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Song, Q.; Chow, K. H.; Salman, Z.; Saadaoui, H.; Hossain, M. D.; Kiefl, R. F.; Morris, G. D.; Levy, C. D. P.; Pearson, M. R.; Parolin, T. J.; Fan, I.; Keeler, T. A.; Smadella, M.; Wang, D.; Yu, K. M.; Liu, X.; Furdyna, J. K.; MacFarlane, W. A.

doi:10.1103/physrevb.84.054414

Cited by 14 publications

(8 citation statements)

References 62 publications

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“…We also note that the linewidth in the TI layer increases with decreasing T, in contrast with the non-TI material, GaAs (10). Another feature we observe is a considerably broader linewidth for the TI surface layer compared with the TI bulk, a result that is opposite of that observed for trivial (non-TI) semiconductors (26).…”

Section: Resultscontrasting

confidence: 46%

“…S6C). Finally, in a β-NMR investigation in GaAs (E g = 1.4 eV, 300 K) in which the effect of implantation energy was studied, no detectable Knight shift was reported in the case of n-GaAs, as the beam energy decreased from 28 to 3 keV (26). In that same study, no concomitant line broadening was observed, as would be expected of a transition to a metallic state.…”

Section: Resultsmentioning

confidence: 87%

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Nanoscale β-nuclear magnetic resonance depth imaging of topological insulators

Koumoulis

Morris

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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Considerable evidence suggests that variations in the properties of topological insulators (TIs) at the nanoscale and at interfaces can strongly affect the physics of topological materials. Therefore, a detailed understanding of surface states and interface coupling is crucial to the search for and applications of new topological phases of matter. Currently, no methods can provide depth profiling near surfaces or at interfaces of topologically inequivalent materials. Such a method could advance the study of interactions. Herein, we present a noninvasive depth-profiling technique based on β-detected NMR (β-NMR) spectroscopy of radioactive 8 Li + ions that can provide "one-dimensional imaging" in films of fixed thickness and generates nanoscale views of the electronic wavefunctions and magnetic order at topological surfaces and interfaces. By mapping the 8 Li nuclear resonance near the surface and 10-nm deep into the bulk of pure and Cr-doped bismuth antimony telluride films, we provide signatures related to the TI properties and their topological nontrivial characteristics that affect the electronnuclear hyperfine field, the metallic shift, and magnetic order. These nanoscale variations in β-NMR parameters reflect the unconventional properties of the topological materials under study, and understanding the role of heterogeneities is expected to lead to the discovery of novel phenomena involving quantum materials.topological insulator | nuclear magnetic resonance | depth profiling | condensed matter physics | nanoscale physics T opological insulators (TIs) are narrow-gap semiconductor materials that are insulating in the bulk and conductive on their surface. The constituent atoms are typically heavy elements with large spin-orbit coupling (SOC). In time-reversal-invariant materials, the electronic structure of TIs is characterized by band inversions from strong SOC at an odd number of time-reversalinvariant momenta in the bulk Brillouin zone. Unlike metals or ordinary insulators (OIs), charge carriers in TIs evolve from metallic to insulating as a function of depth from the surface. The surface-state electrons are characterized by a suppression of backscattering and an intrinsic chirality of spin-momentum locking, making them of interest in spintronics. A number of theoretical predictions of experimental observations have been made including Majorana fermions, condensed-matter axions, and quantized Hall conductance (1, 2). Heterostructure engineering, where a crystal is formed consisting of a sequence of different building blocks (for example, alternating TI and OI layers), can trigger new physical phenomena such as TIs with enhanced bulk band gaps (3) or Weyl semimetals (4).Because topological materials are characterized by sharp changes in electronic properties at their surfaces and at interfaces with other materials, sensitive techniques are required to probe electronic and magnetic properties in a spatially resolved manner down to the atomic length scale. It has become clear that TI properties are spatially de...

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Section: Resultscontrasting

confidence: 46%

Section: Resultsmentioning

confidence: 87%

Nanoscale β-nuclear magnetic resonance depth imaging of topological insulators

Koumoulis

Morris

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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“…4). Thus, a priori, it is not clear how useful 8 Li β-NMR will be in strongly magnetic materials, though there are a few reports in ferromagnets [27,[33][34][35]. The present results provide another example where, at low temperature, the combination of the high applied field and the weak hyperfine coupling of 8 Li make the relaxation in EuO measurable at low temperature.…”

Section: Discussionmentioning

confidence: 80%

β-detected NMR spin relaxation in a thin film heterostructure of ferromagnetic EuO

et al. 2015

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We present β-detected NMR measurements of the spin-lattice relaxation of 8 Li + implanted into an epitaxial heterostructure based on a 100 nm thick film of ferromagnetic (FM) EuO as a function of temperature through its FM transition. In the FM state, the spin-lattice relaxation rate follows the same temperature dependence, determined by magnon scattering mechanisms, observed in the bulk by 153 Eu NMR, but above 40 K, the signal is wiped out. We also find that 8 Li + stopped in material adjacent to the magnetic layer exhibits spin relaxation related to the critical slowing of the Eu spins. A particularly strong relaxation in the Au overlayer suggests an unusual strong nonlocal coupling mechanism to 8 Li in the metal.

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“…Hyperfine coupling to dilute Ti 3+ moments would naturally yield a broadening, due to the distribution of distances to the 8 Li probe. If, however, the Ti 3+ are dense enough that there is a uniform component to the susceptibility near the percolation limit of the metallic state, then a hyperfine coupling could result in a resonance shift as was found in the dilute magnetic semiconductor Ga 1−x Mn x As [46]. Interestingly, K approaches zero (K vs.MgO = −19 ppm), near the temperature where the Li begins to move T ≈ 100 K. Overall, the resonance results are broadly consistent with the interpretation of 1/T 1 and the μ + SR measurements.…”

Section: A Spin-lattice Relaxation In LI 4 Ti 5 O 12mentioning

confidence: 91%

Lithium diffusion in spinel Li4Ti5O12 and LiTi2O4
Sugiyama
¹
,
Umegaki
²
,
Uyama
³

et al. 2017
Phys. Rev. B
20
3
27
0
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Diffusion of Li + in (111) oriented thin films of the spinels Li 4 Ti 5 O 12 and LiTi 2 O 4 has been studied with 8 Li β-detected NMR in the temperature range between 5 and 310 K. In Li 4 Ti 5 O 12 , the spin-lattice relaxation rate (1/T 1) versus temperature shows a clear maximum around 100 K (=T max) which we attribute to magnetic freezing of dilute Ti 3+ local magnetic moments, consistent with the results of magnetization and muon spin relaxation (μ + SR) measurements. The decrease in 1/T 1 with temperature above T max indicates that Li + starts to diffuse with a thermal activation energy (E a) of 0.11(1) eV. In LiTi 2 O 4 , on the contrary, as temperature increases from 200 K, 1/T 1 increases monotonically up to 310 K. This suggests that Li also starts to diffuse above 200 K with E a = 0.16(2) eV in LiTi 2 O 4. Comparison with conventional Li-NMR on Li 4 Ti 5 O 12 implies that both β-NMR and μ + SR sense short-range Li motion, i.e., a jump diffusion of Li + to the nearest neighboring sites.

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β-detected NMR of Li in Ga1−xMnxAs

Cited by 14 publications

References 62 publications

Nanoscale β-nuclear magnetic resonance depth imaging of topological insulators

Nanoscale β-nuclear magnetic resonance depth imaging of topological insulators

β-detected NMR spin relaxation in a thin film heterostructure of ferromagnetic EuO

Lithium diffusion in spinel Li4Ti5O12 and LiTi2O4
Sugiyama
¹
,
Umegaki
²
,
Uyama
³

et al. 2017
Phys. Rev. B
20
3
27
0
View full text Add to dashboard Cite

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β-detected NMR of Li in Ga1−xMnxAs

Cited by 14 publications

References 62 publications

Nanoscale β-nuclear magnetic resonance depth imaging of topological insulators

Nanoscale β-nuclear magnetic resonance depth imaging of topological insulators

β-detected NMR spin relaxation in a thin film heterostructure of ferromagnetic EuO

Lithium diffusion in spinel Li4Ti5O12 and LiTi2O4Sugiyama1, Umegaki2, Uyama3 et al. 2017Phys. Rev. B203270View full textAdd to dashboardCite

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Lithium diffusion in spinel Li4Ti5O12 and LiTi2O4
Sugiyama
¹
,
Umegaki
²
,
Uyama
³

et al. 2017
Phys. Rev. B
20
3
27
0
View full text Add to dashboard Cite