Ultrafast spin-dependent conductivity in colossal magnetoresistance manganites

Summary form only given. The emergent properties of many materials derive from strong electron correlations augmented or mediated under realistic conditions by electron-phonon interactions. An important class of materials whose electronic and transport properties are primarily determined by such many-body effects are mixed-valence manganite perovskites R/sub 1-x/D/sub x/MnO/sub 3/ where R is a trivalent rare earth (e.g., La, Nd) and D is a divalent alkali (e.g., Ca, Sr). For hole doping in the range x/spl sim/0.2-0.5 La/sub 1-x/Ca/sub x/MnO/sub 3/ is, at low temperature, a metallic ferromagnet becoming a paramagnetic insulator at temperature T/sub c/ with a maximum T/sub c/ of /spl sim/270 K for x/spl sim/0.3. Qualitatively, both double exchange (i.e., Mn/sup 3+/-O-Mn/sup 4+//spl rarr/Mn/sup 4+/-O-Mn/sup 3+/) and electron-phonon coupling determine the magnetic and transport properties. The observation of colossal negative magnetoresistance in hole-doped manganites demonstrates the sensitivity of electronic conduction to the underlying magnetic structure. As such, time-resolved terahertz spectroscopy directly probes the interplay between the electronic, lattice, and spin degrees of freedom. We have measured absolute conductivity changes from 0.4-1.0 THz in La/sub 0.7/Ca/sub 0.3/MnO/sub 3/ thin films from 10-230 K with picosecond resolution. Two components observed in the conductivity relaxation are described.