Bulk and surface sensitive x-ray spectroscopic techniques are applied in tandem to show that the valence band edge for ${\mathrm{In}}_2{\mathrm{O}}_3$ is found significantly closer to the bottom of the conduction band than expected on the basis of the widely quoted bulk band gap of 3.75 eV. First-principles theory shows that the upper valence bands of ${\mathrm{In}}_2{\mathrm{O}}_3$ exhibit a small dispersion and the conduction band minimum is positioned at $\Gamma$. However, direct optical transitions give a minimal dipole intensity until 0.8 eV below the valence band maximum. The results set an upper limit on the fundamental band gap of 2.9 eV.

Interfacial magnetoelectric coupling is a viable path to achieve electrical writing of magnetic information in spintronic devices. For the prototypical Fe/BaTiO₃ system, only tiny changes of the interfacial Fe magnetic moment upon reversal of the BaTiO₃ dielectric polarization have been predicted so far. Here, by using X-ray magnetic circular dichroism in combination with high-resolution electron microscopy and first principles calculations, we report on an undisclosed physical mechanism for interfacial magnetoelectric coupling in the Fe/BaTiO₃ system. At this interface, an ultrathin oxidized iron layer exists, whose magnetization can be electrically and reversibly switched on and off at room temperature by reversing the BaTiO₃ polarization. The suppression/recovery of interfacial ferromagnetism results from the asymmetric effect that ionic displacements in BaTiO₃ produces on the exchange coupling constants in the interfacial-oxidized Fe layer. The observed giant magnetoelectric response holds potential for optimizing interfacial magnetoelectric coupling in view of efficient, low-power spintronic devices.

The valence and core levels of ${\text{In}}_2{\text{O}}_3$ and Sn-doped ${\text{In}}_2{\text{O}}_3$ have been studied by hard x-ray photoemission spectroscopy $\left(\text{h}\nu =6000\text{eV}\right)$ and by conventional $\text{Al}\text{K}\alpha$ $\left(\text{h}\nu =1486.6\text{eV}\right)$ x-ray photoemission spectroscopy. The experimental spectra are compared with density-functional theory calculations. It is shown that structure deriving from electronic levels with significant In or Sn $5s$ character is selectively enhanced under 6000 eV excitation. This allows us to infer that conduction band states in Sn-doped samples and states at the bottom of the valence band both contain a pronounced In $5s$ contribution. The In $3d$ core line measured at $\text{h}\nu =1486.6\text{eV}$ for both undoped and Sn-doped ${\text{In}}_2{\text{O}}_3$ display an asymmetric lineshape, and may be fitted with two components associated with screened and unscreened final states. The In $3d$ core line spectra excited at $\text{h}\nu =6000\text{eV}$ for the Sn-doped samples display pronounced shoulders and demand a fit with two components. The In $3d$ core line spectrum for the undoped sample can also be fitted with two components, although the relative intensity of the component associated with the screened final state is low, compared to excitation at 1486.6 eV. These results are consistent with a high concentration of carriers confined close to the surface of nominally undoped ${\text{In}}_2{\text{O}}_3$. This conclusion is in accord with the fact that a conduction band feature observed for undoped ${\text{In}}_2{\text{O}}_3$ in $\text{Al}\text{K}\alpha$ x-ray photoemission is much weaker than expected in hard x-ray photoemission.