Berlin 2015 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 110: Superconductivity: Fe-based Superconductors – Theory
TT 110.1: Talk
Friday, March 20, 2015, 09:30–09:45, H 2053
Mass renormalization and unconventional pairing in multi-band Fe-based superconductors- a phenomenological approach — •S.-L. Drechsler1, S. Johnston2, D. Efremov1, V. Grinenko1, H. Rosner3, and K. Kikoin4 — 1IFW-Dresden — 2Inst. of Quantum Matter, University of Brit. Coulumbia, Vancouver, Canada — 3MPI-cPfS, Dresden, — 4Tel Aviv University, Israel
Combining DFT calculations of the density of states and plasma frequencies with experimental thermodynamic, optical, ARPES, and dHvA data taken from the literature, we estimate both the high-energy (Coulomb, Hund’s rule coupling) and the low-energy (el-boson coupling) electronic mass renormalization [H(L)EMR] for typical Fe-pnictides with Tc<40 K, focusing on (K,Rb,Cs)Fe2As2, (Ca,Na)122, (Ba,K)122, LiFeAs, and LaFeO1−xFxAs with and without As-vacancies. Using Eliashberg theory we show that these systems can NOT be described by a very strong el-boson coupling constant λ ∼≥ 2, being in conflict with the HEMR as seen by DMFT, ARPES and optics. Instead, an intermediate s± coupling regime is realized, mainly based on interband spin fluctuations from one predominant pair of bands. For (Ca,Na)122, there is also a non-negligible intraband el-phonon/orbital fluctuation intraband contribution. The coexistence of magnetic As-vacancies and high-Tc=28 K for LaFeO1−xFxAs1−δ excludes an orbital fluctuation dominated s++ scenario at least for that system. In contrast, the line nodal BaFe2(As,P)2 near the quantum critical point is found as a superstrongly coupled system. The role of a pseudo-gap is briefly discussed for some of these systems.