Ultrafast Dynamics in Complex Materials – Antoinette J. Taylor

Date: Mon. November 15th, 2004, 4:15 pm-5:15 pm
Location: Rockefeller 301

I will discuss the development and application of novel optical spectroscopic techniques to the study of ultrafast dynamics in complex materials. I will first describe all-optical pump probe and optical-pump far-infrared probe experiments on (a) colossal magnetoresistance manganites, (b) superconductors, and (c) heavy fermion materials. The experimental techniques are discussed followed by a brief review of ultrafast electron dynamics in conventional wide band metals that serves as a starting point in understanding dynamics in more complex systems. In. half-metallic manganites, the quasiparticle dynamics in the ferromagnetic metallic state can be understood in terms of a dynamic transfer of the spectral weight which is influenced by the lattice and spin degrees of freedom. For high temperature superconductors, ultrafast quasiparticle dynamics are sensitive to the order parameter and superconducting pair recovery occurs on a picosecond timescale. Heavy fermion compounds reveal an anomalous slowing down of quasiparticle dynamics below the Kondo temperature. These results show that, in general, ultrafast optical spectroscopy provides a sensitive method to probe the dynamics of quasiparticles at the Fermi level. We have further extended these measurements to reveal dynamics in structured materials. In particular, we have developed a diagnostic that combines the nanoscale spatial resolution of an STM with ultrafast temporal resolution. This technique has been used to study electron and hole dynamics following photoexcitation in InAs self-assembled quantum dots. Finally, the interaction of ultrafast optical pulses and microstructured fibers is visualized and studied using novel techniques that simultaneously display the spectral and temporal characteristics of a pulse. These techniques are used to investigate the nonlinear dynamics associated with the interaction between dispersive waves and solitons in the vicinity of the second zero dispersion point of photonic crystal fibers.