2012/07/22 by Antoine Georges, Luca de' Medici, Jernej Mravlje · 5 citations
Physics and Astronomy · #cond-mat.str-el #cond-mat.supr-con
paper · pdf · doi:10.1146/annurev-conmatphys-020911-125045
published as Annual Reviews of Condensed Matter Physics 4, 137-178 (2013) · Submitted to Annual Reviews in Condensed Matter Physics
arxiv created 2012/07/22 · arxiv updated 2013/03/20
Strong electronic correlations are often associated with the proximity of a Mott insulating state. In recent years however, it has become increasingly clear that the Hund's rule coupling (intra-atomic exchange) is responsible for strong correlations in multi-orbital metallic materials which are not close to a Mott insulator. Hund's coupling has two effects: it influences the energetics of the Mott gap and strongly suppresses the coherence scale for the formation of a Fermi-liquid. A global picture has emerged recently, which emphasizes the importance of the average occupancy of the shell as a control parameter. The most dramatic effects occur away from half-filling or single occupancy. The theoretical understanding and physical properties of these `Hund's metals' are reviewed, together with the relevance of this concept to transition-metal oxides of the 3d, and especially 4d series (such as ruthenates), as well as to the iron-based superconductors (iron pnictides and chalcogenides).