Ultrafast optical and far-infrared quasiparticle dynamics in correlated electron materials

We review the application of ultrafast optical spectroscopy in the study of correlated electron materials. The emphasis is on all-optical pump-probe and optical pump-far-infrared probe experiments on (a) colossal-magnetoresistance manganites and (b) high-temperature superconductors. The experimental techniques are discussed followed by a brief review of ultrafast electron dynamics in conventional wide-band metals which serves as a starting point in understanding the dynamics in more complex metallic systems. In the half-metallic manganites, the quasiparticle dynamics in the ferromagnetic metallic state can be understood in terms of a dynamic transfer of spectral weight which is influenced by the lattice and spin degrees of freedom. For the high-temperature superconductors, ultrafast quasiparticle dynamics are sensitive to the order parameter and superconducting pair recovery occurs on a picosecond timescale. These results show that, in general, ultrafast optical spectroscopy provides a sensitive method to probe the dynamics of quasiparticles at the Fermi level.