Ultrafast spectroscopy of manganites.

Abstract

We are investigating the spin-charge-lattice relaxation in La1-xPbxMn1-y-zCuyO3 (x = 0.14, y = 0, 0.01, 0.02, 0.04, 0.06 and z = 0.02, 0.08, 0.11, 0.17, 0.20) single crystal that were grown by the flux melt technique. The substitution of Mn sites with a transitional element Cu allows one to study the critical role of Mn ions in CMR materials. The couplings between the spin, lattice, charge and orbital degrees of freedom in the relaxation dynamics of the nanoscopic magnetic clusters in this CMR system were investigated using Femtosecond time-resolved spectroscopy. Transient reflection spectroscopy been employed to probe quasi-equilibrium state induced by photo-formation of ferromagnetic metal clusters. We observed the presence of periodic oscillations in the transient reflectivity signal near the metal insulator transition. These oscillations are attributed to the multiple reflections due to the acoustic phonon dynamics. The effects of copper doping to the spin and charge dynamics in this novel system were also discussed in light of these new findings.