The collapsed tetragonal phase as a strongly covalent and fully nonmagnetic state: persistent magnetism with interlayer As-As bond formation in Rh-doped Ca$_{0.8}$Sr$_{0.2}$Fe$_2$As$_2$
| Autor: | Zhao, K., Glasbrenner, J. K., Gretarsson, H., Schmitz, D., Bednarcik, J., Etter, M., Sun, J. P., Manna, R. S., Al-Zein, A., Lafuerza, S., Scherer, W., Cheng, J. G., Gegenwart, P. |
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| Rok vydání: | 2017 |
| Předmět: | |
| Zdroj: | Phys. Rev. B 97, 020510 (2018) |
| Druh dokumentu: | Working Paper |
| DOI: | 10.1103/PhysRevB.97.020510 |
| Popis: | A well-known feature of CaFe$_{2}$As$_{2}$-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 Ca$_{0.8}$Sr$_{0.2}$Fe$_{2}$As$_{2}$ 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 that the pressure-induced drop in the $c$ lattice parameter observed in pure CaFe$_{2}$As$_{2}$ is mostly due to a constriction within the FeAs planes. These phenomena are best understood using an often overlooked explanation for the equilibrium Fe-As bond geometry, which is set by a competition between covalent bonding and exchange splitting between strongly hybridized Fe $3d$ and As $4p$ states. In this framework, the collapsed tetragonal phase emerges when covalent bonding completely wins out over 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 byproduct. Comment: 6 pages, 2 figures, and 1 table. Supplemental materials are available by request |
| Databáze: | arXiv |
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