Investigating the Momentum Structure of Superconductivity via Quasiparticle Interference in CsV3Sb5 using Scanning Tunneling Microscopy: Part 2

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 second 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 2, we analyze the quasiparticle interference (QPI) features using theoretical modeling, showing that the dominant QPI signals originate from V d-orbital bands that are even under Mz symmetry. Our calculations both reproduce the experimental observations and reveal how QPI directly reflects the sublattice character. Finally, we formally establish the detailed correspondence between QPI experiments in q-space and the Fermi surfaces geometries in k space, from which we conclude that the superconducting gap is isotropic on the Mz-even Fermi pocket.