Observation of Dirac cone band dispersions in FeSe thin films by photoemission spectroscopy.

The search for novel materials with Dirac cone band dispersion is one of the most challenging and important works for both fundamental physics and technological applications. Here, we studied the electronic structure of FeSe thin films grown on SrTiO$_{\mathrm{3}}$ substrates by angle-resolved photoemission spectroscopy (ARPES). We reveal the existence of Dirac cone band dispersions in FeSe thin films thicker than 1 Unit Cell below the nematic transition temperature, whose apexes are located -10 meV below Fermi energy. The evolution of electronic structures for FeSe thin films as function of temperature, thickness and cobalt doping are systematically studied. The Dirac cones are found to be coexisted with the nematicity in FeSe, disappear when nematicity is suppressed. Our results provide useful guidelines for understanding the novel electronic structure, nematicity and superconductivity in FeSe system..