Contact-induced Andreev bound states in normal-metal/superconductor planar junctions

Tunneling spectroscopy is a powerful tool for investigating the pairing mechanism of superconductors. However, the use of planar tunneling junctions to characterize Andreev bound states associated with unconventional superconductivity remains largely unexplored. Here, we report tunneling spectroscopy studies of normal-metal/superconductor planar junctions, leveraging the newly discovered LaAlO₃/KTaO₃(111) superconducting interface. We observe distinct spectroscopic behaviors for weak and strong tunneling barriers, controlled by the thickness of the LaAlO₃: when the barrier is weak, the metallic contact couples strongly with the interface superconductor, resulting in pronounced double peaks within the superconducting gap; when the barrier is strong, the in-gap peaks diminish and a softened full superconducting gap profile emerges. These observations, supported by theoretical calculations, pinpoint the presence of contact-induced Andreev bound states in planar junctions. This not only reveals the possibility of p-wave superconductivity at the LaAlO₃/KTaO₃ interface but also offers a universal approach to identifying the most sought-after superconducting states.