Frieze charge-stripes in a correlated kagome superconductor CsCr$_3$Sb$_5$

Abstract: Kagome metals have developed into a vibrant playground for materials physics, where geometric frustration, electronic correlations and band topology come together to create a variety of exotic phenomena. Recently synthesized CsCr$_3$Sb$_5$ has provided a rare opportunity to explore unconventional superconductivity in a strongly correlated kagome system with hints of frustrated magnetism and quantum criticality. Using spectroscopic imaging scanning tunneling microscopy, we reveal a cascade of density wave transitions with different symmetries in bulk single crystals of CsCr$_3$Sb$_5$. In particular, we discover a new electronic state $-$ a unidirectional density wave that breaks all mirror symmetries akin to a chiral density wave, but in contrast retains a mirror-glide symmetry. We term this state a frieze charge-stripe order phase, because its symmetry properties agree with one of the fundamental frieze symmetry groups. A combination of high-resolution imaging, Fourier analysis and theoretical simulations uncovers the crucial role of sublattice degrees of freedom in forming this phase, with internal chiral textures of opposite handedness. Our experiments reveal that superconductivity in CsCr$_3$Sb$_5$ develops from a new type of a unidirectional density wave, and set the foundation for exploring electronic states with frieze symmetry groups in quantum materials.