Science Daily October 28, 2019
Development of valleytronics requires stable valley states and easy identification of the valley indices. An international team of researchers (USA- UC Riverside, Japan, Taiwan) have shown that dark excitons and trions in monolayer WSe2 have much longer lifetime and better valley stability than the common bright excitons and trions, therefore, serve as excellent candidates for valleytronic applications. Until now no method could read the valley indices of the dark excitons and trions because their light emission from either valley has exactly the same energy and polarization, making the two valleys indistinguishable from each other. They found that the dark exciton in the K valley decays into a right-handed photon and a left-handed phonon, whereas the dark exciton in the opposite K’ valley decays into a left-handed photon and a right-handed phonon. The handedness of the emitted photon is a clear signature of the valley indices of the dark excitons and trions...read more. Open Access TECHNICAL ARTICLE
(a)–(c) Band configurations, transition dipole, and optical emission of (a) bright exciton, (b) dark exciton, and (c) dark-exciton chiral phonon replica at the K valley in monolayer WSe2. Credit: Phys. Rev. Research 1, 032007(R) – Published 25 October 2019