Ciclo de Seminarios 2007
2007 7 DIC
Viernes 7 de Diciembre
11:00 hs. - Auditorio Emma Pérez Ferreira
Edificio TANDAR
"Spectroscopy of Electrons and Phonons in Two Dimensions: Graphene and Quantum Hall Fluids"
Aron Pinczuk
(*)
Department of Applied Physics and Applied Mathematics
Department of Physics, Columbia University, New York, NY, USA
RESUMEN:
Collective excitation modes of a diverse group of structures that show extreme two-dimensional
properties are probed by inelastic light scattering methods. This talk presents an overview of
recent results that reveal physics that is not accessible by other methods. Graphene, a single
atomic layer of carbon arranged in a honeycomb lattice, is studied by Raman scattering measurements
of the long wavelength optical phonon (the G-band). Gate-modulated low-temperature Raman spectra
reveal that an external electric-field-effect (EFE) has marked impacts on the G-band of graphene by
creating large density modulations of mass-less carriers with linear dispersion (known as Dirac
fermions). The changes of phonon frequency and line-width demonstrate optically a particle-hole
symmetry about the charge-neutral `Dirac-point'. Quantum Hall liquids of electrons in GaAs
structures of high perfection are investigated by measurements of low-lying collective excitation
modes using light scattering methods at miliKelvin temperatures. The light scattering experiments
access directly low-lying "quasiparticle" excitations above the fluid ground states. These are the
excitations that express distinct quantum phases of the electron liquids.
* Supported by ONR, NSF and DOE