Structure of spin excitations in heavily electron-doped Li0.8Fe0.2ODFeSe superconductors

Heavily electron-doped iron-selenide high-transition-temperature (high-T-c) superconductors, which have no hole Fermi pockets, but have a notably high T-c, have challenged the prevailing s(+/-) pairing scenario originally proposed for iron pnictides containing both electron and hole pockets. The microscopic mechanism underlying the enhanced superconductivity in heavily electron-doped iron-selenide remains unclear. Here, we used neutron scattering to study the spin excitations of the heavily electron-doped iron-selenide material Li0.8Fe0.2ODFeSe (T-c = 41K). Our data revealed nearly ring-shaped magnetic resonant excitations surrounding (pi, pi) at similar to 21 meV. As the energy increased, the spin excitations assumed a diamond shape, and they dispersed outward until the energy reached similar to 60 meV and then inward at higher energies. The observed energy-dependent momentum structure and twisted dispersion of spin excitations near (pi, pi) are analogous to those of hole-doped cuprates in several aspects, thus implying that such spin excitations are essential for the remarkably high T-c in these materials.