Suppression of the Spectral Weight of Topological Surface States on the Nanoscale via Local Symmetry Breaking

In topological crystalline insulators the topological conducting surface states are protected by crystal symmetry. Here, We show using scanning tunneling microscopy/spectroscopy that defects that break local mirror symmetry of SnTe suppress electron tunneling over an energy range as large as the bulk band gap, an order of magnitude larger than that produced globally via magnetic fields or uniform structural perturbations [1]. The results reveal the influence of various defects on the electronic properties, including screw dislocations, point defects, and tilt boundaries that lead to dislocation arrays that serve as periodic nucleation sites for pits grown on SrTiO₃ [2,3]. Complementary ab initio calculations show how local symmetry breaking obstructs topological surface states as shown by a threefold reduction of the spectral weight of the topological surface states. The findings highlight the potential benefits of manipulating the surface morphology to create devices that take advantage of the unique properties of surface states and can operate at practical temperatures.
[1] O.E. Dagdeviren et al., Physical Review Materials (in press)
[2] O.E. Dagdeviren et al., Advanced Materials and Interfaces 4, 1601011 (2017)
[3] O.E. Dagdeviren et al., Physical Review B 93, 195303 (2016)