  Motivated by recent interest in perovskite surfaces and heterostructures, we
present an analysis of the Kubo conductivity of a two-dimensional electron gas
(2DEG) formed in the $t_{2g}$ bands of an oxide with perovskite structure. We
find that when the electric field is polarized in the plane of the 2DEG, the
optical conductivity is dominated by nearly independent Drude contributions
from two-dimensional subband Fermi surfaces, whereas for perpendicular-to-plane
polarization it has strong intersubband features. Our analysis suggests that
perpendicular-to-plane optical conductivity studies may help advance
understanding of the interplay between lattice distortions and
electron-electron interactions in complex oxide 2DEG quantum confinement
physics.
