n intervalley trion decay for the first time.
“Although a trion can decay through either intravalley or intervalley decay, the two transitions have the same energy and can hardly be distinguished in the optical spectrum,” Lui said. “But when a magnetic field is applied, the energies of the intravalley and intervalley transitions will become different.”
The team carried out the experiments at the National High Magnetic Field Laboratory in Tallahassee, Florida. They show both the intravalley and intervalley decay paths of the trions.
“Our results provide a more complete, multipath picture of trion dynamics in monolayer WSe2,” said Jeremiah van Baren, a graduate student in Lui’s lab, who shares equal authorship with Liu. “They build on the existing single-path description of trions in 2-D materials and are key to furthering trion-based valleytronic science and technology.”
The research paper, published in Physical Review Letters, is titled “Multipath optical recombination of intervalley dark excitons and trions in monolayer WSe2.” Related results were recently reported by two other research teams led by scientists at Rensselaer Polytechnic Institute and the University of Washington.
Lui, a recent recipient of the National Science Foundation’s prestigious Faculty Early Career Development (CAREER) Award; Liu, and van Baren were joined in the study by Nathaniel Gabor of UC Riverside; Ching-Tang Liang and Yia-Chung Chang of the Research Center for Applied Sciences at the Academia Sinica in Taipei, Taiwan; and Takashi Taniguchi and Kenji Watanabe of the National Institute for Materials Science in Tsukuba, Japan.
Header image caption: Intervalley exciton light emission from monolayer WSe2. Monolayer WSe2 consists of a two-dimensional array of tungsten atoms (cyan balls) and selenium atoms (yellow balls). Its conduction and valence energy bands exhibit two valleys with opposite electron spins (red and blue cups). An electron (green ball) and a hole (purple ball) in the opposite valleys can be bound to form an intervalley exciton (orange-yellow ellipsoid), which decays to emit light with circular polarization (red spiral). (UCR/Erfu Liu)