Condensed Matter Journal Club: "Probing the Momentum Structure of Superconducting Order Parameter with STM"

Determining the momentum dependence and relative sign of the superconducting order parameter is central to understanding unconventional superconductivity. Although scanning tunneling microscopy is a real-space probe, its spectroscopic response can encode momentum-dependent information. In this talk, I will discuss how tunneling measurements can reveal the superconducting gap structure. Recent studies of nickelate superconductors will illustrate both the information contained in gap line shapes and the limitations of identifying nodes from local spectra alone. I will then introduce Bogoliubov quasiparticle interference and sign-sensitive scattering, using iron-based superconductors to demonstrate how gap anisotropy and relative sign changes can be probed. Finally, building on atomic-scale imaging of electronic fluid flow, I will discuss how the Doppler response of tunneling spectra under a rotating in-plane magnetic field probes the nodal structure of the superconducting gap in UTe₂. Throughout, I will highlight the insights that STM can provide into the superconducting order parameter.