Ultrafast Dynamics in Complex Materials
Antoinette J. Taylor
Center for Integrated Nanotechnologies, Los Alamos National Laboratory
In this talk, I will discuss the development and application of novel optical spectroscopic techniques to the study of ultrafast dynamics in complex materials. I will describe ultrafast optics experiments on (a) magnetic materials, (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 [Journal of Physics: Condensed Matter 14, 1455 (2002)]. Multiple probe energies are employed to characterize the ultrafast dynamics from the far-infrared to visible to x-ray regimes, and these probes reveal complementary information of the material dynamics. In magnetoresistive oxides, 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 [Phys. Rev. Lett. 87, 017401 (2001), Phys. Rev Lett. 95 2674044 (2005)]. In other complex oxides, the insulator–to-metal phase transition is investigated [J. Phys. Soc. Jpn. 75 1008 (2006). The measurement of demagnetization in ferromagnetic materials using optically induced terahertz emission will also be described [Opt. Lett. 29, 1805 (2004)]. For high temperature superconductors, ultrafast quasiparticle dynamics are sensitive to the order parameter and superconducting pair recovery occurs on a picosecond timescale [Phys. Rev. Lett. 91, 267002 (2003)]. Heavy fermion compounds reveal an anomalous slowing down of quasiparticle dynamics below the Kondo temperature [Phys. Rev. Lett. 91, 27401 (2003), Phys. Rev. Lett. 96, 037401 (2006)]. These results show that, in general, ultrafast optical spectroscopy provides a sensitive method to probe the dynamics of quasiparticles at the Fermi level.
