Time: 15:15, Jun. 28 (Fri.), 2019

Venue: Rm. M 830, M Building of the Institute of Physics (IOP, CAS)

             Zhong-Guan-Cun South Road, Haidian Dist., Beijing

Speaker: Xiao Hu (WPI-MANA, NIMS, Japan)

Abstract

We demonstrate that topological electromagnetic transports can be realized in microstrips, a typical transmission line [1]. We start from a planar circuit, where capacitors are put on the sites of honeycomb lattice, which shunt the circuit to a common ground, whereas inductors are put over the links between the sites. We clarify that grouping sites into hexagons and making the inductances on the links inside hexagons larger than those between hexagons, a texture respecting the C_6v symmetry [2,3], produces a topological state. The nontrivial topology has its origin in the Dirac dispersion formed by the honeycomb structure, and is induced by the inductance texture which opens a photonic band gap. We then fabricate microstrips with the widths of top metallic strips tuned according to the theoretical design, making use the property that the effective inductance of a strip is inversely proportional to its width. The pseudospin states and the spin-momentum locking in the topological edge states have been revealed experimentally, taking the advantage of the planar and open structure of the microstrips. The present approach provides a novel way to generate optic modes with orbital angular momenta without breaking time-reversal symmetry and space-inversion symmetry.

This work is based on the collaboration with Hong CHEN, Tongji University. XH is supported by CREST (JPMJCR18T4, JST) and KAKENHI (17H02913, JSPS).

References:

[1] Y. Li, Y. Sun, W.-W. Zhu, Z.-W. Guo, J. Jiang, T. Kariyado, H. Chen and X. Hu: Nat. Commun. vol. 9, 4598 (2018).

[2] L.-H. Wu and X. Hu: Phys. Rev. Lett. vol. 114, 223901 (2015).

[3] Y.-T. Yang, Y.-F. Xu, T. Xu, H.-X. Wang, J.-H. Jiang, X. Hu and Z.-H. Hang: Phys. Rev. Lett. vol. 120, 217401 (2018)