Anisotropic Nonequilibrium Lattice Dynamics of Black Phosphorus.

Yoav William Windsor,Hélène Seiler,Ralph Ernstorfer,Thomas Vasileiadis,Patrick-Nigel Hildebrandt,Daniela Zahn,Yingpeng Qi

doi:10.1021/acs.nanolett.0c00734

Yoav William Windsor, Hélène Seiler + Show 5 more

Open Access

https://doi.org/10.1021/acs.nanolett.0c00734

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Abstract

Black phosphorus has recently attracted significant attention for its highly anisotropic properties. A variety of ultrafast optical spectroscopies has been applied to probe the carrier response to photoexcitation, but the complementary lattice response has remained unaddressed. Here we employ femtosecond electron diffraction to explore how the structural anisotropy impacts the lattice dynamics after photoexcitation. We observe two time scales in the lattice response, which we attribute to electron–phonon and phonon–phonon thermalization. Pronounced differences between armchair and zigzag directions are observed, indicating a nonthermal state of the lattice lasting up to ∼60 ps. This nonthermal state is characterized by a modified anisotropy of the atomic vibrations compared to equilibrium. Our findings provide insights in both electron–phonon as well as phonon–phonon coupling and bear direct relevance for any application of black phosphorus in nonequilibrium conditions.

Highlights

Black phosphorus has recently attracted significant attention for its highly anisotropic properties
L ayered van der Waals materials have attracted significant research interest in recent years due to their potential device applications.[1−4] The most prominent 2D material, graphene, exhibits high carrier mobility but lacks a band gap, which is required in many applications
Since any device operates in nonequilibrium conditions, a microscopic understanding of nonequilibrium states in van der Waals (vdW) materials is of particular interest

Summary

Corresponding Authors

Patrick-Nigel Hildebrandt − Fritz Haber Institute of the Max Planck Society 14195 Berlin, Germany; orcid.org/0000-. Yingpeng Qi − Fritz Haber Institute of the Max Planck Society 14195 Berlin, Germany. Heĺ eǹ e Seiler − Fritz Haber Institute of the Max Planck Society 14195 Berlin, Germany; orcid.org/0000-0003-1521-4418.

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