Metamaterials for topological photonics

17 May 2018
Professor Shuang Zhang, University Of Birmingham

Email: s.zhang@bham.ac.uk

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 polarised 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 realising three dimensional Dirac points, each of which represents the merging of two Weyl points with opposite chiralities. Spin polarised Fermi arcs are supported at the surface of the Dirac metamaterial [9].

References

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, L. E. Barr, W. Gao, H. Liu, B. Béri, Y. Xiang, D. Fan, A. P. Hibbins and 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 and 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 and S. Zhang, Three dimensional photonic Dirac points in metamaterials, Physical Review Letters, 119, 213901 (2017).

About the speaker

Professor Shuang Zhang received a BS in physics from Jilin University, China, MS in physics from Northeastern University (USA) and a PhD 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 and 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.