Observation of Exciton-Exciton Interaction Mediated Valley Depolarization in Monolayer MoSe2

Fahad Mahmood, Zhanybek Alpichshev, Yi Hsien Lee, Jing Kong, Nuh Gedik

Research output: Contribution to journalArticlepeer-review

Abstract

The valley pseudospin in monolayer transition metal dichalcogenides (TMDs) has been proposed as a new way to manipulate information in various optoelectronic devices. This relies on a large valley polarization that remains stable over long time scales (hundreds of nanoseconds). However, time-resolved measurements report valley lifetimes of only a few picoseconds. This has been attributed to mechanisms such as phonon-mediated intervalley scattering and a precession of the valley pseudospin through electron-hole exchange. Here we use transient spin grating to directly measure the valley depolarization lifetime in monolayer MoSe2. We find a fast valley decay rate that scales linearly with the excitation density at different temperatures. This establishes the presence of strong exciton-exciton Coulomb exchange interactions enhancing the valley depolarization. Our work highlights the microscopic processes inhibiting the efficient use of the exciton valley pseudospin in monolayer TMDs.

Original languageEnglish (US)
Pages (from-to)223-228
Number of pages6
JournalNano letters
Volume18
Issue number1
DOIs
StatePublished - Jan 10 2018
Externally publishedYes

Keywords

  • 2D materials
  • exciton interactions
  • Transition metal dichalcogenides
  • valley dynamics
  • valley polarization

ASJC Scopus subject areas

  • Bioengineering
  • Chemistry(all)
  • Materials Science(all)
  • Condensed Matter Physics
  • Mechanical Engineering

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