Editors' ChoiceUltrafast Optics

Clocking the dynamics of effective mass

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Science  26 Jan 2018:
Vol. 359, Issue 6374, pp. 408-409
DOI: 10.1126/science.359.6374.408-e

Electrons propagating through a solid interact with the crystal lattice, modifying the electronic motion and giving rise to an effective electron mass. The idea of an effective electron mass is based on the assumption of an unbounded crystal lattice, so the question arises of whether this understanding applies at the scale of small electronic devices. Using ultrafast pump-probe spectroscopy, Kasmi et al. studied the temporal dynamics of photoemitted electrons from a copper target. They found that the electrons require up to 350 attoseconds to reach their effective mass, equating to a propagation distance of just two atomic layers. The results could have bearing on the performance of shrinking electronic circuits, as well as in correctly interpreting ultrafast photoemission process from solids.

Optica 4, 1492 (2017).

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