High-harmonic generation in Su-Schrieffer-Heeger chains

TLDR: In this article, the authors calculate high-harmonic spectra of SSH chains that are coupled to an external laser field of a frequency much smaller than the band gap and 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.

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 and 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 of whether the edges need to be illuminated by the laser for the huge difference in the harmonic spectra to be present.