Giant Modulation of Interlayer Coupling in Twisted Bilayer ReS₂

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Optics

Background:

• Stacking two-dimensional (2D) materials with controlled twist angles offers a method to engineer their electronic and optical properties.
• Transition metal dichalcogenides (TMDs) are a class of 2D materials with significant potential for electronic and optoelectronic applications.

Purpose of the Study:

• To investigate the effect of twist angle on the electronic band structure and interlayer coupling in twisted bilayer (tBL) ReS2.
• To demonstrate the continuous tunability of bandgap energy and exciton properties in tBL ReS2 through precise control of the twist angle.

Main Methods:

• Experimental synthesis and characterization of twisted bilayer ReS2 with varying twist angles (0° to 10°).
• Photoluminescence spectroscopy to measure exciton energy shifts.
• Raman spectroscopy to probe interlayer coupling and lattice dynamics.
• Scanning transmission electron microscopy (STEM) for structural analysis and strain mapping.
• Density functional theory (DFT) calculations to model moiré superlattice structures and bandgap variations.

Main Results:

• Continuous modulation of bandgap energy and interlayer coupling strength in tBL ReS2 by adjusting the twist angle.
• Exciton energy tuning over a 40 meV range by controlling the twist angle, comparable to monolayer vs. bilayer differences.
• Systematic shifts in low- and high-frequency Raman modes correlating with twist-angle-induced changes in interlayer coupling.
• DFT calculations confirm an increase in bandgap with increasing twist angle in moiré superlattice structures.
• Evidence of strong twist-angle-dependent interlayer coupling attributed to the low-symmetry 1T' structure and in-plane anisotropy of ReS2.

Conclusions:

• Twist angle engineering provides a powerful tool for continuously tuning the electronic structure and quantum optical properties of anisotropic 2D materials like ReS2.
• The observed tunability in tBL ReS2 opens new avenues for designing and fabricating reconfigurable quantum materials and devices.
• The findings highlight the importance of interlayer coupling modulation via twist angle in designing novel 2D heterostructures.