4.6 Article

Shear-strain-mediated photoluminescence manipulation in two-dimensional transition metal dichalcogenides

期刊

2D MATERIALS
卷 9, 期 1, 页码 -

出版社

IOP Publishing Ltd
DOI: 10.1088/2053-1583/ac351d

关键词

transition metal dichalcogenides; shear strain; spin-state mixing; spin-flip; photoluminescence

资金

  1. Priority Research Center Program [2013R1A2A2A03068982, 2018R1A2B6008101, 2020R1A6A1A03047771, 2020R1F1A1048657, 2021R1A2C1004209]
  2. Priority Research Center Program through the National Research Foundation of Korea (NRF) - Ministry of Science, ICT & Future Planning [2019R1A6A1A11053838]
  3. Basic Science Research Program through the NRF - Ministry of Education [2021R1I1A2059710]
  4. Air Force Office of Scientific Research [FA9550-17-1-0341]
  5. National Research Foundation of Korea [2021R1I1A2059710] Funding Source: Korea Institute of Science & Technology Information (KISTI), National Science & Technology Information Service (NTIS)

向作者/读者索取更多资源

In two-dimensional transition metal dichalcogenides, strain modulation can manipulate electronic band structures and photoluminescence. A novel method of external bending is used to control the photoluminescence in monolayer WSe2-MoSe2 lateral heterostructures, where both normal strain and shear strain are involved. The dependence of the photoluminescence on bending direction and the violation of optical selection rules under tensile bending are observed, which indicates the mixing of spin subbands induced by shear strain.
In two-dimensional transition metal dichalcogenides, normal strain can modulate electronic band structures, yet leaving the optical selection rules intact. In contrast, a shear strain can perturb the spin-valley locked band structures and possibly induce mixing of the spin subbands which in turn can transfer oscillator strength between spin-allowed bright and spin-forbidden dark excitons. Here, we report a novel scheme to manipulate photoluminescence (PL) in a monolayer WSe2-MoSe2 lateral heterostructures, controlled by an external bending method in which strong out-of-plane shear strain (OSS) of up to 5.6% accompanies weak in-plane normal strain up to 0.72%. The spectra revealed a striking dependence on the bending direction that is stagnant in the negative (compressive) strain region and then rapidly changes with increasing positive (tensile) strain. The dependency of the PL signal under tensile bending was represented not only by the large energy shift (>40 meV) of the lowest excited states of both the WSe2 and MoSe2 monolayers, but also by the tendency to violate the optical selection rules that brightens (darkens) the excitons of the WSe2 (MoSe2) side. The analyses on the observed energy shifts and PL intensity changes confirm the different origins in compressive bending compared with tensile bending. The well-established band-anticrossing is identified to be affecting only the compressive deformation region. The spectral changes in the tensile region, on the other hand, originates mainly from the generation of an off-diagonal perturbation to a spin-specific Hamiltonian induced by OSS. The degree of spin-state mixing, which correlates precisely with the spin-flip coefficient of the theoretical model, is further represented by the OSS matrix elements, the spin splitting energy, and the shear deformation potential.

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