Gate tunable dark trions in monolayer WSe$_2$

TL;DR

This paper reports the observation and electrical control of dark trions in monolayer WSe$_2$, revealing their properties, long lifetime, and potential for electrically tunable trion transport in 2D materials.

Contribution

It demonstrates the direct optical detection and gate tuning of dark trions in monolayer WSe$_2$, including their spin, valley characteristics, and long, tunable lifetimes.

Findings

Dark trions can be continuously tuned between negative and positive charges.

Dark trions have a large binding energy of 14-16 meV.

Their lifetime can be tuned from 0.4 to 1.3 ns.

Abstract

We report the observation and gate manipulation of intrinsic dark trions in monolayer WSe$_2$. By using ultraclean WSe$_2$ devices encapsulated by boron nitride, we directly resolve the weak photoluminescence of dark trions. The dark trions can be tuned continuously between negative and positive charged trions with electrostatic gating. We also reveal their spin triplet configuration and distinct valley optical emission by their characteristic Zeeman splitting under magnetic field. The dark trions exhibit large binding energy (14-16 meV). Their lifetime (~1.3 ns) is two orders of magnitude longer than the bright trion lifetime (~10 ps) and can be tuned between 0.4 to 1.3 ns by electrostatic gating. Such robust, optically detectable, and gate tunable dark trions provide a new path to realize electrically controllable trion transport in two-dimensional materials.