Topological electronic states of bismuth selenide thin films upon structural surface defects

A noticeable effort has been put into developing a consistent understanding of surface electronic structure of topological insulators. Of special interest has been a fundamental feature of their surface electronic states being insensitive to various types of defects and distortions. In the following paper, based on the density functional theory calculations, these topological states are investigated in asymmetric thin films of bismuth selenide with one surface modified by structural distortions. It is shown that the energetics and spatial localisation of the topological electronic states on the modified surface of the film evolve drastically as a consequence of their topological dangling bond nature. It is also shown that all the asymmetric slabs exhibit suppression of the thin film size effect and restoration of massless Dirac electrons on the undistorted surface of the film. The results are relevant for effective band gap engineering in thin films of topological insulators by means of chemical or physical functionalisation.