Polaron transport in the paramagnetic phase of electron-doped manganites

Abstract

The electrical resistivity, Hall coefficient, and thermopower as functions of temperature are reported for lightly electron-doped ${\mathrm{Ca}}_{1\ensuremath{-}x}{\mathrm{La}}_{x}\mathrm{Mn}{\mathrm{O}}_{3}$ $(0\ensuremath{\leqslant}x\ensuremath{\leqslant}0.10)$. Unlike the case of hole-doped ferromagnetic manganites, the magnitude and temperature dependence of the Hall mobility $({\ensuremath{\mu}}_{H})$ for these compounds is found to be inconsistent with small-polaron theory. The transport data are better described by the Feynman polaron theory and imply intermediate coupling $(\ensuremath{\alpha}\ensuremath{\simeq}5.4)$ with a band effective mass ${m}^{*}\ensuremath{\sim}4.3{m}_{0}$ and a polaron mass ${m}_{p}\ensuremath{\sim}10{m}_{0}$.