Discovery of Conjoined Charge Density Waves in the Kagome Superconductor CsV₃Sb₅

The observation of unconventional charge and pairing density waves in a kagome metal CsV₃Sb₅ is a striking analogy to the cuprate high-temperature superconductivity and the cascade orders in twisted bilayer graphene. While electronic instabilities in CsV₃Sb₅ are believed to originate from the V 3d-electrons on the kagome plane, the role of Sb 5p-electrons for 3-dimensional orders is largely unexplored. Here, using resonant tender X-ray scattering and high-pressure X-ray scattering, we report a rare realization of conjoined charge density waves (CDWs) in CsV₃Sb₅, where a 2*2*1 CDW in the kagome sublattice and a Sb 5p-electron assisted 2*2*2 CDW coexist. At ambient pressure, we discover a resonant enhancement on Sb L₁-edge (2s->5p) at the 2*2*2 CDW wavevectors. The resonance, however, is absent at the 2*2*1 CDW wavevectors. Applying hydrostatic pressure, CDW transition temperatures are separated, where the 2*2*2 CDW emerges 4 K above the 2*2*1 CDW at 1 GPa. These observations demonstrate that symmetry-breaking phases in CsV₃Sb₅ go beyond the minimal framework of kagome electronic bands near van Hove filling.