Evolution from Itinerant Antiferromagnet to Unconventional Superconductor with Fluorine Doping in LaFeAs(O1-xFx) Revealed by 75As and 139La Nuclear Magnetic Resonance

2008/04/30 by Yusuke Nakai, Kenji Ishida, Yoichi Kamihara +2 · 298 citations
Materials Science · Physics and Astronomy · #Antiferromagnetism #Coherence (philosophical gambling strategy) #Coherence length #Doping #Iron-based superconductors research #Magnetic and transport properties of perovskites and related materials #Magnetic field #Pseudogap #Spectral line #Spin (aerodynamics) #Superconductivity #Superconductivity in MgB2 and Alloys #cond-mat.str-el #cond-mat.supr-con

paper · pdf · open access · doi:10.1143/jpsj.77.073701

published in Journal of the Physical Society of Japan 77(7), 073701 (Physical Society of Japan) · 5 pages, 5 figures, to appear in Journal of the Physical Society of Japan Vol.77No.7

arxiv created 2008/06/04 · openalex publication_date 2008/06/26 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05

Abstract

We report experimental results of ⁷⁵As and ¹³⁹La nuclear magnetic resonance (NMR) in the iron-based layered La(O_1-xF_x)FeAs (x= 0.0, 0.04 and 0.11) system. In the undoped LaOFeAs, 1/T₁ of ¹³⁹La exhibits a distinct peak at T_N ~ 142 K below which the spectra become broadened due to the internal magnetic field attributed to an antiferromagnetic (AFM) ordering. In the 4% F-doped sample, 1/T₁T exhibits a Curie-Weiss temperature dependence down to 30 K, suggesting the development of AFM spin fluctuations with decreasing temperature. In the 11% F-doped sample, in contrast, pseudogap behavior is observed in 1/T₁T both at the ⁷⁵As and ¹³⁹La site with a gap value of ~172 K. The spin dynamics vary markedly with F doping, which is ascribed to the Fermi-surface structure. As for the superconducting properties for the 4% and 11% F-doped samples, 1/T₁ in both compounds does not exhibit a coherence peak just below T_c and follows a T³ dependence at low temperatures, which suggests unconventional superconductivity with line-nodes. We discuss similarities and differences between La(O_1-xF_x)FeAs and cuprates, and also discuss the relationship between spin dynamics and superconductivity on the basis of F doping dependence of T_c and 1/T₁.

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