Electric-Field Switchable Second-Harmonic Generation in Bilayer MoS₂ by Inversion Symmetry Breaking

Area of Science:

• Nonlinear optics
• Condensed matter physics
• Materials science

Background:

• Naturally inversion-symmetric materials lack second-order nonlinear optical responses.
• Electric fields can break inversion symmetry, enabling nonlinear phenomena.
• Transition metal dichalcogenides, like MoS₂, are promising for optoelectronic applications.

Discussion:

• Demonstrated pronounced electric-field-induced second-harmonic generation (EFISHG) in 2H stacked bilayer MoS₂.
• Applied electric fields (|F| = ±2.6 MV cm^-1) perpendicular to the basal plane to control inversion symmetry breaking.
• Observed strong tunability of the nonlinear conversion efficiency across a range of photon energies (E_ω ∼ 1.25-1.47 eV).

Key Insights:

• Achieved a 60-fold enhancement of the second-order nonlinear signal at E_2ω = 2.49 eV, detuned from exciton resonances.
• The spectral dependence of EFISHG correlates with band structure and wave function admixture, particularly below the C-resonance.
• EFISHG in bilayer MoS₂ is dependent on interlayer coupling.

Outlook:

• The strong tunability of EFISHG in bilayer MoS₂ suggests potential applications in miniaturized, electrically switchable nonlinear optical devices.
• Further research could explore other transition metal dichalcogenides and device architectures for enhanced nonlinear optical properties.