Browsing by Author "Chow, KH"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    8Li+ β-NMR in the cubic insulator MgO
    (IOP Publishing, 2014-12-16) MacFarlane, WA; Parolin, TJ; Cortie, DL; Chow, KH; Hossain, MD; Kiefl, RF; Levy, CDP; McFadden, RML; Morris, GD; Pearson, MR; Saadaoui, H; Salman, Z; Song, Q; Wang, D
    We present extensive high magnetic field β-NMR measurements of 8Li+ implanted in single crystals of MgO. The narrow resonance, consistent with a cubic 8Li+ site, likely the tetrahedral interstitital, is used routinely as a reference for shift measurements. We show the intrinsic linewidth is on the order of 200 Hz, allowing a frequency determination to an accuracy of a few Hz. We find no implantation energy dependence of the resonance within a few ppm, but there is evidence of slow spin dynamics in hole-burning measurements. The spin lattice relaxation is slow. The temperature dependence reveals interesting changes at low temperature whose origin remains uncertain. Open Access CC-BY
  • No Thumbnail Available
    Item
    Ionic and electronic properties of the topological insulator Bi2Te2Se investigated via β-detected nuclear magnetic relaxation and resonance of Li8
    (American Physical Society, 2019-03-08) McFadden, RML; Chatzichristos, A; Chow, KH; Cortie, DL; Dehn, MH; Fujimoto, D; Hossain, MD; Ji, H; Karner, VL; Kiefl, RF; Levy, CDP; Li, R; McKenzie, I; Morris, GD; Ofer, O; Pearson, MR; Stachura, M; Stachura, RJ; MacFarlane, WA
    We report measurements on the high-temperature ionic and low-temperature electronic properties of the three-dimensional topological insulator Bi2Te2Se using ion-implanted Li8β-detected nuclear magnetic relaxation and resonance. With implantation energies in the range 5-28keV, the probes penetrate beyond the expected range of the topological surface state, but are still within 250nm of the surface. At temperatures above ∼150K, spin-lattice relaxation measurements reveal isolated Li+8 diffusion with an activation energy EA=0.185(8)eV and attempt frequency τ0-1=8±3×1011s-1 for atomic site-to-site hopping. At lower temperature, we find a linear Korringa-type relaxation mechanism with a field-dependent slope and intercept, which is accompanied by an anomalous field dependence to the resonance shift. We suggest that these may be related to a strong contribution from orbital currents or the magnetic freeze-out of charge carriers in this heavily compensated semiconductor, but that conventional theories are unable to account for the extent of the field dependence. Conventional NMR of the stable host nuclei may help elucidate their origin. ©2019 American Physical Society.