  We propose a model intended to qualitatively capture the electron-electron
interaction physics of two-dimensional electron gases formed near
transition-metal oxide heterojunctions containing $t_{2g}$ electrons with a
density much smaller than one electron per metal atom. Two-dimensional electron
systems of this type can be described perturbatively using a $GW$ approximation
which predicts that Coulomb interactions enhance quasiparticle effective masses
more strongly than in simple two-dimensional electron gases, and that they
reshape the Fermi surface, reducing its anisotropy.
