Interface Carriers and Enhanced Electron‐Phonon Coupling Effect in Al 2 O 3 /TiO 2 Heterostructure Revealed by Resonant Inelastic Soft X‐Ray Scattering

The electronic structure and the electron‐phonon couplings in a novel mass‐production‐compatible Al 2 O 3 /TiO 2 2D electron system (2DES) are investigated using resonant inelastic soft X‐ray scattering. The experimental data from the samples of various TiO 2 thicknesses unequivocally show that the Ti 3+ state indeed exists at the deep interface to serve as an n ‐type dopant for the 2DES. The electronic structure of Ti 3+ species is scrutinized as entirely separated from that of the Ti 4+ host lattice. Furthermore, features of sub‐eV energy loss phonon modes are clearly observed, indicating substantial electron‐phonon coupling effects. Such low energy loss features are enhanced in thinner TiO 2 samples, implying that polaronic local lattice deformation is enhanced due to the presence of Ti 3+ . These findings suggest that the 2DES properties can be controlled via well‐established TiO 2 engineering, thereby enthroning the binary oxide heterostructure as a promising candidate for 2DES device applications.