  It is shown that LaTiO_3 in superlattices with SrTiO_3 is not a Mott
insulator but a strongly correlated metal. The tetragonal lattice geometry
imposed by the SrTiO_3 substrate leads to an increase of the Ti 3d t2g band
width and a reversal of the t2g crystal field relative to the orthorhombic bulk
geometry. Using dynamical mean field theory based on finite-temperature
multi-band 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 LaTiO_3. The metalicity of these heterostructures is therefore not
an interface property but stems from all LaTiO_3 planes.
