Broadband and Enhanced Second-Harmonic Generation in Metallic 3R-TaS₂

Area of Science:

• Nonlinear Optics
• Materials Science
• Condensed Matter Physics

Background:

• Second-harmonic generation (SHG) is crucial for frequency conversion and probing nonlinear optical properties.
• Metallic 2D materials typically exhibit suppressed SHG due to strong absorption and shallow penetration depth.
• Achieving significant SHG in absorptive metallic 2D systems presents a major challenge in nonlinear photonics.

Purpose of the Study:

• To investigate the SHG response in non-centrosymmetric metallic 3R-TaS2.
• To understand the mechanisms behind broadband SHG in this material.
• To explore methods for enhancing SHG in metallic layered systems.

Main Methods:

• Systematic investigation of SHG in 3R-TaS2 flakes.
• Analysis of wavelength-dependent optical constants and dielectric function.
• Utilizing a reflective gold substrate for SHG enhancement studies.

Main Results:

• Demonstrated strong broadband SHG from 510-705 nm in metallic 3R-TaS2.
• Attributed broadband SHG to non-centrosymmetric structure, dielectric-like visible response, and absence of sharp resonances, alongside free-carrier damping.
• Observed substantial SHG enhancement (up to 45.5x) on a gold substrate, particularly for thinner flakes (68 nm).
• Extracted nonlinear susceptibility comparable to MoS2 despite 3R-TaS2's metallic nature.

Conclusions:

• Strong, broadband nonlinear optical responses are achievable in metallic layered materials.
• Provides insights into the interplay of metallicity, optical properties, and light-matter interactions in van der Waals materials.
• Highlights 3R-TaS2 as a promising material for nonlinear photonic applications.