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  1. Free, publicly-accessible full text available February 21, 2024
  2. Free, publicly-accessible full text available June 1, 2023
  3. Free, publicly-accessible full text available June 28, 2023
  4. Here we show the effect of Li chemical pressure on the structure of layered polymorphs with LiNiB composition: RT -LiNiB (room temperature polymorph) and HT -LiNiB (high temperature polymorph), resulting in stabilization of the novel RT -Li 1+x NiB ( x ∼ 0.17) and HT -Li 1+y NiB ( y ∼ 0.06) phases. Depending on the synthesis temperature and initial Li content, precisely controlled via hydride route synthesis, [NiB] layers undergo structural deformations, allowing for extra Li atoms to be accommodated between the layers. In situ variable temperature synchrotron and time-dependent laboratory powder X-ray diffraction studies suggest Li step-wise deintercalation processes: RT- Li 1+x NiB → RT- LiNiB (high temp.) → LiNi 3 B 1.8 → binary Ni borides and HT -Li 1+y NiB → HT -LiNiB (high temp.) → LiNi 3 B 1.8 → binary Ni borides. Quantum chemistry calculations and solid state 7 Li and 11 B NMR spectroscopy shed light on the complexity of real superstructures of these compounds determined from high resolution synchrotron powder diffraction data.
  5. Abstract

    Complete theoretical understanding of the most complex superconductors requires a detailed knowledge of the symmetry of the superconducting energy-gap$${\mathrm{{\Delta}}}_{\mathbf{k}}^\alpha$$Δkα, for all momentakon the Fermi surface of every bandα. While there are a variety of techniques for determining$$|{\mathrm{{\Delta}}}_{\mathbf{k}}^\alpha |$$Δkα, no general method existed to measure the signed values of$${\mathrm{{\Delta}}}_{\mathbf{k}}^\alpha$$Δkα. Recently, however, a technique based on phase-resolved visualization of superconducting quasiparticle interference (QPI) patterns, centered on a single non-magnetic impurity atom, was introduced. In principle, energy-resolved and phase-resolved Fourier analysis of these images identifies wavevectors connecting allk-space regions where$${\mathrm{{\Delta}}}_{\mathbf{k}}^\alpha$$Δkαhas the same or opposite sign. But use of a single isolated impurity atom, from whose precise location the spatial phase of the scattering interference pattern must be measured, is technically difficult. Here we introduce a generalization of this approach for use with multiple impurity atoms, and demonstrate its validity by comparing the$${\mathrm{{\Delta}}}_{\mathbf{k}}^\alpha$$Δkαit generates to the$${\mathrm{{\Delta}}}_{\mathbf{k}}^\alpha$$Δkαdetermined from single-atom scattering in FeSe where s±energy-gap symmetry is established. Finally, to exemplify utility, we use the multi-atom technique on LiFeAs and find scattering interference between the hole-like and electron-like pockets as predicted for$${\mathrm{{\Delta}}}_{\mathbf{k}}^\alpha$$Δkαof opposite sign.