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2D semiconductors

by Rowe Alistair - published on , updated on

Currently, one of the main research topics in condensed matter physics deals with the electronic properties of ultrathin compounds for which the scientific community has consecrated a significant effort since the discovery of graphene in 2004. This young field experienced a big boost recently thanks to the isolation of atomically thin semiconductors based on transition metal dichalcogenides (TMD), such as MoS2 and WSe2. The direct bandgap of monolayers and their efficient coupling with light makes them versatile and promising fundamental bricks for future nanoelectronics and optoelectronic devices.

Contacts: Fabian Cadiz, Fausto Sirotti

Regarding the electron spin, a remarkable property of TMDs is linked to their unique electronic band structure in the 2D limit. The interplay between broken inversion symmetry and a strong spin-orbit interaction leads to a unique spin texture of the K+ and K- valleys (the corners of the hexagonal Brillouin zone), precisely where the bandgap is located at. In a given valley and at a fixed energy, an electron can have only one possible spin state. Our research focus on the study of the optical and transport properties of spins in these atomically thin semiconductors and their heterostructures. This includes the study of spin/valley dynamics through polarized-luminescence and scanning tunneling microscopy, with an eye towards revealing original effects arising from the quantum nature of electrons at low temperatures and high densities. For more information contact Fabian Cadiz.

(a) Schematic side-view of an heterostructure fabricated in our lab. An MoS2 monolayer is encapsulated between two thin h-BN flakes to provide high optical quality. Thin graphite flakes were used to provide an electrical contact to the monolayer. (b) Optical microscope image of the sample under white light illumination. (c) Dark-field image of the sample, revealing clean interfaces with no visible bubbles after the formation of the heterostructure.

More information:
 Extract from Fabian Cadiz’s HDR manuscript. Download the pdf
 Article written for the journal Le Rayon of the Société Française de Physique (in French)

Current and past projects:
  ANR Project SpinCAT (2018-2023)
  ANR Project Deep2D (2022-)
 ERC Project OneSPIN (2023-)

Recent publications on 2D materials:

Imaging the effect of high photoexcited densities on valley polarization and coherence in MoS2 monolayers (2022)

F. Cadiz, S. Gerl, T. Taniguchi, K. Watanabe
npj 2d materials and applications 6, 27 (2022)

Efficient valley polarization of charged excitons and resident carriers in Molybdenum disulphide monolayers by optical pumping (2022)

S. Park, S. Arscott, T. Taniguchi, K. Watanabe, F. Sirotti, F. Cadiz
Communications Physics 5, 73 (2022)

Imaging Seebeck drift of excitons and trions in MoSe2 monolayers (2021)

S. Park, B. Han, C. Boule, D. Paget, A. C. H. Rowe, F. Sirotti , T. Taniguchi, K. Watanabe, C. Robert, L. Lombez, B. Urbaszek, X. Marie, F. Cadiz
2D Materials 8, 045014 (2021)
DOI: DOI: 10.1088/2053-1583/AC171F

Spin/valey pumping of resident electrons in WSe2 and WS2 monolayers (2021)

C. Robert, S. Park, F. Cadiz, L. Lombez, L. Ren, H. Tornatzky, A. Rowe, D. Paget, F. Sirotti , M. Yang, D. Van Tuan, T. Taniguchi, B. Urbaszek, K. Watanabe, T. Amand, H. Dery, X. Marie
Nature Communications 12, 5455 (2021)
DOI: DOI: 10.1038/S41467-021-25747-5

Exciton diffusion in WSe2 monolayers embedded in a van der Waals heterostructure (2018)

F. Cadiz, C. Robert, E. Courtade, M. Manca, L. Martinelli , T. Taniguchi, K. Watanabe, T. Amand, A. C. H. Rowe , D. Paget , B. Urbaszek, X. Marie
Applied Physics Letters 112, 152106 (2018)
DOI: DOI: 10.1063/1.5026478