Gate Tunable Dark Trions in Monolayer ${\mathrm{WSe}}_{2}$

Gate Tunable Dark Trions in Monolayer ${WSe}_{2}$

Erfu Liu, Jeremiah van Baren, Zhengguang Lu, Mashael M. Altaiary, Takashi Taniguchi, Kenji Watanabe, Dmitry Smirnov, and Chun Hung Lui

Phys. Rev. Lett. 123, 027401 – Published 9 July 2019

Abstract

Monolayer ${WSe}_{2}$ is an intriguing material to explore dark exciton physics. We have measured the photoluminescence from dark excitons and trions in ultraclean monolayer ${WSe}_{2}$ devices encapsulated by boron nitride. The dark trions can be tuned continuously between negative and positive trions with electrostatic gating. We reveal their spin-triplet configuration and distinct valley optical emission by their characteristic Zeeman splitting under a magnetic field. The dark trion binding energies are 14–16 meV, slightly lower than the bright trion binding energies (21–35 meV). The dark trion lifetime ( $\sim 1.3 ns$ ) is two orders of magnitude longer than the bright trion lifetime ( $\sim 10 ps$ ) and can be tuned between 0.4 and 1.3 ns by gating. Such robust, optically detectable, and gate tunable dark trions may help us realize trion transport in two-dimensional materials.

Received 21 January 2019

DOI:https://doi.org/10.1103/PhysRevLett.123.027401

Physics Subject Headings (PhySH)

Excitons Trions

Transition metal dichalcogenides

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Erfu Liu ¹, Jeremiah van Baren¹, Zhengguang Lu^2,3, Mashael M. Altaiary¹, Takashi Taniguchi⁴, Kenji Watanabe⁴, Dmitry Smirnov², and Chun Hung Lui^1,*

¹Department of Physics and Astronomy, University of California, Riverside, California 92521, USA
²National High Magnetic Field Laboratory, Tallahassee, Florida 32310, USA
³Department of Physics, Florida State University, Tallahassee, Florida 32310, USA
⁴National Institute for Materials Science, Tsukuba, Ibaraki 305-004, Japan