title: Localized and delocalized excitons: resonant inelastic x-ray scattering in La(2-x)Sr(x)NiO4 and La(2-x)Sr(x)CuO4.
abstract: The dynamics of doped charge in an antiferromagnetic lattice is central to the description of the insulator-metal transition that occurs on doping the parent high T(c) compounds. In this work we use high resolution resonant inelastic x-ray scattering to investigate the dynamics of the charge-transfer exciton by measuring its energy dispersion in two prototype compounds, La2CuO4 and La2NiO4. We show that this behavior is radically different in the cuprate with respect to a system known to exhibit strong polaronic behavior, namely, the nickelate: the exciton is mobile in the cuprate while it is well localized in the nickelate. Using a simple Wannier-Mott model we can estimate the total hole plus electron effective mass in the cuprate to be 3.5 +/- 0.3 m(e) which would exclude strong localization in the undoped cuprate.
authors.affiliation: Institut de Minéralogie et de Physique des Milieux Condensés, Université Pierre et Marie Curie, case 115, 4 place Jussieu 75252 Paris cedex 05, France.
authors.forename: E
authors.initials: E
authors.lastname: Collart
authors.forename: Abhay
authors.initials: A
authors.lastname: Shukla
authors.forename: J-P
authors.initials: JP
authors.lastname: Rueff
authors.forename: P
authors.initials: P
authors.lastname: Leininger
authors.forename: H
authors.initials: H
authors.lastname: Ishii
authors.forename: I
authors.initials: I
authors.lastname: Jarrige
authors.forename: Y Q
authors.initials: YQ
authors.lastname: Cai
authors.forename: S-W
authors.initials: SW
authors.lastname: Cheong
authors.forename: G
authors.initials: G
authors.lastname: Dhalenne