Atomically thin semiconductors for optolectronics and spintronics: progress and perspectives

Atomic monolayers of transition metal dichalcogenides (TMDs) such as MoS 2 and
WSe 2 have remarkable properties for fundamental research and potential applications :
They are semiconductors with a direct gap in the visible to near infrared region of the
optical spectrum. The interaction of TMD monolayers with light is governed by excitons
[1], electron-­‐hole pairs bound by Coulomb attraction, with binding energies of several
hundred meV and therefore still dominant at room temperature. Light-­‐matter
interaction is enhanced at specific exciton resonances with 20 % of the light absorbed
per monolayer and modulation of several orders of magnitude of second harmonic
generation efficiency, for example. Recent progress in fabrication allows approaching
lifetime broadened optical transitions and in this regime TMD monolayers can in
principle be tuned to 100 % reflectivity i.e. to be perfect mirrors. In addition, chiral
optical selection rules allow for optical manipulation of the spin and valley index of
electrons with polarized lasers, opening research opportunities in spintronics and
valleytronics.
Here we review our current understanding of the optical and polarization
properties of TMD monolayers and heterostructures and how they can be coupled to
photonic structures or magnetic substrates using simple “Scotch tape” exfoliation
techniques for assembly [2], to further explore their properties.

[1] “Excitons in atomically thin transition metal dichalcogenides"
G. Wang, A. Chernikov, M. M. Glazov, T. F. Heinz, X. Marie, T. Amandd, B. Urbaszek
Reviews of Modern Physics 90 (2), 021001 (2018) and arXiv : 1707.05863

[2] “Accessing high optical quality of MoS2 monolayers grown by chemical vapor deposition”
S. Shree, A. George, T. Lehnert, Ch. Neumann, M. Benelajla, C. Robert, X. Marie, K. Watanabe, T.
Taniguchi, U. Kaiser, B. Urbaszek, A. Turchanin arXiv:1907.03342 (submitted)