High Temperature Thermopower in La_{2/3}Ca_{1/3}MnO_3 Films: Evidence   for Polaronic Transport
  Thermoelectric power, electrical resistivity and magnetization experiments, performed in the paramagnetic phase of La_{2/3}Ca_{1/3}MnO_3, provide evidence for polaron-dominated conduction in CMR 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 ln(rho) 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) prop. 1/rho (H) as in non saturated ferromagnetic metals. 
M. Jaime(1), M.B. Salamon (1), M. Rubinstein (2), R.E. Treece (2),   J.S. Horwitz (2), D.B. Chrisey (2) ((1) University of I...