Self-Accelerating Topological Edge States

TL;DR

This paper introduces self-accelerating topological edge states in valley Hall insulators, demonstrating their nondiffracting, self-healing, and corner-circumventing properties, with potential for advanced control of edge excitations.

Contribution

It presents the first demonstration of self-accelerating, nondiffracting topological edge states with both linear and nonlinear properties, expanding topological photonics capabilities.

Findings

Self-accelerating edge states do not diffract despite boundary features.

Nonlinearity significantly influences the shape of edge states.

Edge states can bypass sharp corners with proper apodization.

Abstract

Edge states emerging at the boundaries of materials with nontrivial topology are attractive for many practical applications due to their remarkable robustness to disorder and local boundary deformations, which cannot result in scattering of the energy of the edge states impinging on such defects into the bulk of material, as long as forbidden topological gap remains open in its spectrum. The velocity of the such states traveling along the edge of the topological insulator is typically determined by their Bloch momentum. In contrast, here, using valley Hall edge states forming at the domain wall between two honeycomb lattices with broken inversion symmetry, we show that by imposing Airy envelope on them one can construct edge states which, on the one hand, exhibit \textit{self-acceleration} along the boundary of the insulator despite their fixed Bloch momentum and, on the other hand, \textit{do not diffract} along the boundary despite the presence of localized features in their shapes. We construct both linear and nonlinear self-accelerating edge states, and show that nonlinearity considerably affects their envelopes. Such self-accelerating edge states exhibit self-healing properties typical for nondiffracting beams. Self-accelerating valley Hall edge states can circumvent sharp corners, provided the oscillating tail of the self-accelerating topological state is properly apodized by using an exponential function. Our findings open new prospects for control of propagation dynamics of edge excitations in topological insulators and allow to study rich phenomena that may occur upon interactions of nonlinear envelope topological states.