Evidence for strong5delectron correlations in the pyrochloreY2Ir2O7studied using high-resolution photoemission spectroscopy

Abstract

We report an unusual behavior of highly extended $5d$ electrons in ${\mathrm{Y}}_{2}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7}$ 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 $\ensuremath{\mid}ϵ\ensuremath{-}{ϵ}_{F}{\ensuremath{\mid}}^{2}$ dependence of spectral line shape near ${ϵ}_{F}$ of the high-resolution spectrum at $300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The spectral line shape evolves to a $\ensuremath{\mid}ϵ\ensuremath{-}{ϵ}_{F}{\ensuremath{\mid}}^{1.5}$ dependence below Curie temperature, emphasizing the importance of electron-magnon coupling in the magnetically ordered phase.