Designing a Spin-one Mott Insulator: Complete Charge Transfer in Nickelate-Titanate Heterostructures

$Ab$ $initio$ calculations are performed to show that complete charge transfer may occur from the TiO$_2$ to the NiO$_2$ layers in (LaTiO$_3$)$_1$/(LaNiO$_3$)$_1$ superlattices. Although the two component materials are an $S = 1/2$ Mott insulator and a weakly correlated paramagnetic metal, strong correlation effects on Ni $d$ states can render the superlattice an unusual $S = 1$ charge transfer insulator, with the Ti-$d$ band empty, the Ni in the $d^8$ state and the oxygen bands filled. The charge transfer gap is set by the Ti/Ni $d$ level splitting. Magnetic, photoemission and x-ray scattering experiments are suggested to test the theory. The results show that heterostructuring can lead to very high levels of electron doping of oxides.