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Physics Colloquium, Fall 2018
Thursdays 4:00 p.m., Room 104 Physics
Refreshments served at 3:40 p.m.
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Come learn about the library resources you didn't know you can't live without. Do you know what MERLIN, MOBIUS, ILL, Compendex, OverDrive, Scholars’ Mine, Kanopy, LearningExpress or Scopus mean? Do you know how to find anything other than coffee in the library? Bring your phone, tablet or laptop devices for a hands-on session with a librarian who will enlighten you about everything the library can offer and answer any questions you might have.
Title: The photoeffect revisited: Attosecond time-resolved photoelectron spectroscopy of atoms, nanoparticles, and surfaces
Title: "A journey from physics to biology"
Title: Photofragment Spectra and Dynamic Imaging of Molecules
Abstract: Under a short, intense laser pulse, a molecule exhibits non-linear behavior giving rise to new observable phenomena. Interpreting these phenomena requires a good understanding of the way a strong-field modifies the properties of the molecule, both at the level of its electronic structure and at the level of its dynamics. This theme will be illustrated by the successive discussions of two processes: First, the dissociative ionization of a molecule such as H_2 under the combined effect of a single extreme ultraviolet attosecond pulse and an intense near infrared pulse [F. Kelkensberg et al, Phys. Rev. Lett. 103,123005 (2009)] will be considered. We show how this pump-probe study actually represents a transition-state spectroscopy of the strong-field dissociatiaon step, i.e. of the (probe-pulse-)dressed H_2^+ molecular ion. The way the dissociation dynamics is influenced by the duration of the near infrared probe pulse, and by the time delay between the two pulses, is discussed in terms of adiabatic versus non-adiabatic preparations and transports of time-parameterized Floquet (vibrational) resonances associated with the dissociating molecular ion. Turning next to strong-field molecular ionization, as depicted by the celebrated three-step model, we show and discuss how symmetry conservation of the Symmetry Adapted Linear Combinations (SALC) form of initial orbitals during the ionization of a symmetric molecule governs the general structure of channel-resolved photoelectron spectra, in particular of its high-energy part relevant to Laser-Induced Electron Diffraction (LIED). The issue of stability of such a symmetry-based reading is discussed by considering symmetry breaking during rotations and vibrations of the pre-aligned molecule. The concepts are illustrated mainly on results of simulations of the ionization of a $CO_2$ molecule using a Single-Active Electron (SAE) model. Many-electron wavepacket calculations performed in an attempt to go beyond the SAE approximation then show that many-orbital effects are also to be taken into account as they can reduce the stability of the photoelectron spectra with respect to molecular misalignment.
Title: The Pursuit of Materials Research for Potential Energy Conversion Applications
Abstract: Thermoelectric devices allow for direct conversion between heat and electricity, providing important alternatives for green energy technologies. Yet the efficiency during such energy conversion is limited by the competition between high electrical conductance and low thermal conductance of the modules constructed by thermoelectric materials. In my talk I will report several approaches and directions that have been undertaken in the search for new materials and systems for potential energy conversion applications. For instance, as an example of incorporating both Kondo lattice hybridization and unstable valence states near the Fermi level, enhanced thermoelectric performance of heavy-fermion compounds YbTM2Zn20 (TM = Co, Rh, Ir) was achieved. This result shows that strongly hybridized f-electron intermetallic compounds coupled with “rattling” features in the cage-like structures offers a unique approach to high power factors while maintaining small thermal conductivity values -- ideal systems for thermoelectric applications.
The National High Magnetic Field Laboratory is supported by National Science Foundation through NSF/DMR-1644779 and the State of Florida.