Optical probe of the control of charge-orbital ordering correlation by using the cation configuration in half-doped layered-structure manganites

초록

We have investigated the optical conductivity and Raman spectra of Eu(1/2)Ca(3/2)MnO(4) (long-range charge-orbital ordering, CO-OO) and Eu(1/2)Sr(3/2)MnO(4) (short-range CO-OO). Characteristic optical responses of the CO-OO phase are 1) a higher frequency shift of the 1 eV absorption with its width being narrower in the optical conductivity and 2) development of two Raman-active phonon modes. While these behaviors are apparently identified in the Eu(1/2)Ca(3/2)MnO(4) compound, they are much weaker in Eu(1/2)Sr(3/2)MnO(4). This difference originates from a correlation length of CO-OO with respect to the A-site cation configuration.

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