Visualizing superconductivity in a doped Weyl semimetal with broken inversion symmetry

The Weyl semimetal MoTe₂ offers a rare opportunity to study the interplay between Weyl physics and superconductivity. Recent studies have found that Se substitution can boost the superconductivity up to 1.5 K, but suppresses the T-d structure phase that is essential for the emergence of the Weyl state. A microscopic understanding of the possible coexistence of enhanced superconductivity and the Td phase has not been established so far. Here, we use scanning tunneling microscopy to study an optimally doped superconductor MoTe₁.₈₅Se₀.₁₅ with bulk T-c similar to 1.5K. By means of quasiparticle interference imaging, we identify the existence of a low-temperature Td phase with broken inversion symmetry where superconductivity globally coexists. Furthermore, we find that the superconducting coherence length, extracted from both the upper critical field and the decay of density of states near a vortex, is much larger than the characteristic length scale of the existing chemical disorder. Our findings of robust superconductivity arising from a Weyl semimetal normal phase in MoTe₁.₈₅Se₀.₁₅ make it a promising candidate for realizing topological superconductivity

Platy KTiNbO₅ as a Selective Sr Ion Adsorbent: Crystal Growth, Adsorption Experiments, and DFT Calculations

Recognition and sensing of metal ions at the atomic level is a critical issue in many fields of sciences. In particular, selective adsorption of radioactive ⁹⁰Sr²⁺ ions from nuclear waste has been of interest since the Fukushima Daiichi nuclear disaster. Here we present a combined experimental and computational study of KTiNbO₅ (KTN) as a selective and durable adsorbent for Sr²⁺ ions. KTN grown from nitrate flux at 500–600 °C (KTN_flux) has a zigzag layered gallery space. Structural analysis indicates that KTN_flux crystals are platy with surface areas of 48–86 m² g^–1. These areas are ∼50 times larger than those of KTN prepared by solid-state reaction at 1100 °C (KTN_SSR) as a result of efficient, anisotropic crystal growth. Sr²⁺ adsorption experiments indicate that the Sr²⁺ ion-exchange capacity of KTN_flux is ∼1.04 mmol g^–1, and most of the ion-exchange sites are homogeneous. Kinetic analysis shows that the Sr²⁺ ion-exchange rate on KTN_flux is 1 order of magnitude higher than that on KTN_SSR. The [Na⁺] concentration dependence of the distribution coefficient <i>K</i>_d for Sr²⁺ indicates that KTN_flux shows high affinity for Sr²⁺ and remarkable durability, and <i>K</i>_d > 1.26 × 10⁴ mL g^–1 even at [Na⁺] = 0.1 mol L^–1. The origin of the high selectivity for Sr²⁺ was studied by density functional theory (DFT). Our calculations indicate that the high preference for Sr²⁺ is due to confinement within subnanometer-sized pockets built from oxygen species of both the anionic metalate frameworks and intercalated water molecules, forming monocapped heptahedra or octahedra that resemble the active sites of enzymes

Observation of a van Hove singularity of a surface Fermi arc with prominent coupling to phonons in a Weyl semimetal

A van der Waals coupled Weyl semimetal NbIrTe4 is investigated by combining scanning tunneling microscopy/spectroscopy and first-principles calculations. We observe a sharp peak in the tunneling conductance near the Fermi energy (E-F). Comparison with calculations indicates that the peak originates from a van Hove singularity (vHs) associated with a Lifshitz transition of the surface Fermi-arc state. Interestingly, our tunneling spectroscopy also shows signatures of strong electron-boson coupling. This is potentially due to an anomalously enhanced charge susceptibility coming from the near-E-F vHs formation