Colossal infrared nonlinear optical anisotropy in a 2D charge-transfer Mott insulator

Area of Science:

• Condensed Matter Physics
• Materials Science
• Optoelectronics

Background:

• Mott insulators are characterized by electron-electron correlations causing localized charge carriers and a charge gap.
• Charge transfer in correlated materials significantly influences their magnetic and optical properties.
• Van der Waals materials offer unique platforms for exploring novel physical phenomena due to weak interlayer coupling.

Purpose of the Study:

• To investigate the nonlinear optical properties of 2D antiferromagnetic charge-transfer Mott insulators.
• To demonstrate and characterize the third-harmonic generation (THG) anisotropy in Vanadium Oxychloride (VOCl).
• To explore the potential applications of VOCl in nanophotonics and optoelectronics.

Main Methods:

• Experimental characterization of third-harmonic generation (THG) anisotropy in VOCl.
• Broadband infrared (IR) spectroscopy to study nonlinear anisotropy modulation.
• Theoretical calculations to support experimental findings on symmetry and electronic coupling.

Main Results:

• VOCl exhibits giant THG anisotropy (ρ_THG up to 187) at 1280 nm, the highest among van der Waals materials.
• Nonlinear anisotropy significantly increases with decreasing IR excitation wavelength (72-fold enhancement from 2028 nm to 1280 nm).
• Layer-independent third-order susceptibilities (χ⁽³⁾ ~ 10^-19 m²/V²) due to weak interlayer electronic coupling.

Conclusions:

• The colossal THG anisotropy in 2D VOCl arises from the interplay of Mott insulation, charge transfer, and broken C₃ symmetry.
• VOCl's unique optical anisotropy makes it a promising candidate for next-generation nanophotonic and optoelectronic devices.
• This work highlights the potential of 2D correlated Mott insulators for advanced optical applications.