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Strain-induced Two-dimensional Topological Crystalline Insulator

Liwei Jing

Department of Physics, Nanoscience Center, Ä¢¹½Ö±²¥, FI-40014 Jyväskylä, Finland

Abstract

The hallmark of two-dimensional topological crystalline insulators (TCIs) is the existence of gapless edge modes propagating against the backscattering along the sample boundary while the bulk is gapped, in which topological nature is protected by the crystal symmetry ^[1]. TCIs feature an even number of massless Dirac cones, which can be tuned by electric field, temperature or strain, rendering them potential candidates for spintronics or magnetoelectronics applications. The odd number of atomic layers in tin telluride (SnTe) films have been predicted to host nontrivial edge states in two dimensions ^{[1, 2]}. However, the experimental evidence is still lacking. Here we report scanning tunneling microscopy experiments on bilayer SnTe islands with biaxial compressive strain that show one-dimensional helical conducting edge states within the band gap along the straight and sharp edges, which are preserved by mirror symmetry through the non-zero Chern number. By visualizing the edge modes, we provide direct spectroscopic evidence of their one-dimensional nature and robustness against disorder. Importantly, we demonstrate topological edge states can be opened with a band gap by spontaneous symmetry breaking via intrinsic atomic defects at the edges. Moreover, we experimentally show that closely adjacent topological edge states can interact with each other, leading to the energy shift. Our experiments realize an ultimately tuneable platform for the further study of interactions in the quantum Hall regime.

In this seminar, I will present more details about experimental and theoretical proofs of topological non-trivial character in our observed edge states. 

References

1. Junwei Liu, Timothy H. Hsieh, Peng Wei, Wenhui Duan, Jagadeesh Moodera & Liang Fu, Nature Materials 13, 178-183 (2014)
2. Augusto L. Araújo, Gerson J. Ferreira & Tome M. Schmidt, Scientific Reports 8, 9452 (2018)