Magnetotransport Signatures of Superconducting Cooper Pairs Carried by Topological Surface States in Bismuth Selenide.

As topological insulators (TIs) are becoming increasingly intriguing, the community is exploring transformative applications that require interfacing TIs with other materials such as ferromagnets or superconductors. Herein, we report on the manifestations of superconducting electrons carried by topological surface states (TSS) in Bi2Se3 films. As key signatures of TSS-carried Cooper pairs, we uncover the hysteresis of magnetoresistance (MR) and the switching behavior of anisotropic magnetoresistance (AMR). For in-plane fields perpendicular to the injected current, AMR shows negative switching (resistance drop) when the contacts become superconducting, which is consistent with a cooperative Zeeman effect enabled by the spin-momentum locking of TSS. The MR and AMR behaviors are robust, occurring reliably in multiple samples, from different sources, and with different defect concentrations. Our findings can guide novel developments in superconductor/TI quantum devices relying on supercurrent detection as well as lead to more refined transport signatures of Majorana zero-modes in the future.

Guided VLS growth of epitaxial lateral Si nanowires.

Using the Au-seeded vapor-liquid-solid technique, epitaxial single-crystal Si nanowires (NWs) can be grown laterally along Si(111) substrates that have been miscut toward [112¯]. The ratio of lateral-to-vertical NWs increases as the miscut angle increases and as disilane pressure and substrate temperature decrease. By exploiting these trends, conditions can be identified whereby all of the deposited Au seeds form lateral NWs. Growth is guided along the nanofaceted substrate via a mechanism that involves pinning of the trijunction at the liquid/solid interface of the growing nanowire.

On the electronic and geometric structures of armchair GeC nanotubes: a hybrid density functional study.

Ab initio calculations within the framework of hybrid density functional theory and the finite cluster approximation have been performed for the electronic and geometric structures of three different types of armchair germanium carbide nanotube, from (3, 3) to (11, 11). Full geometry and spin optimizations with unrestricted symmetry have been performed. Physically pertinent quantities of interest such as the cohesive energies, band gaps, radial buckling, density of states, dipole moments, and Mulliken charge distributions have been investigated in detail for all nanotubes. For type I nanotubes, the largest cohesive energy obtained is 4.092 eV/atom, whereas for type II and type III nanotubes, the values are 3.987 eV/atom and 3.968 eV/atom, respectively. For optimized type I nanotubes, Ge atoms moved toward the tube axis and C atoms moved in the opposite direction after relaxation, opposite to the trends observed in types II and III. The band gaps for type I nanotubes are larger than the bulk 3C-GeC gap, varying between 2.666 and 3.016 eV, while type II and type III nanotubes have significantly lower band gaps, with all nanotubes being semiconducting in nature. Mulliken charge analysis indicates primarily ionic behavior for type I GeC nanotubes and a mixed ionic with covalent behavior for the other two types. None of the tubes appear to be magnetic. Applications in the field of nano-optoelectronic devices, molecular electronics, and band gap engineering are envisioned for GeC nanotubes.