High-order minibands and interband Landau level reconstruction in graphene moiré superlattices

The propagation of Dirac fermions in graphene through a long-period periodic potential would result in a band folding together with the emergence of a series of cloned Dirac points (DPs) [C.-H. Park et al., Nat. Phys. 4, 213 (2008); C.-H. Park et al.Phys. Rev. Lett. 101, 126804 (2008)]. In highly aligned graphene/hexagonal boron nitride (G/hBN) heterostructures, the lattice mismatch between the two atomic crystals generates a unique kind of periodic structure known as a moiré superlattice. Of particular interest is the emergent phenomena related to the reconstructed band-structure of graphene, such as the Hofstadter butterfly [L. A. Ponomarenko et al., Nature (London) 497, 594 (2013); B. Hunt et al., Science 340, 1427 (2013); C. R. Dean et al., Nature(London) 497, 598 (2013)], topological currents [R. V Gorbachev et al., Science 346, 448 (2014)], gate-dependent pseudospin mixing [Z. Shi et al., Nat. Phys. 10, 743 (2014)], and ballistic miniband conduction [M. Lee et al., Science 353, 1526 (2016)]. However, most studies so far have been limited to the lower-order minibands, e.g., the first and second minibands counted from charge neutrality, and consequently the fundamental nature of the reconstructed higher-order miniband spectra still remains largely unknown. Here we report on probing the higher-order minibands of precisely aligned graphene moiré superlattices by transport spectroscopy. Using dual electrostatic gating, the edges of these high-order minibands, i.e., the third and fourth minibands, can be reached. Interestingly, we have observed interband Landau level (LL) crossing inducing gap closures in a multiband magnetotransport regime, which originates from band overlap between the second and third minibands. As observed, high-order minibands and LL reconstruction qualitatively match our simulated results.