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arXiv · 0807.3968

Element-Specific Phonon Density of States of Iron in LaFeAsO_{1-x}F_{x} and La_{1-x}Ca_{x}FePO

S. Higashitaniguchi·M. Seto·S. Kitao·Y. Kobayashi·M. Saito·R. Masuda·T. Mitsui·Y. Yoda·Y. Kamihara·M. Hirano·H. Hosono
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Abstract

We have measured element-specific Fe-phonon densities of states (Fe-PDOS) of LaFeAsO_{1-x}F_{x} (x = 0, 0.11) and La_{1-x}Ca_{x}FePO (x = 0.13) by using nuclear resonant inelastic scattering of synchrotron radiation. The Fe-PDOS of superconductor LaFeAsO_{0.89}F_{0.11} (Tc = 26 K) and that of non-superconductor LaFeAsO have similar structures to both below Tc (15 K) and above Tc (298 K) and, therefore, fluorine doping does not have notable effect on the Fe-PDOS. As for the superconductor La_{0.87}Ca_{0.13}FePO (Tc = 5.4K), the entire structure of Fe-PDOS resembles with that of LaFeAsO_{1-x}F_{x}, but the energy of the highest peak is higher than that of LaFeAsO_{1-x}F_{x}. These peaks are attributed to vibrational modes between Fe and pnicogen (As and P) and the temperature-dependent energy shifts are observed for LaFeAsO_{1-x}F_{x}. Observed Fe-PDOS of LaFeAsO_{1-x}F_{x} agrees well with an previously calculated Fe-PDOS spectrum with a first-principles calculation and shows the structural resemblance with an calculated Eliashberg function #alpha^2F(x) giving small electron-phonon coupling. Therefore, our results indicate that phonons are not the main contributors to the Tc superconductivity of LaFeAsO_{1-x}F_{x}. From the experimental viewpoint, comparison of our observed Fe-PDOS and an experimentally obtained bosonic glue spectrum will be an important clue as to whether phonons are the main contributors to superconductivity in iron-pnictide superconductors.

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S. Higashitaniguchi, M. Seto, S. Kitao, Y. Kobayashi, M. Saito, R. Masuda, T. Mitsui, Y. Yoda, Y. Kamihara, M. Hirano, H. Hosono. 2008-07-25. Element-Specific Phonon Density of States of Iron in LaFeAsO_{1-x}F_{x} and La_{1-x}Ca_{x}FePO. https://arxiv.org/abs/0807.3968

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