New correlated electron physics from new materials

Many important advances in the physics of strongly correlated electron systems have been driven by the development of new materials: for instance the filled skutterudites MT4X12 (M 1⁄4 alkali metal, alkaline earth, lanthanide, or actinide; T 1⁄4 Fe, Ru, or Os; X 1⁄4 P, As, or Sb), certain lanthanide and actinide intermetallic compounds such as URu2 xRexSi2 and CeTIn5 (T 1⁄4 Co, Rh, or Ir), and layered oxypnictides and related materials. These types of complex multinary dand f-electron compounds have proven to be a vast reservoir of novel strongly correlated electron ground states and phenomena. In these materials, the occurrence of such a wide range of ground states and phenomena arises from a delicate interplay between competing interactions that can be tuned by partial or complete substitution of one element for another, as well as the application of pressure, and magnetic fields, resulting in rich and complex electronic phase diagrams in the hyperspace of temperature, chemical composition, pressure and magnetic field. It seems clear that this type of ‘‘materials driven physics’’ will continue to play a central role in the development of the field of strongly correlated electron systems in the future, through the discovery of newmaterials that exhibit unexpected phenomena and experiments on knownmaterials in an effort to optimize their physical properties and test relevant theories. & 2009 Elsevier B.V. All rights reserved.