Browsing by Author "Cava, RJ"

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    Atomic substitution and carbon isotope effect in superconducting MgCNi 3
    (AIP Publishing, 2006-09-07) Klimczuk, T; Gupta, V; Avdeev, M; Jorgensen, JD; Cava, RJ
    The superconductor MgCNi3 has been chemically doped by substitution of Ru and Fe for Ni and B for C. Neither ferromagnetism nor increasing TC is observed, suggesting that MgCNi3 has optimal superconducting properties at its intrinsic composition and electron count The effect of Carbon isotope substitution on Tc is reported: the carbon isotope effect coefficient is αc = 0.54±0.03. This indicates that carbon‐based phonons play a critical role in the superconductivity. © 2006 American Institute of Physics.
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    Local electronic and magnetic properties of the doped topological insulators Bi2Se3:Ca and Bi2Te3 : Mn investigated using ion-implanted 8Li β-NMR
    (American Physical Society (APS), 2020-12-28) McFadden, RML; Chatzichristos, A; Cortie, DL; Fujimoto, D; San Hor, Y; Ji, H; Karner, VL; Kiefl, RF; Levy, CDP; Li, RH; McKenzie, I; Morris, GD; Pearson, MR; Stachura, M; Cava, RJ; MacFarlane, WA
    We report β-NMR measurements in Bi2Se3:Ca and Bi2Te3:Mn single crystals using Li+8 implanted to depths on the order of 100 nm. Above ∼200K, spin-lattice relaxation reveals diffusion of Li+8, with activation energies of ∼0.4eV (∼0.2eV) in Bi2Se3:Ca (Bi2Te3:Mn). At lower temperatures, the NMR properties are those of a heavily doped semiconductor in the metallic limit, with Korringa relaxation and a small, negative, temperature-dependent Knight shift in Bi2Se3:Ca. From this, we make a detailed comparison with the isostructural tetradymite Bi2Te2Se [McFadden, Phys. Rev. B 99, 125201 (2019)2469-995010.1103/PhysRevB.99.125201]. In the magnetic Bi2Te3:Mn, the effects of the dilute Mn moments predominate, but remarkably the Li+8 signal is not wiped out through the magnetic transition at 13 K, with a prominent critical peak in the spin-lattice relaxation that is suppressed in a high applied field. This detailed characterization of the Li+8 NMR response is an important step toward using depth-resolved β-NMR to study the low-energy properties of the chiral topological surface state in the Bi2Ch3 tetradymite topological insulator. ©2024 American Physical Society.