Hall-Effect Sign Anomaly and Small-Polaron Conduction in (La1−xGdx)0.67Ca0.33MnO3

Abstract

The Hall coefficient of Gd-doped ${\mathrm{La}}_{2/3}{\mathrm{Ca}}_{1/3}{\mathrm{MnO}}_3$ exhibits Arrhenius behavior over a temperature range from ${2T}_c$ to ${4T}_c$, with an activation energy very close to $\frac{2}{3}$ that of the electrical conductivity. Although both the doping level and thermoelectric coefficient indicate holelike conduction, the Hall coefficient is electronlike. This unusual result provides strong evidence in favor of small-polaronic conduction in the paramagnetic regime of the manganites.