Phonon-Assisted Double Exchange in Perovskite Manganites

Measurements of the temperature dependence of the thermoelectric power and the resistivity of ${}^{18}\mathrm{O}{/}^{16}\mathrm{O}$ isotope-exchanged $({\mathrm{La}}_{1-x}{\mathrm{Nd}}_x{)}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{MnO}}_3$ samples have confirmed the existence of vibronic electronic states below $T_c$ in the narrow range of bandwidths where static, cooperative Jahn-Teller (J-T) deformations are suppressed and dynamic J-T deformations introduce vibrational modes into the interatomic spin-spin interactions. A giant isotope effect on $T_c$ is related to a mass-enhanced change in both the density and mobility of the mobile charge carriers at $T_c$.