Magnetotransport in manganites and the role of quantal phases: theory and experiment.

While low-temperature Hall resisitivity rhoxy of La2/3(Ca,Pb)1/3MnO3 single crystals can be separated into ordinary (OHE) and anomalous (AHE) contributions, no such decomposition is possible near the Curie temperature Tc. Rather, the rhoxy data collapse to a single function of the reduced magnetization m=M/Msat, with an extremum at approximately 0.4 m. 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.