Of Substitution and Doping: Spatial and Electronic Structure in Fe Pnictides

Abstract

A highly intriguing aspect in iron-pnictide superconductors is the composition-dependent electronic structure, in particular the question if and how charge carriers are introduced to the system upon substitution of Ba by alkali metals or of Fe by other transition metals, TM. We report on a systematic study of spatial structure and electronic states by x-ray diffraction and x-ray absorption on a large number of compositions in the (Ba,K)(Fe,TM) 2 As 2 family. The coherent combination of detailed structural information with an in-depth analysis of the electronic structure allows us to sensitively disentangle (charge-carrier) "doping" effects from "substitutional" effects. Results include a doping character that is site-decoupled, as well as TM 3d energy-level schemes that exhibit non-standard level sequences and even t 2 -e level crossings. Our study indicates that doping per se seems to play a lesser role than expected for pnictide superconductivity and magnetism.

Electronic structures and spin states of BaFe2As2 and SrFe2As2 probed by x-ray emission spectroscopy at Fe an

“…A systematic study of the electronic structures of the doped BaFe 2 As 2 and SrFe 2 As 2 has been reported by XAS at L 2,3 absorption edge. 27,28 Although the shift in the energy position of the L 3 -edge observed maximum peak, the study indicated that the doping plays a lesser role for pnictide superconductivity and magnetism. We note that the XAS study at the Fe and As K absorption edges was advantageous because we now know the spin state and the d-p hybridization, respectively.…”

Rediscovering the Crystal Chemistry of Borides

“…Borides with networks of boron atoms: crystal structure of AlB 2 (ICSD 193381, AlB 2(hex) structure). [295] Boron atoms are in gray, metal atoms are in blue.…”

Effect of Biaxial Strain on the Phase Transitions of Ca(Fe1−xCox)Böhmer1, Sapkota2, Kreyßig3 et al. 2017Phys. Rev. Lett.281340View full textAdd to dashboardCite

“…The variety of suitable tuning parameters includes diverse chemical substitutions [17,20], hydrostatic pressure [17,21,22], epitaxial strain in thin films [23][24][25] and uniaxial pressure [26][27][28][29][30]. In Ca(Fe 1−x Co x ) 2 As 2 , substitution of Co for Fe suppresses a coupled first-order magneto-structural transition at T s,N and induces superconductivity with a maximum T c of 16 K [31].…”