^75As-NMR/NQR study of Ba_(1-x)K_xFe_2As_2

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Date/Time:Thursday, 06 Oct 2011 - Thursday, 06 Oct 2011
Location:ROOM 5 PHYSICS Hall
Phone:512-294-2964
Channel:Condensed Matter Physics
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Hideto Fukazawa

Department of Physics, Chiba University

After the discovery of superconductivity in F-doped LaFeAsO with a superconducting transition temperature Tc = 26 K [1], K-substituted (hole-doped) BaFe2As2 was reported as the first oxygen-free iron-pnictide superconductor with Tc = 38 K [2]. The important feature of Ba1-xKxFe2As2 is that superconductivity occurs even for x = 1, although Tc itself is much lower (Tc ~ 3.5 K) than the optimum Tc. Antiferromagnetic (AF) phase which exhibits in parent compound is suppressed with increasing x and disappears around x = 0.3. For x > 0.3, spin fluctuation which arises from interband scattering between hole Fermi surface (FS) and electron FS seems to remain. Hole and electron FSs are observed at x = 0.4 by ARPES [3]. However, hole FS at Γ point becomes larger and electron FS at X point shrinks and finally change into hole FS with increase of hole career. Although it is expected that spin fluctuation becomes weaker with increasing x, the result of NQR experiment indicates that there is AF fluctuation even at x = 1 [4]. This is consistent with the results of inelastic neutron scattering which revealed that there is incommensurate AF fluctuation Q = ((1+-2 ), (1+-2 ),0) with  = 0.16 [5]. In order to reveal the overall feature of spin fluctuation in Ba1-xKxFe2As2 we performed 75As-NMR/NQR of Ba1-xKxFe2As2 [6]. In our presentation, we report the recent results of 75As-NMR/NQR of Ba1-xKxFe2As2 using single crystals (0.2 < x <= 1). If time permits, we also report the recent study of Ba1-xKxFe2As2 under pressure [7].

[1] Y. Kamihara et al.: JACS 130 (2008) 3296.
[2] M. Rotter et al.: PRL 101 (2008) 107006.
[3] T. Sato et al.: PRL 103 (2009) 047002.
[4] H. Fukazawa et al.: JPSJ 78 (2009) 083712.
[5] C. H. Lee et al.: PRL 106 (2011) 067003.
[6] M. Hirano et al.: manuscript in preparation.
[7] T. Yamazaki et al.: PRB 81 (2010) 224511.