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| VOLUME 91 | ISSUE 10 |
PAGE 567
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| Anion height dependence of Tc and density of states in iron based superconductors
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E. Z. Kuchinskii, I. A. Nekrasov1), M. V. Sadovskii1)
Institute for Electrophysics RAS, Ural Branch, 620016 Ekaterinburg, Russia
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Abstract
Systematic ab initio LDA calculations were performed for all
the typical representatives of recently discovered class of iron based
high-temperature superconductors: REOFe(As,P) (RE=La,Ce,Nd,Sm,Tb),
Ba2Fe2As, (Sr,Ca)FFeAs, Sr4Sc2O6Fe2P2, LiFeAs and
Fe(Se,Te). Non-monotonic behavior of total density of states at the Fermi
level is observed as a function of anion height relative to Fe layer with
maximum at about  1.37Å, attributed to changing Fe - As
(P,Se,Te) hybridization. This leads to a similar dependence of
superconducting transition temperature Tc as observed in the experiments.
The fit of this dependence to elementary BCS theory produces semiquantitative
agreement with experimental data for Tc for the whole class of iron based
superconductors. The similar fit to Allen - Dynes formula underestimates
Tc in the vicinity of the maximum, signifying the possible importance of
non - phonon pairing in this region. These results unambiguously demonstrate
that the main effect of Tc variation between different types of iron
based superconductors is due to the corresponding variation of the density of
states at the Fermi level.
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