Research Projects

Rhombohedral pentalayer graphene (R5G) exhibits intrinsic flat bands at charge neutrality, supporting strong electron correlations (e.g., correlated insulators) and topological states (e.g., Chern insulators with (C = -3, -5)) without moiré engineering [1]. However, recently, a moiré superlattice (SL) of R5G/hBN at a twist angle of 0.77⁰ has been reported showing integer and fractional quantum anomalous Hall effect (I/FQAHE) [2]. The graphene-based moiré SL surpasses the FQAHE shown by twisted MoTe₂ due to superior material quality and higher carrier mobility [3], [4]. However, moiré SLs suffer from a lack of tunability of the SL symmetry and the SL potential, hindering better control over the electronic properties. On the contrary, patterned dielectric superlattices (PDSLs) [5] and patterned back/top gate superlattices (PGSLs) [6], [7] impose artificial, designable periodic potentials on 2D materials, enabling band structure engineering with high dynamic tunability. Unlike moiré systems, PDSLs or PGSLs allow control over symmetry (square, triangular) and achieve sub-50-nm periodicities. The interplay between the flat bands and the imposed SL will allow us to probe how external potentials influence intrinsic band topology and correlated phenomena. Interestingly, the artificial SL modulation and the device fabrication processes can be independently optimized and later combined together, where hBN provides not only an atomically flat and cleaner interface but also well-defined electrostatic potential boundaries. Scientific Gap: While R5G supports intrinsic flat-band physics, its tunability is limited. Integrating artificial superlattices (PDSLs or PGSLs) could: - Externally imposed periodic potentials from the artificial antidot lattice couple with the intrinsic flat bands of R5G. - Further flatten bands to enhance correlations. - Enable FQAHE at zero magnetic field [2]. - Offer dynamic control over symmetry-breaking phases. References: [1] T. Han et al., Nat. Nanotechnol., vol. 19, no. 2, pp. 181–187, Feb. 2024 [2] Z. Lu et al., Nature, vol. 626, no. 8000, pp. 759–764, Feb. 2024 [3] J. Cai et al., Nature, vol. 622, no. 7981, pp. 63–68, Oct. 2023 [4] Y. Zeng et al., Nature, vol. 622, no. 7981, pp. 69–73, Oct. 2023 [5] C. Forsythe et al., Nat. Nanotechnol., vol. 13, no. 7, pp. 566–571, Jul. 2018 [6] D. Barcons Ruiz et al., Nat. Commun., vol. 13, no. 1, p. 6926, Nov. 2022 [7] S. Dubey et al., Nano Lett., vol. 13, no. 9, pp. 3990–3995, Sep. 2013