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arXiv · 2205.04318

Ultrafast transport mediated homogenization of photoexcited electrons governs the softening of the $A_\mathrm{1g}$ phonon in bismuth

Fabian Thiemann·Germán Sciaini·Alexander Kassen·Ulrich Hagemann·Frank Meyer zu Heringdorf·Michael Horn-von Hoegen
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Abstract

In order to determine the role of non-thermal transport of hot carriers which is decisive for the dissipation of energy in condensed matter we performed time-resolved broadband femtosecond transient reflectivity measurements on $7-197 \mathrm{nm}$ thick Bi(111) films epitaxially grown on Si(111). We monitored the behavior of the Fourier amplitude and the central frequency of the coherent $A_\mathrm{1g}$ phonon mode as function of the incident fluence, film thickness, and probe wavelength in the range of $580 -700 \mathrm{nm}$. The frequency redshift that follows photoexcitation was used as a robust quantity to determine the effective distribution of excited carriers that governs the displacive excitation mechanism of coherent $A_\mathrm{1g}$ phonons in Bi. For Bi films up to $50 \mathrm{nm}$ thickness a homogeneous excitation due to the ultrafast transport of hot charge carriers is observed, limited by a carrier penetration depth of $60 \mathrm{nm}$ independent of the totally deposited laser energy.

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Fabian Thiemann, Germán Sciaini, Alexander Kassen, Ulrich Hagemann, Frank Meyer zu Heringdorf, Michael Horn-von Hoegen. 2022-05-05. Ultrafast transport mediated homogenization of photoexcited electrons governs the softening of the $A_\mathrm{1g}$ phonon in bismuth. https://doi.org/10.1103/physrevb.106.014315

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