Analysis of metal-insulator crossover in strained SrRuO3 thin films by X-ray photoelectron spectroscopy

The electronic properties of strontium ruthenate SrRuO3 perovskite oxide thin films are modified by epitaxial strain, as determined by growing on different substrates by pulsed laser deposition. Temperature dependence of the transport properties indicates that tensile strain deformation of the SrRuO3 unit cell reduces the metallicity of the material as well as its metal-insulator-transition (MIT) temperature. On the contrary, the shrinkage of the Ru-O-Ru buckling angle due to compressive strain is counterweighted by the increased overlap of the conduction Ru-4d orbitals with the O-2p ones due to the smaller interatomic distances resulting into an increased MIT temperature, i.e., a more conducting material. In particular, in the more metallic samples, the core level X-ray photoemission spectroscopy lineshapes show the occurrence of an extra-peak at the lower binding energies of the main Ru-3d peak that is attributed to screening, as observed in volume sensitive photoemission of the unstrained material