9734131 Schroeder This is a CAREER Award which will investigate the fundamental properties of intrinsically anisotropic high-TC cuprate superconductors using powerful, sophisticated, and polarization-sensitive time-resolved ultrafast spectroscopic techniques. An ultrabroadband femtosecond terahertz (THz) probe pulse (generated by optical rectification of a 50fs optical pulse) will be used to spectrally time resolve the far-infrared transient response of high-TC superconductors induced by an optical pump pulse through the change in the reflectivity produced by the perturbed complex conductivity. Since the spectral extent of the linearly polarized THz probe pulse includes the superconducting gap 2A, this technique will be used to monitor directly the optically-induced perturbations to the anisotropic order parameter A, the pseudogap in under-doped materials, and transient inter- and intra-plane coupling between Cu-O layers and chains using untwinned Yttrium- and Barium-based cuprate crystals. In addition, to aid the understanding of the time-resolved THz spectra, two-photon excited-state angle-resolved photoemission spectroscopy will be employed to determine the relevant characteristics (lifetime and momentum) of the optically-coupled unoccupied states above the Fermi level. All measurements will be performed as a function of TITC to elucidate temperature dependencies. The results from these carefully designed ultrafast spectroscopic measurements should have a great impact on our understanding of the unique properties of high-TC superconductors in a manner parallel to that provided by similar femtosecond optical techniques in semiconductor physics. The educational component will involve both undergraduate physics majors and students from Chicago area high schools in research in the investigators laboratory that is connected to the goals of the project. %%% This is a CAREER Award which uses sophisticated optical methods to study high temperature superconductor s. The discovery in 1986 of copper-oxide-based ceramic materials, which exhibit zero electrical resistance at liquid nitrogen (-3 F) (rather than liquid helium (-450 F)) temperatures, has ignited technological interest in superconductivity as a means of dramatically reducing energy distribution costs, developing efficient high-speed levitating transportation, and making ultrafast electronic switches. However, despite a decade of exciting research into the properties of high-temperature superconductors (HTSCs), a definitive experiment leading to a clear understanding of the physical mechanism responsible for superconductivity in these unique materials has not been forthcoming. The goal of this research program is to exploit the sub-picosecond (shorter than one-thousand-billionth of a second) temporal resolution provided by today's laser technology to study the fundamental physical processes occurring in HTSCs. Specifically, ultrashort pulses of far-infrared radiation will be used to monitor the response of HTSCs in an effort to time-resolve the mechanism responsible for superconductivity in these ceramic materials. These ultrafast optical investigations will open a new regime of study for superconductivity in which radiation is used to monitor directly the electronic dynamics of the superconducting state. The results from these novel spectroscopic studies should have a significant impact on our understanding of the unique properties of HTSCs which, in turn, may lead to the development of superconductors operating at even higher temperatures. Indeed, similar ultrafast optical techniques have already improved our understanding and design of everyday semiconductor devices. The educational component will involve both undergraduate physics majors and students from Chicago area high schools in research in the investigators laboratory that is connected to the goals of the project. ***
