Doctoral Dissertations

Date of Award

8-2010

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Physics

Major Professor

George Siopsis

Committee Members

George Siopsis, John J. Quinn, Takeshi Egami, David J. Singh

Abstract

First principles calculations provide a powerful tool for sorting out the interplay of chemical composition and structure with the physical properties of materials. In this dissertation, I discuss the physical properties and their microscopic basis within this framework for following illustrative examples. (i) The Zintl phase hydrides, where I find H is anionic and the formation of covalent sp2 bonds in the Al/Ga/Al-Si planes, which is a highly unusual bonding configuration for these elements. (ii) PbTe, which shows strong coupling between the longitudinal acoustic and transverse optic modes that may explain its low thermal conductivity. (iii) The double perovskites BiPbZnNbO6 and BiSrZnNbO6, where introducing size disorder at A-site prevents the BO6 octahedra from tiling and enhances the polar behavior. (iv) FeSe, which shares the salient electronic and magnetic features of other Fe superconductors and cannot be described as a conventional electron phonon superconductor. (v) NbFe2, which is near a magnetic quantum critical point and shows strong competition between various magnetic orderings that may explain its unusual non-Fermi liquid behavior at very low temperatures. (vi) The nickel analogues of Fe superconductors LaNiPO and BaNi2As2, where I show that superconductivity is of conventional electron-phonon type in contrast to the Fe-based superconductors. (vii) Noncentrosymmetric LaNiC2, which I find is a conventional electron-phonon superconductor with intermediate coupling.

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