Ph.D. Candidate: Alfred Cheung
Research Advisor: Srinivas Raghu
Date: Monday Nov. 25, 2019
Time: 12 PM
Location: McCullough 335
Title: Unconventional superconductors and interplay with spin-orbit coupling and electronic interactions
Abstract: It can be said that a lot of present day research on superconductivity is focused on unconventional superconductors. That is not surprising given that any superconductor that is not well described by the conventional BCS theory is defined to be unconventional, from the high-Tc cuprates to heavy fermion superconductors, among many classes. In this thesis, we will study various examples of unconventional superconductors and how their behaviors are driven and affected by interactions such as spin-orbit coupling, external magnetic fields, and atomic electronic interactions. The first part of this thesis focuses on how spin-orbit coupling and atomic interactions interplay to affect the kinds of on-site superconducting pairing states that are allowed by symmetry. Using group theory and mean field equations, we deduce the conditions under which spin triplet, orbital singlet on-site pairing states can be stabilized in multi-orbital d-electron based systems. Next, we turn to an entirely separate class of unconventional superconductors -- the uranium based heavy fermion superconductor UCoGe where we again apply group theory and Landau theory analyses to make predictions on the phase diagram of this system. The phase diagram of UCoGe permits coexistence of superconductivity and ferromagnetism. We study the nature of the phase transitions between the superconducting, ferromagnetic, and coexisting phases.