Center for Artificial Low Dimensional Electronic Systems

Atomic Scale Characterization of Strongly-Correlated Materials using STEM/EELS

Ji-Hwan Kwon

November 28(Tue) - November 28(Tue), 2017

Atomic Scale Characterization of Strongly-Correlated Materials using STEM/EELS

Ji-Hwan Kwon

Korea Research Institute of Standards and Science

High-T_c superconductors have attracted great interest due to their profound fundamental questions and impact for the practical applications. Short coherence length and strong dependence of doping level on critical temperature makes high-T_c superconductors sensitive to structural defects such as grain boundary, stacking faults, and planar/point defects. Aberration-corrected scanning transmission electron microscopy (STEM) combined with electron energy loss spectroscopy (EELS) allows us to investigate the atomic and electronic structures of the materials in an atomic-scale. In this talk, we reveal a various type of defects in iron-based superconductor (FeTe) and cuprate (YBa₂Cu₃O_7-x/YBCO). Fe_1+yTe thin films become a superconductor when doped with oxygen, in which the interstitially incorporated oxygen plays crucial role for emergence of superconductivity. Interstitial oxygen is directly detected by EELS and impact of interstitial oxygen on electronic/magnetic structures are studied by density functional theory. In heavy ion irradiated YBCO, a various type of defects due to irradiation are shown and spatially resolved EELS on planar defect is discussed.