Fermi Pressure and Coulomb Repulsion Driven Rapid Hot Plasma Expansion in a van der Waals Heterostructure.

Choi, Junho; Embley, Jacob; Blach, Daria D; Perea-Causín, Raül; Erkensten, Daniel; Kim, Dong Seob; Yuan, Long; Yoon, Woo Young et al. · Nano Lett · 2023

basic_science · Level V

Where this comes from

Abstract

Transition metal dichalcogenide heterostructures provide a versatile platform to explore electronic and excitonic phases. As the excitation density exceeds the critical Mott density, interlayer excitons are ionized into an electron-hole plasma phase. The transport of the highly non-equilibrium plasma is relevant for high-power optoelectronic devices but has not been carefully investigated previously. Here, we employ spatially resolved pump-probe microscopy to investigate the spatial-temporal dynamics of interlayer excitons and hot-plasma phase in a MoSe<sub>2</sub>/WSe<sub>2</sub> twisted bilayer. At the excitation density of ∼10<sup>14</sup> cm<sup>-2</sup>, well exceeding the Mott density, we find a surprisingly rapid initial expansion of hot plasma to a few microns away from the excitation source within ∼0.2 ps. Microscopic theory reveals that this rapid expansion is mainly driven by Fermi pressure and Coulomb repulsion, while the hot carrier effect has only a minor effect in the plasma phase.