title: Charge ordering and magnetopolarons in Na0.82CoO2.
abstract: Using spectral ellipsometry, we measured the dielectric function of a Na(0.82(2))CoO2 crystal that exhibits bulk antiferromagnetism with T(N)=19.8 K. We identify two prominent transitions as a function of temperature. The first one at 280 K involves marked changes of the electronic and lattice responses that are indicative of charge ordering in the CoO2 layers. The second transition occurs around T(N)=19.8 K and reveals sizable spin-charge coupling. The data are discussed in terms of charge ordering and formation of magnetopolarons due to a charge-induced spin-state transition of adjacent Co3+ ions.
authors.affiliation: Max-Planck-Institute for Solid State Research, Stuttgart, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Bernhard
authors.forename: A V
authors.initials: AV
authors.lastname: Boris
authors.forename: N N
authors.initials: NN
authors.lastname: Kovaleva
authors.forename: G
authors.initials: G
authors.lastname: Khaliullin
authors.forename: A V
authors.initials: AV
authors.lastname: Pimenov
authors.forename: Li
authors.initials: L
authors.lastname: Yu
authors.forename: D P
authors.initials: DP
authors.lastname: Chen
authors.forename: C T
authors.initials: CT
authors.lastname: Lin
authors.forename: B
authors.initials: B
authors.lastname: Keimer