Dr. Matthew White, University of Vermont
Host: Matthew Sfeir
Metal-dielectric photonic crystal organic light emitting diodes: band structure, defect engineering, and topological states.
Abstract: We investigate the band structure of metal-dielectric photonic crystals comprising stacked organic semiconductor microcavities with silver metal mirrors. Employing organic semiconductor dielectric layers allows the unit cells in the crystal to function as optoelectronic devices including OLEDs and photodetectors, whether addressed individually or collectively. Geometric variables and material composition are presented to tune the band structure and corresponding photonic wave functions within the crystal. When single defects are introduced into crystals, individual unit cells with aperiodic dimensionality of the organic dielectric layer, the resulting mid-gap defect states are shown to hybridize with a photonic band at certain resonant dimensions. The resonance of the defect cavity affects the transmittance of light through the device, disrupting or enhancing the coupling between otherwise resonant cavities. If the defect is periodic throughout the crystal, the effects on band structure are very different. We introduce a periodic defect to every other metal layer, which doubles the size of the unit cell and has previously been shown to induce a Peierls bandgap. Defining a ratio R of the thickness of the even numbered and odd numbered metal layers, the condition R=1 results in no Peierls gap as the cavities are uniform. We demonstrate that by varying that ratio from R<1 to R>1, there is a point where the band collapses resulting in topological edge states, heavily localized in the two outer-most cavities. Topological domain walls are introduced within the bulk of a crystal with similar properties to soliton-like domain walls in the Su-Schrieffer-Heeger model.
Biography: Matthew White is an Associate Professor of Physics and the director of the Materials Science Graduate Program at the University of Vermont. His research focuses on materials and devices for light harvesting and light emission, ranging from stability of commercial photovoltaic modules to nanostructured photonic devices. Prior to joining UVM, he was a postdoctoral researcher and then a fixed-term assistant professor in the Institute for Physical Chemistry at the Johannes Kepler University in Linz, Austria. He earned his PhD in Physics from the University of Colorado, Boulder, and a BS in Physics and Mathematics from the University of Washington.
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