  We investigate correlation physics in high-density, two-dimensional electron
liquids that reside in narrow SrTiO3 quantum wells. The quantum wells are
remotely doped via an interfacial polar discontinuity and the three-dimensional
(3D) carrier density is modulated by changing the width of the quantum well. It
is shown that even at 3D densities well below one electron per site,
short-range Coulomb interactions become apparent in transport, and an
insulating state emerges at a critical density. We also discuss the role of
disorder in the insulating state.
