Stacking Faults Enabled Second Harmonic Generation in Centrosymmetric van der Waals RhI₃

Area of Science:

• Materials Science
• Condensed Matter Physics
• Optoelectronics

Background:

• Van der Waals (vdW) materials offer potential for nonlinear optical applications.
• Stacking faults in vdW materials can alter crystal symmetry and second harmonic generation (SHG).
• The origin and tunability of stacking-fault-governed SHG in vdW materials are not well understood.

Purpose of the Study:

• To theoretically reveal the origin of stacking-fault-governed SHG in vdW materials.
• To investigate the tunability of SHG through structural modifications and external stimuli.
• To establish a foundation for designing vdW materials for nonlinear nano-optics.

Main Methods:

• Theoretical calculations to identify the origin of SHG in stacking faults.
• Experimental structural characterization and SHG measurements.
• Application of hydrostatic pressure to study structural evolution and its effect on SHG.

Main Results:

• Identified AC̅ stacking faults in RhI₃ as the source of SHG, dominated by electronic transitions along Γ-M and Γ-K paths.
• Confirmed the stacking-fault-governed SHG experimentally.
• Observed up to 6.9 times SHG enhancement under hydrostatic pressure due to compression-induced changes in electronic transitions and interlayer interactions.

Conclusions:

• Stacking faults in vdW materials provide a mechanism for controlling SHG.
• Hydrostatic pressure can significantly tune SHG response in RhI₃ by altering its electronic and structural properties.
• Strategic design of stacking faults offers a promising route for advanced nonlinear nano-optics.