title: Collective phase-like mode and the role of lattice distortions at TN ~TC in RMn2O5 (R= Pr, Sm, Gd, Tb, Bi).
abstract: We report on electronic collective excitations in RMn(2)O(5) (R =Pr, Sm, Gd, Tb) showing condensation starting at and below ~T(N) ~T(C)~ 40-50 K. Their origin is understood as partial delocalized e(g) electron orbitals in the Jahn-Teller distortion of the pyramid dimer with strong hybridized Mn(3+)-O bonds. Our local probes, Raman, infrared, and x-ray absorption, back the conclusion that there is no structural phase transition at T(N)~T(C). Ferroelectricity is magnetically assisted by electron localization triggering lattice polarizability by unscreening. We have also found phonon hardening as the rare earth is sequentially replaced. This is understood as a consequence of lanthanide contraction. It is suggested that partially f-electron screened rare earth nuclei might be introducing a perturbation to e(g) electrons prone to delocalize as the superexchange interaction takes place.
authors.affiliation: Laboratorio Nacional de Investigación y Servicios en Espectroscopía Óptica-Centro CEQUINOR, Universidad Nacional de La Plata, La Plata, Argentina. neemmassa@gmail.com
authors.forename: Néstor E
authors.initials: NE
authors.lastname: Massa
authors.forename: Ali F
authors.initials: AF
authors.lastname: García-Flores
authors.forename: Domingos
authors.initials: D
authors.lastname: De Sousa Meneses
authors.forename: Leire
authors.initials: L
authors.lastname: del Campo
authors.forename: Patrick
authors.initials: P
authors.lastname: Echegut
authors.forename: Gilberto F L
authors.initials: GF
authors.lastname: Fabbris
authors.forename: María Jesús
authors.initials: MJ
authors.lastname: Martínez-Lope
authors.forename: José Antonio
authors.initials: JA
authors.lastname: Alonso