In-situ strain engineering of the Dirac surface states in Bi₂Se₃ films

A controlled manipulation of the bulk band gap and spin-polarized Dirac surface states of topological insulators is of great fundamental importance and relevant to novel device applications. A promising pathway involves the application of strain, which alters the interatomic lattice spacing and thus induces corresponding changes in the electronic band structure. By performing angle-resolved photoemission spectroscopy (ARPES) and X-ray diffraction (XRD) measurements during in-situ tensile tests of ultrathin epitaxial Bi₂Se₃ films on flexible substrates we demonstrate that the band structure of the prototypical topological insulator Bi₂Se₃ can be reversibly tuned in-situ by means of elastic strain. In accordance with our first principle calculations, the Dirac point reversibly shifts to larger binding energies with increasing tensile strain as a result of the decreasing inter quintuple-layer distance. Our study is an important step forward towards using strain as an in-situ tool for tailoring of the functional properties of topological materials and opens new routes for a momentum-resolved quantification of strain-induced band-structure changes.