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Phys. Rev. B 78, 174507 (2008) [5 pages]

Iron-specific phonon density of states in the superconductors LaFeAsO1−xFx and La1−xCaxFePO

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Satoshi Higashitaniguchi1,2, Makoto Seto1,2,3, Shinji Kitao1,2, Yasuhiro Kobayashi1,2, Makina Saito1,2, Ryo Masuda2,3, Takaya Mitsui2,3, Yoshitaka Yoda2,4, Yoichi Kamihara5, Masahiro Hirano5, and Hideo Hosono5,6,7
1Research Reactor Institute, Kyoto University, Kumatori-cho, Sennan-gun, Osaka 590-0494, Japan
2CREST, Japan Science and Technology Agency, Honcho Kawaguchi, Saitama 332-0012, Japan
3Japan Atomic Energy Agency, 1-1-1 Koto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan
4Japan Synchrotron Radiation Research Institute, 1-1-1 Koto, Sayo-cho, Sayo-gun, Hyogo 679-5198, Japan
5ERATO-SORST, JST, Frontier Research Center, Tokyo Institute of Technology, Mail Box S2-13, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan
6Materials and Structures Laboratory, Tokyo Institute of Technology, Mail Box R3-1, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan
7Frontier Research Center, Tokyo Institute of Technology, Mail Box S2-13, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan

Received 22 August 2008; published 7 November 2008

We measured element-specific Fe-phonon densities of states (Fe-PDOSs) of LaFeAsO1−xFx (x=0,0.11) and La1−xCaxFePO (x=0.13) by nuclear resonant inelastic scattering of synchrotron radiation. Since the bands crossing the Fermi edge are mainly Fe 3d bands, Fe is the key element for iron pnictide superconductivity, and therefore element-specific Fe-PDOS offers crucial information on the phonon contribution in iron pnictide superconductors. The measured Fe-PDOSs of superconductor LaFeAsO0.89F0.11 (Tc=26 K) and that of nonsuperconductor LaFeAsO have similar structures both below Tc (15 K) and above Tc (298 K); therefore, fluorine doping does not have a notable effect on the Fe-PDOS. The measured Fe-PDOS of LaFeAsO1−xFx agrees well with Fe-PDOS spectrum determined from a previous first-principles calculation and shows structural resemblance with a calculated Éliashberg function α2F(ω), which indicates small electron-phonon coupling. Therefore, our results indicate that phonons are not the main contributors to the high-Tc superconductivity of LaFeAsO1−xFx.

© 2008 The American Physical Society

URL:
http://link.aps.org/doi/10.1103/PhysRevB.78.174507
DOI:
10.1103/PhysRevB.78.174507
PACS:
74.25.Kc, 63.10.+a, 71.90.+q, 76.80.+y
 
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