Second harmonic generation from artificially stacked transition metal dichalcogenide twisted bilayers

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Optical second harmonic generation (SHG) is a sensitive technique for probing crystalline symmetry.
• Previous SHG studies on few-layer transition metal dichalcogenides (TMDs) primarily focused on ideal Bernal stacking.
• SHG in non-ideally stacked TMD structures remains largely unexplored.

Purpose of the Study:

• To investigate SHG in twisted homo- and heterostructural TMD bilayers with arbitrary stacking angles.
• To demonstrate the application of SHG for characterizing stacking orientation, crystal polarity, and domain boundaries in van der Waals heterostructures.
• To establish SHG as an efficient, sensitive, and nondestructive characterization method.

Main Methods:

• Fabrication of twisted TMD bilayers through artificial stacking.
• Measurement and analysis of optical second harmonic generation (SHG) signals.
• Polarization-resolved SHG spectroscopy to probe structural properties.

Main Results:

• SHG from twisted TMD bilayers results from coherent superposition of SH fields from individual layers.
• The interference pattern in SHG is dependent on the stacking angle and independent of constituent materials.
• SHG successfully probed domain boundaries and crystal polarity in mirror twins of chemically grown TMDs.

Conclusions:

• SHG is a versatile tool for analyzing stacking configurations in van der Waals heterostructures.
• The interference effect in SHG provides a sensitive measure of stacking angle and material interfaces.
• SHG offers a nondestructive method for detailed characterization of complex layered materials.