Observation of a long-range unidirectional charge density wave in kagome superconductor KV₃Sb₅

The interplay between 2a₀×2a₀ charge density wave (CDW), nematicity and superconductivity in AV₃Sb₅ (A = K, Rb, Cs) compounds gives rise to a rich landscape of intriguing physical phenomena. In addition to the 2a₀ × 2a₀ CDW, a unidirectional 4a₀ stripe CDW is also observed on the Sb surface of RbV₃Sb₅ and CsV₃Sb₅. However, reports of stripe-like CDWs in KV₃Sb₅ have been limited. Here, we report the first observation of a long-range unidirectional stripe order with a 6a₀ modulation period on the Sb surface of KV₃Sb₅, coexisting with the 2a₀ × 2a₀ CDW. Notably, the intensity of the 6a₀ stripes in STM topographies exhibits pronounced contrast reversal between opposite bias voltages. Additionally, the wave vector of the 6a₀ modulation shows no energy-dependent dispersion, confirming its CDW origin. Furthermore, the 6a₀ CDW is robust under a 7 T out-of-plane magnetic field and persists over a temperature range from 215 mK to 720 mK. These results provide compelling evidence for the emergence of a long-range unidirectional CDW in KV₃Sb₅.