Ab Initio Studies of the Electronic Structure and Electrical Transport in Epitaxially Strained RuO₂ Thin Films

The discovery of strain-induced superconductivity in rutile RuO₂ thin films has attracted considerable attention from the scientific community. Superconducting behavior of RuO₂ films has been linked to the changes in the electronic structure of strained RuO₂ crystal lattice resulting in significant increase of the density of states at the Fermi level. We applied ab initio density functional computational methods to study the influence of epitaxial strain and doping on the electronic and transport properties of RuO₂ thin films grown on TiO₂ substrates. Our calculations were performed using the PBE exchange-correlation functional with the inclusion of Hubbard correction and spin-orbit coupling. The emergence of flat bands in the electronic structure of RuO₂ and their potential role in mediating superconductivity was investigated by applying biaxial epitaxial strain along the (110), (100), and (001) crystal orientations of rutile RuO₂. Additionally, we examined the impact of doping the RuO₂, focusing on shift in the Fermi level and its alignment with conditions favorable for superconductivity. Our results suggest that the combined influence of strain and doping may offer a viable route to stabilize superconducting phases in RuO₂ thin films.