Ultrafast conductivity dynamics in colossal magnetoresistance manganites -art. no. 017401

Ultrafast picosecond measurements of optically induced changes in the absol ute conductivity (0.4-1.0 THz) of La0.7M0.3MnO3 thin films (M = Ca, Sr) fro m 10 K to similar to0.9T(c) reveal a two-component relaxation. A fast, simi lar to2 ps, conductivity decrease arises from an optically induced modifica tion of the effective phonon temperature. The slower component, related to spin-lattice relaxation, has a lifetime that increases upon approaching T-c from below in accordance with an increasing spin specific heat. We show th at, for T much less than T-c, partial derivative sigma/partial derivativeT is primarily determined by thermally disordered phonons while spin fluctuat ions dominate near T-c.