CM-AMO Seminar | Light Scattering from the Collective Modes of Electrons, Xiaoqing (Elaine) Li (Univ of Texas at Austin)

Speaker: Xiaoqing (Elaine) Li (Univ of Texas at Austin)

Abstract: A powerful approach for investigating properties of matter is light scattering. In this talk, I will discuss how scattering is used to probe collective modes of electrons in two distinct systems.

The first example focuses on light scattering from collective electron oscillations in metals called plasmons. We investigated a low-symmetry heterogeneous nanostructure comprised of simple yet distinct gold nanoparticles (NPs): a sphere and a rod. When the two NPs are coupled via near field interaction, a Fano resonance emerges from the interference between the dark, quadrupole mode of the rod and the bright, dipolar mode of the sphere. Polarization sensitive and tomography-like scattering measurements from different directions allowed us to determine the relative position and orientation between the two NPs on the nanometer scale. We coined the term "plasmonic protractor" to suggest this simple nanostructure may be useful for studying in-situ conformational changes such as rotation and bending at the single molecule level.

The second example focuses on light scattering from collective spin oscillations in ferromagnetic materials called magnons. Magnons, or spin waves, are the normal modes of magnetic excitations, just as phonons are the normal modes of lattice vibrations. Using a technique called micro Brillouin light scattering, we were able to spatially map out the spin wave intensity in magnetic microstructures.