Filtering the photoluminescence spectra of atomically thin semiconductors with graphene

Stéphane Berciaud

IPCMS-DMONS

Atomically thin semiconductors made from transition metal dichalcogenides (TMDs) are model systems for investigations of strong light-matter interactions and applications in nanophotonics, opto-electronics and valley-tronics. However, the typical photoluminescence spectra of TMD monolayers display a large number of intrinsic and extrinsic features that are particularly challenging to decipher. On a practical level, monochromatic TMD-based emitters would be beneficial for low-dimensional devices but no solution has yet been found to meet this challenge. Here, using a counter-intuitive strategy that consists in interfacing TMD monolayers with graphene, a system known as an efficient luminescence quencher [1], we demonstrate bright, single and narrow-line photoluminescence arising solely from TMD neutral excitons. This observation stems from two effects: (i) complete neutralization of the TMD by the adjacent graphene leading to the absence of optical features from charged excitons (ii) selective non-radiative transfer of TMD excitons to graphene, that is sufficiently rapid to quench radiative recombination of long-lived excitonic species without significantly affecting bright excitons, which display much shorter, picosecond radiative lifetimes at low temperatures [2]. Our approach is systematically applied to four tungsten and molybdenum-based TMDs and establishes TMD/graphene heterostructures as a unique set of opto-electronic building blocks. As an outlook, the implications of our results for opto-valleytronics and chiral optics [3] will be discussed in light of our recent demonstration of large valley polarization and coherence in TMD-graphene heterostructures [4].

This work was done with E. Lorchat, L. E. Parra-Lopez and G. Froehlicher, S. Azzini, T. Chervy, T.W. Ebbesen and C. Genet at U. Strasbourg; C. Robert, D. Lagarde, and X. Marie at INSA Toulouse.

References:

[1] G. Froehlicher, E. Lorchat, S. Berciaud, Phys. Rev. X 8, 011007 (2018)

[2] E. Lorchat, L. E. Parra López et al., arXiv :1908.10690

[3] T. Chervy, S. Azzini, et al., ACS Photonics 5, 1281 (2018)

[4] E. Lorchat, S. Azzini, T. Chervy et al., ACS Photonics 5, 5047 (2018)