title: Atypical Exciton-Phonon Interactions in WS2 and WSe2 Monolayers Revealed by Resonance Raman Spectroscopy.
abstract: Resonant Raman spectroscopy is a powerful tool for providing information about excitons and exciton-phonon coupling in two-dimensional materials. We present here resonant Raman experiments of single-layered WS2 and WSe2 using more than 25 laser lines. The Raman excitation profiles of both materials show unexpected differences. All Raman features of WS2 monolayers are enhanced by the first-optical excitations (with an asymmetric response for the spin-orbit related XA and XB excitons), whereas Raman bands of WSe2 are not enhanced at XA/B energies. Such an intriguing phenomenon is addressed by DFT calculations and by solving the Bethe-Salpeter equation. These two materials are very similar. They prefer the same crystal arrangement, and their electronic structure is akin, with comparable spin-orbit coupling. However, we reveal that WS2 and WSe2 exhibit quite different exciton-phonon interactions. In this sense, we demonstrate that the interaction between XC and XA excitons with phonons explains the different Raman responses of WS2 and WSe2, and the absence of Raman enhancement for the WSe2 modes at XA/B energies. These results reveal unusual exciton-phonon interactions and open new avenues for understanding the two-dimensional materials physics, where weak interactions play a key role coupling different degrees of freedom (spin, optic, and electronic).
authors.affiliation: Departamento de Fisica, Universidade Federal de Minas Gerais (UFMG) , Caixa Postal 702, 30123-970 Belo Horizonte, Brazil.
authors.forename: E
authors.initials: E
authors.lastname: Del Corro
authors.affiliation: Institute of Condensed Matter and Nanosciences (IMCN), Université catholique de Louvain (UCL) , Chemin des Etoiles 8, bte L7. 03. 01, 1348 Louvain-la-Neuve, Belgium.
authors.forename: A
authors.initials: A
authors.lastname: Botello-Méndez
authors.affiliation: Institute of Condensed Matter and Nanosciences (IMCN), Université catholique de Louvain (UCL) , Chemin des Etoiles 8, bte L7. 03. 01, 1348 Louvain-la-Neuve, Belgium.
authors.forename: Y
authors.initials: Y
authors.lastname: Gillet
authors.affiliation: Department of Physics and Center for 2-Dimensional and Layered Materials, Pennsylvania State University , University Park, Pennsylvania 16802, United States.
authors.forename: A L
authors.initials: AL
authors.lastname: Elias
authors.affiliation: Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute , Troy, New York 12180-3590, United States.
authors.forename: H
authors.initials: H
authors.lastname: Terrones
authors.affiliation: Department of Physics and Center for 2-Dimensional and Layered Materials, Pennsylvania State University , University Park, Pennsylvania 16802, United States.
authors.forename: S
authors.initials: S
authors.lastname: Feng
authors.affiliation: Departamento de Fisica, Universidade Federal de Minas Gerais (UFMG) , Caixa Postal 702, 30123-970 Belo Horizonte, Brazil.
authors.forename: C
authors.initials: C
authors.lastname: Fantini
authors.affiliation: National High Magnetic Field Lab, Florida State University , 1800 E. Paul Dirac Drive, Tallahassee, Florida 32310, United States.
authors.forename: Daniel
authors.initials: D
authors.lastname: Rhodes
authors.affiliation: National High Magnetic Field Lab, Florida State University , 1800 E. Paul Dirac Drive, Tallahassee, Florida 32310, United States.
authors.forename: N
authors.initials: N
authors.lastname: Pradhan
authors.affiliation: National High Magnetic Field Lab, Florida State University , 1800 E. Paul Dirac Drive, Tallahassee, Florida 32310, United States.
authors.forename: L
authors.initials: L
authors.lastname: Balicas
authors.affiliation: Institute of Condensed Matter and Nanosciences (IMCN), Université catholique de Louvain (UCL) , Chemin des Etoiles 8, bte L7. 03. 01, 1348 Louvain-la-Neuve, Belgium.
authors.forename: X
authors.initials: X
authors.lastname: Gonze
authors.affiliation: Institute of Condensed Matter and Nanosciences (IMCN), Université catholique de Louvain (UCL) , Chemin des Etoiles 8, bte L7. 03. 01, 1348 Louvain-la-Neuve, Belgium.
authors.forename: J-C
authors.initials: JC
authors.lastname: Charlier
authors.affiliation: Department of Physics and Center for 2-Dimensional and Layered Materials, Pennsylvania State University , University Park, Pennsylvania 16802, United States.|Department of Chemistry and Department of Materials Science and Engineering, Pennsylvania State University , University Park, Pennsylvania 16802, United States.
authors.forename: M
authors.initials: M
authors.lastname: Terrones
authors.affiliation: Departamento de Fisica, Universidade Federal de Minas Gerais (UFMG) , Caixa Postal 702, 30123-970 Belo Horizonte, Brazil.
authors.forename: M A
authors.initials: MA
authors.lastname: Pimenta
keywords: Two-dimensional materials; exciton−phonon interaction; first-principles calculations; resonant Raman spectroscopy; transition metal dichalcogenides