Collapsed tetragonal phase as a strongly covalent and fully nonmagnetic state: 
Persistent magnetism with interlayer As-As bond formation in Rh-doped Ca0.8Sr0.2
Fe2As2

Zhao, K.; Glasbrenner, J.; Gretarsson, H.; Schmitz, D.; Bednarcik, J.; Etter, M.; Sun, J.; Manna, R.; Al-Zein, A.; Lafuerza, S.; Scherer, W.; Cheng, J.; Gegenwart, P.

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Collapsed tetragonal phase as a strongly covalent and fully nonmagnetic state: Persistent magnetism with interlayer As-As bond formation in Rh-doped Ca_0.8Sr_0.2Fe₂As₂

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Gretarsson, H.
Max Planck Society;

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Zhao, K., Glasbrenner, J., Gretarsson, H., Schmitz, D., Bednarcik, J., Etter, M., et al. (2018). Collapsed tetragonal phase as a strongly covalent and fully nonmagnetic state: Persistent magnetism with interlayer As-As bond formation in Rh-doped Ca_0.8Sr_0.2Fe₂As₂. Physical Review B, 97(2): 020510.

Cite as: https://hdl.handle.net/21.11116/0000-000E-E0AF-0

Abstract

A well-known feature of the CaFe2As2-based superconductors is the pressure-induced collapsed tetragonal phase that is commonly ascribed to the formation of an interlayer As-As bond. Using detailed x-ray scattering and spectroscopy, we find that Rh-doped Ca0.8Sr0.2Fe2As2 does not undergo a first-order phase transition and that local Fe moments persist despite the formation of interlayer As-As bonds. Our density functional theory calculations reveal that the Fe-As bond geometry is critical for stabilizing magnetism and the pressure-induced drop in the c lattice parameter observed in pure CaFe2As2 is mostly due to a constriction within the FeAs planes. The collapsed tetragonal phase emerges when covalent bonding of strongly hybridized Fe 3d and As 4p states completely wins out over their exchange splitting. Thus the collapsed tetragonal phase is properly understood as a strong covalent phase that is fully nonmagnetic with the As-As bond forming as a by-product.