Electronic band structure of ABC-stacked trilayer graphene and its tuning

Multilayer graphene has attracted intensive investigations since the ground-breaking realisation of superconductivity in magic-angle twisted bilayer graphene. Most recently, people realise that even with the non-twisted multilayer graphene, many interesting complex collective behavior, especially superconductivity, can be achieved upon applying external fields and doping.

Specifically, the ABC (or Rhombohedral)-stacked trilayer graphene has a cubic dispersion in low energy with a flat band near the Fermi level, which serves as an ideal platform for achieving interaction-driven collective phenomena, including superconductivity and ferromagnetism. However, the ABC-stacking phase is less energy-favored than the ABA-stacking phase. Up to now, most fabricated ABC-stacked trilayer graphene flakes are tiny (less than 5 * 5 μm^2) and usually mixed with the much larger ABA-stacked flakes, making the high-quality ARPES measurement on its band structure difficult.

Using a specific exfoliation method, our collaborator succeeds in fabricating large area ABC-stacked trilayer graphene (around 50 * 50 μm^2). The thicknesses of different regions are measured with AFM and labeled. The stacking order and sample quality have been characterized with Raman scattering and SNOM.

At LOREA, the spatial scan mode measuring either the band near the Fermi level or core levels combined with big-data analysis techniques (clustering and principle component analysis) has been developed and used to detect regions with different thicknesses.

With the help of the small beam spot size (20 * 15 μm^2) and the spatial scan mode, we hope to identify the ABC-stacked regions and further take high-quality ARPES data on its band structure, understanding better the electron-electron and electron-phonon interactions in this system and providing important insights to its unconventional superconductivity.