Adsorption and diffusion of Li on an Ru(001) surface: an NMR study

Ebinger, H.D.; Arnolds, Heike; Polenz, C.; Polivka, B.; Preyß, W.; Veith, Richard C.; Fick, D.; Jänsch, H.J.

doi:10.1016/s0039-6028(98)00492-0

Cited by 28 publications

(19 citation statements)

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“…Therefore the decay of nuclear polarization with time ͑relaxation͒ in general can be expressed as the sum of four exponentials. 49 It is not always possible to disentangle them with high enough precision. However, the slowest relaxation rate could always be determined accurately.…”

Section: Experimental Technique and Setupmentioning

confidence: 99%

“…A brief sketch of the theoretical treatment is given in Appendix A of Ref. 49. More details can be found in several monographs [39][40][41] and in other publications.…”

Section: B Relaxation Mechanismsmentioning

confidence: 99%

“…To describe the frequency spectrum of a fluctuating interaction the time autocorrelation function G͑t͒ and its Fourier transform j͑͒, the spectral density, is used. 39,41,49 According to the BPP model, 57 named after the initials of its authors, the autocorrelation function may be parametrized as…”

Section: B Relaxation Mechanismsmentioning

confidence: 99%

“…͑3͒-͑5͔͒, which indeed was observed experimentally on surfaces too. 49,53 In general, the relaxation rate then displays a resonance like behavior in temperature with a maximum at a temperature for which L c = 1. The temperature at which the "resonance" of the relaxation rate ␣ occurs depends on the other hand through L ͑B͒ c = 1 only weakly ͑logarithmically͒ on the external magnetic field ͓Eqs.…”

Section: B Relaxation Mechanismsmentioning

confidence: 99%

“…49 For a diffusion maximum ͑ L c =1͒ to occur at about 1000 K, one requires a diffusion energy of about 1 eV using a "typical" prefactor of 0 =10 −13 s. 60,61 Considering the high diffusion energies found for Li adsorption on Si surfaces at higher temperatures 53,62 this does not sound unreasonable. But a fit to the data using Eqs.…”

Section: B Relaxation Mechanismsmentioning

confidence: 99%

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MetallicSi(111)−(7×7)-reconstruction: A surface close to a Mott-Hubbard metal-insulator transition

et al. 2005

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Li adsorption at extremely low coverages ͑10 −3 ML and below͒ on the metallic Si͑111͒-͑7 ϫ 7͒ surface has been studied by ␤-NMR experiments ͑measurement of T 1 -times͒. Instead of increasing linearly with the sample temperature, as expected for a metallic system, the relaxation rate ␣ =1/T 1 is almost constant in between 50 K and 300 K sample temperature and rises considerably above. Comparison with T 1 -times around 900 K ͑ob-served with 6 Li-NMR͒ excludes adsorbate diffusion as the cause of the relaxation rate. Thus the almost temperature independent relaxation rate below 300 K points to an extremely localized and thus narrow band ͑width about 10 meV͒ which pins the Fermi energy. It is responsible for the metallicity of the ͑7 ϫ 7͒-reconstruction. Because of the steeply rising relaxation rate beyond 300 K this narrow band is located energetically within a gap ͑approximately 100-500 meV wide͒ in between a lower filled and an upper empty ͑Hubbard͒ band. Due to its extremely narrow width it can hardly be detected in photo electron experiments. In dynamical mean field theories based on Hubbard Hamiltonians this kind of density of states is typical for correlated electron systems close to a Mott-Hubbard metal-insulator transition.

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Section: Experimental Technique and Setupmentioning

confidence: 99%

“…A brief sketch of the theoretical treatment is given in Appendix A of Ref. 49. More details can be found in several monographs [39][40][41] and in other publications.…”

Section: B Relaxation Mechanismsmentioning

confidence: 99%