title: Janus-faced influence of Hund's rule coupling in strongly correlated materials.
abstract: We show that in multiband metals the correlations are strongly affected by Hund's rule coupling, which depending on the filling promotes metallic, insulating or bad-metallic behavior. The quasiparticle coherence and the proximity to a Mott insulator are influenced distinctly and, away from single- and half-filling, in opposite ways. A strongly correlated bad metal far from a Mott phase is found there. We propose a concise classification of 3d and 4d transition-metal oxides within which the ubiquitous occurrence of strong correlations in Ru- and Cr-based oxides, as well as the recently measured high Néel temperatures in Tc-based perovskites are naturally explained.
authors.affiliation: Laboratoire de Physique des Solides, UMR8502 CNRS-Université Paris-Sud, Orsay, France.
authors.forename: Luca
authors.initials: L
authors.lastname: de' Medici
authors.forename: Jernej
authors.initials: J
authors.lastname: Mravlje
authors.forename: Antoine
authors.initials: A
authors.lastname: Georges