Electronic and optical properties in helical trilayer graphene under compression

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanotechnology

Background:

• Graphene-based heterostructures exhibit tunable electronic and optical properties.
• Helical trilayer graphene (hTLG) offers unique structural configurations due to interlayer rotation and stacking.
• Understanding the interplay of symmetry and compression is crucial for designing novel electronic and optical devices.

Purpose of the Study:

• To investigate the impact of initial vertical stacking and interlayer compression on the electronic and linear optical properties of high-angle helical trilayer graphene (hTLG).
• To characterize the symmetry differences in real and reciprocal space for different hTLG structures.
• To explore the tunability of electronic band structure, density of states, optical conductivity, and absorption.

Main Methods:

• Fabrication of three distinct hTLG periodic structures with a fixed interlayer rotation angle (21.78°).
• Characterization of atomic models using 2D real-space moiré patterns and calculated diffraction patterns.
• Density functional theory (DFT) calculations to study electronic and optical properties under varying interlayer compression (δ).

Main Results:

• Distinct symmetry differences were observed in the moiré and diffraction patterns of the hTLG structures.
• Electronic properties showed electron-hole asymmetry, with strong hole localization at high compression (δ ≤ -19%).
• High real parts of 2D linear optical conductivity (Re[σ2D]) were achieved, reaching up to 18σ0 at specific frequencies and compression (δ = -21.6%).
• Enhanced optical absorption was observed in the visible spectrum.

Conclusions:

• The initial vertical stacking and interlayer compression are critical parameters that significantly influence the electronic and optical characteristics of hTLG superlattices.
• hTLG systems demonstrate potential for applications requiring tunable optical conductivity and absorption.
• The findings highlight the importance of structural control in designing advanced graphene-based materials.