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Materials Characterization

Clues for absence of superconductivity in an iron-based material


Figure 1: Temperature-dependence of Hall effect (RH) and Seebeck (S) are associated with a large Fermi surface modification at the structural transition (dashed line) between collapsed-tetragonal to tetragonal phase, preventing superconductivity of CaFe2As2 at low temperatures. The change in the Fermi surface topology for this single crystal is confirmed in this manuscript, by angle-resolved photoemission spectroscopy.

The electronic properties of CaFe2As2, using a combination of bulk transport measurements and surface photoemission spectroscopy, have revealed reasons for the lack of superconductivity. These results support the suggested role of magnetism and spin fluctuations in iron-based superconductors. 

In unconventional superconductors, weak magnetism and strong spin-lattice coupling collaborate towards the emergence of high-temperature superconducting state. CaFe2As2 has a special position among the iron-based superconductors, due to its complex relationship between magnetism and superconductivity.

In this study, the lack of magnetism and superconductivity in the low-temperature phase of CaFe2As2 is associated with specific features of the electronic structure. Using extensive low temperature transport (see Figure 1), x-ray diffraction, and high-resolution angle-resolved photoelectron spectroscopy measurements, together with a theoretical model, we show evidence for a large modification of the electronic properties when the structure changes on cooling, fully explain the lack of magnetism and bulk superconductivity. These results extend our understanding of the electronic structure effects that lead to superconductivity.

K. Gofryk, B. Saparov, T. Durakiewicz, A. Chikina, S. Danzebacher, D. V. Vyalikh, M. J. Graf, and A. S. Sefat, “Fermi-surface reconstruction and complex phase equilibria in CaFe2As2,” Phys. Rev. Lett. 112, 186401 (2014).

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