Evidence of Josephson junction behavior in top-gated LaAlO3-SrTiO3

We demonstrate top-gate tunable Josephson junction like behavior in the two dimensional electron gas at the LaAlO3-SrTiO3 interface. A combination of global back-gating and local top-gating is used to define the junctions, providing an efficient way for much finer spatial control over the properties of the interface, as compared to back-gating alone. The variation of critical currents and zero bias resistances with temperature shows that the junctions behave like short, overdamped weak links. This technique could be an important tool to illuminate the nature of superconductivity in the LaAlO3-SrTiO3 interface system. The two dimensional electron gas (2DEG) at the interface of the insulating oxides LaAlO3 (LAO) and SrTiO3 (STO), has attracted a lot of attention since its discovery in 2004 [1, 2, 3]. It was found that the 2DEG undergoes a superconducting transition below about 300 mK [4]. An important question is the nature of superconductivity, as it occurs in two dimensions, in an environment of strong spin-orbit coupling [5], and in coexistence with magnetism [6, 7, 8]. Various theories have been proposed to explain superconductivity in this system, including a Fulde-Ferrel-Larkin-Ovchinnikov state [9], a mixed parity state [10], and a conventional superconducting state involving electrons from dxy orbitals in a few TiO2 layers of ST