Study on the Electronic Band Structure of the Spinel Superconductor LiTi2O4

Abstract: This master’s thesis focuses on investigating the electronic properties of the superconducting spinel compound LiTi2O4 by means of computational and experimental effort. The title compound has been extensively studied in the past years, being the only known superconducting spinel oxide with relatively high Tc = 11.5 K. Even so, the origin of its superconducting mechanism is under debate, and its anomalous superconductivity is still inquired. Thanks to the recently developed ability to produce high-quality epitaxial LiTi2O4 thin films, a renewed research interest in this compound has matured. With this work, we partake in this challenge and present combined experimental and computational results on the electronic band structure of the material. Density functional theory (DFT) has been employed for the first principle electronic structure calculations performed with the Quantum ESPRESSO software. Furthermore, thin-film samples were in-situ realized with the pulsed laser deposition (PLD) method and investigated through the angle-resolved photoemission spectroscopy (ARPES) technique conducted at the ULTRA end-station of the SLS synchrotron facility at PSI in Switzerland. Here, we report the computed electronic band structure of LiTi2O4, with a detailed investigation of its density of states and Fermi surface. Further, we compare these calculations with the obtained experimental ARPES data. Emerging from this study are results supporting the non-conventional superconducting nature of LiTi2O4, which presents coexisting correlation effects, such as electron-phonon coupling and enhanced electron-electron interactions.