期刊
PHYSICAL REVIEW LETTERS
卷 112, 期 19, 页码 -出版社
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevLett.112.196602
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资金
- Foundation for Fundamental Research on Matter (FOM)
- Netherlands Organization for Scientific Research (NWO/OCW)
- ERC Synergy grant
- German Academic Exchange Service (DAAD)
The fractal spectrum of magnetic minibands (Hofstadter butterfly), induced by the moire superlattice of graphene on a hexagonal crystal substrate, is known to exhibit gapped Dirac cones. We show that the gap can be closed by slightly misaligning the substrate, producing a hierarchy of conical singularities (Dirac points) in the band structure at rational values phi= (p / q) (h / e) of the magnetic flux per supercell. Each Dirac point signals a switch of the topological quantum number in the connected component of the quantum Hall phase diagram. Model calculations reveal the scale-invariant conductivity sigma = 2qe(2) / pi h and Klein tunneling associated with massless Dirac fermions at these connectivity switches.
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