A novel ultrafast terahertz probe has traced dark composite particles and confirmed, for the first time, that their formation occurs on the femtosecond timescale in single-walled carbon nanotubes. Dark particles, known as dark excitons, are composite pairs of quasielectrons and electron holes. Single-walled carbon nanotubes have unique electrical properties governed by the presence of dark and bright particles. Because dark excitons cannot emit a photon like their bright counterparts, they do not interact with visible light, rendering them difficult to trace. Researchers instead used short pulsed terahertz light, outside the visible spectrum, and an ultrafast camera technique to directly monitor their formation and time evolution. This novel method allowed them to capture and quantify dark particle formation on the femtosecond scale, or to one quadrillionth of a second. The direct visualization and quantification fundamentally change the conventional view on dark exciton characteristics and formation dynamics. This technique may also evolve into a benchmark approach for quantitative exciton management in single-walled carbon nanotube-based device development.
Ultrafast Terahertz Probes of Interacting Dark Excitons in Chirality-Specific Semiconducting Single-Walled Carbon Nanotubes