Coupled charge-spin dynamics of the magnetoresistive pyrochlore Tl2Mn2O7 probed using ultrafast midinfrared spectroscopy

Optical-pump midinfrared probe spectroscopy is used to investigate coupled charge-spin dynamics in the magnetoresistive pyrochlore Tl2Mn2O7. We find that the temporal persistence of the photoexcited carrier density is strongly influenced by spin disorder above and below the ferromagnetic Curie temperature. Our results are consistent with a picture whereby spin disorder leads to spatial segregation of the initially excited Tl 6s-O 2p electron-hole pairs, effectively reducing the probability for recombination. This further implies that colossal magnetoresistance in these materials may be driven primarily by Mn t2g spin disorder.