Planar hyperbolic polaritons: an opportunity for new tools for thermal and nanoscale applications
A multi-institutional team of scientists led by ECE’s Paul Palmberg Professor Tony Low provides a comprehensive review of the properties of planar hyperbolic polaritons and the ways in which these particles can be tuned to achieve functional and technological applications. The review is published in Nature Communications, a premier journal that covers the natural sciences, and is titled, “Planar hyperbolic polaritons in 2D van der Waals materials.” The team discusses the origin of planar hyperbolic polariton modes, their experimental observations, a review of their properties and ways in which they can be tuned for potential applications in areas such as memory and information processing, sensing, optics, and others. The scientific collaboration spans across institutions in the United States and abroad (names of collaborating institutions and authors included at the end).
Polaritons are quasiparticles, the hybrid outcome of light-matter interactions. While electrons with their short wavelength have enabled miniaturized electronic components (critical to memory and storage applications) and photons with their longer wavelength have helped enable long range communication functionalities, polaritons as hybrid particles can shrink the wavelength of light and operate as a bridge between electrons and photons, a characteristic that can be harnessed for use in photonic and optoelectronic applications.
Planar hyperbolic polaritons are quasiparticles with a directional feature and can exist only in anisotropic materials. The anisotropy of the material allows for the directional confinement of the electromagnetic wave, and the limited propagation angle leads to a frequency curve that is shaped like a hyperbola. These particles have been theoretically predicted, and more recently they have been experimentally demonstrated in 3D materials. However, the discovery of planar hyperbolic polaritons in natural 2D van der Waals (vdW) materials has been particularly exciting as they present the opportunity to develop tools for the control of electromagnetic fields at the nanoscale (while overcoming the limitations of conventional nanostructured hyperbolic metamaterials and metasurfaces).
According to Low, a senior author of the study, "By manipulating the properties of hyperbolic polaritons, we can look to unlock new applications and advancements in various industries such as polariton qubit bus for a compact quantum computer."
The existence of polaritons in 2D van der Waals materials entails that they are more amenable to manipulation by techniques such as twisting, intercalation, modulation, patterning, and other engineering measures that can alter the properties and characteristics of the hyperbolic polariton. This in turn opens up opportunities for developing new applications or improving existing ones. One such example is their possible use in quantum and spin photonic applications. The scientists also foresee their use as waveguides to aid in developing on-chip architectures for quantum information processing. 2D hyperbolic materials present the ability to tune the spin angular momentum of surface waves from transverse to longitudinal, which is a functionality that could be valuable for spintronics. The authors also see their potential use in thermal applications such as high temperature coatings, near-field thermophotovoltaics, radiative cooling, and heat sinks. Radiative heat transfer via planar polaritons is very efficient which makes for their use in such applications. Joshua Caldwell, a senior author of the study and professor at Vanderbilt University says, "Potential applications of this research could be improving thermal management in specific devices such as transistors." They might also have a place in sensing applications as many 2D polaritons are in the mid-infrared range which coincides with molecular vibrational excitations. Their high confinement means they could also potentially provide location-specific information about a molecule or other similar target. Transformation optics and polarization engineering are two other areas of promise that the scientists have identified.
The research team offered insights into the physical phenomena, including techniques to manipulate the hyperbolic polaritons. Low and Caldwell are looking forward to the next step in this research through funding from the Multidisciplinary University Research Initiative (MURI) Program grant through the U.S. Office of Naval Research.
In addition to Low and Caldwell, the research team included Hongwei Wang, Sang-Hyun Oh, Jian-Ping Wang, Phaedon Avouris (University of Minnesota Twin Cities), Anshuman Kumar (IIT Bombay), Siyuan Dai (Auburn University), Xiao Lin (Zhejiang University), Zubin Jacob, Evgenii Narimanov (Purdue University), Vinod Menon (University of New York), Young Duck Kim (Kyung Hee University), Luis Martin Moreno (Universidad de Zaragoza), and Joshua Caldwell (Vanderbilt University).
To read the full paper “Planar hyperbolic polaritons in 2D van der Waals materials,” visit the Nature Communications website.