Recent studies of models for manganites in the bulk and in superlattices

In this talk, we will review our recent double-exchange model studies for manganites and some related experimental discoveries. First, we will briefly address the existence of a clear CMR effect in numerical simulations, and the short-range spin and charge correlations and local density of states in this CMR regime [1,2]. Second, we will analyze manganite superlattices (LaMnO$_3$)$_{2n}$/(SrMnO$_3$)$_n$. The reconstruction of charge density, spin order, and orbital order at the interfaces and the relation with a novel experimentally observed metal-insulator transition (MIT) at $n=3$ will be discussed [3]. Finally, the multiferroic spiral spin order in the undoped manganite $R$MnO$_3$ ($R$=Tb, Dy) will also be briefly studied under the double-exchange framework [4]. \\[4pt] [1] R. Yu, S. Dong, C. \c{S}en, G. Alvarez, and E. Dagotto. Phys. Rev. B 77, 214434 (2008).\\[0pt] [2] C. \c{S}en, G. Alvarez, and E. Dagotto, Phys. Rev. Lett. 98, 127202 (2007).\\[0pt] [3] S. Dong, R. Yu, S. Yunoki, G. Alvarez, J.-M. Liu, and E. Dagotto, Phys. Rev. B 78, in press(R) (2008).\\[0pt] [4] S. Dong, R. Yu, S. Yunoki, J.-M. Liu, and E. Dagotto, Phys. Rev. B 78, 155121 (2008).