Contrast in spin-valley polarization due to competing indirect transitions in few-layer WS2 and WSe2

Research output: Contribution to journalArticleAcademic

Abstract

Controlling the momentum of carriers in semiconductors, known as valley polarization, is a new resource for optoelectronics and information technologies. Materials exhibiting high polarization are needed for valley-based devices. Few-layer WS$_2$ shows a remarkable spin-valley polarization above 90%, even at room temperature. In stark contrast, polarization is absent for few-layer WSe$_2$ despite the expected material similarities. Here, we explain the origin of valley polarization in both materials due to the interplay between two indirect optical transitions. We show that the relative energy minima at the $\Lambda$- and K-valleys in the conduction band determine the spin-valley polarization of the K-K transition. Polarization appears as the energy of the K-valley rises above the $\Lambda$-valley as a function of temperature and number of layers. Our results advance the understanding of the high spin-valley polarization in WS$_2$. This insight will impact the design of both passive and tunable valleytronic devices operating at room temperature.
Original languageEnglish
JournalarXiv
Publication statusPublished - 2 Jun 2020

Bibliographical note

22 pages, 6 figures, 2 tables

Keywords

  • excitonics
  • diffusion
  • annihilation
  • Purcell effect
  • nanoantennas

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