The 1T polytype of TaS2 has been studied extensively as a strongly correlated system. As 1T-TaS2 is thinned toward the 2D limit, its phase diagram shows significant deviations from that of the bulk material. Optoelectronic maps of ultrathin 1T-TaS2 have indicated the presence of nonequilibrium charge density wave phases within the hysteresis region of the nearly commensurate (NC) to commensurate (C) transition. We perform scanning tunneling microscopy on exfoliated ultrathin flakes of 1T-TaS2 within the NC-C hysteresis window, finding evidence that the observed nonequilibrium phases consist of intertwined, irregularly shaped NC-like and C-like domains. After applying lateral electrical signals to the sample, we image changes in the geometric arrangement of the different regions. We use a phase separation model to explore the relationship between electronic inhomogeneity present in ultrathin 1T-TaS2 and its bulk resistivity. These results demonstrate the role of phase competition morphologies in determining the properties of 2D materials.

We describe an experimental protocol to characterize magnetic field dependent microwave losses in superconducting niobium microstrip resonators. Our approach provides a unified view that covers two well-known magnetic field dependent loss mechanisms: quasiparticle generation and vortex motion. We find that quasiparticle generation is the dominant loss mechanism for parallel magnetic fields. For perpendicular fields, the dominant loss mechanism is vortex motion or switches from quasiparticle generation to vortex motion, depending on cooling procedures. In particular, we introduce a plot of the quality factor versus the resonance frequency as a general method for identifying the dominant loss mechanism. We calculate the expected resonance frequency and the quality factor as a function of the magnetic field by modeling the complex resistivity. Key parameters characterizing microwave loss are estimated from comparisons of the observed and expected resonator properties. Based on these key parameters, we find a niobium resonator whose thickness is similar to its penetration depth is the best choice for X-band electron spin resonance applications. Finally, we detect partial release of the Meissner current at the vortex penetration field, suggesting that the interaction between vortices and the Meissner current near the edges is essential to understand the magnetic field dependence of the resonator properties.

The topological insulator/superconductor heterostructure is one of the most promising platforms to create and manipulate Majorana bound states. Here, we used molecular beam epitaxy to grow high-quality (Bi_0.5Sb_0.5)_2Te_3 films on Nb surfaces. To promote proper (Bi_0.5Sb_0.5)_2Te_3 film nucleation in the early growth stage, we developed a two-step growth method. Bi, Sb, and Te clusters were first evaporated at a low temperature of 180 °C, which is below the typical growth temperature and then annealed to form a crystalized passivation layer. Second, a standard (Bi_0.5Sb_0.5)_2Te_3 film was grown under the normal deposition temperature of 280 °C. We used reflection high-energy electron diffraction, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction to further characterize the (Bi_0.5Sb_0.5)_2Te_3 film and passivation layer quality. Finally, the top Nb film was laid down by magnetron sputtering at room temperature. The hetero-Nb/epitaxial (Bi_0.5Sb_0.5)_2Te_3/Nb stacks were further fabricated into micro-Josephson junctions and showed clear Josephson currents demonstrating an excellent material quality.

The surface states of a topological insulator (TI) can be induced with superconductivity through proximity with a conventional s-wave superconductor (S). To study the coupling between two superconducting TI surfaces, we report the growth and fabrication of vertical Josephson junctions with the topological insulators (Bi0.5Sb0.5)(2)Te-3 sandwiched between Nb electrodes. We observed two Josephson critical currents on the I-V characteristic at 3.5 K, attributed to the bulk Nb and the proximity-induced superconducting (Bi0.5Sb0.5)(2)Te-3 surfaces, respectively. The enhancement of conductance at these two critical currents leads to a bump and a plateau on the differential conductance spectroscopy. By further cooling down to 300 mK, a zero bias conductance peak (ZBCP) appears on the plateau, which is taken as a feature from the unconventional paring at the (Bi0.5Sb0.5)(2)Te-3-Nb interface.

Die Belegung der unpolaren ZnO(100)-Oberfläche mit CO2 bei 95 K führt zur Bildung einer ungewöhnlichen dreizähnigen Carbonatspezies. Die Kombination experimenteller Techniken, wie der hochauflösenden Elektronenenergieverlustspektroskopie (HREELS, siehe Bild), mit einer präzisen theoretischen Analyse gibt einen detaillierten Einblick in die Aktivierung von CO2 auf der Zinkoxidoberfläche.

Greenhouse gas "al dente": Exposure of the nonpolar ZnO(100) surface to CO2 at 95 K leads to the formation of an unusual tridentate carbonate species (see picture; C green, O red, Zn gray). Use of several experimental techniques (for example, high-resolution electron energy loss spectroscopy (HREELS)) and theoretical calculations provides insight into the activation of CO2 on the surface.

Zur Hälfte dissoziiert: Experimentelle und rechnerische Befunde lassen den Schluss zu, dass Wasser auf defektfreien Oberflächen von Zinkoxid eine weitreichend geordnete Überstruktur bildet, in der jedes zweite Wassermolekül dissoziiert ist (siehe Bild). Die Ergebnisse sind von allgemeiner Relevanz für die heterogene Katalyse.