Interplay of electronic correlations, magnetism and lattice dynamics in correlated solids
Creators: name: Khanal, Ghanashyam
Publisher: name: No Publisher Supplied
Year: 2022

description: Strongly correlated electron systems have been at the forefront of modern condensed matter physics research in recent years. In these systems, the interplay of localized electronic states due to strong electron-electron interactions and more itinerant electrons give rise to a myriad of correlated behaviors giving rise to different emergent phenomena including metal-insulator transitions, giant magnetoresistance, heavy fermion behavior, and high-temperature superconductivity among many others. As such, these materials have huge applications in modern technological advancements including modern quantum computers. However, due to the many-body nature of these correlated particles, finding the exact solution to a lot of these problems is extremely difficult if not impossible. So, modern-day research has depended heavily on theoretical computer simulations of these systems with various approximations to understand the nature and the consequence of these electronic correlations. Dynamical mean-field theory (DMFT) in combination with density functional theory (DFT), commonly called DFT+DMFT, is one of the most powerful ab-initio techniques available to address strongly correlated materials from first principles. In the last two decades, we have seen on several occasions the remarkable predictive power on electronic, magnetic, and crystal structures of these strongly correlated materials. This thesis is the result of applications of this powerful theory and its extension for lattice dynamics of strongly correlated materials. This thesis is organized as follows. After an introduction to strongly correlated materials in chapter 1, we introduce the DFT+DMFT method for correlated materials in chapter 2. Chapters 3, 4, 5, and 6 include the application of this tool to many different materials that have been part of various projects I have been involved in. In chapter 3, we present the accurate crystal structure prediction as well as the electronic correlation effects on lattice dynamics of iron-based superconductors. Chapter 4, shows the electronic and magnetic structure calculations for the series of high-pressure phases of iron-oxides. These materials, due to many experimental challenges, have only been synthesized in the last few years, and host a lot of interesting mechanisms including but not limited to one-dimensional conductivity. We study a completely different series of materials called Kamiokite, in chapter 5. These systems due to the presence of both 3d and 4d electrons, both of which are interesting in themselves, show different correlated behavior from different magnetic transitions and giant magnetoelectric coupling to huge charge excitations. As the last project, we present some of the early results of an ongoing research project in chapter 6. We show the effects of electronic correlations on the lattice dynamics of the Kagome metal CoSn. We report large correlation effects on the phonon spectra contributed not only by the correlated atom Co but also by the Sn atom. Chapter 7 concludes with the summary of each of the projects followed by references and appendices.