Large trigonal-field effect on spin-orbit coupled states in a pyrochlore iridate

The half-filled topmost valence band of Ir4+ in several iridates such as Sr2IrO4, IrO2, and CaIrO3 has been proposed to originate mainly from the spin-orbit coupled J(eff) = 1/2 states. In pyrochlore iridates R2Ir2O7 (R: rare earth), some exotic electronic states are theoretically proposed by assuming J(eff) = 1/2 states. However, the octahedral coordination around Ir is trigonally distorted, which may affect the energy level scheme of Ir 5d states. Here, we report spectra of resonant elastic and inelastic x-ray scattering in Eu2Ir2O7 at the Ir L edges. A large suppression of the magnetic scattering signal at the Ir L-II edge supports the J(eff) = 1/2 picture rather than the S = 1/2 one. The inelastic scattering spectrum indicates that the magnitude of the trigonal field on the Ir4+ states is evaluated to be comparable to the spin-orbit interaction. The energy diagram of the 5d state is proposed based on the simple cluster model.