Apparent breakdown of Raman selection rule at valley exciton resonances in monolayer Mo S2

Steven G. Drapcho, Jonghwan Kim, Xiaoping Hong, Chenhao Jin, Sufei Shi, Sefaattin Tongay, Junqiao Wu, Feng Wang

Research output: Contribution to journalArticle

6 Citations (Scopus)

Abstract

The valley degree of freedom in atomically thin transition metal dichalcogenides (TMDCs) has generated great interest due to the possibility of using it to store and control information in analogy to the spin degree of freedom in spintronics. A signature of the valley pseudospin is the selective coupling of valley excitons to photons with defined helicity. This selectivity can have important consequences for a variety of optical phenomena associated with the valley excitons. Here we report that Raman features that seemingly violate the Raman selection rules can become prominent at valley exciton resonances in atomically thin MoS2. Specifically, the Raman selection rule requires the excitation and scattering photons to have opposite circular polarizations for the in-plane E′ mode phonon, but we observe an apparent E′ Raman peak for excitation and scattered photons with the same circular polarization at exciton resonances. We attribute this peak to a defect-assisted process that involves phonons in the transverse optical E′ branch slightly away from the Γ point, a process that can be enhanced by the selective coupling of valley pseudospin to photon helicity. Thus, the valley pseudospin, in addition to the crystal symmetry, may be important in understanding the Raman scattering spectra for excitations close to valley exciton resonances.

Original languageEnglish (US)
Article number165417
JournalPhysical Review B
Volume95
Issue number16
DOIs
StatePublished - Apr 13 2017

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valleys
breakdown
excitons
photons
circular polarization
degrees of freedom
excitation
phonons
selectivity
transition metals
signatures
Raman spectra
defects
symmetry
scattering
crystals

ASJC Scopus subject areas

  • Condensed Matter Physics

Cite this

Apparent breakdown of Raman selection rule at valley exciton resonances in monolayer Mo S2. / Drapcho, Steven G.; Kim, Jonghwan; Hong, Xiaoping; Jin, Chenhao; Shi, Sufei; Tongay, Sefaattin; Wu, Junqiao; Wang, Feng.

In: Physical Review B, Vol. 95, No. 16, 165417, 13.04.2017.

Research output: Contribution to journalArticle

Drapcho, Steven G. ; Kim, Jonghwan ; Hong, Xiaoping ; Jin, Chenhao ; Shi, Sufei ; Tongay, Sefaattin ; Wu, Junqiao ; Wang, Feng. / Apparent breakdown of Raman selection rule at valley exciton resonances in monolayer Mo S2. In: Physical Review B. 2017 ; Vol. 95, No. 16.
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