Switching of Intra-orbital Spin Excitations in Electron-doped Iron Pnictide Superconductors

Abstract

We investigate the doping dependence of the magnetic excitations in the two-superconducting-dome system LaFeAsO_1−xD_x. Using inelastic neutron scattering, spin fluctuations at different wave numbers were observed under both superconducting domes around x =0.1 and 0.4 but vanished at x =0.2 corresponding to the T_c valley. Theoretical calculations indicate that the characteristic doping dependence of the spin fluctuations is rationally explained as a consequence of the switching of the two intra-orbital nestings within Fe-3d_{YZ, ZX} and Fe-3d_X2−Y2 by electron doping. The present results imply that the multiorbital nature plays an important role in the doping and/or material dependence of the T_c of the iron pnictide superconductors.