Ultrafast Materials Science

Robert Schoenlein, Program Leader

The fundamental properties of condensed matter are investigated using advanced ultrafast and nonlinear optical techniques. Laser systems and sources with femtosecond resolution and spectral coverage extending from the near UV to the THz are combined with novel measurement techniques including surface harmonic and sum frequency generation, heterodyne four-wave mixing, multiple-pulse photon echo, transient anisotropy, time-resolved transmission, reflectivity, linear/circular dichroism, and other pump-probe schemes. Time-resolved optical measurements are an important complement to the emerging capabilities in ultrafast x-ray science, which applies x-ray spectroscopy and diffraction to the study of atomic and electronic structural dynamics in condensed matter using novel femtosecond beamlines at the Advanced Light Source.

Robert A. Kaindl

• Investigation of ultrafast quantum processes in complex materials, e.g. exploring the dynamics of quasiparticles and Cooper pairs in cuprate superconductors and other correlated-electron systems.
• Fundamental electronic dynamics, low-energy excitations, and light-matter interactions in advanced nanoscale materials. Carrier confinement in such materials can lead to strongly enhanced carrier interactions, controlled energy relaxation dynamics, and non-equilibrium distributions with implications for energy applications.
• Development of new ultrafast sources and spectroscopies tunable across much of the electromagnetic spectrum, from THz to X-rays, for tailored excitation and probing of fundamental material resonances.

Joseph W. Orenstein

• Studies of spin transport in highly correlated systems, such as the transition-metal oxides (TMO), where novel effects such as spin-charge separation may be observed. Unique expertise includes ultrafast transient spin grating spectroscopy and time-resolved magneto-optic Kerr (TR-MOKE) measurements. Present focus on SrRuO3 films (fabricated by the Ramesh and Suzuki groups) to understand the physics of spin transport and its dependence on temperature in CaxSr1-xRuO3 .
• Application of time-domain terahertz spectroscopy (TDS-THz) to study novel metallic states at TMO interfaces, specifically those at lattice-matched interfaces between perovskite TMO’s with different d shell occupancy under preparation by the Ramesh and Suzuki groups
• An abrupt transition in quasiparticle dynamics in BSCCO is suggestive of a quantum critical point at or near optimal doping. Is this universal to all cuprate semiconductors? Quasiparticle recombination experiments in La substituted Bi-2201 and LSCO materials will clarify the mechanism, experiments on Zn doped BSCCO are planned.
• Explore the ultrafast dynamics of correlated multiferroic oxide nanostructures
  

Robert W. Schoenlein

• Investigation of ultrafast electronic phase transitions in correlated transition-metal oxides and related materials via ultrafast visible, infrared, and THz spectroscopy. The objective is to advance our understanding of the order parameter(s) connecting competing phases by separating correlated phenomena in the time domain.
• Novel ultrafast switching of ultrafast electronic phases such as charge-ordering and insulator/metal transitions in correlated materials by tailored excitation - e.g. photodoping, electronic charge-transfer, or coherent vibrational pumping. Present focus is on CMR manganites and related CDW compounds.
• Application of ultrafast x-ray spectroscopy to probe electronic structural dynamics in correlated materials. Present focus is on transition-metal compound, where femtosecond L-edge spectroscopy reveals new information on the d-electron dynamics. Time-resolved x-ray diffraction (at absorption edges) can uniquely reveal the dynamics of charge/orbital ordering phenomena.
• Investigation of photo-induced electronic phase transitions in ferroelectrics, organics, nanostructures, and other novel materials using advanced ultrafast techniques
  

Y.R. Shen

• Optical spectroscopy on mono- and bi-layer graphene sheets to understand their electronic band structures and their dependence on bias potential. (in collaboration with the Crommie group)
• Ultrafast carrier dynamics in graphene sheets via time-resolved pump/probe spectroscopy. (in collaboration with the Crommie group)
• Laser spectroscopy of excitonic transitions in single single-wall carbon nanotubes of very small diameters, and nanotubes perturbed by adsorbed molecules or BN doping. (in collaboration with the Institute of Physics in Beijing
• Phase-sensitive sum-frequency vibrational spectroscopy of water interfaces to obtain new understanding of water interfacial structures. Water/oxide interfaces are of particular importance in geoscience. (in collaboration with Waychunas’ group).
• Sum-frequency vibrational spectroscopy of surface optical phonons of oxides, in particular, transition metal oxides and complex oxides.; also Si/silicate, and electrochemical interfaces.