Optical conductivity study on Gd1.4Ce0.6Sr2 Ru1−x Mnx Cu2O10

IR conductivity measurements on Mn-doped Gd1.4Ce0.6Sr2RuCu2O10 have been carried out. As a result of Mn substitution at the Ru site, carried out for concentrations of 0.0, 0.01, 0.02, 0.05, 0.10 and 0.30, interesting non-monotonic behaviour is observed in the mode parameters as well as in the electronic background in the IR spectra. All these spectral parameters show an extremum for a manganese concentration of about 0.05. These changes can be qualitatively understood in terms of the interaction of phonons with the electronic background introduced by Mn doping. While up to a Mn content of 5% the system is driven towards a more resistive state, a noticeable increase in the electron-phonon interaction is observed for higher Mn concentrations. A variation in the carrier density due to substitution of Mn, as evidenced by the spectral weight changes in the mid IR band, also supports this picture.