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arXiv · 1911.12212

Local electronic and magnetic properties of the doped topological insulators Bi$_{2}$Se$_{3}$:Ca and Bi$_{2}$Te$_{3}$:Mn investigated using ion-implanted $^{8}$Li $β$-NMR

Ryan M. L. McFadden·Aris Chatzichristos·David L. Cortie·Derek Fujimoto·Yew San Hor·Huiwen Ji·Victoria L. Karner·Robert F. Kiefl·C. D. Philip Levy·Ruohong Li·Iain McKenzie·Gerald D. Morris·Matthew R. Pearson·Monika Stachura·Robert J. Cava·W. Andrew MacFarlane
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Abstract

We report $β$-detected nuclear magnetic resonance ($β$-NMR) measurements in Bi$_{2}$Se$_{3}$:Ca (BSC) and Bi$_{2}$Te$_{3}$:Mn (BTM) single crystals using $^{8}$Li$^{+}$ implanted to depths on the order of 100 nm. Above $\sim 200$ K, spin-lattice relaxation (SLR) reveals diffusion of $^{8}$Li$^{+}$, with activation energies of $\sim 0.4$ eV ($\sim 0.2$ eV) in BSC (BTM). At lower temperatures, the nuclear magnetic resonance (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 BSC. From this, we make a detailed comparison with the isostructural tetradymite Bi$_{2}$Te$_{2}$Se (BTS) [McFadden et al., Phys Rev. B 99, 125201 (2019)]. In the magnetic BTM, the effects of the dilute Mn moments predominate, but remarkably the $^{8}$Li signal is not wiped out through the magnetic transition at 13 K, with a prominent critical peak in the SLR that is suppressed in a high applied field. This detailed characterization of the $^{8}$Li NMR response is an important step towards using depth-resolved $β$-NMR to study the low-energy properties of the chiral topological surface state (TSS). With the bulk NMR response now established in several Bi$_{2}$Ch$_{3}$ tetradymite topological insulators (TIs), the prospect of directly probing their chiral TSS using the depth resolution afforded by $β$-NMR remains strong.

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Ryan M. L. McFadden, Aris Chatzichristos, David L. Cortie, Derek Fujimoto, Yew San Hor, Huiwen Ji, Victoria L. Karner, Robert F. Kiefl, C. D. Philip Levy, Ruohong Li, Iain McKenzie, Gerald D. Morris, Matthew R. Pearson, Monika Stachura, Robert J. Cava, W. Andrew MacFarlane. 2020-12-06. Local electronic and magnetic properties of the doped topological insulators Bi$_{2}$Se$_{3}$:Ca and Bi$_{2}$Te$_{3}$:Mn investigated using ion-implanted $^{8}$Li $β$-NMR. https://doi.org/10.1103/physrevb.102.235206

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