Speaker: Thomas Folland (University of Iowa)

Title: Surface phonon polaritons; coupling long wavelength light to nanoscale optical transitions

Abstract: Optically active transitions in the infrared (λ=3-300µm) provide a means for accessing and controlling both the optical and electronic properties of materials. Despite many of such transitions having strong dipole moments and nonlinearities, the current generation of infrared technology is often insufficient to fully explore nano- to meso-scale quantum phenomena in this spectral range due to the length-scale mis-match. To achieve strong coherent interactions between materials and long wavelength infrared light, we can exploit surface polaritons. These quasiparticles occur when light couples to coherently oscillating charges in a material, commonly electrons or polar phonons, forming tightly confined evanescent waves. In this colloquium I will discuss how surface phonon polaritons in low symmetry materials offer unique opportunities for coupling long wavelength light into confined spaces with high momentum selectivity. Specifically, we will discuss the case of monoclinic beta-gallium oxide, a monoclinic semiconductor where its low-symmetry crystal structure leads to ‘shear polaritons’ with unusual propagation properties. We will then go on to highlight how surface phonon polaritons can be leveraged in order to enhance coupling to two different types of infrared transitions – vibrational modes and intersubband states. Exploring the weak to strong coupling regime, we anticipate the ability to develop high sensitivity infrared optoelectronics and control chemical energy transfer.

Short bio: Prof. Folland is part of the Condensed Matter and Materials Physics research area at the University of Iowa Department of Physics and Astronomy, focusing on mid- and far-infrared nanophotonics and quantum materials research, from fundamental properties to device applications. His graduate work involved the development of frequency tunable terahertz lasers, implemented using graphene plasmonics. After his doctoral work, he took a postdoc position in the lab of Prof. Joshua Caldwell in the school of Mechanical Engineering at Vanderbilt University. At Vanderbilt, he led the setup of the Caldwell lab and developed new approaches to infrared spectroscopy for the study of nanophotonics systems, including 2D materials and semiconductors. He started his faculty position at the University of Iowa in the Department of Physics and Astronomy in Fall 2020. At Iowa, Prof Folland is working on developing infrared detectors and light sources leveraging nanophotonics, with the goal of coupling long wavelength light to quantum systems. His research interests are highly interdisciplinary, encompassing elements of physics, materials science, electrical engineering, and chemistry.