function and the mean squared displacement were used as the main dynamical quantities. Two different colloid packing fractions have been studied. For the lower packing fraction, $\alpha$-scaling holds and the wave-vector analysis of the correlation function shows that gelation is a regular non-ergodicity transition within MCT. The leading mechanism for this novel non-ergodicity transition is identified as bond formation caused by the short range attraction. The time scale and diffusion coefficient also show qualitatively the expected behaviour, although different exponents are found for the power-law divergences of these two quantities. The non-Gaussian parameter was also studied and very large correction to Gaussian behaviour found. The system with higher colloid packing fraction shows indications of a nearby high-order singularity, causing $\alpha$-scaling to fail, but the general expectations for non-ergodicity transitions still hold.Comment: 13 pages, 15 figure

Single in situ Interface Characterization Composed of Niobium and a Selectively Grown (Bi1−x_{1-x}Sbx_x)2_2Te3_3 Topological Insulator Nanoribbon

With increasing attention in Majorana physics for possible quantum bit applications, a large interest has been developed to understand the properties of the interface between a $s$-type superconductor and a topological insulator. Up to this point the interface analysis was mainly focused on in situ prepared Josephson junctions, which consist of two coupled single interfaces or to ex-situ fabricated single interface devices. In our work we utilize a novel fabrication process, combining selective area growth and shadow evaporation which allows the characterization of a single in situ fabricated Nb/$\mathrm{(Bi_{0.15}Sb_{0.85})_2Te_3}$ nano interface. The resulting high interface transparency is apparent by a zero bias conductance increase by a factor of 1.7. Furthermore, we present a comprehensive differential conductance analysis of our single in situ interface for various magnetic fields, temperatures and gate voltages. Additionally, density functional theory calculations of the superconductor/topological insulator interface are performed in order to explain the peak-like shape of our differential conductance spectra and the origin of the observed smearing of conductance features.Comment: Main manuscript: 11 pages, 6 figures, Supplementary material: 10 pages, 9 figure

Integration of selectively grown topological insulator nanoribbons in superconducting quantum circuits

We report on the precise integration of nm-scale topological insulator Josephson junctions into mm-scale superconducting quantum circuits via selective area epitaxy and local stencil lithography. By studying dielectric losses of superconducting microwave resonators fabricated on top of our selective area growth mask, we verify the compatibility of this in situ technique with microwave applications. We probe the microwave response of on-chip microwave cavities coupled to topological insulator-shunted superconducting qubit devices and observe a power dependence that indicates nonlinear qubit behaviour. Our method enables integration of complex networks of topological insulator nanostructures into superconducting circuits, paving the way for both novel voltage-controlled Josephson and topological qubits.Comment: 11 pages, 6 figure

Níveis de lisina digestível em rações, em que se manteve ou não a relação aminoacídica, para frangos de corte de 1 a 21 dias de idade, mantidos em estresse por calor

Dois ensaios foram conduzidos para avaliar os efeitos de níveis de lisina digestível em rações em que se manteve ou não a relação aminoacídica sobre o desempenho de frangos de corte machos de 1 a 21 dias de idade, criados em alta temperatura. O delineamento experimental utilizado em ambos os ensaios foi o inteiramente casualizado. As aves, no ensaio 1, foram distribuídas em cinco tratamentos (0,92; 0,98; 1,04; 1,10 e 1,16% de lisina digestível em ração convencional), oito repetições e dez aves por repetição. No ensaio 2, os frangos foram distribuídos em quatro tratamentos (1,04; 1,10; 1,16 e 1,22% de lisina digestível em rações mantendo a relação aminoacídica), oito repetições e dez aves por repetição. No ensaio 1, os tratamentos influenciaram quadraticamente o ganho de peso e o consumo de ração, que aumentaram até os níveis de 1,14 e 1,09% de lisina, respectivamente. Embora a conversão alimentar tenha melhorado de forma linear, o modelo LRP foi o que melhor se ajustou aos dados, estimando em 1,097% o nível de lisina a partir do qual ocorreu um platô. Não houve efeito dos tratamentos sobre os pesos absolutos do coração, fígado e intestinos, enquanto o peso absoluto da moela aumentou linearmente. O peso absoluto da carcaça aumentou, enquanto os pesos relativos do coração e do fígado reduziram quadraticamente com os tratamentos. No ensaio 2, os tratamentos influenciaram de forma linear crescente o ganho de peso e a conversão alimentar, enquanto o consumo de ração não variou. Os tratamentos influenciaram linearmente o peso absoluto da carcaça, enquanto os pesos absoluto e relativo das vísceras não variaram. Concluiu-se que frangos de corte machos, de 1 a 21 dias de idade, mantidos em estresse por calor, exigem, no mínimo, 1,14 e 1,22% de lisina digestível em ração convencional e em ração em que se manteve a relação aminoacídica, respectivamente.Two trials were conducted to evaluate the effects of digestible lysine levels in diets maintaining or not the relationship of amino acids, on performance of broilers from 1 to 21 days, kept under heat stress. A completely randomized experimental design was used in both trials. In the trial 1, the broilers were allotted in five treatments (0.92; 0.98; 1.04; 1.10 and 1.16% of lysine in conventional diets), eight replicates and ten broilers per replicate. In the trial 2, the broilers were allotted in four treatments (1.04; 1.10; 1.16 and 1.22% of lysine in diet maintaining the relationship of amino acids), eight replicates and ten broilers per replicate. In the trial 1, the digestible lysine levels influenced quadraticly the weight gain and the feed intake that increased up to 1.14 and 1.09%, respectively. Although feed:gain ratio had changed by linear way, the LRP model adjusted better to the data, estimating in 1.097% the lysine level where occurred a "plateau". There was no effect of treatments on absolute weights of heart, liver and intestines, while the absolute weight of gizzard increased linearly. The absolute weight of carcass increased while the relative weights of heart and liver reduced quadraticly. In the trial 2, the treatments influenced in a crescent linear way the weight gain and the feed:gain ratio while the feed intake was not influenced. The treatments influenced linearly the absolute weight of carcass while the absolute and relative weights of the organs were not influenced. It was concluded that male broilers, in the period from 1 to 21 days of age, kept under heat stress, require at least 1.14 and 1.22% of digestible lysine in conventional diet and in diet maintaining the relationship of amino acid, respectively

Biomimicry of the adhesive organs of stick insects (Carausius morosus)

Adhesive organs enable insects to reversibly adhere to substrates even during rapid locomotion. In this process a very fast but reliable change of adhesion and detachment is realised. These abilities had aroused high interest by scientists many years ago, trying to create artificial reusable adhesion devices. Within the frame of this thesis the detailed structures and the functionalites of the adhesive organs of the stick insect Carausius morosus were analysed and based on the obtained data artificial adhesion devices were constructed and finally validated. Initially, the morphology and the ultrastructure of the adhesive organs was analysed using SEM, TEM, CLSM, micro-CT, FIB and light microscopy. By these analyses the detailed ultrastructure of the smooth adhesive organs of stick insects, the so called arolia, and of the hairy adhesive organs, the so called euplantulae, could be revealed. Especially, new insights into the structure of the treelike branching fibres within the procuticula were obtained, which support the thin membranous epicuticula by which arolia are covered. Presumably, this very thin epicuticula can conform to the smallest surface roughnesses and the treelike branching fibres support the epicuticula without preventing its flexibility. Due to this design smooth adhesive organs most likely can conform to substrates so close, that adhesion forces on the basis of van der Waals forces were developed. Several further issues concerning the adhesion of stick insects were analysed in the course of this thesis. Among others the development of a new method for the determination of the Young´s modulus of thin and superficial membranes enabled to determine the Young´s modulus of the epicuticula. In this method arolia of stick insects adhering upside down to a latex membrane were stretched by stretching the latex membrane. Meanwhile, the elongation of the contact area between the arolium and the latex membrane was recorded. The observed elongations were analysed using finite element simulations yielding Young´s moduli of about 60 MPa. This value is much higher than the values determined or assumed for the epicuticula of adhesive organs before. Based on all results four construction plans for the fabrication of artificial adhesion devices were developed. All construction plans contained an outer, thin, flexible and adhesive membrane out of a silicone, which was supported by different resilient substructures. In the first adhesion device the substructure consisted of a silicone foam and in the second adhesion device the substructure was formed by an array of parallel fibres, orientated at an angle of 57 deg. The third adhesion device included thin flock fibres, which were orientated about perpendicularly to the adhesive surface of the adhesion device and which were infused with a very elastical silicone gel. In the fourth adhesion device the substructure was solely made out of the same elastic silicone gel, which found a use in the third adhesion device. During the course of this thesis the constructional ideas how to fabricate artificial adhesion devices were submitted to the Deutsches Patent- und Markenamt. Among the four adhesion devices the one with flock fibres showed the highest adhesion force of about 1.25 N/sq cm, which is a bit higher than the adhesion force of stick insects without the contribution of friction. This high adhesion force seems to be based on the reinforcement of the adhesion device with fibres, by which pulling forces are uniformly transferred to the contact area of the adhesion device to the substrate. A non-uniform loading of the contact area easily leads to a local detachment at the area of the highest loading, which could lead to a gradual detachment of the whole adhesion device. Such a gradual detachment goes along with small adhesion forces. Taking into account all results, a new construction plan for the fabrication of artificial adhesion devices was developed. According to this plan adhesion devices should be covered with a preferably thin membrane with a high Young´s modulus. This membrane should be supported by a substructure made of a resilient and elastic foam or gel. Besides, the substructure should be reinforced by very thin fibres, which equip the adhesion devices with a high tensile strength without reducing the resiliency of the substructure. Biomimetic adhesion devices fabricated according to this construction plan should show high adhesion forces as well as high resistances against abrasion and contamination