All ETDs from UAB

Advisory Committee Chair

David J Hilton

Advisory Committee Members

Richard Haglund

Rohit Prasankumar

Yogesh Vohra

Lowell Wenger

Document Type

Dissertation

Date of Award

2014

Degree Name by School

Doctor of Philosophy (PhD) College of Arts and Sciences

Abstract

This dissertation covers two projects on materials with bulk electronic properties that result from strong electron-electron interactions. The first project focuses on the heavy-fermion superconductor CeCoIn5. To elucidate the electronic properties of CeCoIn5, we performed high-pressure electronic characterization and X-ray diffraction. The crystalline structure of CeCoIn5 is in the P4/mmm space group at pressures up to 51.2 GPa. Using a designer diamond anvil cell, we measured the pressure-dependent resistance up to 35 GPa at ambient temperature. To determine the resistivity, we numerically modeled the diamond anvil cell using a finite element analysis approach. The resistivity was obtained as a function of pressure at room temperature, yielding a maximum at 8.2 GPa. This peak in resistivity may be similar to the reported pressure maximum in similar materials such as CeCu2Si2. The second project of this thesis focussed on studies of the bulk electronic properties of the insulator to metal phase transition material Vanadium Dioxide (VO2). We performed three experiments to elucidate the electronic properties of this transition. We performed an experiment using nondegenerate ultrafast pump-probe spectroscopy on samples of varying surface morphology as functions of pump fluences. The growth of metallic domains from the initial heating of the pump pulse was numerically modeled with finite element analysis and showed a dependence on the initial distribution of metallic domains. Our results are consistent with heterogenous nucleation and growth of metallic islands in the parent semiconducting phase and indicate the role of surface morphology on the ultrafast response. We observed that the electronic response in the transition temperature region can not be fit with a linear superposition of the low and high temperature responses, which is consistent with a strongly correlated metal phase in the transition region. We also performed high-pressure resistance and X-ray crystallography to characterize the high-pressure metallization of VO2. We observed an exponential decay in the resistance of VO2 as a function of pressure. Using density functional theory on our crystallography results, we observed a softening of a conduction pathway between vanadium dimers that may explain the observed exponential decay in resistance.

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