Optical spectral weights and the ferromagnetic transition temperature of colossal-magnetoresistance manganites: Relevance of double exchange to real materials

We present a detailed quantitative comparison of double-exchange models to experimental data on the colossal magnetoresistance manganese perovskites. Our results settle a controversy by showing that physics beyond double-exch ange is important even in La0.7Sr0.3MnO3, which has been regarded as a conv entional double-exchange system. We show that the crucial quantity for comp arisons of different calculations to each other and to data is the conducti on band kinetic energy K, which is insensitive to the details of the band s tructure and can be experimentally determined from optical conductivity mea surements. The seemingly complicated dependence of T-c on the Hund's coupli ng J and carrier concentration n is shown to reflect the variation of K wit h J, n and temperature. We present results for the optical conductivity whi ch allow interpretation of experiments and show that a feature previously i nterpreted in terms of the Hund's coupling was misidentified. We also corre ct minor errors in the phase diagram presented in previous work.