arXiv:1001.1098v1 [cond-mat.str-el] 7 Jan 2010 Genesis of coexisting itinerant and localized electrons in Iron Pnictides Luca de’ Medici · Syed R. Hassan · Massimo Capone Received: date / Accepted: date The two classes of materials share indeed several fea- tures among which we may quote the structure, which is quite similar, with FeAs layers playing a similar role of CuO planes, and the observation that in both cases su- perconductivity appears doping a magnetically ordered parent compound, and follows a dome behavior as a function of doping. An important different lies in the nature of the par- ent compound. In the cuprates the half-filled system is an insulator which is usually considered a Mott insu- lator, testifying the central role of electron correlations (Even if it has been recently proposed that the degree of correlation can be smaller than usually believed[2]). The undoped pnictides are instead still metallic, de- spite the magnetic ordering, suggesting a weaker de- gree of electronic correlations. The actual strength of correlation in pnictides is lively debated: while there is no obvious reason to invoke correlation as the key player in the game as it happens in cuprates, it has been proposed that these compounds are actually close to a Mott transition[3]. Another peculiarity of pnictides is that, according to density-functional theory calculations, all the five d-bands of iron are relevant as opposed to the sin- gle copper band of the cuprates. Multiple bands cross- ing the Fermi level are confirmed by angular resolved photoemission. The relevance of multiband effects can solve the discrepancy between different estimates of the role of correlations. Indeed electron correlation can in- duce a much richer physics in multiband systems with respect to single band. In particular, different bands can be affected differently by correlations, and even- tually one can have an orbital-selective Mott transi- tion (OSMT), in which some bands become insulat- ing and others are metallic. Signatures of an orbital- selective behavior have been detected by angle-resolved Since 1986, each time a new ”high-temperature” su- perconductor has been discovered, it has been a nat- ural temptation to compare the new materials to the cuprates, looking for unifying aspects which could shed light on the key mechanism for high-temperature super- conductivity. This temptation is probably stronger then ever in the case of the iron-based ”pnictides”, the sec- ond family of transition-metal-based superconductors with critical temperature exceeding 50K[1]. Abstract We show how the general features of the electronic structure of the Fe-based high-Tc supercon- ductors are a natural setting for a selective localiza- tion of the conduction electrons to arise. Slave-spin and Dynamical mean-field calculations support this picture and allow for a comparison of the magnetic properties with experiments. Keywords Iron Pnictides · Orbital-selective Mott transition PACS 71.30.+h, 71.10.Fd, 71.27.+a 1 Introduction Noname manuscript No. (will be inserted by the editor) L. de’ Medici Laboratoire de Physique des Solides, Univ. Paris-Sud, CNRS, UMR 8502, F-91405 Orsay Cedex, France. Tel.: +33-1-6915-4540 Fax: +33-1-6915-6086 E-mail: demedici@lps.u-psud.fr S.R. Hassan The Institute of Mathematical Sciences C.I.T. Cam- pus,Taramani, Chennai 600 113, India M. Capone SMC, CNR-INFM, and Universit` a di Roma ”La Sapienza”, Piazzale Aldo Moro 2, I-00185 Roma, Italy and ISC-CNR, Via dei Taurini 19, I-00185 Roma, Italy