The origin of the optical side band in the spectrum of tungsten-based transition metal dichalcogenide monolayers.*

Recent experiments have shown that a new dominant peak emerges in the low-energy side of the optical spectrum of monolayer WSe2 and WS2 at high electron density or at strong excitation [1]. This peak is absent in the spectrum of molybdenum-based monolayers or in the hole-doped case [2]. In this talk, we will show that the band structure of monolayer transition-metal dichalcogenides gives rise to an intriguing mechanism through which shortwave plasmons are paired up with excitons. The coupling elucidates the origin for the optical side band that is observed repeatedly in monolayers of WSe2 and WS2 but not understood. The theory makes it clear why exciton-plasmon coupling has the right conditions to manifest itself distinctly only in the optical spectra of electron-doped tungsten-based monolayers [3].

[1] A. M. Jones et. al., Nature Nano. 8, 634 (2013); J. Shang et. al., ACS Nano 9, 647 (2015); G. Plechinger et. al., Phys. Stat. Sol. RRL 9, 457 (2015); Y. You et. al., Nature Phys. 11, 477 (2015).
[2] Z. Wang et. al., Nano Lett. 17, 740 (2017).
[3] Dinh Van Tuan, Benedikt Scharf, Igor Zutic, and Hanan Dery, arXiv:1704.01981, Phys. Rev. X (in press)