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We have measured element-specific Fe-phonon densities of states (Fe-PDOS) ofLaFeAsO_{1-x}F_{x} (x = 0, 0.11) and La_{1-x}Ca_{x}FePO (x = 0.13) by usingnuclear resonant inelastic scattering of synchrotron radiation. The Fe-PDOS ofsuperconductor LaFeAsO_{0.89}F_{0.11} (Tc = 26 K) and that ofnon-superconductor LaFeAsO have similar structures to both below Tc (15 K) andabove Tc (298 K) and, therefore, fluorine doping does not have notable effecton 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}, butthe energy of the highest peak is higher than that of LaFeAsO_{1-x}F_{x}. Thesepeaks are attributed to vibrational modes between Fe and pnicogen (As and P)and the temperature-dependent energy shifts are observed forLaFeAsO_{1-x}F_{x}. Observed Fe-PDOS of LaFeAsO_{1-x}F_{x} agrees well with anpreviously calculated Fe-PDOS spectrum with a first-principles calculation andshows the structural resemblance with an calculated Eliashberg function#alpha^2F(x) giving small electron-phonon coupling. Therefore, our resultsindicate that phonons are not the main contributors to the Tc superconductivityof LaFeAsO_{1-x}F_{x}. From the experimental viewpoint, comparison of ourobserved Fe-PDOS and an experimentally obtained bosonic glue spectrum will bean important clue as to whether phonons are the main contributors tosuperconductivity in iron-pnictide superconductors.

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