Influence of the Material Band Structure on Attosecond Many-Body Electron-Electron Interactions in Transition Metals.

Many-body electron-electron interactions play prominent roles in correlated electron systems. Here we show that by using attosecond pulse trains, we can observe many-body electron-electron interactions that occur on attosecond timescales during photoemission. We extract the time delays associated with photoemission from occupied bands in Ni and Cu into free-electron final states. This allows us to show that photoemission from the $d$ band of Cu is delayed by \textasciitilde 100 attoseconds relative to photoemission from the same band of Ni. We attribute this difference to the fact that the $d$ band in Ni is not fully occupied, resulting in enhanced electron-electron scattering. Finally, we present a unified picture of electron-electron interactions in transition metals across a broad energy range, from \textasciitilde 0.5eV to 40eV.