High-order fractal quantum oscillations in highly doped graphene/BN superlattices*

High temperature quantum oscillations have been reported in graphene/BN superlattices beyond secondary Dirac points both for electron and hole doping [1,2]. These so-called Brown-Zak (BZ) oscillations originate from periodic emergence of delocalized Bloch states in high magnetic field. However, the BZ oscillations is much less visible for hole doping than for electron doping due to strong electron-hole asymmetry. Here, we employed a newly developed electron beam doping technique to induce high electron and hole carrier densities in graphene/BN superlattices while maintaining high mobilities. Enhanced BZ oscillations are observed beyond the third-generation neutrality points at high temperatures. High-order magnetic Bloch states are also seen even for hole doping, demonstrating the effectiveness of our doping technique. Theoretical simulation of the magnetotransport provides qualitative agreement of the carrier density dependence of BZ oscillations with our experimental results.

References:
[1] R. K. Kumar, X. Chen, et al, Science 357, 181 (2017).
[2] R. K. Kumar, A. Mishchenko, et al, PNAS 115, 5135 (2018).