[PAST EVENT] Zhen Xing: Physics Dissertation Defense
Zhen Xing, Final Oral Examination for the Ph.D., Title: "Charge Dynamics in the Metallic and Superconducting States of the Electron-doped 122-type Iron Arsenides."
Abstract: Understanding charge dynamics and the origin of superconductivity in iron-based materials is one of the most important topics in condensed matter physics. Among different structures of iron-based materials, 122-type iron arsenides are of considerable interest due to their diverse phase diagrams, relatively high superconducting transition temperatures, and the availability of high quality single crystals. In this dissertation, we study charge dynamics of the electron-doped 122-type iron arsenides in the metallic and superconducting states using broadband infrared spectroscopy. We observe significant electron-electron interactions in the metallic tetragonal state of rare-earth doped (La- and Pr-doped) CaFe2As2. We also observe weakening of electronic correlations and a decrease of Drude spectral weight upon the transition to the collapsed tetragonal phase in Pr-doped CaFe2As2. By investigating the infrared absorption spectra of BaFe1.9Pt0.1As2, we find that this superconductor has fully gapped Fermi surfaces. Importantly, we observe strong-coupling electron-boson interaction features in the infrared absorption spectra. By using two modeling methods which include strong-coupling effects via the Eliashberg function, we obtain a good quantitative description of the energy gaps and the strong-coupling features. Our experimental data and analysis provide compelling evidence that superconductivity in BaFe1.9Pt0.1As2 is induced by the coupling of electrons to a low energy bosonic mode.
Bio: Zhen Xing was born in Harbin, Heilongjiang, China. He developed great interest in natural science since he was a little boy. He received his B.S. at Harbin Institute of Technology in 2011 and in the same year he began advanced studies of physics at William & Mary. He joined Dr. Qazilbash's group in the summer 2012 and has been working on infrared spectroscopy of metallic and superconducting iron arsenides.