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Strain-induced partially flat band, helical snake states and interface superconductivity in topological crystalline insulators

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Abstract

Topological crystalline insulators in IV–VI compounds host novel topological surface states consisting of multi-valley massless Dirac fermions at low energy. Here we show that strain generically acts as an effective gauge field on these Dirac fermions and creates pseudo-Landau orbitals without breaking time-reversal symmetry. We predict the realization of this phenomenon in IV–VI semiconductor heterostructures, due to a naturally occurring misfit dislocation array at the interface that produces a periodically varying strain field. Remarkably, the zero-energy Landau orbitals form a flat band in the vicinity of the Dirac point, and coexist with a network of snake states at higher energy. We propose that the high density of states of this flat band gives rise to interface superconductivity observed in IV–VI semiconductor multilayers at unusually high temperatures, with non-Bardeen–Cooper–Schrieffer behaviour. Our work demonstrates a new route to altering macroscopic electronic properties to achieve a partially flat band, and provides a starting point for realizing novel correlated states of matter.

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Figure 1: Strain-induced Dirac point shift on the (001) surface of a topological crystalline insulator such as SnTe or Pb1−xSnxSe(Te).
Figure 2: The spontaneous formation of a misfit dislocation array gives rise to a periodically varying strain field and pseudo-magnetic field, at the interface.
Figure 3: The pseudo-magnetic field from strain creates flat bands and snake states.

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  • 12 November 2014

    In the version of this Article originally published, the title of reference 36 was incorrect and should have read 'Superfluidity in system with fermion condensate'. This error has now been corrected in all versions of the Article.

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Acknowledgements

We thank M. Serbyn and A. Allais for helpful discussions, as well as Y. Ando and R. Cava for valuable comments on the manuscript. This work is supported by DOE Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under award DE-SC0010526 (L.F.). E.T. acknowledges support from NSF Grants DMR-1005541, NSFC 11074140 and NSFC 11274192.

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Correspondence to Liang Fu.

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Tang, E., Fu, L. Strain-induced partially flat band, helical snake states and interface superconductivity in topological crystalline insulators. Nature Phys 10, 964–969 (2014). https://doi.org/10.1038/nphys3109

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