Novel physical phenomena arising at the interface of complex oxide heterostructures offer exciting opportunities for the development of future electronic devices. Using the prototypical LaAlO3/SrTiO3 interface as a model system, we employ a single-step lithographic process to realize gate-tunable Josephson junctions through a combination of lateral confinement and local side gating. The action of the side gates is found to be comparable to that of a local back gate, constituting a robust and efficient way to control the properties of the interface at the nanoscale. We demonstrate that the side gates enable reliable tuning of both the normal-state resistance and the critical (Josephson) current of the constrictions. The conductance and Josephson current show mesoscopic fluctuations as a function of the applied side gate voltage, and the analysis of their amplitude enables the extraction of the phase coherence and thermal lengths. Finally, we realize a superconducting quantum interference device in which the critical currents of each of the constriction-type Josephson junctions can be controlled independently via the side gates.@en

The realization of interfaces between different transition metal oxides has heralded a new era of materials and physics research. Notably, it enabled a uniquely diverse set of coexisting physical properties to be combined with an ever-increasing degree of experimental control. The primary focus of this thesis is the celebrated interface between the two wide band-gap insulators LaAlO3 and SrTiO3, which exhibits a variety of phenomena such as conductivity, superconductivity and spin–orbit coupling—all of which are gate-tunable, demonstrating the promise of this system for fundamental research and technological applications alike. We start by discussing the role of spin–orbit coupling in the magnetotransport properties of the system. Namely, we show how it can drive a giant in-plane magnetoresistance. On a more technically challenging perspective, we realize tunable Josephson junctions by means of lateral confinement and local side-gating. This technique, due to its simplicity, can be expanded to a broad group of interfacial systems. We then investigate LaAlO3/SrTiO3 interfaces along the (111) crystallographic direction, discovering that it condenses into a superconducting ground state and elucidating the important role played by electronic correlations. Finally, this thesis ends with a twist to the story. Moving away from epitaxial interfaces, we employ an innovative technique to obtain free-standing oxide films by etching a water-soluble sacrificial buffer layer. This exciting development paves the way to integrating complex oxides with van der Waals materials and engineering new phases in hybrid devices. @en

We report on the discovery and transport study of the superconducting ground state present at the (111)LaAlO3/SrTiO3 (LAO/STO) interface. The superconducting transition is consistent with a Berezinskii-Kosterlitz-Thouless transition and its two-dimensional nature is further corroborated by the anisotropy of the critical magnetic field, as calculated by Tinkham. The estimated superconducting layer thickness and coherence length are 10 and 60nm, respectively. The results of this work provide insight to clarify the microscopic details of superconductivity in LAO/STO interfaces, in particular in what concerns the link with orbital symmetry.@en

We investigate the thickness-dependent electronic properties of ultrathin SrIrO3 and discover a transition from a semimetallic to a correlated insulating state below 4 unit cells. Low-temperature magnetoconductance measurements show that spin fluctuations in the semimetallic state are significantly enhanced while approaching the transition point. The electronic properties are further studied by scanning tunneling spectroscopy, showing that 4 unit cell SrIrO3 is on the verge of a gap opening. Our density functional theory calculations reproduce the critical thickness of the transition and show that the opening of a gap in ultrathin SrIrO3 requires antiferromagnetic order.@en

The two-dimensional superconductor that forms at the interface between the complex oxides lanthanum aluminate (LAO) and strontium titanate (STO) has several intriguing properties that set it apart from conventional superconductors. Most notably, an electric field can be used to tune its critical temperature (T c; ref. 7), revealing a dome-shaped phase diagram reminiscent of high-T c superconductors. So far, experiments with oxide interfaces have measured quantities that probe only the magnitude of the superconducting order parameter and are not sensitive to its phase. Here, we perform phase-sensitive measurements by realizing the first superconducting quantum interference devices (SQUIDs) at the LAO/STO interface. Furthermore, we develop a new paradigm for the creation of superconducting circuit elements, where local gates enable the in situ creation and control of Josephson junctions. These gate-defined SQUIDs are unique in that the entire device is made from a single superconductor with purely electrostatic interfaces between the superconducting reservoir and the weak link. We complement our experiments with numerical simulations and show that the low superfluid density of this interfacial superconductor results in a large, gate-controllable kinetic inductance of the SQUID. Our observation of robust quantum interference opens up a new pathway to understanding the nature of superconductivity at oxide interfaces.@en

Phenomena that are absent of bulk TMO compounds can emerge at their interfaces when they are grown on top of each-other. A prototypical example of such emerging states is found at the LaAlO 3/SrTiO 3 interface, which also attracted most of the initial interest for this new field of research (in the TMO context). Here we review some properties of this peculiar interface as investigated by transport measurements allowing the studies of different effects such as magnetism, superconductivity or Rashba effect; hence indirectly accessing the band structures studied by the methods presented in the rest of the book.@en