Emergence of massless Dirac fermions in graphene's Hofstadter butterfly at switches of the quantum Hall phase connectivity
| Autor: | Diez, M., Dahlhaus, J. P., Wimmer, M., Beenakker, C. W. J. |
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| Rok vydání: | 2014 |
| Předmět: | |
| Zdroj: | Phys. Rev. Lett. 112, 196602 (2014) |
| Druh dokumentu: | Working Paper |
| DOI: | 10.1103/PhysRevLett.112.196602 |
| Popis: | The fractal spectrum of magnetic minibands (Hofstadter butterfly), induced by the moir\'e super- lattice of graphene on an 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. Comment: 4 pages, 6 figures + appendix (3 pages, 1 figure) |
| Databáze: | arXiv |
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