Abstract
Electrons in graphene are described by relativistic Dirac–Weyl spinors with a two-component pseudospin1,2,3,4,5,6,7,8,9,10,11,12. The unique pseudospin structure of Dirac electrons leads to emerging phenomena such as the massless Dirac cone2, anomalous quantum Hall effect2,3, and Klein tunnelling4,5 in graphene. The capability to manipulate electron pseudospin is highly desirable for novel graphene electronics, and it requires precise control to differentiate the two graphene sublattices at the atomic level. Graphene/boron nitride moiré superlattices, where a fast sublattice oscillation due to boron and nitrogen atoms is superimposed on the slow moiré period, provides an attractive approach to engineer the electron pseudospin in graphene13,14,15,16,17,18. This unusual moiré superlattice leads to a spinor potential with unusual hybridization of electron pseudospins, which can be probed directly through infrared spectroscopy because optical transitions are very sensitive to excited state wavefunctions. Here, we perform micro-infrared spectroscopy on a graphene/boron nitride heterostructure and demonstrate that the moiré superlattice potential is dominated by a pseudospin-mixing component analogous to a spatially varying pseudomagnetic field. In addition, we show that the spinor potential depends sensitively on the gate-induced carrier concentration in graphene, indicating a strong renormalization of the spinor potential from electron–electron interactions.
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Acknowledgements
We thank Z. Li and J. Song for helpful discussions. Device fabrication and optical measurements in this work were mainly supported by the Office of Naval Research (award N00014-13-1-0464). Electrical characterizations and theoretical analysis were supported by Office of Basic Energy Science, Department of Energy under contract Nos DE SC0003949 and DE AC02 05CH11231 (Materials Science Division). F.W. acknowledges support from a David and Lucile Packard fellowship. G.Z. acknowledges support from the National Basic Research Program of China (Grant No. 2013CB934500, 2012CB921302) and the National Natural Science Foundation of China (Grant No. 61325021, 91223204). 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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F.W. and G.Z. conceived the research. W.Y. and X.L. grew the samples. Z.S., L.J. and D.F. fabricated the devices. Z.S., L.J., J.H. and H.A.B. carried out the optical measurements. C.J., F.W. and Z.S. developed the theory. Z.S., C.J., F.W. and G.Z. wrote the manuscript. All authors discussed the results and commented on the paper.
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Shi, Z., Jin, C., Yang, W. et al. Gate-dependent pseudospin mixing in graphene/boron nitride moiré superlattices. Nature Phys 10, 743–747 (2014). https://doi.org/10.1038/nphys3075
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DOI: https://doi.org/10.1038/nphys3075
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