Strong-field-driven electric currents in condensed-matter systems are opening new frontiers in petahertz electronics. In this regime, new challenges are arising as the roles of band structure and coherent electron–hole dynamics have yet to be resolved. Here, by using high-harmonic generation spectroscopy, we reveal the underlying attosecond dynamics that dictates the temporal evolution of carriers in multi-band solid-state systems. We demonstrate that when the electron–hole relative velocity approaches zero, enhanced constructive interference leads to the appearance of spectral caustics in the high-harmonic generation spectrum. We introduce the role of the dynamical joint density of states and identify its mapping into the spectrum, which exhibits singularities at the spectral caustics. By studying these singularities, we probe the structure of multiple unpopulated high conduction bands.
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The data that support the findings of this study are available from the corresponding author upon reasonable request.
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N.D. is the incumbent of the Robin Chemers Neustein Professorial Chair. N.D. acknowledges financial support from the Minerva Foundation, the Israeli Science Foundation, the Crown Center of Photonics and the European Research Council. M.K. acknowledges financial support from the Minerva Foundation and the Koshland Foundation.
The authors declare no competing interests.
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Uzan, A.J., Orenstein, G., Jiménez-Galán, Á. et al. Attosecond spectral singularities in solid-state high-harmonic generation. Nat. Photonics 14, 183–187 (2020). https://doi.org/10.1038/s41566-019-0574-4