Elena Corbae, Stanford University

Abstract

While the superconducting transition temperature of hole doped BaFe₂As₂ decreases from the optimally doped region, superconductivity does not completely disappear even for the fully doped KFe₂As₂ compound. This presents a stark difference compared to the overdoped region of the cuprates and thus offers an opportunity to gain insight into the universality and diversity of these novel superconductors. Additionally, electronic structure calculations lack consistent results across doping levels, with no experimental benchmark. Angle Resolved Photoemission Spectroscopy (ARPES) is a natural technique to investigate these anomalies. Thus far, most ARPES superconducting gap measurements of Ba_1-xK_xFe₂As₂ have focused in the vicinity of optimal doping (x=0.4). This is mainly due to limitations of energy resolution and sample temperature of the ARPES instrument compared to the superconducting gap magnitude and transition temperature away from the optimal doping. We use ARPES to study three doping levels (x=0.53, 0.78, 0.89) of Ba_1-xK_xFe₂As₂ above optimal doping at low temperatures and high energy resolution. We find there is a strong renormalization change of bands across the Lifshitz transition. We further seek to understand the origin of this change and its relation to the displayed physical phenomena.