Kinks in the dispersion of strongly correlated electrons

The properties of condensed matter are determined by single-particle and collective excitations and their mutual interactions. These quantum-mechanical excitations are characterized by an energy, E, and a momentum, ℏk, which are related through their dispersion, Ek. The coupling of excitations may lead to abrupt changes (kinks) in the slope of the dispersion. Kinks thus carry important information about the internal degrees of freedom of a many-body system and their effective interaction. Here, we report a novel, purely electronic mechanism leading to kinks, which is not related to any coupling of excitations. Namely, kinks are predicted for any strongly correlated metal whose spectral function shows a three-peak structure with well-separated Hubbard subbands and a central peak, as observed, for example, in transition-metal oxides. These kinks can appear at energies as high as a few hundred millielectron volts, as found in recent spectroscopy experiments on high-temperature superconductors1,2,3,4 and other transition-metal oxides5,6,7,8. Our theory determines not only the position of the kinks but also the range of validity of Fermi-liquid theory.