  Transition metal oxides with a wide variety of electronic and magnetic
properties offer an extraordinary possibility to be a platform for developing
future electronics based on unconventional quantum phenomena, for instance, the
topology. The formation of topologically non-trivial states is related to
crystalline symmetry, spin-orbit coupling, and magnetic ordering. Here, we
demonstrate how lattice distortions and octahedral rotation in SrNbO$_3$ films
induce the band topology. By employing angle-resolved photoemission
spectroscopy (ARPES) and density functional theory (DFT) calculations, we
verify the presence of in-phase $a^0a^0c^+$ octahedral rotation in ultra-thin
SrNbO$_3$ films, which causes the formation of topologically-protected Dirac
band crossings. Our study illustrates that octahedral engineering can be
effectively exploited for implanting and controlling quantum topological phases
in transition metal oxides.
