Elastic strain has the potential for a controlled manipulation of the band gap and spin-polarized Dirac states of topological materials, which can lead to pseudomagnetic field effects, helical flat bands, and topological phase transitions. However, practical realization of these exotic phenomena is challenging and yet to be achieved. Here we show that the Dirac surface states of the topological insulator BiSe can be reversibly tuned by an externally applied elastic strain. Performing in situ X-ray diffraction and in situ angle-resolved photoemission spectroscopy measurements during tensile testing of epitaxial BiSe films bonded onto a flexible substrate, we demonstrate elastic strains of up to 2.1% and quantify the resulting changes in the topological surface state. Our study establishes the functional relationship between the lattice and electronic structures of BiSe and, more generally, demonstrates a new route toward momentum-resolved mapping of strain-induced band structure changes.

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Ambiguity exists in the literature on the crystal structure of Ag

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The kinetics of intermetallic compound (IMC) formation in thermally evaporated Ag-In bilayers, with In on top of Ag, was investigated using X-ray diffractometry, applied to the surfaces of the bilayer specimens, as well as scanning electron microscopy, applied to cross-sections of the bilayer specimens, prepared by a focused ion beam instrument. IMC formation was followed at room temperature as well as at elevated temperatures of 50 °C, 60 °C, and 70 °C. Two distinct growth regimes were observed coinciding with the availability of pure In. The AgIn2 IMC nucleated initially, followed by nucleation of the Ag2In IMC. The growth of AgIn2 was found to be controlled by both diffusional processes as well as interfacial reactions. The growth of the Ag2In IMC is dominantly diffusion-controlled. An interdiffusion coefficient of D=1.1±3.9·10−4 cm2 s−1 exp(−60.5±9.2 kJ mol−1R−1T−1) was obtained for the Ag2In IMC. The observations were discussed in terms of the interplay of thermodynamic and kinetic constraints.