Metamaterials with Spatiotemporal Modulation and Parity-Time Symmetry for Advanced Wave Manipulation

Metamaterials have attracted significant attention for their extraordinary properties, not found in natural materials. Realized as regular arrangements of relatively simple elements, metamaterials have been so far shown to exhibit unique phenomena, such as negative refraction, cloaking, anomalous Snell's law, and extraordinary field enhancement. However, like natural materials, metamaterials are bounded by fundamental physical principles, such as time-reversal symmetry and passivity, which limit their functionalities and applicability range. In this talk, I will present the opportunities offered by spatiotemporal modulation and parity-time symmetry for overcoming such limitations. Spatiotemporal modulation allows realizing effective motion in cases where physical motion is impractical or totally impossible. I will show that by applying this powerful concept to appropriately designed metamaterial structures it is possible to break time-reversal symmetry and achieve giant non-reciprocity without magnetic materials. Applications in microwaves, optics and acoustics will be presented, including increasing the speed of wireless communications systems, achieving efficient light flow control in optical integrated networks and manipulating thermal flow in acoustical nanosystems. The second part of my talk will be focused on parity-time symmetry, which in classical-wave systems is realized through spatially balanced loss and gain. I will show that parity-time symmetry allows obtaining exotic phenomena, such as invisible sensing, negative refraction and cloaking, without the loss and bandwidth limitations of metamaterials. Furthermore, I will show that parity-time symmetry is not simply a way to compensate loss in passive structures but a really new physical paradigm where loss and gain are uniquely combined to yield unprecedented phenomena. More broadly, during my talk, I will discuss the opportunities created by spatial and temporal symmetries for advanced manipulation of wave phenomena.
Dimitrios L. Sounas received the Diploma/M.Eng. and Ph.D. degrees in electrical and computer engineering with the highest honors from the Aristotle University of Thessaloniki, Greece in 2004 and 2009, respectively. From August 2010 to October 2012, he was a Post-Doctoral Fellow with the Electromagnetic Theory and Applications Research Group, ‰cole Polytechnique de Montréal, and since November 2012, he has been a Post-Doctoral Fellow with the Metamaterials and Plasmonics Research Group, The University of Texas at Austin. His research interests span over a broad range of areas, including electromagnetis, optics, metamaterials, plasmonics, non-reciprocity, spatiotemporal modulation, parity-time symmetry and graphene. Dr. Sounas has been the author or the co-author of 36 journal papers, 64 conference papers, 2 book chapters and 4 patents, among which papers in highly selective journals, including Science, Nature Physics, Nature Communications, ACS Photonics and Physical Review Letters. His work has been covered by the general media and recently resulted in a startup company on magnetic-free circulators.