Kondo effect and ferromagnetic ordering at the $n$-type SrTiO$_3$ - LaAlO$_3$ conducting interface

The intriguing phenomenon of electrical conductivity at the interface between two insulators is one of the possible consequences of electronic reconstruction of materials. In analogy with interface conduction, the question arises whether or not it is possible to induce magnetism at the contact between two nonmagnetic materials. We show how a polar discontinuity at the $n$-type conducting interface between the nonmagnetic perovskites SrTiO$_3$ and LaAlO$_3$ can induce a local magnetic moment on the Ti site. The resulting interface magnetism manifests itself in the form of ferromagnetic ordering at 0.3 K and the scattering of conduction electrons on the magnetic local moment, which provides a large negative magnetoresistance of 30\%. The scattering can be described in terms of the Kondo effect with a Kondo temperature of 50 K. Electronically reconstructed interfaces now provide another versatile class of solid state Kondo systems, next to dilute impurities in metals and artificial quantum dots.