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Exciton-dominated Dielectric Function of Atomically Thin MoS2 Films



Yilin Yu, Yifei Yu, Yongqing Cui, Wei Li, Gurarslan Alper, Peelaers Hartwin, Aspnes David, Chris Van de Walle, Nhan Van Nguyen, Zhang Yong-Wei, Linyou Cao


The control of photons by field effects, like the gating of electrons, can revolutionize a wide range of fields by enabling active photonic devices whose functions could be manipulated with sophistication and speeds comparable to what achieved in modern computers. However, the nature of conventional materials poses a formidable challenge for the field effect control of optical functionality. The optical constant, which fundamentally dictates optical functionality, of all the materials studied to date is genetically determined by bandstructures of the materials1,2. Bandstructures are very difficult to be tuned by field effects and this subsequently limits the capabilities of efficiently manipulating optical constants for functionality control. Here we demonstrate that atomically thin MoS2 films < 5 layers presents a new type of materials with optical constant in the entire visible range dominated by excitonic effects, rather than bandstructures. In stark contrast with what predicted from the bandstructure, a monotonic increase with the layer number, the optical constant of the MoS2 films decreases with the layer number increasing. This is because the truly atomic-scale dimension of the films is substantially smaller than the size of excitons and can induce extraordinarily strong excitonic effects to overwhelm the role of the bandstructure. As excitons are subject to control of external fields3-8, our result indicate that atomically thin MoS2 films may open up a new age of field-effect photonics controlled by external fields with unprecedented speed, efficiency, and bandwidth.


Optical function, MoS2, Broadband


Yu, Y. , Yu, Y. , Cui, Y. , Li, W. , Alper, G. , Hartwin, P. , David, A. , Van de Walle, C. , Nguyen, N. , Yong-Wei, Z. and Cao, L. (2015), Exciton-dominated Dielectric Function of Atomically Thin MoS2 Films, Nature, [online],, (Accessed July 12, 2024)


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Created November 24, 2015, Updated December 16, 2021