Regensburg 2016 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 85: Focus Session: Physics and Application of Emergent 2D-semiconductors and their Heterostructures 2
HL 85.1: Topical Talk
Donnerstag, 10. März 2016, 15:00–15:30, H8
Bright and dark excitons in transition metal dichalcogenide monolayers — Cedric Robert1, Gang Wang1, Aslihan Suslu2, Bin Chen2, Sije Yang2, Sarah Alamdari2, Iann Gerber1, Thierry Amand1, Sef Tongay2, Bernhard Urbaszek1, and •Xavier Marie1 — 1Universite de Toulouse, INSA-CNRS-UPS, LPCNO, 135 avenue de Rangueil, 31077 Toulouse cedex, France — 2School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, AZ 85287, USA
Highly crystalline Mo(1-x)WxSe2 has been synthetized to show engineering of the direct optical bandgap and the spin-orbit (SO) coupling in ternary alloy monolayers. We have investigated the impact of the tuning of the SO splitting on the optical and polarization properties. In particular, we have measured the effect of tuning of the conduction band SO splitting on the bright versus dark exciton state population i.e. photoluminescence (PL) intensity. We show that the MoSe2 PL intensity decreases as a function of temperature by an order of magnitude, whereas for WSe2 we measure surprisingly an order of magnitude increase over the same temperature range (T=4-300K). The ternary material shows a trend between these two extreme behaviors [1]. These results are interpreted on the basis of the reversal of the sign of the spin-orbit splitting in the CB for MoSe2 and WSe2 leading to different temperature dependences of the emission yield. The additional role of the electron-hole exchange interaction on the bright/dark exciton states splitting will also be discussed on the basis of ab-initio calculations. [1] G. Wang, et al, Nature Com. 6, 10110 (2015)