Photo- and Thermally-Induced Huge Layer Decoupling in Twisted Bilayer WSe₂

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Twisted bilayer systems exhibit unique electronic and magnetic properties due to moiré superlattices.
• Understanding the 3D atomic structure is crucial for controlling these emergent phenomena.
• Direct visualization of nanoscale structures in 2D materials is challenging.

Purpose of the Study:

• To develop a quantitative 3D structural analysis technique for atomically thin materials.
• To investigate the structural relaxation and interlayer coupling in twisted bilayer WSe2.
• To explore the influence of twist angle, temperature, and optical excitation on interlayer spacing.

Main Methods:

• Automated dark-field electron tomography with sub-ångström precision.
• Application to twisted bilayer WSe2.
• Ultrafast optical measurements.

Main Results:

• Precise visualization of twist-angle-dependent structural relaxation and domain walls (10-20 nm).
• Observed significant interlayer spacing expansion (>0.1 Å) in marginally twisted WSe2 (θ ≤ 0.1°).
• Demonstrated temperature-driven interlayer decoupling and optically induced separation (~0.2 Å) on picosecond timescales.

Conclusions:

• The developed technique provides quantitative 3D structural insights into atomically thin materials.
• Interlayer coupling in twisted bilayer WSe2 is intrinsically fragile and dynamically tunable.
• Findings offer new avenues for engineering moiré-based 2D heterostructures.