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Trion Valley Coherence in Monolayer Semiconductors



Kai Hao, Lixiang Xu, Wu Fengcheng, Philip Nagler, Kha Tran, Xin Ma, Tobias Korn, Allan H. MacDonald, Xiaoqin Li, Galan Moody


The emerging field of valleytronics aims to exploit the valley pseudospin of electrons residing near Bloch band extrema as an information carrier. Recent experiments demonstrating optical generation and manipulation of exciton valley coherence (the superposition of electron-hole pairs at opposite valleys) in monolayer transition metal dichalcogenides (TMDs) provide a critical step towards control of this quantum degree of freedom. The charged exciton (trion) in TMDs is an intriguing alternative to the neutral exciton for control of valley pseudospin because of its long spontaneous recombination lifetime, its robust valley polarization, and its coupling to residual electronic spin. Trion valley coherence has however been unexplored due to experimental challenges in accessing it spectroscopically. In this work we employ ultrafast two-dimensional coherent spectroscopy to resonantly generate and detect trion valley coherence in monolayer MoSe2 demonstrating that it persists for a few-hundred femtoseconds. We conclude that the underlying mechanisms limiting trion valley coherence are fundamentally different from those applicable to exciton valley coherence. Based on these observations, we suggest possible strategies for extending valley coherence times in two-dimensional materials.
2D Materials


valleytronics, two-dimensional materials, charged exciton, coherence


Hao, K. , Xu, L. , Fengcheng, W. , Nagler, P. , Tran, K. , Ma, X. , Korn, T. , MacDonald, A. , Li, X. and Moody, G. (2017), Trion Valley Coherence in Monolayer Semiconductors, 2D Materials, [online],, (Accessed April 13, 2024)
Created May 21, 2017, Updated October 12, 2021