(a) The LaAlO3/SrTiO3 interface. At the interface, a polar discontinuity between neutral SrTiO3 planes and charged LaAlO3 planes produces a diverging potential. For LaAlO3 thicknesses above three unit cells, an electronic reconstruction occurs, transferring from the LaAlO3 surface to the interface 1/2 electron per unit cell . (b) From Dikin et al. , hysteresis in the magnetic-field dependence of sample resistance for different temperatures at a fixed gate voltage, Vg=-100 V. (c) Schematic of the phase separation scenario. Pavlenko et al.  propose that ferromagnetism is linked to oxygen vacancies, which locally produce an increase in carrier density favoring localized ferromagnetic regions (yellow), and that the electronic reconstruction is responsible for the metallic and superconducting regions.