Photoinduced dynamics of flat bands in the kagome metal CoSn

TL;DR

This study uses time-resolved photoelectron spectroscopy to investigate how flat bands in the kagome metal CoSn respond to ultrafast photoexcitation, revealing their resilience and the dynamics of electron localization.

Contribution

It provides the first direct observation of photoinduced changes in flat bands of CoSn, linking ultrafast electron localization disruption to band dispersion modifications.

Findings

Flat bands shift and broaden immediately after photoexcitation.

Broadening persists for at least one picosecond.

Flat bands show resilience to near-infrared light.

Abstract

CoSn is a prototypical kagome compound showing lattice-born flat bands with suppressed bandwidth over large parts of the Brillouin zone. Here, by means of time- and angle-resolved photoelectron spectroscopy, we provide direct evidence of the response to photoexcitation of the flat bands, that underlie information about localization in real space. In particular, we detect a sudden shift and broadening of the flat bands, while after one picosecond only a broadening survives. We ascribe both these effects to an ultrafast disruption of electron localization, which renormalizes the effective electron-electron interaction and affects the flat band dispersion. Since both variations are in the order of a few meV, our measurements suggest that the flat bands are resilient to near-infrared photoexcitation.