CFN Colloquium

"Controlling Light Matter Interactions in Layered Materials with Conventional and Topological Band Structures"

Presented by Prof. Ritesh Agarwal, University of Pennsylvania

Friday, September 6, 2019, 4:00 pm — CFN, Bldg 735, Seminar Room, 2nd Floor

Strongly confined electrical, optical and thermal excitations drastically modify material's properties and break local symmetries that can enable precisely tunable novel responses and new functionalities. We will discuss the effect of engineered plasmonic lattice on light matter interactions in 2D excitonic crystals to produce novel responses such as enhanced and tunable emission, Fano resonances and strong exciton-plasmon polaritons, which can be precisely controlled by geometry and applied fields to produce new device concepts. Our recent work on collective polaritonic modes and the formation of a complete polaritonic bandgap in few-layered excitonic semiconductors coupled to plasmons will also be presented along with our ability to control them via externally applied electric fields. We will also discuss our efforts to explore the optoelectronic properties of MoxW1-xTe2, which are type-II Weyl semimetals, i.e., gapless topological states of matter with broken inversion and/or time reversal symmetry, which exhibit unconventional responses to externally applied fields. We have observed spatially dispersive circular photogalvanic effect (s-CPGE) over a wide spectral region (0.2 - 2.0 eV range) in these materials. This effect shows exclusively in the Weyl phase and vanishes upon temperature induced topological phase change. Since the photon energy leads to interband transitions between different electronic bands, we use the density matrix formalism to describe the photocurrent response under chiral optical excitation with a spatially inhomogeneous beam. We will discuss how spatially inhomogeneous optical excitation and unique symmetry and band structure of Weyl semimetals produces CPGE in these systems. The effect of band inversion, Berry curvature and asymmetric carrier relaxation in this material system on the s-CPGE signal will also be discussed along with the implications for designing new optoelectronic devices. Short B

Hosted by: Chang-Yong Nam

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