@article{oai:niigata-u.repo.nii.ac.jp:00002598,
 author = {Ono, Yoshiaki and Yanagi, Yuki and Adachi, Naoko and Yamakawa, Youichi},
 issue = {8},
 journal = {Solid State Communications, Solid State Communications},
 month = {Apr},
 note = {We investigate the electronic states and the superconductivity in the two-dimensional 16-band d–p model extracted from a tight-binding fit to the band structure of iron pnictides, in the presence of both the Coulomb interaction between Fe d-electrons and the electron–lattice coupling g with the orthorhombic mode which is crucial for reproducing the recently observed ultrasonic softening of the elastic constant C66. Due to the cooperative effects of these interactions, the ferro-orbital order with different occupations of dyz and xdzx orbitals occurs and induces the tetragonal-orthorhombic structural transition at Ts, together with the stripe-type antiferromagnetic (AFM) order below TNTN. For a large gg case, we obtain the phase diagram consistent with the doped iron pnictides with Ts>TN for x>0, where the s++-wave superconductivity is mediated by the ferro-orbital fluctuation which is largely enhanced near the ferro-orbital QCP at Xc with Ts→0. On the other hand, for a small g case, the simultaneous phase transition occurs at Ts=TN even for x>0, where the s±-wave superconductivity is mediated by the AFM fluctuation. Both the s-wave states with full superconducting gaps are consistent with most of the experiments but only the former is considered to account for the small Tc-suppression against nonmagnetic impurities.},
 pages = {701--710},
 title = {Structural transition, ferro-orbital order and its fluctuation-mediated s++-wave superconductivity in iron pnictides},
 volume = {152},
 year = {2012}
}