Engineering the Reststrahlen band with hybrid plasmon/ phonon excitations
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lasmonics, Photonics, and Metamaterials Research Letter
Engineering the Reststrahlen band with hybrid plasmon/ phonon excitations W. Streyer, Micro and Nanotechnology Laboratory, University of Illinois at Urbana Champaign, Electrical and Computer Engineering, 208 North Wright St, Urbana, Illinois, USA K. Feng, University of Notre Dame, Electrical Engineering, Notre Dame, Indiana, USA Y. Zhong, Micro and Nanotechnology Laboratory, University of Illinois at Urbana Champaign, Electrical and Computer Engineering, 208 North Wright St, Urbana, Illinois, USA A.J. Hoffman, University of Notre Dame, Electrical Engineering, Notre Dame, Indiana, USA D. Wasserman, Micro and Nanotechnology Laboratory, University of Illinois at Urbana Champaign, Electrical and Computer Engineering, 208 North Wright St, Urbana, Illinois, USA Address all correspondence to D. Wasserman at [email protected] (Received 25 September 2015; accepted 11 December 2015)
Abstract There has been increasing interest in so-called phononic materials, which can support surface modes known as surface phonon polaritons, consisting of electromagnetic waves coupled to lattice vibrations at the surface of a polar material. While such excitations have a variety of desirable features, they are limited to the spectral range between a material’s longitudinal and transverse optical phonon frequencies. In this work, we demonstrate that for materials whose free-carrier concentrations can be controlled, hybrid plasmonic/phononic modes can be supported across a range of frequencies including those generally forbidden by purely phononic materials.
The study of optical surface waves has been an active and growing field of research for many decades, and one which has benefitted greatly from recent advances in nanopatterning and -structuring. These advances have allowed for the demonstration of nanoscale, sub-diffraction optical structures, and devices based on the strong optical confinement achievable with tightly bound surface waves. The vast majority of these works have focused on surface plasmons, polariton excitations consisting of charge density oscillations coupled to propagating or localized electromagnetic modes—sometimes referred to as “particle plasmons”[1,2] or “Mie plasmons”[3–5]—at the interface between a conductor and dielectric.[6–9] Such excitations form the basis of the field of plasmonics, and have been utilized to demonstrate a wide range of novel optical and optoelectronic devices.[10–14] Typically, the field of plasmonics has utilized noble metals (particularly Au and Ag) as their plasmonic materials. For such traditional plasmonic materials, strong subwavelength confinement occurs when the real part of the permittivity is negative, and of the order of the surrounding dielectric’s (positive) permittivity; for Au and Ag, this occurs in the visible to near-IR wavelength ranges.[15] At longer wavelengths, traditional plasmonic materials begin to behave more like perfect electrical conductors, precluding much of the subwavelength confinement associated with these meta
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