Inhomogeneous multi carrier superconductivity at LaXO₃/SrTiO₃ (X = Al or Ti) oxide interfaces

Several experiments reveal the inhomogeneous character of the superconducting state that occurs when the carrier density of the two-dimensional electron gas formed at the LaXO₃/SrTiO₃ (X = Al or Ti) interface is tuned above a threshold value by means of gating. By reanalyzing previous measurements that highlight the presence of two kinds of carriers (low- and high-mobility), we shall provide a description of multi carrier magneto transport in an inhomogeneous two-dimensional electron gas, gaining insight into the properties of the physics of the systems under investigation. We shall then show that the measured resistance, superfluid density, and tunneling spectra result from the percolative connection of superconducting 'puddles' with randomly distributed critical temperatures embedded in a weakly localizing metallic matrix. We shall also show that this scenario is consistent with the characteristics of the superconductor-to-metal transition driven by a magnetic field. A multi carrier description of the superconducting state within a weak-coupling, BCS-like model will be also discussed. (paper)