Valence and origin of metal-insulator transition in Mn doped SrRuO3 studied by electrical transport, X-ray photoelectron spectroscopy and LSDA+U calculation

We have studied the valence and electronic properties of Mn doped SrRuO₃ using electrical transport measurement, X-ray photoelectron spectroscopy (XPS) and local (spin) density approximation plus Coulomb interaction strength calculation (LSDA+U). The resistivity data revealed that the system undergoes transition from metal to insulator at the critical Mn doping level, x∼0.2, which is accompanied by the structural transition from orthorhombic to tetragonal crystal symmetry. Besides, the significant reduction of the spectral weight at the coherent zone (0.8 eV) of the valence band is observed for x>0.2. The core XPS spectra suggest that both the transition elements exist in the mixed ionic pair, Ru⁺⁴/Ru⁺⁵↔Mn⁺³/Mn⁺⁴. The detail analysis of the results suggests that the Coulomb correlation effect in conjugation with localization of the charge carriers predominate over the mixed ionic pair effect and responsible for the metal-insulator transition in the series.