Abstract
Metamaterials have attracted tremendous attention due to their exotic optical properties and functionalities that are not attainable from naturally occurring materials [1]. In particular, metamaterials can be designed to introduce strong spin-orbit coupling for light and consequently nontrivial topological properties. In this talk, I will start with a brief introduction to the concepts of Berry curvature, Chern number and topological photonics. I will show that combination of chirality [2, 3] and hyperbolicity – an extreme form of anisotropy [4], can result in nontrivial topological orders in metamaterials and consequently topologically protected photonic surface states that are immune from scattering by defects and sharp edges [5]. The Weyl points in such systems result from the crossing between the bulk longitudinal plasmon mode and the transverse circularly polarized propagating modes [6]. The photonic ‘Fermi arcs’ were directly observed in the microwave regime [7], which showed Riemann-surface like helicoid configuration in the energy-momentum space [8]. I will further introduce a metamaterial approach for realizing three dimensional Dirac points, each of which represents the merging of two Weyl points with opposite chiralities. Spin polarized Fermi arcs are supported at the surface of the Dirac metamaterial [9].
[1] J. B. Pendry, Phys. Rev. Lett. 85, 3966 (2000)
[2] J. B. Pendry, Science,306, 1353 (2004)
[3] S. Zhang, Y.-S. Park, J. Li, X. Lu, W. Zhang, and X. Zhang, Phys. Rev. Lett. 102, 023901 (2009)
[4] J. Yao, Z. Liu, Y. Liu, Y. Wang, C. Sun, G. Bartal, A. M. Stacy, and X. Zhang, Science 321, 930 (2008)
[5] W Gao, M Lawrence, B Yang, F Liu, F Fang, B Béri, J Li, and S Zhang, Physical Review Letters, 114, 037402 (2015)
[6] W Gao, B Yang, M Lawrence, F Fang, B Béri, S Zhang, “Photonic Weyl degeneracies in magnetized plasma”, Nature Communications, 7, 12435 (2016)
[7] B Yang, Q Guo, B Tremain, LE Barr, W Gao, H Liu, B Béri, Y Xiang, D Fan, AP Hibbins & S Zhang, “Direct observation of topological surface-state arcs in photonic metamaterials”, Nature Communications, 8, 97 (2017)
[8] B Yang, Q Guo, B Tremain, R Liu, L E Barr, Q Yan, W Gao, H Liu, Y Xiang, J Chen, C Fang, A Hibbins, L Lu, S Zhang, “Ideal Weyl points and helicoid surface states in artificial photonic crystal structures”, Science, in press (2018)
[9] Q Guo, B Yang, L Xia, W Gao, H Liu, J Chen, Y Xiang, S Zhang, “Three dimensional photonic Dirac points in metamaterials”, Physical Review Letters, 119, 213901 (2017)
Biography
Professor Shuang Zhang received BS in Physics from Jilin University, China, MS. in Physics from Northeastern University (USA) and Ph.D in Electrical Engineering from the University of New Mexico. From December 2005 to August 2006, he was a Postdoctoral Research Fellow at the University of Illinois at Urbana-Champaign, and from August 2006 to March 2010, he was first a Postdoctoral Research Fellow and later an Assistant Research Engineer at the University of California Berkeley. In March 2010, he took the position of Reader in the School of Physics & Astronomy, University of Birmingham, and was promoted to professor in March, 2013. Professor Zhang is the recipient of IUPAP (International Union of Pure and Applied Physics) Young Scientist Prize in Optics, the Royal Society Wolfson Research Merit Award in 2016. He was elected a Fellow of the Optical Society of America (OSA) in 2016.
Anyone interested is welcome to attend.