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Electron -phonon coupling in local moment systems

Hae-Kyung Jeong, University of Nebraska - Lincoln

Abstract

Phonon-related effects are strongly evident in electron spectroscopies related to band structure. These effects are seen in the unusual electronic and structural transitions exhibited at the surfaces of some local moment systems. ^ Vibrational motion of the ErAs (100) surface has been investigated. The effective surface Debye temperature, indicative of the dynamic motion of lattice normal to the surface, is 35 ± 10K. This is much smaller than the bulk Debye temperature of 353 ± 63K. This huge difference between the effective surface and bulk Debye temperature, by far more than a factor of 2 , indicates a surface layer relaxation outwards the vacuum. There is a strong signature of this surface layer lattice spacing relaxation in the shifting core level binding energy to higher binding energy in x-ray photoemission. The surface to bulk core level shift, as a function of temperature, is also an indication of a surface electronic structure perturbed from the bulk. The momentum-resolved inelastic electron energy loss has been exploited to measured the surface and bulk plasmons of ErAs (100). The effects of the electronic band structure are seen in the weak plasmon dispersion, and a contribution to the surface and bulk plasmons, from the Er 5d bands, is indicated in the decrease in the surface plasmon frequency by about 10% from the free electron value and a ratio of bulk and surface plasmon energies of about 3 , not 2 . So, electrons may couple with phonons in a number of different ways. ^ Strained Gd (0001) has spin-dependent band crossing at EF along M¯. So we can expect spin-dependent electron-phonon couplings. Spin-dependent Debye temperatures are investigated, which are 79 ± 35K and 125 ± 35K for spin majority and minority, respectively. ^ Furrowed transition metal surfaces such as Mo (112) and W (112) are remarkable for their profound anisotropy in adatom dynamics and electronic structures. Sub mono-layers of gadolinium on the furrowed substrates form the p (1 x 7) and c (2 x 2) structures, depending on coverage. These quasi-one dimensional structures of gadolinium exhibit a lattice-stiffness phase transition near 230K. This transition is evident from the effective Debye temperature extracted from the elastic scattering intensities in both low energy electron diffraction (LEED) and x-ray photoemission spectroscopy (XPS). Below the transition temperature of 230 K the gadolinium overlayer lattice is much stiffer than that observed higher temperatures. There are also changes in electronic structure and band symmetries with different coverage. This phase transition is related to the quasi-one dimensional chain structures and is not intrinsic to thicker Gd films. ^

Subject Area

Physics, Condensed Matter

Recommended Citation

Jeong, Hae-Kyung, "Electron -phonon coupling in local moment systems" (2003). ETD collection for University of Nebraska - Lincoln. AAI3116582.
http://digitalcommons.unl.edu/dissertations/AAI3116582

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