Unconventional superconductivity in iron-based van der Waals heterostructures*

High-temperature superconductivity is a holy grail of condensed matter physics. It shifts the conventional BCS paradigm and opens an appealing future for application. In this context, iron-based superconductors (FeSC) play a vital role in understanding unconventional superconductivity in multiorbital systems. Moreover, the interplay between strong electronic correlations, magnetism, nematicity, and band topology gives rise to universal sign-changed superconducting pairing orders accompanied by a rich phase diagram that depends on the exact compound composition. For these reasons, making a unified theoretical description of superconductivity in this system is still challenging. Previous measurements of FeSC were mainly focused on macroscopic-size samples, while potentially significant quantum effects in finite-size samples have yet to be explored. In this talk, we discuss fabricated van der Waals structures based on exfoliated thin flakes of FeSC. Using scanning tunneling microscopy and spectroscopy, we discovered modulation of superconductivity, in huge contrast with its bulk crystal counterpart. We further discussed several possible mechanisms for the origin of the exotic behaviors with the help of a microscopic model. Our results reveal new insights into the unconventional nature of FeSC and provide a novel method to study other unconventional superconductors.