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F. Libisch:
"The optical response oftransition metaldichalcogenides";
Talk: IWEPNM 2020, Kirchberg in Tirol (invited); 2020-03-08 - 2020-03-13.

The optical response of monolayer transition metal dichalcogenides (TMDs) offers awide range of intriguing properties, such as sharp lines in photoluminescence spec-tra that serve as single photon emitters, or highly sensitive second-order harmonicgeneration. I review our recent contributions to uncover the associated microscopicprocesses. To model single-photon emitters, we employ a multiscale tight-bindingsimulation for the optical spectra of WSe2under non-uniform strain and in the pres-ence of point defects [1]. Strain locally shifts excitonic energy levels into the bandgap where they hybridize with localized intragap defect states. We identify inter-valley defect excitonic states as the likely candidates for antibunched single-photonemission. We also calculate the second-order harmonic response of various TMDsand find excellent agreement to recent measurements [2]. We demonstrate and ex-plain a surprisingly high sensitivity to small changes in the band structure, providinga way to sensitively probe strain in semiconducting TMDs.
[1]L. Linhart et al., PRL 123, 146401 (2019).
[2]L. Mennel et al., Nature Comm. 9, 516 (2018)

TMDs, nonlinear response, Single photon emitters