  Heterointerfaces in complex oxide systems open new arenas in which to test
models of strongly correlated material, explore the role of dimensionality in
metal-insulator-transitions (MITs) and small polaron formation. Close to the
quantum critical point Mott MITs depend on band filling controlled by random
disordered substitutional doping. Delta-doped Mott insulators are potentially
free of random disorder and introduce a new arena in which to explore the
effect of electron correlations and dimensionality. Epitaxial films of the
prototypical Mott insulator GdTiO3 are delta-doped by substituting a single
(GdO)+1 plane with a monolayer of charge neutral SrO to produce a
two-dimensional system with high planar doping density. Unlike metallic SrTiO3
quantum wells in GdTiO3 the single SrO delta-doped layer exhibits thermally
activated DC and optical conductivity that agree in a quantitative manner with
predictions of small polaron transport but with an extremely high
two-dimensional density of polarons, ~ 7E14 cm-2
