Rotation symmetry breaking in the normal state of a kagome superconductor KV₃Sb₅

Recently discovered kagome superconductors AV₃Sb₅ (A=K, Rb, Cs) provide a fresh opportunity to realize and study correlation-driven electronic phenomena on a kagome lattice. The observation of a 2a₀ by 2a₀ charge density wave (CDW) in the normal state of all members of AV₃Sb₅ kagome family has generated an enormous amount of theoretical and experimental interest. We use low-temperature spectroscopic-imaging scanning tunneling microscopy to reveal a pronounced intensity anisotropy between different 2a₀ CDW directions in KV₃Sb₅. In particular, by examining the strength of ordering wave vectors as a function of energy in Fourier transforms of differential conductance maps, we find that one of the CDW directions is distinctly different compared to the other two. This observation points towards an intrinsic rotation symmetry broken electronic ground state, where the symmetry is reduced from C₆ to C₂. Our experiments, combined with earlier observations of a stripe 4a₀ charge ordering in CsV₃Sb₅, establish correlation-driven rotation symmetry breaking as a unifying feature of AV₃Sb₅ kagome superconductors.