High-temperature thermopower in La2/3Ca1/3MnO3 films: Evidence for polaronic transport

Thermoelectric power, electrical resistivity, and magnetization experiments, performed in the paramagnetic phase of La2/3Ca1/3MnO3, provide evidence for polaron-dominated conduction in colossal magnetoresistance materials. At high temperatures, a large, nearly-field-independent difference between the activation energies for resistivity rho and thermopower S, a characteristic of Holstein polarons, is observed, and Inp ceases to scale with the magnetization. On approaching T-c, both energies become field dependent, indicating that the polarons are magnetically polarized. Below T-c, the thermopower follows a law S(H)similar to 1/rho(H) as in nonsaturated ferromagnetic metals.