NMR investigation of the iron-based superconductors Ca4(Mg,Ti)3Fe2As2O8−y and Ca5(Sc,Ti)4Fe2As2O11−y
Y. Tomita, H. Kotegawa, Y. Tao, H. Tou, H. Ogino, S. Horii, K. Kishio, J. Shimoyama
DOI 10.1103/PhysRevB.86.134527 · Physical Review B
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Abstract
75As and 45Sc NMR measurements unravel the electronic state for Fe-based superconductors with perovskite-type blocking layers Ca4(Mg,Ti)3Fe2As2O8−y (Tconset=47 K) and Ca5(Sc,Ti)4Fe2As2O11−y (Tconset=41 K). In Ca5(Sc,Ti)4Fe2As2O11−y, the nuclear spin relaxation rate 1/T1 shows pseudogap behavior below ∼80 K, suggesting that the electronic state is similar to that of the LaFeAs(O,F) system with moderate electron doping. The presence of the pseudogap behavior gives an interpretation that the holelike band (so-called γ pocket) is located just below the Fermi level from the analogy to the LaFeAs(O,F) system and the disappearance of the γ pocket yields the suppression of the low-energy spin fluctuations. On the other hand, in Ca4(Mg,Ti)3Fe2As2O8−y, satisfying the structural optimal condition for higher Tc among the perovskite systems, the extrinsic contribution, which presumably originates in the Ti moment, is observed in 1/T1T; however, the moderate temperature dependence of 1/T1T appears by its suppression under high magnetic field. In both systems, the high Tc of ∼40 K is realized in the absence of the strong development of the low-energy spin fluctuations. The present results reveal that the structural optimization does not induce the strong development of the low-energy spin fluctuations. If we consider that superconductivity is mediated by spin fluctuations, the structural optimization is conjectured to provide a benefit to the development of the high-energy spin fluctuations irrespective to the low-energy part.
Source-reported materials — not catalogue approval
| Formula | Reported Tc (K) | Pressure (GPa) | Type |
|---|---|---|---|
| Ca4(Mg,Ti)3Fe2As2O8-y Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 47 | Pressure unresolved | onset |
| Ca5(Sc,Ti)4Fe2As2O11-y Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 41 | Pressure unresolved | onset |
| Ca4(Mg,Ti)3Fe2As2O8-y Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 43 | Pressure unresolved | onset |
| Ca5(Sc,Ti)4Fe2As2O11-y Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 36 | Pressure unresolved | onset |
| Sr4(Mg,Ti)2Fe2As2O6-y Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 36.7 | Pressure unresolved | onset |
| Sr4V2Fe2As2O6-y Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 37.2 | Pressure unresolved | onset |
| Ca4(Sc,Ti)3Fe2As2O8-y Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 34.8 | Pressure unresolved | onset |
| Ca6(Sc,Ti)5Fe2As2O14-y Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 43.3 | Pressure unresolved | onset |
| Ca5(Mg,Ti)4Fe2As2O11-y Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 43 | Pressure unresolved | onset |
| Ca8(Mg,Ti)6Fe2As2O18-y Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 41.7 | Pressure unresolved | onset |
| Ca6(Al,Ti)4Fe2As2O12-y Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 39 | Pressure unresolved | onset |
| Ca4Al2Fe2As2O6-y Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 28.3 | Pressure unresolved | onset |
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