HIGH-TEMPERATURE THERMOPOWER IN LA2 3CA1/3MNO3 FILMS - EVIDENCE FOR POLARONIC TRANSPORT/

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