Date of Award
Doctor of Philosophy
Physics and Astronomy
B. H. Harmon
Studies of the electron-phonon interaction were carried out for fcc La by the efficient tight-binding method. This scheme was then extended and generalized to surface studies. Application of this extended scheme to the W(001) surface provided detailed information about the driving mechanism for surface reconstruction. Together with the further studies on the Mo(001) surface, our investigation showed very promising potential applications of this scheme to various surface phonon and surface phase transition studies;For the fcc La, first-principles pseudopotential band-structure calculations were performed and revealed a small but sharp nesting feature of the Fermi surface. Then the non-orthogonal tight binding parameters were derived from the first-principles results and lattice dynamics calculations were carried out with the tight-binding scheme. The calculated phonon dispersion curves showed very good agreement with neutron scattering data. Our detailed analysis revealed the crucial role played by d-electron, the speculated role of the f-levels contribution was clarified, and the phonon spectrum under high pressure (>50 Kbar) was predicted. The unique properties of fcc La, for example, the negative thermal expansion coefficient and relatively high superconducting temperature, were explained in terms of the anomalously strong electron-phonon coupling. Also, the possible connection with the interesting phase transformation observed at high pressure was explored;The calculations for W(001) p(1x1) surface phonons successfully demonstrated the electronic origin of the c(2x2) surface reconstruction. The reason for the stable M[subscript]1 and soft M[subscript]5 surface phonon modes was found to be the dramatic differences in their electron-phonon coupling matrix elements. The subtle interplay between the Fermi surface nesting and real-space d-orbital interaction was found to cause the surface reconstruction. Subsequent studies on the Mo(001) surface further established the relationship between these competing effects and surface reconstruction geometries. Our calculated surface phonon dispersion curves for W(001) were later confirmed by helium scattering experimental results. ftn*DOE Report IS-T 1286. This work was performed under contract No. W-7450-Eng-82 with the U.S. Department of Energy.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Wang, Xuewen, "Theoretical investigations of phonon anomalies in fcc La and W(001) " (1987). Retrospective Theses and Dissertations. 9315.