Spin-phonon coupling and superconductivity in iron pnictides

Early electron-phonon (el-ph) coupling calculations for iron pnictide system based on standard non-spin-polarized perturbation theory indicate that conventional el-ph coupling cannot explain the observed high Tc in these systems. However, the experimental phonon spectrum indicates features which are not produced in the standard linear response non-magnetic phonon calculations. The magnetic phonon calculations clearly indicate that the observed phonon-DOS at room temperature is much closer to the magnetic phonon-DOS rather than non-magnetic DOS and Fe-magnetism must present in the iron-pnictide systems all the time [1-2]. Thus we need to calculate the magnetic el-phonon coupling with the Fe-spins included before we can rule out any type of phonon-mediated mechanism. In order to carry out such complex self-consistent magnetic el-ph coupling calculations we are developing a finite-displacement method in which both the phonon energies and the corresponding el-ph coupling constant are easily calculated. Implications of our results on the mechanism of superconductivity in iron pnictides will be discussed. Finally, we will compare our calculations with the available phonon energy and line-width measurements. \\[4pt] [1] T. Yildirim, Phys. Rev. Lett. 102, 037003 (2009). \\[0pt] [2] T. Yildirim, Physica C 469, 425-441 (2009).