Quantum confinement of Mott electrons in ultrathin LaNiO ₃/LaAlO₃ superlattices

We investigate the electronic reconstruction in (LaNiO₃) _n/(LaAlO₃)₃ (n=3, 5, and 10) superlattices due to the quantum confinement (QC) by dc transport and resonant soft x-ray absorption spectroscopy. In proximity to the QC limit, a Mott-type transition from an itinerant electron behavior to a localized state is observed. The system exhibits tendency toward charge-order during the transition. Ab initio cluster calculations are in good agreement with the absorption spectra, indicating that the apical ligand hole density is highly suppressed, resulting in a strong modification of the electronic structure. At the dimensional crossover cellular dynamical-mean-field calculations support the emergence of a Mott insulator ground state in the heterostructured ultrathin slab of LaNiO₃.