Zero Temperature Insulator-Metal Transition in Doped Manganites

We study the transition at T=0 from a ferromagnetic insulating to a ferromagnetic metallic phase in manganites as a function of hole doping using an effective low-energy model Hamiltonian proposed by us recently. The model incorporates the quantum nature of the dynamic Jahn-Teller(JT) phonons strongly coupled to orbitally degenerate electrons as well as strong Coulomb correlation effects and leads naturally to the coexistence of localized (JT polaronic) and band-like electronic states. We study the insulator-metal transition as a function of doping as well as of the correlation strength U and JT gain in energy E_{JT}, and find, for realistic values of parameters, a ground state phase diagram in agreement with experiments. We also discuss how several other features of manganites as well as differences in behaviour among manganites can be understood in terms of our model.Comment: To be published in Europhysics Letter

Raman scattering in charge-ordered Pr0.63Ca0.37MnO3Pr_{0.63} Ca_{0.37}MnO_3: anomalous temperature dependence of linewidth

We report on the evolution of the Raman-active $A_g$ phonon modes in the charge-ordered manganite $Pr_{0.63} Ca_{0.37}MnO_3$as a function of temperature from 300 K to 25 K. Our studies reveal that the linewidths of the $A_g(2)$ and $A_g(4)$ phonons increase as temperature decreases. This anomalous temperature dependence of phonon lineshapes, seen for the first time in charge-ordered manganites, can be quantitatively understood in terms of a strong spin-phonon coupling involving t_2_g spins and $A_g$ phonons

Raman scattering in charge-ordered Pr<SUB>0.63</SUB>Ca<SUB>0.37</SUB>MnO<SUB>3</SUB>: anomalous temperature dependence of linewidth

We report on the evolution of the Raman-active Ag phonon modes in the charge-ordered manganite Pr0.63Ca0.37MnO3 as a function of temperature from 300 K to 25 K. Our studies reveal that the linewidths of the Ag(2) and Ag(4) phonons increase as temperature decreases. This anomalous temperature dependence of phonon lineshapes, seen for the first time in charge-ordered manganites, can be quantitatively understood in terms of a strong spin-phonon coupling involving t2g spins and Ag phonons