Impact of indirect transitions on valley polarization in WS2 and WSe2

Rasmus H. Godiksen, Shaojun Wang, T.V. Raziman, Jaime Gómez Rivas, Alberto G. Curto (Corresponding author)

Research output: Contribution to journalArticleAcademicpeer-review

6 Citations (Scopus)
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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 WS2 shows a remarkable spin-valley polarization above 90%, even at room temperature. In stark contrast, polarization is absent for few-layer WSe2 despite the expected material similarities. Here, we explain the origin of valley polarization in both materials based on the interplay between two indirect optical transitions. We show that the relative energy minima at the Λ- and K-valleys in the conduction band determine the spin-valley polarization of the direct K-K transition. Polarization appears as the energy of the K-valley rises above the Λ-valley as a function of temperature and number of layers. Our results advance the understanding of the high spin-valley polarization in WS2. This insight will impact the design of both passive and tunable valleytronic devices operating at room temperature.

Original languageEnglish
Pages (from-to)17761-17769
Number of pages9
JournalNanoscale
Volume14
Issue number47
DOIs
Publication statusPublished - 21 Dec 2022

Bibliographical note

Funding Information:
We thank Marcos H. D. Guimarães for useful discussions. This work was financially supported by the Netherlands Organisation for Scientific Research (NWO) through Gravitation grant “Research Centre for Integrated Nanophotonics” (024.002.033) and an NWO START-UP grant (740.018.009) and the Innovational Research Incentives Scheme (VICI Grant No. 680-47-628). Shaojun Wang was supported by the Starting Grant of Soochow University (Q415900120) and the Priority Academic Program Development (PAPD) of Jiangsu Higher Education Institutions.

Publisher Copyright:
© 2022 The Royal Society of Chemistry.

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