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 0 ; in Fig. 1c LaO + , AlO 2 – , LaO + , TiO 2 0 , SrO + , TiO 2 0 should have read LaO 3 3– , Al 3+ , LaO 3 3– , Ti 4+ , SrO 3 4– , Ti 4+ . In Fig. 3c the upper-right equation read – σ s = – e /2 a 2 but should have read – σ s = e /2 a 2 and in Fig. 3f the lower-right equation read – σ s = – e /2√3 a 2 but should have read σ s = – e /2√3 a 2 . These errors have now been corrected in the online version of the Letter.