Abstract
Graphene/hexagonal boron nitride (h-BN) has emerged as a model van der Waals heterostructure1 as the superlattice potential, which is induced by lattice mismatch and crystal orientation, gives rise to various novel quantum phenomena, such as the self-similar Hofstadter butterfly states2,3,4,5. Although the newly generated second-generation Dirac cones (SDCs) are believed to be crucial for understanding such intriguing phenomena, fundamental knowledge of SDCs, such as locations and dispersion, and the effect of inversion symmetry breaking on the gap opening, still remains highly debated due to the lack of direct experimental results. Here we report direct experimental results on the dispersion of SDCs in 0°-aligned graphene/h-BN heterostructures using angle-resolved photoemission spectroscopy. Our data unambiguously reveal SDCs at the corners of the superlattice Brillouin zone, and at only one of the two superlattice valleys. Moreover, gaps of approximately 100 meV and approximately 160 meV are observed at the SDCs and the original graphene Dirac cone, respectively. Our work highlights the important role of a strong inversion-symmetry-breaking perturbation potential in the physics of graphene/h-BN, and fills critical knowledge gaps in the band structure engineering of Dirac fermions by a superlattice potential.
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Change history
07 October 2016
In the version of this Letter originally published, the term labelling the centre of the superlattice Brillouin zone in Fig. 4j mistakenly contained a prime. This has now been corrected in all versions of the Letter.
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Acknowledgements
We thank V. I. Fal’ko for useful discussions. This work is supported by the National Natural Science Foundation of China (Grant No. 11274191, 11334006, and 11427903), Ministry of Science and Technology of China (Grant No. 2015CB921001, 2016YFA0301004) and Tsinghua University Initiative Scientific Research Program (2012Z02285). E.Y.W. is grateful for support from the Advanced Light Source Doctoral Fellowship Program. The Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under Contract No. DE-AC02-05CH11231.
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S.Z. designed the research project. E.W., S.D., W.Y., M.Y., G.W., K.D., A.V.F. and S.Z. performed the ARPES measurements and analysed the ARPES data. X.L., S.W., G.C., G.Z. and Y.Z. prepared the graphene samples. J.J. discussed the data. E.W. and S.Z. wrote the manuscript, and all authors commented on the manuscript.
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Wang, E., Lu, X., Ding, S. et al. Gaps induced by inversion symmetry breaking and second-generation Dirac cones in graphene/hexagonal boron nitride. Nature Phys 12, 1111–1115 (2016). https://doi.org/10.1038/nphys3856
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DOI: https://doi.org/10.1038/nphys3856
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