Thickness-dependent electronic structure of ultrathin SrRuO3 films studied by in situ photoemission spectroscopy

In situ thickness-dependent photoemission spectroscopy (PES) has been performed on SrRuO3 (SRO) layers deposited on SrTiO3 substrates to study the structure-induced evolution of the electronic structure. The PES spectra showing the existence of two critical film thicknesses reveal that a metal-insulator transition occurs at a film thickness of 4–5 monolayers (ML) and the evolution of Ru 4d-derived states around the Fermi level (EF) saturates at about 15 ML. The observed spectral behavior well matches the electric and magnetic properties and thickness-dependent evolution of surface morphology of the ultrathin SRO films. These experimental results suggest the importance of the disorder associated with the unique growth-mode transition in SRO films.