Publisher Correction: Direct imaging of the electron liquid at oxide interfaces.

In the version of this Letter originally published, in two instances in Fig. 1 the layers in the cross-sectional view of the (001) interface were incorrectly labelled: in Fig. 1b SrO should have read SrO; in Fig. 1c LaO, AlO, LaO, TiO, SrO, TiO should have read LaO, Al, LaO, Ti, SrO, Ti. In Fig. 3c the upper-right equation read -σ = -e/2a but should have read -σ = e/2a and in Fig. 3f the lower-right equation read -σ = -e/2√3a but should have read σ = -e/2√3a. These errors have now been corrected in the online version of the Letter.