# Attosecond screening dynamics mediated by electron localization in transition metals

## Abstract

Transition metals, with their densely confined and strongly coupled valence electrons, are key constituents of many materials with unconventional properties1, such as high-temperature superconductors, Mott insulators and transition metal dichalcogenides2. Strong interaction offers a fast and efficient lever to manipulate electron properties with light, creating promising potential for next-generation electronics3,4,5,6. However, the underlying dynamics is a hard-to-understand, fast and intricate interplay of polarization and screening effects, which are hidden below the femtosecond timescale of electronic thermalization that follows photoexcitation7. Here, we investigate the many-body electron dynamics in transition metals before thermalization sets in. We combine the sensitivity of intra-shell transitions to screening effects8 with attosecond time resolution to uncover the interplay of photo-absorption and screening. First-principles time-dependent calculations allow us to assign our experimental observations to ultrafast electronic localization on d orbitals. The latter modifies the electronic structure as well as the collective dynamic response of the system on a timescale much faster than the light-field cycle. Our results demonstrate a possibility for steering the electronic properties of solids before electron thermalization. We anticipate that our study may facilitate further investigations of electronic phase transitions, laser–metal interactions and photo-absorption in correlated-electron systems on their natural timescales.

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## Data availability

The data that support the findings of this study are available via https://doi.org/10.3929/ethz-b-000345468 or from the corresponding author upon reasonable request.

## Code availability

The Octopus code for TDDFT is available at https://octopus-code.org.

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## Acknowledgements

The authors acknowledge discussions with E. Krasovskii. S.A.S. and A.R. thank M. J. T. Oliveira for helping with the generation of a transferable pseudopotential for Ti, dealing with semicore electrons. This work was supported by the National Center of Competence in Research – Molecular Ultrafast Science and Technology (NCCR MUST) funded by the Swiss National Science Foundation. The authors acknowledge financial support from the European Research Council (ERC-2015-AdG-694097) and the European Union’s Horizon 2020 Research and Innovation programme under grant agreement no. 676580 (NOMAD). S.A.S. acknowledges support from the Alexander von Humboldt Foundation.

## Author information

M.V., S.A.S., L.G., A.R. and U.K. supervised the study. M.V., F.S., N.H., L.K. and M.L. conducted the experiments. M.V. and F.S. analysed the experimental data. S.A.S. and A.R. developed the theoretical modelling. All authors were involved in the interpretation of data and contributed to the final manuscript.

Correspondence to M. Volkov.

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