Determining the complex second-order optical susceptibility in macroscale van der Waals heterobilayers

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanophotonics

Background:

• Transition metal dichalcogenide (TMD) heterobilayers, such as MoSe2/WS2, are promising for advanced optical and electronic applications.
• Second-order nonlinear optical phenomena, like second-harmonic generation (SHG), are crucial for frequency conversion and optical signal processing.
• Understanding the complex susceptibility and interlayer effects in these heterostructures is vital for device optimization.

Purpose of the Study:

• To experimentally characterize the second-order susceptibility (χ⁽²⁾) of MoSe2/WS2 heterobilayers, including their complex phases.
• To develop and apply a heterodyne-detection scheme for precise SHG measurements.
• To quantify the contribution of interlayer effects to SHG in these heterostructures.

Main Methods:

• Development of a heterodyne-detection scheme for second-harmonic generation (SHG).
• Application of the scheme to macroscale MoSe2/WS2 heterobilayer samples prepared via gold-tape exfoliation.
• Comparison of SHG signals from monolayer and heterobilayer regions to assess interlayer effects.

Main Results:

• The heterodyne scheme successfully distinguished crystal domain orientations and characterized complex susceptibility phases relative to quartz.
• Interlayer effects on SHG were found to be within the experimental uncertainty caused by sample inhomogeneity.
• Quantitative data on the second-order susceptibility of MoSe2/WS2 heterobilayers was obtained over large sample areas.

Conclusions:

• The study provides fundamental quantitative insights into the second-order nonlinear optical properties of MoSe2/WS2 heterobilayers.
• The developed heterodyne technique is effective for characterizing complex nonlinear optical responses in 2D material systems.
• These findings are essential for the rational design of nanophotonic devices utilizing stacking engineering in TMD heterostructures.