Kink in the dispersion of f-electrons*

Many-body interactions may result in the formation of long- lived heavy quasi-particles that exhibit kinks in their energy dispersion. Kinks are often seen in d-electron correlated systems and are attributed to many different origins, such as coupling to phonons, extended spin-fluctuations, or electron- electron correlations. We have found that the renormalization of a 5f electron band in USb2 leads to the formation of a kink characterized by two distinct regions with different quasiparticle masses, peak asymmetries, lifetimes and a record- breaking small width of 3meV. The kink energy scale of 17meV originates from renormalization of a point-like Fermi surface, and is a factor of two smaller than previously measured in correlated materials.