Dark-exciton valley dynamics in transition metal dichalcogenide alloy monolayers

Autor(es)

Braganca, Helena ^{[1, 2]} ; Riche, Flavio ^[2] ; Qu, Fanyao ^[2] ; Lopez-Richard, Victor ^[1] ; Marques, Gilmer Eugenio ^[1]

Afiliação do(s) autor(es)

^[1] Univ Fed Sao Carlos, Dept Fis, BR-13565905 Sao Carlos, SP - Brazil

^[2] Univ Brasilia, Inst Fis, BR-70919970 Brasilia, DF - Brazil

• Tipo de documento: Artigo Científico
• Fonte: SCIENTIFIC REPORTS; v. 9, MAR 14 2019.
• Citações Web of Science: 1

Resumo

We report a comprehensive theory to describe exciton and biexciton valley dynamics in monolayer Mo1-xWxSe2 alloys. To probe the impact of different excitonic channels, including bright and dark excitons, intravalley biexcitons, intervalley scattering between bright excitons, as well as bright biexcitons, we have performed a systematic study from the simplest system to the most complex one. In contrast to the binary WSe2 monolayer with weak photoluminescence (PL) and high valley polarization at low temperatures and the MoSe2, that presents high PL intensity, but low valley polarization, our results demonstrate that it is possible to set up a ternary alloy with intermediate W-concentration that holds simultaneously a considerably robust light emission and an efficient optical orientation of the valley pseudospin. We find the critical value of W-concentration, x(c), that turns alloys from bright to darkish. The dependence of the PL intensity on temperature shows three regimes: while bright monolayer alloys display a usual temperature dependence in which the intensity decreases with rising temperature, the darkish alloys exhibit the opposite behavior, and the alloys with x around x(c) show a non-monotonic temperature response. Remarkably, we observe that the biexciton enhances significantly the stability of the exciton emission against fluctuations of W-concentration for bright alloys. Our findings pave the way for developing high-performance valleytronic and photo-emitting devices. (AU)

• Processo FAPESP: 17/23668-8 - Efeitos de muitos corpos sobre qubits do Vale e sobre novas propriedades magneto-ópticas de monocamadas de metais de transição dicalcogenados
• Beneficiário: Helena de Souza Bragança Rocha
• Modalidade de apoio: Bolsas no Brasil - Pós-Doutorado