Investigating the Momentum Structure of Superconductivity via Quasiparticle Interference in CsV3Sb5 using Scanning Tunneling Microscopy: Part 1

The AV₃Sb₅ (A = Cs, K, Rb) family of kagome materials exhibits the coexistent charge density wave (CDW) ordering and superconductivity. Among them, CsV₃Sb₅ stands out for its distinctive behavior, displaying a C₆-symmetric 2 × 2 CDW around 100 K and a C₂-symmetric 1 × 4 CDW upon further cooling to 40 K. This rich electronic landscape makes CsV₃Sb₅ an appealing platform for exploring the interplay between CDW ordering and superconductivity. However, experimental studies are challenged by the complex multi-band structure near the Fermi level and the small superconducting gap.

In the first part of this two-part presentation, we report sub-Kelvin scanning tunneling spectroscopy (STS) measurements of CsV3Sb5 with high energy resolution, combined with tight-binding and ab initio calculations of its electronic structure. Here, in Part 1, we perform STS measurements with high energy and momentum resolution to study the energy dependence of quasiparticle interference (QPI) and CDW features. We demonstrate that the QPI features all follow the average superconducting gap closely, as do most of the CDW features. This suggests that the superconducting gap is isotropic on the Fermi surfaces accessible to STS.