Guest: Coşkun Kocabaş

Title: Topological Control of Light (MAT, PHYS)

Date/Time: October 16, 2024, 13:40

Location: https://sabanciuniv.zoom.us/j/3297128289

Abstract: Classification of materials based on their physical properties has shaped the development of modern civilisations. Using the right materials together with fine-tuning of their physical properties, has enabled novel engineered devices. Over the last decade, we have witnessed a new materials classification based on topological concepts. We can group materials using integer numbers associated with the symmetry of their electronic band structure. Recently those innovative concepts have been applied for optical systems to investigate topological phases of light on tailored optical materials. However, examples in the literature are passive optical systems with built-in topology. Active control of topology and device applications remains a challenge. This talk explores the topological control of light across different domains, demonstrating how topological singularities can be harnessed to manipulate electromagnetic waves. First, I will show how exceptional points (EPs) singularities in graphene-based terahertz devices enable precise control over light propagation. By tuning a gate voltage, we can modulate both the intensity and phase of terahertz pulses using a topological phase transition while crossing an EP. We were able to reconstruct the complex energy landscape and explore non-Hermitian physics behind the observed topological properties. In a second approach, we apply topological principles to thermal light. By controlling the reflection topology of thermal emitters, we observed a topological phase transition in thermal radiation by varying a single parameter. The critical point of zero reflection is topologically protected, and boundaries between spatial domains host interface states with near-unity thermal emissivity. Together, these examples illustrate rich physics of topological singularities providing new tools for controlling light, from the terahertz regime to thermal radiation, with potential applications in THz communications and thermal management. 

Bio: Coskun Kocabas received his BS degree in physics from METU, Ankara, Turkey, in 2001, and his PhD from the University of Illinois at Urbana-Champaign, USA, in 2007. Following his doctoral studies, he conducted postdoctoral research at Harvard University in the Department of Chemistry and Chemical Biology. From 2009 to 2017, he was a faculty member in the Department of Physics at Bilkent University. In 2017, he joined the University of Manchester as a professor in the Department of Materials and National Graphene Institute. His research group focuses on the synthesis of novel quantum materials and their integration into electronic and photonic devices, with a particular emphasis on the optical applications of graphene and other 2D materials. He has published over 100 papers in leading journals such as Science, Nature Nanotechnology, PNAS, Nature Communications, and Nano Letters, accumulating more than 10000 citations and an h-index of 45. Kocabas has received several prestigious research awards, including the ERC Consolidator Grant, ERC Proof of Concept Grant, Marie Curie Fellowship, and Young Investigator Award. He is also the founder of SmartIR Ltd, a university spin-off company focused on commercializing graphene-based optical technologies.