Mixed Mott-Hubbard and charge transfer nature of 4H-SrMnO₃thin film on Si (100)

Room temperature electronic structure of polycrystalline 4H-SrMnO₃thin film grown on Si (100) substrate has been studied using resonance photo emission spectroscopy and soft x-ray absorption spectroscopy measurements. Presence of charge transfer screen Mn 3dfinal state along with the 3d^n-1final state at the valence band edge of 4H-SrMnO₃thin film confirms that the ground state is strongly mixed between Mn 3dand O 2pstates. The estimated equivalent values of on-site Coulomb interaction energy (U) and O 2pto Mn 3d- charge transfer energy (Δ) (U≈ Δ ≈ 4.8 eV) from the combination of occupied and unoccupied spectra further confirm the intermediate Mott-Hubbard and charge transfer insulator nature of 4H-SrMnO₃film. Despite having similar Mn 4+ valence state in 4H-SrMnO₃and cubic SrMnO₃, 4H phase is observed to reveal much higher band gap ∼1.5 eV than the cubic phase (0.3 eV), which arises due to different MnO₆octahedra environment.