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X-WR-CALNAME:UNAM Nanoteknoloji Araştırma Merkezi
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DTSTART;TZID=Europe/Moscow:20221007T160000
DTEND;TZID=Europe/Moscow:20221007T170000
DTSTAMP:20260907T081412
CREATED:20220928T063521Z
LAST-MODIFIED:20220928T063553Z
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SUMMARY:Perfect transfer of waves
DESCRIPTION:Q-Han Park\nKorea University \n\nWaves\, both classical and quantum\, are reflected when they encounter different media or potential regions. Reflection is a fundamental property of waves underlying numerous scientific applications. Nevertheless\, in many cases removing reflection is a key issue to secure transmission and increase device efficiencies. Since the early works of Brewster and Rayleigh\, much effort has been made to remove reflection\, or achieve so called anti-reflection (AR). The most well-known AR coating\, based on a simple interference principle of optics\, only works for specific frequencies and incidence angles. Despite efforts to extend AR to broader frequency\, progress was achieved mainly by the trial-and-error optimization in designing multilayer AR structures. So far\, AR has been regarded as a technological issue without much room for further fundamental understanding. \nHere\, we uncover a principle of universal impedance matching (UIM) that allows a complete removal of reflection regardless of the incidence angle and the frequency of incoming waves. In the case of electromagnetic waves\, we reformulate the Maxwell’s equation in terms of impedance and admittance functions and directly establish the inverse scattering relation between scattered fields and material parameters\, i.e.\, permittivity and permeability. Particularly\, from the inverse scattering relation we find that the perfectly vanishing reflection\, omnidirectional and frequency independent\, can be explicitly realized by spatiotemporally dispersive materials. As a demonstration\, we introduce an UIM coating that enables the perfect transmission of white light in heterogeneous transparent media. We also present an experimental realization of UIM using metamaterials. \nThe complete removal of reflection based on UIM can be extended to various physical situations\, such as light reflection at curved surface interfaces\, reflection at the junction two different waveguides\, total internal reflections\, reflection of acoustic and elastic waves and reflection of quantum matter waves at potential steps. We explain how UIM can be extended to these physical systems and applied to practical devices. \n \n  \n  \nAbout Speaker\n  \nDr. Q-Han Park is currently Professor in Physics at Korea University in South Korea. He received his Ph.D. degree in Physics from Brandeis University\, United States in 1987. He was a Postdoctoral Research Fellow at University of Cambridge with Stephen Hawking from 1990 to 1992. Afterwards he was a research associate at CERN\, Switzerland\, a visiting scholar at MIT\, United States\, and a senior visiting fellow at the Institute of Optics\, United States. He then joined Kyunghee University in South Korea as Assistant Professor in 1992\, and moved to Korea University in 2001. \nDr. Park served as a director of Research Institute Basic Sciences in Korea\, and an associated editor for Optics Express of the Optical Society of America. Dr. Park is currently Fellow of the Korean Academy of Science and Technology\, American Optical Society\, Optical Society of Korea\, and Korean Physical Society. He is also serving as Director of the Center for Electromagnetic Metamaterials of Korea University and Consultant of Samsung Advanced Institute of Technology. He has received the prestigious Korean Science Award by the Ministry of Science and ICT in 2020. \nDr. Park’s research has been focused on high energy physics until the year of 2000 and switched to the field of optics. Since then\, he published high impact papers on optics including five papers in Nature Photonics and holds 35 patents. In earlier works\, he made significant theoretical advances in Plasmonics. His recent research topics include universal impedance matching and non-local metamaterials. He has authored more than 200 journal articles and 47 patents. More details can be found on his homepage (http://nol.korea.ac.kr/). \nTopic: Nanocolloquium Series\nTime: Oct 7\, 2022 04:00 PM Istanbul\nJoin Zoom Meeting\nhttps://zoom.us/j/5876884794?pwd=OUNFRTZKZDNRMm5MWjJjSlhnMXFNUT09\nMeeting ID: 587 688 4794\nPasscode: 871377 \n  \n\n \n  \n 
URL:https://unam.bilkent.edu.tr/en/event/perfect-transfer-of-waves/
CATEGORIES:Nanocolloquium Series
ATTACH;FMTTYPE=image/jpeg:https://unam.bilkent.edu.tr/en/wp-content/uploads/2022/09/Q-Han-Park.jpg
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BEGIN:VEVENT
DTSTART;TZID=Europe/Moscow:20221014T160000
DTEND;TZID=Europe/Moscow:20221014T170000
DTSTAMP:20260907T081412
CREATED:20221010T073501Z
LAST-MODIFIED:20221010T073501Z
UID:6804-1665763200-1665766800@unam.bilkent.edu.tr
SUMMARY:Spintronics with novel two-dimensional materials
DESCRIPTION:Ahmet Avsar\nThe National University of Singapore \n\nExploitation of the intrinsic spin of an electron\, spintronics\, could facilitate the development of multifunctional and novel devices. As regards to material selection\, two-dimensional (2D) crystals and their van der Waals heterostructures could enable new spintronics functionalities that are inaccessible in conventional bulk materials [1]. To exploit the full potential of such heterostructures\, the family of 2D spin transport and magnetic materials needs to be expanded. \nIn this talk\, I will present our efforts in exploring novel materials for this emerging field. Firstly\, I will introduce ultra-thin\, semiconducting black phosphorus as a promising spin transport channel material and discuss our recent efforts focused on investigating the impact of its unique crystal structure on spin dynamics [2]. Then\, I will demonstrate inducing magnetism into an otherwise non-magnetic 2D material with the creation of some specific types of defects [3]. Finally\, I will provide an outlook about the potential of heterostructures based on such novel 2D materials for fundamental spintronics research and applications in information storage and logic devices. \n[1] A. Avsar et al.\, Rev. Mod. Phys. 92\, 021003 (2020).\n[2] A. Avsar et al.\, Nat. Phys. 13\, 888-894 (2017) & L. Cording et al.\, submitted.\n[3] A. Avsar et al.\, Nat. Nano.\, 14\, 674-678 (2019) & A. Avsar et al.\, Nat. Comm.\, 11\, 4806 (2020). \n \n  \n  \nAbout Speaker\n  \nDr Ahmet Avsar is an Assistant Professor and NRF Fellow in the Department of Material Science and Engineering at the National University of Singapore (NUS). Prior to joining NUS\, he was an Assistant Professor of Physics at Newcastle University (United Kingdom)\, and worked as an EPFL Fellow (co-funded by the European Marie Curie COFUND programme) at the Swiss Federal Institute of Technology Lausanne (EPFL\, Switzerland) between 2016 and 2020 after completing his PhD in Physics at NUS.\nAs an experimental condensed matter physicist specialized in two-dimensional (2D) materials\, Ahmet Avsar is interested in exploitation of the multiple quantum degrees of freedom (spin\, pseudospin and valley) available to 2D materials in the ultimate atomically thin limit for applications in energy-efficient information technologies (For more information: https://sites.google.com/site/aavsar). \nTopic: UNAM Nanocolloquium Series \nTime: Oct 14\, 2022 04:00 PM  \nHybrid Event \nUNAM Conference Hall\, \n& \nJoin Zoom Meeting \nhttps://zoom.us/j/5876884794?pwd=OUNFRTZKZDNRMm5MWjJjSlhnMXFNUT09\nMeeting ID: 587 688 4794\nPasscode: 871377 \n  \n\n \n  \n 
URL:https://unam.bilkent.edu.tr/en/event/spintronics-with-novel-two-dimensional-materials/
CATEGORIES:Nanocolloquium Series
ATTACH;FMTTYPE=image/jpeg:https://unam.bilkent.edu.tr/en/wp-content/uploads/2022/10/ahmet-avsar.jpg
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