Magnetotransport in Manganites and the Role of Quantal Phases: Theory and Experiment

While low-temperature Hall resisitivity ${\ensuremath{\rho}}_{\mathrm{xy}}$ of ${\mathrm{La}}_{2/3}(\mathrm{C}\mathrm{a},\mathrm{P}\mathrm{b}{)}_{1/3}{\mathrm{MnO}}_{3}$ single crystals can be separated into ordinary (OHE) and anomalous (AHE) contributions, no such decomposition is possible near the Curie temperature ${T}_{c}$. Rather, the ${\ensuremath{\rho}}_{\mathrm{xy}}$ data collapse to a single function of the reduced magnetization $m\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}M/{M}_{\mathrm{sat}}$, with an extremum at $\ensuremath{\approx}0.4m$. A new mechanism for the AHE in the inelastic hopping regime is identified that reproduces the scaling curve. An extension of Holstein's model for the hopping OHE, the mechanism arises from the combined effects of the double-exchange-induced quantal phase in triads of Mn ions and spin-orbit interactions.