Development of Fabrication Process for Twisted Rhombohedral Trilayer-Bilayer Graphene Transport Devices

Abstract

This work presents the development and refinement of a fabrication methodology for twisted rhombohedral trilayer-bilayer graphene (tRTBG) transport devices. The tRTBG system is predicted to host flat electronic bands with high Chern numbers at twist angles of 1.1°~1.4°, promoting highly correlated, potentially fractionalized topological phases. This methodology covers parameters for exfoliation, identification, isolation, and stacking of graphene and hexagonal Boron Nitride flakes into van der Waals heterostructures via AFM and polymer-based dry transfer techniques, as well as modified PC/PDMS transfer slide properties. The resulting heterostructures are patterned into devices using electron-beam lithography, reactive ion etching, and Cr/Au metal evaporation. We find that increased O2 plasma cleaning and baking times of SiO2 wafers prior to and during exfoliation promotes the generation of large, pristine flakes with regions of both bilayer and trilayer graphene. Four devices were successfully fabricated using this methodology, and initial 4K transport measurements confirm functional operation and reveal features consistent with the predicted tRTBG band structure, including a displacement field-dependent band gap at ν = 0 and a resistive bump within the range 0<ν<1, suggestive of emergent states at millikelvin temperatures. This methodology provides a reproducible route for the fabrication of tRTBG devices and establishes the foundation for future work aimed at more thorough characterization of the underlying physics of this system.