Origin of metallicity of LaTiO3/SrTiO3 heterostructures

It is shown that LaTiO3, in superlattices with SrTiO3, is a strongly correlated metal rather than a Mott insulator. The tetragonal lattice geometry imposed by the SrTiO3 substrate leads to an increase of the Ti 3dt(2g) bandwidth and a reversal of the t(2g) crystal field relative to the orthorhombic bulk geometry. Using dynamical mean field theory based on finite-temperature multiband exact diagonalization, we show that, as a result of these effects, local Coulomb interactions are not strong enough to induce a Mott transition in tetragonal LaTiO3. The experimentally observed metallicity of LaTiO3/SrTiO3 heterostructures is therefore caused not only by the interface but also by the tetragonal geometry of the LaTiO3 layers.