Mixed Mott–Hubbard and charge transfer nature of 4H–SrMnO₃ thin film on Si (100)

Abstract

Room temperature electronic structure of polycrystalline 4H–SrMnO3 thin 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 3d n L final state along with the 3d n-1 final state at the valence band edge of 4H–SrMnO3 thin film confirms that the ground state is strongly mixed between Mn 3d and O 2p states. The estimated equivalent values of on-site Coulomb interaction energy (U) and O 2p to 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–SrMnO3 film. Despite having similar Mn 4+ valence state in 4H–SrMnO3 and 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 MnO6 octahedra environment.

Structural phase transition of G-type antiferromagnetic SrMnO3 under pressure

“…At P = 0 GPa, the results in figure 3 clearly indicate that the G-AFM type of 4H-SrMnO 3 (blue solid line) exhibits the lowest enthalpy per formula unit compared to the other phases, demonstrating its higher energetic favorability and stability under low-pressure conditions. These findings regarding the enthalpy difference support the stability of the G-AFM type of 4H-SrMnO 3 at P = 0 GPa, and also align remarkably well with previous experimental investigations [16,17,21,32]. For instance, Battle et al conducted an extensive study on the 4H-SrMnO 3 phase by employing neutron diffraction and magnetism measurements, and their results unequivocally supported the presence of the G-AFM type below 278 K [17].…”

“…With this optimized grid size, the calculated value of Hubbard U for the 3d-Mn atom remained at 4.552 eV (red dashed line in figure 2). Importantly in this work, the computed Hubbard U value exhibited excellent agreement with the experimental observations (U exp » 4.8 eV) [32]. Furthermore, the computed Hubbard U value remains consistent across both the FM and G-AFM phases.…”

“…The difference in band gap between the two structures can be attributed to the distinct local MnO 6 environments. In 3C-SrMnO 3 , the Mn ions are positioned at the center of the MnO 6 octahedra, while in 4H-SrMnO 3 , the Mn site is slightly displaced towards the face-sharing O sites, resulting in a larger band gap [25,32].…”

“…The choice of the Hubbard U value for the DFT+U calculation has been a challenge due to the unknown exact values in these interactions [29,30]. Previous studies have computed the Hubbard U values in the range of 3.0-6.0eV for 3d-Mn state in SrMnO 3 and similar Mn oxide systems [29,[31][32][33].…”

Time Evolution of the Structural, Electronic, and Magnetic Phases in Relaxed SrCoO3 Thin Films

“…To investigate the origin of the different regions of the VBS, we performed resonant photoemission spectroscopy (RPES) by recording VBS at 50 and 68 eV. In RPES, the observed photoemission enhancement of a region in the VBS with respect to the photon energy can be attributed to the TM 3d derived state. − The Co 3p → 3d threshold occurs at ∼67–68 eV in SrCoO 3 ; therefore, the VBS taken at 50 and 68 eV are the off-resonance and on-resonance spectra, respectively. Figure c displays the time evolution of the difference spectra, derived from subtracting the off-resonance spectra from the on-resonance spectra.…”