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Title: First-principles investigation of electron-phonon interactions in novel superconductors
Author: Fisher, Harry
ISNI:       0000 0004 5361 4639
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2014
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Despite over 100 years of scientific research, a full understanding of superconductivity remains elusive. While it is known that the electron-phonon interaction is responsible for the formation of Cooper pairs in conventional superconductors, many superconductors exhibit behaviour suggestive of more exotic pairing mechanisms. In this thesis, two novel superconducting materials are considered, monolayer transition metal dichalcogenide, MoS2, and iron-based superconductor, LaFeAsO1−xFx. The former is ideal for the study of the electron-phonon interaction, as it not only has potential applications as an atomically thin transistor, but also displays a dome-shaped superconductive state as a function of electron doping. In the latter, the superconductive state emerges from a magnetic parent compound upon flourine doping. Its high critical temperature is thought to be enhanced by magnetic fluctuation rather than being purely phonon-mediated. By using novel first-principles techniques, the electron-phonon interaction in electron doped single-layer MoS2 is investigated. The superconducting gap is calculated using the Migdal-Eliashberg theory, and by considering the electronic structure and lattice dynamics in this material, an explanation is provided for the experimentally observed doping-dependent critical temperature in this material. The origin of the doping-induced transition from a magnetic phase to a nonmagnetic phase in LaFeAsO1−xFx is determined. A new model to capture the effects of the fluorine dopants is developed, which has implications for the electron-phonon interaction in this material.
Supervisor: Giustino, Feliciano Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Physical Sciences ; Materials Sciences ; Materials modelling ; Electron-phonon ; Density functional theory ; Superconductivity