Ferromagnetic tip induced unconventional superconductivity in Weyl semimetal

Emergent superconductivity in topological-kagome-magnet/metal heterostructures

Itinerant kagome lattice magnets exhibit many novel correlated and topological quantum electronic states with broken time-reversal symmetry. Superconductivity, however, has not been observed in this class of materials, presenting a roadblock in a promising path toward topological superconductivity. Here, we report that novel superconductivity can emerge at the interface of kagome Chern magnet TbMn6Sn6 and metal heterostructures when elemental metallic thin films are deposited on either the top (001) surface or the side surfaces. Superconductivity is also successfully induced and systematically studied by using various types of metallic tips on different TbMn6Sn6 surfaces in point-contact measurements. The anisotropy of the superconducting upper critical field suggests that the emergent superconductivity is quasi-two-dimensional. Remarkably, the interface superconductor couples to the magnetic order of the kagome metal and exhibits a hysteretic magnetoresistance in the superconducting states. Taking into account the spin-orbit coupling, the observed interface superconductivity can be a surprising and more realistic realization of the p-wave topological superconductors theoretically proposed for two-dimensional semiconductors proximity-coupled to s-wave superconductors and insulating ferromagnets. Our findings of robust superconductivity in topological-Chern-magnet/metal heterostructures offer a new direction for investigating spin-triplet pairing and topological superconductivity.

Superconductivity in quasi-2D InTaX2(X = S, Se) type-II Weyl semimetals

Herein, first-principles calculations were employed to study the electronic, topological, and superconducting properties of InTaX₂(X = S, Se). InTaX₂exhibits nodal lines in the absence of spin-orbit coupling (SOC); on SOC inclusion, the nodal lines form Weyl rings with the Weyl points classified as a type-II Weyl semimetal (WSM) with tilted cones. Using Green functions method calculations, surface states distinguishable from the bulk states, and Fermi arcs surface states were visualized on the (001) easily cleavable indium terminated surface of both materials. The electron-phonon calculations using the Allen-Dynes relations predict InTaSe₂and InTaS₂to be superconducting around 2.38 K and 3.25 K. The prediction of these exotic properties in InTaX₂(X = S, Se) makes them suitable for experimental validation of topological superconductivity in type-II WSMs.

Systematic electrochemical etching of various metal tips for tunneling spectroscopy and scanning probe microscopy

Hard point-contact spectroscopy and scanning probe microscopy/spectroscopy are powerful techniques for investigating materials with strong expandability. To support these studies, tips with various physical and chemical properties are required. To ensure the reproducibility of experimental results, the fabrication of tips should be standardized, and a controllable and convenient system should be set up. Here, a systematic methodology to fabricate various tips is proposed, involving electrochemical etching reactions. The reaction parameters fall into four categories: solution, power supply, immersion depth, and interruption. An etching system was designed and built so that these parameters could be accurately controlled. With this system, etching parameters for copper, silver, gold, platinum/iridium alloy, tungsten, lead, niobium, iron, nickel, cobalt, and permalloy were explored and standardized. Among these tips, silver and niobium's new recipes were explored and standardized. Optical and scanning electron microscopies were performed to characterize the sharp needles. Relevant point-contact experiments were carried out with an etched silver tip to confirm the suitability of the fabricated tips.