Regensburg 2016 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 59: Optical Properties II

HL 59.9: Vortrag

Mittwoch, 9. März 2016, 17:30–17:45, H10

Theory for the edge-state optical absorption in two-dimensional transition metal dichalcogenide flakes — •Maxim Trushin — University of Konstanz, Konstanz, Germany

The edge states provide electrical conductivity in quantum Hall systems and other two-dimensional (2d) topological insulators. Their role in optical and transport properties of other 2d materials, like 2d transition metal dichalcogenides [1], still remains illusive. There are indications that the optical absorption in MoS₂ at excitation energies below the band gap could be due to the edge states [2]. Here, we elaborate this problem from the theoretical point of view. We model the border between semiconductor and vacuum by means of the spatially dependent band gap: It is finite within the semiconducting region but infinite outside [3]. This model neglects the detail of the edge at the atomic level, but offers an analytical formula for the linear as well as saturable absorption. We show that the relative absorption of a single 50 nm-size MoS₂ flake is of the order of 0.01 % that corresponds to the absorption of a MoS₂-enriched polymer film of a few percent. We also find that at high radiation intensities the edge-state electron temperature can reach a few thousands Kelvin, whereas the bulk electrons and holes remain at lattice temperature. Our outcomes can be directly utilized for understanding of the subgap absorption in MX₂ flakes [2] and pave the way towards application of MS₂-based optoelectronic devices. [1] K.F. Mak et al. Phys. Rev. Lett. 105, 136805 (2010). [2] R. I. Woodward et al. Photon. Res. 3, A30 (2015). [3] M.V. Berry and R.J. Mondragon. Proc. R. Soc. (London) A 412, 53 (1987).