Flat-Band Electronic Structure and Interlayer Spacing Influence in Rhombohedral Four-Layer Graphene

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Physics

Background:

• The electronic properties of multilayer graphene are highly dependent on the stacking order of its layers.
• Rhombohedral stacking is theoretically predicted to induce flat electronic bands, leading to exotic quantum phenomena.

Purpose of the Study:

• To investigate the impact of stacking sequence and interlayer spacing on the electronic structure of four-layer graphene.
• To experimentally verify theoretical predictions of flat bands in specific stacking configurations.

Main Methods:

• Growth of four-layer graphene on a 3C-SiC(111) substrate.
• Characterization using low-energy electron microscopy (LEEM).
• First-principles density functional theory (DFT) calculations.
• Experimental verification with angle-resolved photoelectron spectroscopy (ARPES).

Main Results:

• Distinct band structures were observed for ABAB (Bernal), ABCA (rhombohedral), and ABCB (turbostratic) stacking sequences.
• Experimental data confirmed the existence of rhombohedral stacking and a nearly dispersionless flat band near the Fermi level.
• Interlayer spacing was found to tune the flat-band region's properties, including momentum width, bandgap, and curvature.

Conclusions:

• The stacking sequence critically determines the electronic band structure of multilayer graphene.
• Rhombohedral stacking leads to flat bands with tunable properties, offering potential for novel electronic states.
• Interlayer spacing is a key parameter for controlling these flat bands and their associated exotic phenomena like superconductivity.