| Autor: |
Wang P; Department of Physics and Astronomy, University of California , Riverside, California 92521, United States., Cheng B; Department of Physics and Astronomy, University of California , Riverside, California 92521, United States., Martynov O; Department of Physics and Astronomy, University of California , Riverside, California 92521, United States., Miao T; Department of Physics and Astronomy, University of California , Riverside, California 92521, United States., Jing L; Department of Physics and Astronomy, University of California , Riverside, California 92521, United States., Taniguchi T; Advanced Materials Laboratory, National Institute for Materials Science , Tsukuba, Ibaraki 305-0044, Japan., Watanabe K; Advanced Materials Laboratory, National Institute for Materials Science , Tsukuba, Ibaraki 305-0044, Japan., Aji V; Department of Physics and Astronomy, University of California , Riverside, California 92521, United States., Lau CN; Department of Physics and Astronomy, University of California , Riverside, California 92521, United States., Bockrath M; Department of Physics and Astronomy, University of California , Riverside, California 92521, United States. |
| Abstrakt: |
Graphene's quantum Hall features are associated with a π Berry's phase due to its odd topological pseudospin winding number. In nearly aligned graphene-hexagonal BN heterostructures, the lattice and orientation mismatch produce a superlattice potential, yielding secondary Dirac points in graphene's electronic spectrum, and under a magnetic field, a Hofstadter butterfly-like energy spectrum. Here we report an additional π Berry's phase shift when tuning the Fermi level past the secondary Dirac points, originating from a change in topological winding number from odd to even when the Fermi-surface electron orbit begins to enclose the secondary Dirac points. At large hole doping inversion symmetry breaking generates a distinct hexagonal pattern in the longitudinal resistivity versus magnetic field and charge density. Major Hofstadter butterfly features persist up to ∼100 K, demonstrating the robustness of the fractal energy spectrum in these systems. |
