Abstract
Two-dimensional (2D) transition metal dichalcogenides (TMDs) are drawing increasing interest due to their relatively high carrier mobilities, valley pseudospins, and gapped electronic structures, which all indicate interesting nonlinear optical properties of these 2D materials. However, such nonlinear optical properties are so far less investigated and their correlation with the electronic structure of the material is rarely probed. In this work, we have systematically investigated the spatial self-phase modulation (SSPM) of MoSe2 flakes in a suspension form, which is a coherent third-order nonlinear optical effect. The nonlinear susceptibility χ(3) and its wavelength-dependence are measured, yielding a value of 1.1 × 10−9 e.s.u. (SI: 1.53 × 10−17 m2/V2) at 532 nm laser excitation for effective one-layer MoSe2.
Highlights
The discovery of graphene has aroused tremendous interest in two-dimensional (2D) materials
It has been demonstrated that spatial self-phase modulation (SSPM) provides a way to induce non-local ac electron coherence in the TMDs16 and measure their nonlinear optical susceptibilities
Investigating the nonlinear optical properties of these novel materials is quite essential since, if the optical properties of these newly discovered quantum materials are superb, it will for the first time make it possible to integrate electronic and optoelectronic devices in one material system, which is so far challenging to realize in the indirect-gap silicon and no-gap graphene systems
Summary
Response Spatial Self-Phase received: 10 September 2015 accepted: 05 February 2016 Published: 26 February 2016. In SSPM investigations, N directly reflects the optical phase (i.e., the exact nonlinear effect as reflected by n2 and χ(3)) and is correlated to the electronic phase and coherence of the material[16] It is a more essential and intrinsic observable than the ring diameter D, because D can be modified by the linear refractive index n0. The nonlinear refractive index n2, the third-order nonlinear susceptibility χ(3), can be directly and quantitatively obtained through a convenient way[16,17] This experimental method has been developed to be a general way for measuring the χ(3) of 2D layered quantum materials[16,17]. Comparison with absorption has been carried out, further demonstrating SSPM as a useful method in probing the electronic band structure of layered materials
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