Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session Y3: Exotic electronic structures of complex materials and phases |
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Sponsoring Units: DCMP Chair: Richard Martin, University of Illinois at Urbana-Champaign Room: Colorado Convention Center Korbel 2A-3A |
Friday, March 9, 2007 11:15AM - 11:51AM |
Y3.00001: The electronic structure of a liquid Pb film Invited Speaker: Our understanding of the electronic structure of condensed matter in the liquid phase is far from complete. We used angle-resolved photoemission spectroscopy (ARPES) in order to study the evolution of the electronic bands, the Fermi surface and the spectral function of a lead monolayer on Cu(111) as the film went through its melting transition at 568 K [1]. The crystalline copper substrate provides the reciprocal lattice vectors, absent in the liquid state, that are needed in ARPES for wave-number conservation in the excitation process, and the well-resolved copper bands serve as an important reference frame for identifying the dramatic changes in the lead states. Electron spectra and momentum distribution maps of the liquid film reveal three important features: the persistence of a Fermi surface, the filling of band gaps, and the localization of the wave functions upon melting. Distinct coherence lengths for different sheets of the Fermi surface are found, indicating a strong dependence of the localization lengths on the character of the constituent atomic wave functions. \newline \newline [1] F. Baumberger, W. Auw\"arter, T. Greber, J. Osterwalder, Science 306, 2221 (2004). [Preview Abstract] |
Friday, March 9, 2007 11:51AM - 12:27PM |
Y3.00002: Thin-Film Electronic Structure: Beyond the ``Particle in a Box" Model Invited Speaker: The quantization of electronic states in thin metallic films is now well-established, having been observed in a number of systems including films on metal as well as semiconductor substrates. The impact of this quantization on the films' physical properties has been demonstrated in several studies, including the dependence on thickness of films' thermal stabilities, work functions, and superconductivity transition temperatures. In the simplest model, the electrons are confined to the film by the substrate and vacuum interfaces, which work as ``mirrors'' to reflect the electrons back into the film, resulting in discrete standing-wave states. In this picture, the substrate forms a reflecting barrier due to a mismatch of electronic structures between it and the overlayer, and the main result is the formation of discrete energy subbands. In this talk, photoemission results will be presented from a variety of thin-film systems that show more interesting electronic structures due to interactions with the substrate and interface. The systems studied highlight different effects, including interfacial scattering and diffraction, hybridization of film and substrate states, and the formation of a composite quantum well from a thin metallic film on a semiconductor. In the latter case, the semiconductor depletion region forms part of the system via coherent coupling between film and substrate electronic states. In collaboration with S. J. Tang, N. J. Speer, D. Ricci, M. Upton, L. Basile, S.-L. Chang, Y.-R. Lee, and T.-C. Chiang. [Preview Abstract] |
Friday, March 9, 2007 12:27PM - 1:03PM |
Y3.00003: Ultrahigh-resolution photoemission from superconductors and strongly-correlated materials Invited Speaker: I would like to introduce the ultra-high resolution photoemission study of several superconductors and strongly correlated materials using UV-laser-photoemission [1]. The laser-PES system has the performance of about 360-$\mu $eV resolution at about 3 K at present. We will also introduce the newly developed laser-PES system that has the higher performance. Recently, it is found that the diamond becomes superconductor when the boron is doped heavily. We observed the superconducting gap and several phonon structures in the ultra-high resolution photoemission spectra of the doped diamond [2]. We would like to introduce several superconductors including organic materials. It is found, for the first time, as a transition metal compound that LiV$_{2}$O$_{4}$ is a heavy Fermion material. We have directly observed a sharp peak structure at 4 meV just above $E_{F}$ in $d$-electron heavy Fermion LiV$_{2}$O$_{4}$ [3]. The spectral shape and the temperature dependence of the peak structure are very similar to those of the Kondo resonance in conventional $f$-electron heavy Fermion compounds. The present result can be well described within Kondo scenario. I also show several ARPES results on superconductors and strongly-correlated materials. \newline \newline [1] T. Kiss, et al., Phys. Rev. Lett. \textbf{94}, 057001 (2005). \newline [2] Ishizaka et al., unpublished \newline [3]A. Shimoyamada,et al., H. Ueda, Y. Ueda, S. Shin, Phys. Rev. Lett. \textbf{96}, 026403 (2006). [Preview Abstract] |
Friday, March 9, 2007 1:03PM - 1:39PM |
Y3.00004: The spectral function and quasiparticle dynamics of graphene thin films Invited Speaker: Graphene, a single layer of carbon atoms arranged in a simple honeycomb lattice, is the building block of graphite, fullerenes, and carbon nanotubes and has fascinating electronic properties deriving from the effectively massless, relativistic behavior of its charge carriers. The study of many-body interactions among these carriers is of interest owing to their contribution to superconductivity in these systems. I will report synthesis of graphene thin films (1-4 layers) grown on SiC and the evolution of their band structure using angle-resolved photoemission spectroscopy (ARPES). We determined the spectral function for graphene as a function of doping, which encodes the many-body interactions among the quasiparticles in the system---namely the charge and vibrational excitations. Our measurements show that the bands around the Dirac crossing point are heavily renormalized by electron-electron, electron-plasmon, and electron-phonon coupling, showing that these interactions must be considered on an equal footing in attempts to understand the quasiparticle dynamics in graphene and related systems. At very high doping (comparable to graphite intercalation compounds (GICs)) renormalization of the carrier mass near $E_{F}$ becomes significant for electrons moving in certain directions, supporting the importance of electron-phonon coupling in superconductivity in GICs. [Preview Abstract] |
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