Tightly bound excitons in monolayer WSe2

TL;DR

This paper investigates exciton binding energies and excited states in monolayer WSe2, revealing large binding energies and deviations from simple models, with implications for 2D optoelectronic devices.

Contribution

It provides the first detailed measurement of exciton binding energies and excited states in monolayer WSe2, highlighting nonlocal dielectric effects.

Findings

Exciton binding energy in WSe2 is 0.37 eV.

Excited states are observable at room temperature.

Exciton spectrum deviates from 2D hydrogenic model.

Abstract

Exciton binding energy and excited states in monolayers of tungsten diselenide (WSe2) are investigated using the combined linear absorption and two-photon photoluminescence excitation spectroscopy. The exciton binding energy is determined to be 0.37eV, which is about an order of magnitude larger than that in III-V semiconductor quantum wells and renders the exciton excited states observable even at room temperature. The exciton excitation spectrum with both experimentally determined one- and two-photon active states is distinct from the simple two-dimensional (2D) hydrogenic model. This result reveals significantly reduced and nonlocal dielectric screening of Coulomb interactions in 2D semiconductors. The observed large exciton binding energy will also have a significant impact on next-generation photonics and optoelectronics applications based on 2D atomic crystals.