Revealing the electronic structure of iridates with light and how it can be controlled through epitaxy

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Abstract
In this thesis we use molecular beam epitaxy (MBE) growth combined with in situ angle-resolved photoemission spectroscopy (ARPES) to control the electronic structure of iridates via epitaxial strain, doping and heterostructuring, where spin-orbit coupling (SOC) and Coulomb repulsion (U) are comparable energy scales leading to emergent correlated and topological properties. We describe adsorption controlled growth methods used to synthesize phase pure, crystalline, iridate thin films including IrO2, SrIrO3 and Sr2IrO4. We report ARPES measurements on IrO2, and discover that it hosts Dirac nodal lines (DNLs). These DNLs are protected against spin-orbit coupling and cross the Fermi level. This means that they are likely responsible for the electronic properties. We demonstrate high quality crystal growth on multiple faces of TiO2 and show, using density functional theory calculations, that epitaxial strain on certain substrates can gap these DNL states. We use substitutional diffusion to synthesize Sr2-xKxIrO4 and measure its electronic structure for the first time. We demonstrate that intrinsic hole doping collapses the Mott gap in contrast with previous reports on Sr2Ir1-xRhxO4. We show that the doping phase diagram of Sr2IrO4 is more symmetric than previously known. This result is significant because it provides insight into the comparison between iridates and cuprate superconductors and informs the search for superconductivity in iridates. Finally, we employ ARPES to investigate how the low-energy electronic structure is modified at an oxide interface. We synthesize and measure a series of heterostructures (SrIrO3)n/(SrRuO3)20 n=1-8 and demonstrate that the interface results in 0.13 electrons being transferred to SrRuO3. This technique provides previously inaccessible information about the electronic structure, giving us novel insights into the origin of the magnetic properties of these heterostructures.
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210 pages
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Date Issued
2020-12
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Keywords
Interfaces; Iridates; Photoemission; Quantum Materials; Spectroscopy; Thin films
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Committee Chair
Shen, Kyle M.
Committee Co-Chair
Committee Member
Kim, Eunah
Schlom, Darrell
Degree Discipline
Physics
Degree Name
Ph. D., Physics
Degree Level
Doctor of Philosophy
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Government Document
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Attribution-NonCommercial-ShareAlike 4.0 International
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dissertation or thesis
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