Electronic transport in low dimensional LaAlO3 /SrTiO3 heterointerface

The large variety of phenomena exhibited by the interface between two band-insulators LaAlO₃ and SrTiO₃ has attracted intense research activity in recent years. In this talk, I discuss the results of electronic transport properties of two-dimensional electron gas formed at the LaAlO₃/SrTiO₃ heterointerface.

LaAlO₃/SrTiO₃ interface exhibits superconductivity at low temperatures. Transport studies reported in this system seem to indicate that the superconductivity is two dimensional in nature, with a charge carrier density dependent T_BKT. We have experimentally studied low frequency resistance fluctuations (noise) and its higher order statistics near the superconducting transition region by varying the temperature, gate voltage and magnetic field. From the analysis of the higher order statistics of resistance fluctuations, we find large non-Gaussian components (NGC) in resistance fluctuations appear near T_BKT, which signifies strong correlations among interacting vortices in the system. The NGC are found to be completely absent above T_C. Theoretical simulations indicate that the large non-Gaussian resistance fluctuations are manifestation of a percolative transition of a Josephson-coupled superconducting network.

LaAlO₃/SrTiO₃ interface exhibits coexistence of superconductivity and ferromagnetism, and they are gate tunable. In general, superconductivity and ferromagnetism are antagonistic to each other. So, the appearance of two co-existing phase at the interface has opened up a new direction of research in condensed matter physics. In this talk, I discuss the results of perpendicular magnetic field dependence of sheet resistance above superconducting transition temperature (T/T_BKT = 2). From our experiments, we identify a gate voltage tunable Lifshitz transition in this system. We observed a novel transient superconducting state (TSS) in the presence of a magnetic field applied perpendicular to the interface.  We find that the TSS appeared concomitantly with a Lifshitz transition as a consequence of the interplay between ferromagnetism, superconductivity and the finite relaxation time of the in-plane magnetization in this system.

We demonstrate that the resistance fluctuations (noise) have strikingly different features on either side of the Lifshitz transition. Below the Lifshitz transition, noise is dominated by carrier density fluctuations arising from trapping-detrapping of charge carriers from defects in the underlying SrTiO₃ substrate. Above the Lifshitz transition, we propose that the noise presumably originate from the scattering of carriers from different available conduction channels.