Seminarium Fizyki Materii Skondensowanej

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, k, which are related through their dispersion, E(k). 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. A novel, purely electronic mechanism leading to kinks, which is not related to any coupling of excitations will be discussed in my talk. 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. Our theory determines not only the position of the kinks but also the range of validity of Fermi-liquid theory. K. Byczuk, M. Kollar, K. Held, Y.-F. Yang, I. A. Nekrasov, Th. Pruschke and D. Vollhardt, Nature Physics 3, 168 - 171 (2007)