Hall-Effect Sign Anomaly and Small-Polaronic Conduction in   (La_{1-x}Gd_x)_{0.67}Ca_{0.33}MnO_3
  The Hall coefficient of Gd-doped La_{2/3}Ca_{1/3}MnO_3 exhibits Arrhenius behavior over a temperature range from 2T_c to 4T_c, with an activation energy very close to 2/3 that of the electrical conductivity. Although both the doping level and thermoelectric coefficient indicate hole-like conduction, the Hall coefficient is electron-like. This unusual result provides strong evidence in favor of small-polaronic conduction in the paramagnetic regime of the manganites. 
M. Jaime (1), H. T. Hardner (1), M.B. Salamon (1), M. Rubinstein (2),   P. Dorsey (2), D. Emin (3) ((1) University of Illino...