Prolonged photo-carriers generated in a massive-and-anisotropic Dirac material

TL;DR

This study uses advanced spectroscopy to observe long-lived photo-generated carriers in black phosphorus, revealing its potential for excitonic condensation and broadband optoelectronic applications.

Contribution

It provides direct evidence of prolonged photo-carrier lifetimes in black phosphorus and confirms its suitability for excitonic condensation due to anisotropic Dirac dispersions.

Findings

Photo-carriers have lifetimes exceeding 400 ps.

Massive-and-anisotropic Dirac dispersions confirmed.

Black phosphorus is a promising platform for excitonic condensation.

Abstract

Transient electron-hole pairs generated in semiconductors can exhibit unconventional excitonic condensation. Anisotropy in the carrier mass is considered as the key to elongate the life time of the pairs, and hence to stabilize the condensation. Here we employ time- and angle-resolved photoemission spectroscopy to explore the dynamics of photo-generated carriers in black phosphorus. The electronic structure above the Fermi level has been successfully observed, and a massive-and-anisotropic Dirac-type dispersions are confirmed; more importantly, we directly observe that the photo-carriers generated across the direct band gap have the life time exceeding 400 ps. Our finding confirms that black phosphorus is a suitable platform for excitonic condensations, and also open an avenue for future applications in broadband mid-infrared BP-based optoelectronic devices.