Band structure engineering of 2D materials using patterned dielectric superlattices

Abstract

The ability to manipulate electrons in two-dimensional materials with external electric fields provides a route to synthetic band engineering. By imposing artificially designed and spatially periodic superlattice potentials, electronic properties can be further altered beyond the constraints of naturally occurring atomic crystals1,2,3,4,5. Here, we report a new approach to fabricate high-mobility superlattice devices by integrating surface dielectric patterning with atomically thin van der Waals materials. By separating the device assembly and superlattice fabrication processes, we address the intractable trade-off between device processing and mobility degradation that constrains superlattice engineering in conventional systems. The improved electrostatics of atomically thin materials allows smaller wavelength superlattice patterns relative to previous demonstrations. Moreover, we observe the formation of replica Dirac cones in ballistic graphene devices with sub-40 nm wavelength superlattices and report fractal Hofstadter spectra6,7,8 under large magnetic fields from superlattices with designed lattice symmetries that differ from that of the host crystal. Our results establish a robust and versatile technique for band structure engineering of graphene and related van der Waals materials with dynamic tunability.

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Fig. 1: Patterned dielectric superlattice design.
Fig. 2: Transport measurements and band structure of a triangular SL device.
Fig. 3: Fractal Hofstadter spectrum under magnetic field.
Fig. 4: Magnetic subband structure in triangular and square SL systems.

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Acknowledgements

Development of the device concept and fabrication process was supported by the Office of Naval Research (ONR) Young Investors Program (no. N00014-17-1-2832). Investigation of the fractal band structure under applied magnetic fields was supported by the National Science Foundation (DMR-1462383). C.F. was supported by National Science Foundation (NSF) Graduate Research Fellowship Program (DGE-14-44869) and the NSF Integrative Graduate Education and Research Training fellowship program (DGE-1069240). A portion of this work was performed at the National High Magnetic Field Laboratory, which is supported by National Science Foundation Cooperative Agreement no. DMR-0654118, the State of Florida and the US Department of Energy. STM work is supported by the ONR (no. N00014-14-1-0501). P.M. acknowledges the support of New York University (NYU) Shanghai (Start-up Funds), NYU-ECNU (East China Normal University) Institute of Physics, and the NSF of China Research Fund for International Young Scientists (grant no. 11550110177). This research was carried out on the High Performance Computing resources at NYU Shanghai. M.K. was supported by JSPS (Japan Society for the Promotion of Science) KAKENHI (grant no. JP25107005, JP25107001 and JP15K21722). P.K. acknowledges support from ONR Multidisciplinary University Research Initiatives program on Quantum Optomechanics (grant no. N00014-15-1-2761).

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C.F., P.K. and C.R.D. conceived of the experiment. C.F. fabricated the samples, performed transport measurements and analysed transport data. P.M. and M.K. provided theoretical modelling of the system. X.Z. and A.P. performed STM measurements and analysed STM data. C.F., P.M., M.K., A.P., P.K. and C.R.D. co-wrote the paper. K.W. and T.T. provided hBN material for device fabrication.

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Correspondence to Cory R. Dean.

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Supplementary Figures 1–14, Supplementary References

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Forsythe, C., Zhou, X., Watanabe, K. et al. Band structure engineering of 2D materials using patterned dielectric superlattices. Nature Nanotech 13, 566–571 (2018). https://doi.org/10.1038/s41565-018-0138-7

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