Supercurrent interference in HgTe Josephson junctions

Wires made of topological insulators (TI) are a promising platform for searching for Majorana bound states. These states can be probed by analyzing the fractional ac Josephson effect in Josephson junctions with the TI wire as a weak link. An axial magnetic field can be used to tune the system from trivial to topologically nontrivial. Here we investigate the oscillations of the supercurrent in such wire Josephson junctions as a function of the axial magnetic field strength and different contact transparencies. Although the current flows on average parallel to the magnetic field we observe h/2e, h/4e- and even h/8e-periodic oscillations of the supercurrent in samples with lower contact transparencies. Corresponding tight-binding transport simulations using a Bogoliubov-de Gennes model Hamiltonian yield the supercurrent through the Josephson junctions, showing in particular the peculiar h/4e-periodic oscillations observed in experiments. A further semiclassical analysis based on Andreev-reflected trajectories connecting the two superconductors allows us to identify the physical origin of these oscillations. They can be related to flux-enclosing paths winding around the TI-nanowire, thereby highlighting the three-dimensional character of the junction geometry compared to common planar junctions

Rare earth elements of ROV sample GeoB12338-2 from the Makran accretionary complex

Authigenic carbonates forming at an active methane-seep on the Makran accretionary prism mainly consist of aragonite in the form of microcrystalline, cryptocrystalline, and botryoidal phases. The d13Ccarbonate values are very negative (-49.0 to -44.0 per mill V-PDB), agreeing with microbial methane as dominant carbon source. The d18Ocarbonate values are exclusively positive (+ 3.0 to + 4.5 per mill V-PDB) and indicate precipitation in equilibrium with seawater at bottom water temperatures. The content of rare earth elements and yttrium (REE + Y) determined by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and solution ICP-MS varies for each aragonite variety, with early microcrystalline aragonite yielding the highest, cryptocrystalline aragonite intermediate, and later botryoidal aragonite the lowest REE + Y concentrations. Shale-normalised REE + Y patterns of different types of authigenic carbonate reflect distinct pore fluid compositions during precipitation: Microcrystalline aragonite shows high contents of middle rare earth elements (MREE), reflecting REE patterns ascribed to anoxic pore water. Cryptocrystalline aragonite exhibits a seawater-like REE + Y pattern at elevated total REE + Y concentrations, indicating higher concentrations of REEs in pore waters, which were influenced by seawater. Botryoidal aragonite is characterised by seawater-like REE + Y patterns at initial growth stages followed by an increase of light rare earth elements (LREE) with advancing crystal growth, reflecting changing pore fluid composition during precipitation of this cement. Conventional sample preparation involving micro-drilling of carbonate phases and subsequent solution ICP-MS does not allow to recognise such subtle changes in the REE + Y composition of individual carbonate phases. To be able to reconstruct the evolution of pore water composition during early diagenesis, an analytical approach is required that allows to track the changing elemental composition in a paragenetic sequence as well as in individual phases. High-resolution analysis of seep carbonates from the Makran accretionary prism by LA-ICP-MS reveals that pore fluid composition not only evolved in the course of the formation of different phases, but also changed during the precipitation of individual phases

ZMI - Newsletter 2/2004

EU-Projekt REMES seit Mai am ZMI - Neuer Kooperationspartner für das ZMI - BiPolAr - eine Internet-Adresse für visuelles digitales Material aus der Politik - Europathemen – das interaktive Format zur Europa-Diskussion - HWP-Projekt "Flexible eLearning-Module für die Lehrer-Weiterbildung" - Entwicklung einer E-Learning-Komponente für den Masters-Studiengang Sprachtechnologie und Fremdsprachendidaktik - Projekt "eLearning-Plattform" präsentiert sich im Uni-Forum - "Blended Learning" bei der HDW - indirekter-freistoss.de zur EM - D i s k u r s 04 mit HOFFEN AM MONTAG - Interaktivität bei den Hessischen Theatertagen - Frankfurt Institute for Advanced Studies - Rechtskonformes eGovernment – eGovernment-konformes Rech

4π -periodic supercurrent tuned by an axial magnetic flux in topological insulator nanowires

Topological insulator (TI) nanowires in proximity to conventional superconductors have been proposed as a tunable platform to realize topological superconductivity and Majorana zero modes. The tuning is done using an axial magnetic flux φ which allows transforming the system from trivial at φ = 0 to topologically nontrivial when half a magnetic flux quantum φ_0/2 threads the cross-section of the wire. Here, we explore the expected topological transition in TI-wire-based Josephson junctions as a function of magnetic flux by probing the 4π-periodic fraction of the supercurrent, which is considered an indicator of topological superconductivity. Our data suggest that this 4π-periodic supercurrent is at lower magnetic field largely of trivial origin but that, at magnetic fields above ∼φ_0/4, topological 4π-periodic supercurrents take over