# High-harmonic generation in Su-Schrieffer-Heeger chains

## TL;DR

This paper investigates high-harmonic generation in SSH chains, revealing significant differences in harmonic yield between topological phases, and demonstrates the robustness of these effects against disorder and phase transitions.

## Contribution

It shows that the simple SSH model captures key topological effects in high-harmonic generation, highlighting the role of edge states in the process.

## Key findings

- Large differences in harmonic yield between topological phases.
- Robustness of topological effects against disorder and phase transitions.
- Edge illumination is not necessary for the observed spectral differences.

## Abstract

Su-Schrieffer-Heeger (SSH) chains are the simplest model systems that display topological edge states. We calculate high-harmonic spectra of SSH chains that are coupled to an external laser field of a frequency much smaller than the band gap. We find huge differences between the harmonic yield for the two topological phases, similar to recent results obtained with more demanding time-dependent density functional calculations [D. Bauer, K.K. Hansen, Phys. Rev. Lett. 120, 177401 (2018)]. This shows that the tight-binding SSH model captures the essential topological aspects of the laser-chain interaction (while higher harmonics involving higher bands or screening in the metal phase are absent). We study the robustness of the topological difference with respect to disorder, a continuous phase transition in position space, and on-site potentials. Further, we address the question whether the edges need to be illuminated by the laser for the huge difference in the harmonic spectra to be present.