31 August 2018
Topological insulators are unusual materials that have complete bulk bandgap, but admit conduct-ance through topologically protected edge states. When time-reversal symmetry of Hamiltonian governing the system is broken and insulator is placed in contact with the material having distinct topology, the in-gap states appear at the edge of the insulator that travel along its edge only in one direction. They persist in the presence of disorder and do not experience backscattering upon in-teraction with defects due to topological protection.
The latter property makes edge states excellent candidates for future information processing schemes but, on the other hand, it is an obstacle for the realization of complex switching architec-tures based on edge states because immunity to disorder or missing elements implies suppressed scattering into the bulk of the insulator.
In a recent paper published in Laser and Photonics Reviews, and selected to appear on the cover of the August issue of the journal, researchers from Xi’an Jiaotong University together with ICFO re-searchers Yaroslav V. Kartashov and UPC Prof and Director of ICFO Lluis Torner, have reported on the existence of a physical mechanism that allows to resonantly couple topological excitations propagating at the opposite edges of polariton topological insulator built as a honeycomb arrays of microcavity pillars.
This mechanism uses weak periodic temporal modulations of parameters of microcavity pillars that leads to resonant switching between topological states with the same Bloch momentum, but lo-cated at the opposite edges. The proposed coupling mechanism based on topologically protected states can be used in various topological photonic and condensed matter systems, including Flo-quet insulators, gyromagnetic photonic crystals, semiconductor quantum wells, arrays of coupled resonators, and many others.
Figure Caption: Resonant coupling between topologically protected states propagating at the opposite edges of polariton topological insulator constructed from microcavity pillars. Coupling is stimulated by weak periodic temporal modulation of parameters of microcavity pillars.