SmO thin films: A flexible route to correlated flat bands with nontrivial topology

Using density functional theory based calculations, we show that the correlated mixed-valent compound SmO is a three-dimensional strongly topological semimetal as a result of a 4f -5d band inversion at the X point. The [001] surface Bloch spectral density reveals two weakly interacting Dirac cones that are quasidegenerate at the (M) over bar point and another single Dirac cone at the (Gamma) over bar point. We also show that the topological nontriviality in SmO is very robust and prevails for a wide range of lattice parameters, making it an ideal candidate to investigate topological nontrivial correlated flat bands in thin-film form. Moreover, the electron filling is tunable by strain. In addition, we find conditions for which the inversion is of the 4f -6s type, making SmO to be a rather unique system. The similarities of the crystal symmetry and the lattice constant of SmO to the well studied ferromagnetic semiconductor EuO, makes SmO/EuO thin film interfaces an excellent contender towards realizing the quantum anomalous Hall effect in a strongly correlated electron system