Correlations drive the attosecond response of strongly-correlated insulators

TL;DR

This study uses attosecond spectroscopy and advanced calculations to reveal how electron correlations in nickel oxide are rapidly quenched within a few femtoseconds, fundamentally differing from band insulators.

Contribution

It provides the first direct measurement of Hubbard U renormalization in NiO and demonstrates the ultrafast dynamics of electron correlations in strongly-correlated insulators.

Findings

Correlated insulators exhibit a laser-driven quench of electron correlations.

Hubbard U is renormalized within a few femtoseconds.

Structural changes occur on longer timescales.

Abstract

Attosecond spectroscopy of materials has provided invaluable insight into light-driven coherent electron dynamics. However, attosecond spectroscopies have so far been focused on weakly-correlated materials. As a result, the behavior of strongly-correlated systems is largely unknown at sub- to few-femtosecond timescales, even though it is typically the realm at which electron-electron interactions operate. Here we conduct attosecond-resolved experiments on the correlated insulator nickel oxide, and compare its response to a common band insulator, revealing fundamentally different behaviors. The results, together with state-of-the art time-dependent $\textit{ab initio}$ calculations, show that the correlated system response is governed by a laser-driven quench of electron correlations. The evolution of the on-site electronic interaction is measured here at its natural timescale, marking the first direct measurement of Hubbard $U$ renormalization in NiO. It is found to take place within a few femtoseconds, after which structural changes slowly start to take place. The resulting picture sheds light on the entire light-induced response of a strongly-correlated system, from attosecond to long-lived effects.