Dr. Ni Ni

Department of Chemistry, Frick Laboratory at Princeton University

Manipulating T_c in Fe-based Superconductors through Doping and Interlayer Coupling

Searching for new superconductors and determining the key factors impacting T_c are at the core of research in superconductivity. Recently, Fe-based superconductors, the second high temperature superconductor family besides the cuprates, have been discovered to show T_cs up to 55K. The interplay of the magnetism, superconductivity and structure in Fe-based superconductors makes them a great platform for understanding unconventional superconductivity. First, the temperature-dopant concentration (T-x), temperature-extra electrons (T-e), and temperature-pressure (T-P) phase diagrams of the Ba(Fe_1-xTM_x)₂As₂ series will be presented. Quantitative analysis shows that there exists a limited range of electron counts for which superconductivity can be stabilized if the structural and magnetic phase transitions of the parent compound BaFe₂As₂ are sufficiently suppressed. Furthermore, the T_c on the underdoped side can be related to the suppression of the structural / magnetic phase transition, while T_cmax on the overdoped side is determined by the electron concentration. Second, the crystal structures and properties of two structurally and chemically similar Fe based superconductors, Pt doped Ca₁₀(Pt₃As₈)(Fe₂As₂)₅ (the ″10-3-8 phase″) with highest T_c around 11K, and Ca₁₀(Pt₄As₈)(Fe₂As₂)₅ (the ″10-4-8 phase″) with the highest T_c around 38 K, will be shown. The structural and chemical analysis of these compounds emphasizes the importance of strong interlayer coupling in enhancing T_c in Fe based superconductors.