Robustness of the unidirectional stripe order in the kagome superconductor CsV3Sb5

V-based kagome materials A V 3 Sb 5 ( A = K, Rb, Cs) have attracted much attention due to their novel properties such as unconventional superconductivity, giant anomalous Hall effect, charge density wave (CDW) and pair density wave. Except for the 2 a 0 × 2 a 0 CDW (charge density wave with in-plane 2 × 2 superlattice modulation) in A V 3 Sb 5 , an additional 1 × 4 (4 a 0 ) unidirectional stripe order has been observed at the Sb surface of RbV 3 Sb 5 and CsV 3 Sb 5 . However, the stability and electronic nature of the 4 a 0 stripe order remain controversial and unclear. Here, by using low-temperature scanning tunneling microscopy/spectroscopy (STM/S), we systematically study the 4 a 0 stripe order on the Sb-terminated surface of CsV 3 Sb 5 . We find that the 4 a 0 stripe order is visible in a large energy range. The STM images with positive and negative bias show contrast inversion, which is the hallmark for the Peierls-type CDW. In addition, below the critical temperature about 60 K, the 4 a 0 stripe order keeps unaffected against the topmost Cs atoms, point defects, step edges and magnetic field up to 8 T. Our results provide experimental evidences on the existence of unidirectional CDW in CsV 3 Sb 5 .