Oct. 23 Club Meeting: Dr. Amar Karki

Paper to be discussed:

High Tc Fe-As based superconductors with skutterudite intermediary layers

1. Ni Ni, 
2. Jared M. Allred, 
3. Benny C. Chan, and 
4. Robert Joseph Cava

PNAS ∣ November 8, 2011 ∣ vol. 108 ∣ no. 45 ∣ E1019–E1026

Abstract:

It has been argued that the very high transition temperatures of the highest T_ccuprate superconductors are facilitated by enhanced CuO₂ plane coupling through heavy metal oxide intermediary layers. Whether enhanced coupling through intermediary layers can also influence T_c in the new high T_c iron arsenide superconductors has never been tested due the lack of appropriate systems for study. Here we report the crystal structures and properties of two iron arsenide superconductors, Ca₁₀(Pt₃As₈)(Fe₂As₂)₅ (the “10-3-8 phase”) and Ca₁₀(Pt₄As₈)(Fe₂As₂)₅ (the “10-4-8 phase”). Based on -Ca-(Pt_nAs₈)-Ca-Fe₂As₂- layer stacking, these are very similar compounds for which the most important differences lie in the structural and electronic characteristics of the intermediary platinum arsenide layers. Electron doping through partial substitution of Pt for Fe in the FeAs layers leads to T_c of 11 K in the 10-3-8 phase and 26 K in the 10-4-8 phase. The often-cited empirical rule in the arsenide superconductor literature relating T_c to As-Fe-As bond angles does not explain the observed differences inT_c of the two phases; rather, comparison suggests the presence of stronger FeAs interlayer coupling in the 10-4-8 phase arising from the two-channel interlayer interactions and the metallic nature of its intermediary Pt₄As₈ layer. The interlayer coupling is thus revealed as important in enhancing T_c in the iron pnictide superconductors.

Time: Oct. 23 2012, Tuesday noon.

Location: Rm. 435, Nicholson Hall

Foods and drinks will be provided.