Evidence for strong 5d electron correlations in the pyrochlore Y₂Ir₂O₇ studied using high-resolution photoemission spectroscopy

We report an unusual behavior of highly extended 5d electrons in Y₂Ir₂O₇ belonging to the pyrochlore family of great current interest, using high-resolution photoemission spectroscopy. The experimental bulk spectra reveal signature of an intense lower Hubbard band in addition to the weak intensities in the vicinity of the Fermi level, ϵ_F. This provides direct evidence for strong electron correlation among the 5d electrons, which is in sharp contrast to the observation in other Ir compounds. The influence of electron correlation is also manifested by close to ∣ϵ−ϵ_F∣² dependence of spectral line shape near ϵ_F of the high-resolution spectrum at 300 K. The spectral line shape evolves to a ∣ϵ−ϵ_F∣^1.5 dependence below Curie temperature, emphasizing the importance of electron-magnon coupling in the magnetically ordered phase.