Steering edge currents through a Floquet topological insulator

TL;DR

This paper explores how adding a diagonal potential in a Floquet topological insulator enables control over edge and bulk light transport, revealing new states and potential for steering topologically protected light flow.

Contribution

It introduces the effect of a diagonal potential on Floquet topological insulators, showing how it influences edge and doublon states and enables transport control.

Findings

Diagonal potential can prohibit hopping onto the diagonal.

System can split into two triangular lattices at specific potentials.

Temporal delay observed in wavefunction propagation.

Abstract

Periodic driving may cause topologically protected, chiral transport along edges of a 2D lattice that, without driving, would be topologically trivial. We study what happens if one adds a different on-site potential along the diagonal of such a 2D grid. In addition to the usual bulk and edge states, the system then also exhibits doublon states, analogous to two interacting particles in one dimension. A particle initially located at an edge propagates along the system's boundary. Its wavefunction splits when it hits the diagonal and continues propagating simultaneously along the edge and the diagonal. The strength of the diagonal potential determines the ratio between both parts. We show that for specific values of the diagonal potential, hopping onto the diagonal is prohibited so that the system effectively separates into two triangular lattices. For other values of the diagonal potential, we find a temporal delay between the two contributions traveling around and through the system. This behavior could enable the steering of topologically protected transport of light along the edges and through the bulk of laser-inscribed photonic waveguide arrays.