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arXiv · 0909.0318

Origin of critical-temperature enhancement of an iron-based high-T_c superconductor, LaFeAsO_{1-x}F_{x} : NMR study under high pressure

T. Nakano·N. Fujiwara·K. Tatsumi·H. Okada·H. Takahashi·Y. Kamihara·M. Hirano·H. Hosono
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Abstract

Nuclear magnetic resonance (NMR) measurements of an iron (Fe)-based superconductor LaFeAsO_{1-x}F_x (x = 0.08 and 0.14) were performed at ambient pressure and under pressure. The relaxation rate 1/T_1 for the overdoped samples (x = 0.14) shows T-linear behavior just above T_c, and pressure application enhances 1/T_1T similar to the behavior of T_c. This implies that 1/T_1T = constant originates from the Korringa relation, and an increase in the density of states at the Fermi energy D(E_F) leads to the enhancement of T_c. In the underdoped samples (x = 0.08), 1/T_1T measured at ambient pressure also shows T-independent behavior in a wide temperature range above T_c. However, it shows Curie-Weiss-like T dependence at 3.0 GPa accompanied by a small increase in T_c, suggesting that predominant antiferromagnetic fluctuation suppresses development of superconductivity or remarkable enhancement of T_c. The qualitatively different features between underdoped and overdoped samples are systematically explained by a band calculation with hole and electron pockets.

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T. Nakano, N. Fujiwara, K. Tatsumi, H. Okada, H. Takahashi, Y. Kamihara, M. Hirano, H. Hosono. 2010-03-11. Origin of critical-temperature enhancement of an iron-based high-T_c superconductor, LaFeAsO_{1-x}F_{x} : NMR study under high pressure. https://doi.org/10.1103/physrevb.81.100510

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