Physics (Internal)

Strain engineering Dirac surface states in topological crystalline insulator heteroepitaxial thin films

This event is part of the Biophysics/Condensed Matter Seminar Series.

Abstract: Controllable manipulation of materials at the atomic length scales is necessary for realizing the next generation of nanodevices. A promising pathway involves the application of strain, which can be used to tune the inter-atomic lattice spacing and induce an accompanying change in the electronic structure. In newly discovered topological crystalline insulators (TCIs), the unique crystalline protection of the surface state (SS) band structure has led to a series of intriguing predictions of strain generated phenomena, from the appearance of pseudo-magnetic fields and helical flat bands, to the tunability of the SS Dirac nodes (Tang and Fu, arXiv:1403.7523). However, practical realization of this exotic phenomenology via strain engineering is experimentally challenging and is yet to be achieved. In our experiments, we grow heteroepitaxial thin films of SnTe and use Fourier-transform scanning tunneling microscopy (STM) to study the effects of strain on the interference patterns of scattered electrons. We find that strain continuously tunes the momentum space position of the Dirac points, consistent with theoretical predictions. Our measurements provide the first direct experimental evidence for the pronounced effects of strain on the topological SS band structure, and demonstrate the fundamental mechanism necessary for using TCIs in strain-based applications.